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Magnetic resonance imaging-guided transcatheter implantation of a prosthetic valve in aortic valve position: Feasibility study in swine
Abstract
Successful transcatheter aortic valve implantation in the aortic valve position has been recently reported ([1,2][1]). However, implantation remains challenging, and malpositioning of the device can lead to a life-threatening situation. In contrast to conventional X-ray angiography, magnetic
... There has been an emerging trend of clinical studies performed using Ees/Ea coupling to detect changes in patients with different PH etiologies and disease severity. In patients with a clinical diagnosis of CTED/CTEPH (McCabe et al. 2014), PH and associated systemic sclerosis (Tedford et al. 2013), and those with PH and without overt RV failure (Kuehne et al. 2004), it was demonstrated that Ees/Ea uncoupling was due to a disproportional increase in Ea and the inability to augment contractility (Ees). These observations suggest that in early stage PH, decreased Ees/Ea coupling is mainly reflected in increased afterload (Ea) and insufficient augmentation of RV contractility. ...
... These observations suggest that in early stage PH, decreased Ees/Ea coupling is mainly reflected in increased afterload (Ea) and insufficient augmentation of RV contractility. However, in late stage PH, the continued progression of the disease state leads to the clinical development of RV failure and further impairs Ees/Ea coupling due to decreased contractility (Ees) (Kuehne et al. 2004). While there is potential for Ees/Ea coupling to be used as a marker of RV function and illustrate the transition from RV adaptation to RV maladaptation, it still remains unclear at what specific coupling ratio the RV becomes uncoupled to the PA. ...
... Furthermore, fentanyl can adversely affect contractility and we inserted the conductance catheter apically in the animal model that may have further diminished RV contractility. Nevertheless, it remains the most commonly studied model (Kuehne et al. 2004;Grignola et al. 2007;Read et al. 2011;Simonneau et al. 2013;McCabe et al. 2014). The animal model assessed the effect of acute afterload perturbation on RV function whereas in the human model the RV is chronically loaded and the influence of remodelling in the human model is a possible and important unaccounted confounder. ...
... There has been an emerging trend of clinical studies performed using Ees/Ea coupling to detect changes in patients with different PH etiologies and disease severity. In patients with a clinical diagnosis of CTED/CTEPH (McCabe et al. 2014), PH and associated systemic sclerosis (Tedford et al. 2013), and those with PH and without overt RV failure (Kuehne et al. 2004), it was demonstrated that Ees/Ea uncoupling was due to a disproportional increase in Ea and the inability to augment contractility (Ees). These observations suggest that in early stage PH, decreased Ees/Ea coupling is mainly reflected in increased afterload (Ea) and insufficient augmentation of RV contractility. ...
... These observations suggest that in early stage PH, decreased Ees/Ea coupling is mainly reflected in increased afterload (Ea) and insufficient augmentation of RV contractility. However, in late stage PH, the continued progression of the disease state leads to the clinical development of RV failure and further impairs Ees/Ea coupling due to decreased contractility (Ees) (Kuehne et al. 2004). While there is potential for Ees/Ea coupling to be used as a marker of RV function and illustrate the transition from RV adaptation to RV maladaptation, it still remains unclear at what specific coupling ratio the RV becomes uncoupled to the PA. ...
... Furthermore, fentanyl can adversely affect contractility and we inserted the conductance catheter apically in the animal model that may have further diminished RV contractility. Nevertheless, it remains the most commonly studied model (Kuehne et al. 2004;Grignola et al. 2007;Read et al. 2011;Simonneau et al. 2013;McCabe et al. 2014). The animal model assessed the effect of acute afterload perturbation on RV function whereas in the human model the RV is chronically loaded and the influence of remodelling in the human model is a possible and important unaccounted confounder. ...
Chronic thromboembolic disease (CTED) is suboptimally defined by a mean pulmonary artery pressure (mPAP) <25 mmHg at rest in patients that remain symptomatic from chronic pulmonary artery thrombi. To improve identification of right ventricular (RV) pathology in patients with thromboembolic obstruction, we hypothesized that the RV ventriculo-arterial (Ees/Ea) coupling ratio at maximal stroke work (Ees/Eamax sw) derived from an animal model of pulmonary obstruction may be used to identify occult RV dysfunction (low Ees/Ea) or residual RV energetic reserve (high Ees/Ea). Eighteen open chested pigs had conductance catheter RV pressure-volume (PV)-loops recorded during PA snare to determine Ees/Eamax sw. This was then applied to 10 patients with chronic thromboembolic pulmonary hypertension (CTEPH) and ten patients with CTED, also assessed by RV conductance catheter and cardiopulmonary exercise testing. All patients were then restratified by Ees/Ea. The animal model determined an Ees/Eamax sw = 0.68 ± 0.23 threshold, either side of which cardiac output and RV stroke work fell. Two patients with CTED were identified with an Ees/Ea well below 0.68 suggesting occult RV dysfunction whilst three patients with CTEPH demonstrated Ees/Ea ≥ 0.68 suggesting residual RV energetic reserve. Ees/Ea > 0.68 and Ees/Ea < 0.68 subgroups demonstrated constant RV stroke work but lower stroke volume (87.7 ± 22.1 vs. 60.1 ± 16.3 mL respectively, P = 0.006) and higher end-systolic pressure (36.7 ± 11.6 vs. 68.1 ± 16.7 mmHg respectively, P < 0.001). Lower Ees/Ea in CTED also correlated with reduced exercise ventilatory efficiency. Low Ees/Ea aligns with features of RV maladaptation in CTED both at rest and on exercise. Characterization of Ees/Ea in CTED may allow for better identification of occult RV dysfunction.
... With the development of these technologies, MR guided interventions have evolved into clinically viable options for a variety of minimally invasive surgical and therapeutic applications [124][125][126] . MR guidance of vascular intervention would be extremely useful in the diagnosis and treatment of many disease processes, which might include, but not be limited to, stroke therapy, embolotherapy 127 , angioplasty and stent deployment 83,84,88 , cardiac catheterization 103 , and endovascular delivery of drugs, genes [128][129][130] , stem cells [131][132][133] , and prosthetic valves 134 , where information about the vessel wall, atherosclerotic plaques, and perivascular tissue in real-time is of great interest. ...
... In addition to improved control over the catheter tip using MARC steering, for example, visualization of the pulmonary vein walls in RF ablation for atrial fibrillation using MRI would further facilitate successful procedural outcome. Other procedures taking advantage of these characteristics might include, but not be limited to, endovascular delivery of cardiac stem cells to infracted myocardium [131][132][133] , delivery of drugs, genes [128][129][130] , and prosthetic valves 134 , stroke therapy, embolotherapy 127 , angioplasty and stent deployment 83,84,88 , cardiac catheterization 90, 103,206 . Ultimately, the driving force for advancing the field of interventional MRI will be demonstration that MR guidance is of greater clinical utility for specific procedures than x-ray fluoroscopy, or new therapies that cannot be performed without MR guidance. ...
... Percutaneous transcatheter placement of valved stents has evolved, in the past 5 years, into an exciting and dynamic field of research. MRI has been shown to be particularly useful, not only in postinterventional assessment of function, but also in guiding the implantation of valved stents under conditions of complex anatomy, such as that of the coronary arteries or the mitral valve ( Figure 2) [18,19]. ...
... Heart Metab. 2007; 34:[19][20][21][22][23] ...
Mortality rates in patients with congenital heart disease have decreased significantly over the past decades. However, many of these patients require long-term care and repeated cardiac interventional or surgical procedures. This requires the development of optimized diagnostic tools that are better able to guide therapy, the establishment of non ionizing and less invasive interventional methods, and the progressive replacement of surgical by transcatheter techniques. Interventional magnetic resonance imaging (iMRI) has the potential to make important steps towards these goals. This review presents the current situation and expected future developments in the field of iMRI, with a focus on congenital heart diseases. Heart Metab. 2007;34:19–23.
... As a single imaging modality, CMR provided (a) comprehensive diagnostic evaluation of the relevant cardiac and vascular anatomy for adequate interventional planning, (b) reliable procedural guidance in real-time, (c) immediate evaluation of procedure-related complications, and (d) postinterventional validation of treatment success. The concept of rtCMR-guided TAVI was first described by Kuehne et al. in 2004. This archetype study in the preclinical , pioneering days of TAVI demonstrated the general technical feasibility and potential value of rtCMR guidance in acute animal experiments [24]. ...
... The concept of rtCMR-guided TAVI was first described by Kuehne et al. in 2004. This archetype study in the preclinical , pioneering days of TAVI demonstrated the general technical feasibility and potential value of rtCMR guidance in acute animal experiments [24]. The authors implanted entirely custom-built self-expanding, nitinolbased stent-valves into the native aortic valves of sevenFigure 5 Transsubclavian TAVI under CMR guidance using real-time TrueFISP sequences. ...
Real-time cardiovascular magnetic resonance (rtCMR) is considered attractive for guiding TAVI. Owing to an unlimited scan plane orientation and an unsurpassed soft-tissue contrast with simultaneous device visualization, rtCMR is presumed to allow safe device navigation and to offer optimal orientation for precise axial positioning. We sought to evaluate the preclinical feasibility of rtCMR-guided transarterial aortic valve implatation (TAVI) using the nitinol-based Medtronic CoreValve bioprosthesis.
rtCMR-guided transfemoral (n = 2) and transsubclavian (n = 6) TAVI was performed in 8 swine using the original CoreValve prosthesis and a modified, CMR-compatible delivery catheter without ferromagnetic components.
rtCMR using TrueFISP sequences provided reliable imaging guidance during TAVI, which was successful in 6 swine. One transfemoral attempt failed due to unsuccessful aortic arch passage and one pericardial tamponade with subsequent death occurred as a result of ventricular perforation by the device tip due to an operating error, this complication being detected without delay by rtCMR. rtCMR allowed for a detailed, simultaneous visualization of the delivery system with the mounted stent-valve and the surrounding anatomy, resulting in improved visualization during navigation through the vasculature, passage of the aortic valve, and during placement and deployment of the stent-valve. Post-interventional success could be confirmed using ECG-triggered time-resolved cine-TrueFISP and flow-sensitive phase-contrast sequences. Intended valve position was confirmed by ex-vivo histology.
Our study shows that rtCMR-guided TAVI using the commercial CoreValve prosthesis in conjunction with a modified delivery system is feasible in swine, allowing improved procedural guidance including immediate detection of complications and direct functional assessment with reduction of radiation and omission of contrast media.
... Feasibility of MR-guided valvular procedures has been tested in animal studies mostly since 2004, 111 especially in the aortic valve position, and thereby achieving a TRL of 5. ...
Background
Cardiac magnetic resonance (CMR) provides excellent temporal and spatial resolution, tissue characterization, and flow measurements. This enables major advantages when guiding cardiac invasive procedures compared with X-ray fluoroscopy or ultrasound guidance. However, clinical implementation is limited due to limited availability of technological advancements in magnetic resonance imaging (MRI) compatible equipment. A systematic review of the available literature on past and present applications of interventional MR and its technology readiness level (TRL) was performed, also suggesting future applications.
Methods
A structured literature search was performed using PubMed. Search terms were focused on interventional CMR, cardiac catheterization, and other cardiac invasive procedures. All search results were screened for relevance by language, title, and abstract. TRL was adjusted for use in this article, level 1 being in a hypothetical stage and level 9 being widespread clinical translation. The papers were categorized by the type of procedure and the TRL was estimated.
Results
Of 466 papers, 117 papers met the inclusion criteria. TRL was most frequently estimated at level 5 meaning only applicable to in vivo animal studies. Diagnostic right heart catheterization and cavotricuspid isthmus ablation had the highest TRL of 8, meaning proven feasibility and efficacy in a series of humans.
Conclusion
This article shows that interventional CMR has a potential widespread application although clinical translation is at a modest level with TRL usually at 5. Future development should be directed toward availability of MR-compatible equipment and further improvement of the CMR techniques. This could lead to increased TRL of interventional CMR providing better treatment.
... Device closure of atrial septal defects is another application that has been explored [88][89][90]. Further animal studies also offer potential interventions in CHD such as transcatheter implantation of a prosthetic valve [91], percutaneous ventricular septal defect closure [92] and transcatheter creation of cavopulmonary shunts [93, 94•]. Based on encouraging preclinical studies, the application of interventions has now been extended to humans. ...
Purpose of Review
Cardiac catheterization therapies to treat or palliate infants, children and adults with congenital heart disease have developed rapidly worldwide in both technical innovation and device development in the previous three decades. By reviewing of current status of novel or development of devices and techniques, we will discuss what is likely to happen in paediatric heart intervention in the next decade.
Recent Findings
Recently, biodegradable stents and devices, transcatheter pulmonary valve implantation for the native right ventricle outflow tract and MRI-guided interventions have been progressing rapidly with good immediate to early results. These are expected to be introduced and spread in the next decade although there are still challenges to overcome.
Summary
The future of paediatric heart intervention is very promising with rapid development of technological progress.
... [146][147][148][149] CMR-guided percutaneous pulmonary and aortic valve stent implantation have also been performed successfully. 140,150 More complex interventions, such as percutaneous coronary catheterization and intervention, have also been demonstrated in healthy animals using CMR 151-154 but limitations in spatial resolution are unlikely to result in coronary interventions being a key area for CMR-guided interventions. ...
Diagnostic and interventional cardiac catheterization is routinely used in the diagnosis and treatment of congenital heart disease. There are well-established concerns regarding the risk of radiation exposure to patients and staff, particularly in children given the cumulative effects of repeat exposure. Magnetic resonance imaging (MRI) offers the advantage of being able to provide better soft tissue visualization, tissue characterization, and quantification of ventricular volumes and vascular flow. Initial work using MRI catheterization employed fusion of x-ray and MRI techniques, with x-ray fluoroscopy to guide catheter placement and subsequent MRI assessment for anatomical and hemodynamic assessment. Image overlay of 3D previously acquired MRI datasets with live fluoroscopic imaging has also been used to guide catheter procedures.Hybrid x-ray and MRI-guided catheterization paved the way for clinical application and validation of this technique in the assessment of pulmonary vascular resistance and pharmacological stress studies. Purely MRI-guided catheterization also proved possible with passive catheter tracking. First-in-man MRI-guided cardiac catheter interventions were possible due to the development of MRI-compatible guidewires, but halted due to guidewire limitations.More recent developments in passive and active catheter tracking have led to improved visualization of catheters for MRI-guided catheterization. Improvements in hardware and software have also increased image quality and scanning times with better interactive tools for the operator in the MRI catheter suite to navigate through the anatomy as required in real time. This has expanded to MRI-guided electrophysiology studies and radiofrequency ablation in humans. Animal studies show promise for the utility of MRI-guided interventional catheterization. Ongoing investment and development of MRI-compatible guidewires will pave the way for MRI-guided diagnostic and interventional catheterization coming into the mainstream.
... In the last decade, transcatheter aortic valve replacement (TAVR) has been studied for treating the patients of high surgical risk. The bioprosthetic valves are delivered through catheters transfemorally [8] [9] [10] [11] [12] [13] or transapically [14] [15] [16] [17] [18] and are implanted within the diseased aortic valve. In current clinical practice, the transfemoral approach is the first choice, while the transapical method is only chosen for patients who have poor vascular access [19]. ...
Minimally invasive cardiac surgery is less traumatic and therefore leads to quicker recovery. With the assistance of engineering technologies on devices, imaging, and robotics, in conjunction with surgical technique, minimally invasive cardiac surgery will improve clinical outcomes and expand the cohort of patients that can be treated. We used transapical aortic valve implantation as an example to demonstrate that minimally invasive cardiac surgery can be implemented with the integration of surgical techniques and engineering technologies. Feasibility studies and long-term evaluation results prove that transapical aortic valve implantation under MRI guidance is feasible and practical. We are investigating an MRI compatible robotic surgical system to further assist the surgeon to precisely deliver aortic valve prostheses via a transapical approach. Ex vivo experimentation results indicate that a robotic system can also be employed in in vivo models.
... Intraoperative MRI guided T-AVI was first attempted around the year 2004. It was reported that due to the radiofrequency shielding effect of ferromagnetic stents, imaging quality was impaired during and after valve deployment, but was, in principle still possible [31]. Immel et al. presented an experiment in which they equipped self-expanding stents with resonance circuits to overcome the shielding effect [32]. ...
Transcatheter aortic valve implantation (T-AVI) has shown good results in high-risk patients with severe aortic stenosis. Throughout the whole process of T-AVI, different imaging modalities are indispensable. Preoperatively, multislice computed tomography, angiography and transesophageal echo (TEE) are utilized for patient selection, valve selection, approach selection and the planning of implant placement. Intraoperatively, angiography and TEE are used for controlling placement of the guidewire and valve positioning. Quality control and follow-up require TEE imaging and can require additional CT or angiography studies. In the first half of this paper, we discuss the applicability of different imaging modalities for T-AVI in the light of the current best practice.
In the second half of this paper, we present an overview on research projects in medical engineering which aim at development of image-based methods for increasing patient safety during T-AVI. Template-based implantation planning, as it is applied in dental, orthopedic and other surgical disciplines, is proposed as an aid during implant selection in order to help reduce the incidence of complications such as atrioventricular node block and paravalvular leaks. Current research tries to apply state-of-the-art engineering techniques, such as computational fluid dynamics to optimize valve selection and positioning. For intraoperative assistance during valve positioning, real-time image processing methods are proposed to track target landmarks and the stented valve.
... This was an important step toward MR-guided treatment of this congenital disease [138]. Kuehne et al. [139] demonstrated successful implant of a self-expanding stent valve in the aorta via percutaneous access under MR fluoroscopy. Transcatheter aortic valve implantation, either retrograde through a transfemoral approach or antegrade through a transapical approach, has become a clinical reality in the treatment of critical aortic stenosis in high-risk patients. ...
Vascular and cardiac disease remains a leading cause of morbidity and mortality in developed and emerging countries. Vascular and cardiac interventions require extensive fluoroscopic guidance to navigate endovascular catheters. X-ray fluoroscopy is considered the current modality for real time imaging. It provides excellent spatial and temporal resolution, but is limited by exposure of patients and staff to ionizing radiation, poor soft tissue characterization and lack of quantitative physiologic information. MR fluoroscopy has been introduced with substantial progress during the last decade. Clinical and experimental studies performed under MR fluoroscopy have indicated the suitability of this modality for: delivery of ASD closure, aortic valves, and endovascular stents (aortic, carotid, iliac, renal arteries, inferior vena cava). It aids in performing ablation, creation of hepatic shunts and local delivery of therapies. Development of more MR compatible equipment and devices will widen the applications of MR-guided procedures. At post-intervention, MR imaging aids in assessing the efficacy of therapies, success of interventions. It also provides information on vascular flow and cardiac morphology, function, perfusion and viability. MR fluoroscopy has the potential to form the basis for minimally invasive image-guided surgeries that offer improved patient management and cost effectiveness.
... Left heart MRI guided cardiac interventions have also been performed without the use of a guidewire in the LV, in an animal model for transcatheter implantation of a prosthetic valve in the aortic valve position, 35 where the use of susceptibility markers enabled precise position monitoring of the interventional instrument and in patients who underwent balloon dilation of aortic coarctation. 36 In the last study, the procedures were preceded and followed by conventional catheterization to assess the arch angiographically and measure pressure gradients across the coarctation segment and a non MR-safe guidewire was used. ...
Percutaneous cardiac interventions are currently performed under x-ray guidance. Magnetic resonance imaging (MRI) has been used to guide intravascular interventions in the past, but mainly in animals. Translation of MR-guided interventions into humans has been limited by the lack of MR-compatible and safe equipment, such as MR guide wires with mechanical characteristics similar to standard guide wires. The aim of the present study was to evaluate the safety and efficacy of a newly developed MR-safe and compatible passive guide wire in aiding MR-guided cardiac interventions in a swine model and describe the 2 first-in-man solely MR-guided interventions.
In the preclinical trial, the new MR-compatible wire aided the performance of 20 interventions in 5 swine. These consisted of balloon dilation of nondiseased pulmonary and aortic valves, aortic arch, and branch pulmonary arteries. After ethics and regulatory authority approval, the 2 first-in-man MR-guided interventions were performed in a child and an adult, both with elements of valvar pulmonary stenosis. Catheter manipulations were monitored with real-time MRI sequence with interactive modification of imaging plane and slice position. Temporal resolution was 11 to 12 frames/s. Catheterization procedure times were 110 and 80 minutes, respectively. Both patients had successful relief of the valvar stenosis and no procedural complications.
The described preclinical study and case reports are encouraging that with the availability of the new MR-compatible and safe guide wire, certain percutaneous cardiac interventions will become feasible to perform solely under MR guidance in the future. A clinical trial is underway in our institution.
... To reduce trauma and speed recovery for the patient; minimally invasive aortic valve replacement, both a percutaneous transfemoral approach123456 and a left ventricular transapical approach789101112, have been reported. Compared to the former, transapical aortic valve implantation provides a direct and short access to the native valve. ...
Aortic valves have been implanted on self-expanding (SE) and balloon-expandable (BE) stents minimally invasively. We have demonstrated the advantages of transapical aortic valve implantation (tAVI) under real-time magnetic resonance imaging (rtMRI) guidance. Whether there are different advantages to SE or BE stents is unknown. We report rtMRI-guided tAVI in a porcine model using both SE and BE stents, and compare the differences between the stents.
A total of 22 Yucatan pigs (45-57 kg) underwent tAVI. Commercially available stentless bioprostheses (21-25 mm) were mounted on either BE platinum-iridium stents or SE-nitinol stents. rtMRI guidance was employed as the intraoperative imaging. Markers on both types of stents were used to enhance visualization in rtMRI. Pigs were allowed to survive and had follow-up MRI scans and echocardiography at 1, 3, and 6 months postoperatively.
rtMRI provided excellent visualization of the aortic valve implantation mounted on both stent types. The implantation times were shorter with the SE stents (60 ± 14s) than with the BE stents (74 ± 18s), (p=0.027). The total procedure time was 31 and 37 min, respectively (p=0.12). It was considerably easier to manipulate the SE stent during deployment, without hemodynamic compromise. This was not always the case with the BE stent, and its placement occasionally resulted in coronary obstruction and death. Long-term results demonstrated stability of the implants with preservation of myocardial perfusion and function over time for both stents.
SE stents were easier to position and deploy, thus leading to fewer complications during tAVI. Future optimization of SE stent design should improve clinical results.
... Complementary to mitigation of radiation exposure and nephrotoxicity of contrast media, the TAVI procedure would benefit from real-time CMR guidance due to its inherent unsurpassed soft-tissue contrast and its 2D and 3D imaging capabilities in any oblique orientation during navigation of the large-diameter catheters through the vasculature and, even more importantly, during precise axial positioning of the stent-valve and deployment. So far, only two provocative initial demonstrations in the preclinical era of TAVI have addressed the feasibility and potential value of combined device and tissue imaging by CMR guidance in animal models using entirely hand-made devices far from clinical approval and applicability [23,24]. In contrast, CMR suitability of approved and already commercially available TAVI devices which might be readily transferred into CMR application has not yet been evaluated. ...
Cardiovascular magnetic resonance (CMR) is considered an attractive alternative for guiding transarterial aortic valve implantation (TAVI) featuring unlimited scan plane orientation and unsurpassed soft-tissue contrast with simultaneous device visualization. We sought to evaluate the CMR characteristics of both currently commercially available transcatheter heart valves (Edwards SAPIEN™, Medtronic CoreValve®) including their dedicated delivery devices and of a custom-built, CMR-compatible delivery device for the Medtronic CoreValve® prosthesis as an initial step towards real-time CMR-guided TAVI.
The devices were systematically examined in phantom models on a 1.5-Tesla scanner using high-resolution T1-weighted 3D FLASH, real-time TrueFISP and flow-sensitive phase-contrast sequences. Images were analyzed for device visualization quality, device-related susceptibility artifacts, and radiofrequency signal shielding.
CMR revealed major susceptibility artifacts for the two commercial delivery devices caused by considerable metal braiding and precluding in vivo application. The stainless steel-based Edwards SAPIEN™ prosthesis was also regarded not suitable for CMR-guided TAVI due to susceptibility artifacts exceeding the valve's dimensions and hindering an exact placement. In contrast, the nitinol-based Medtronic CoreValve® prosthesis was excellently visualized with delineation even of small details and, thus, regarded suitable for CMR-guided TAVI, particularly since reengineering of its delivery device toward CMR-compatibility resulted in artifact elimination and excellent visualization during catheter movement and valve deployment on real-time TrueFISP imaging. Reliable flow measurements could be performed for both stent-valves after deployment using phase-contrast sequences.
The present study shows that the Medtronic CoreValve® prosthesis is potentially suited for real-time CMR-guided placement in vivo after suggested design modifications of the delivery system.
... CMR has guided-needle (18) and laser (19) atrial septal puncture and delivery of Nitinol closure devices for atrial septal defects (20)(21)(22) in swine. The use of CMR has enhanced positioning (with regard to myocardial fibrous skeleton and coronary arteries) and monitoring of transcatheter (23) and surgical transapical (24) (Fig. 1) aortic valve implants in swine with immediate evaluation of valve performance and flow. Hybrid imaging guidance for valve placement is also under development with the use of an adjacent "CMR-friendly" X-ray fluoroscope at the edge of the magnet (25). ...
Cardiovascular magnetic resonance (CMR) combines excellent soft-tissue contrast, multiplanar views, and dynamic imaging of cardiac function without ionizing radiation exposure. Interventional cardiovascular magnetic resonance (iCMR) leverages these features to enhance conventional interventional procedures or to enable novel ones. Although still awaiting clinical deployment, this young field has tremendous potential. We survey promising clinical applications for iCMR. Next, we discuss the technologies that allow CMR-guided interventions and, finally, what still needs to be done to bring them to the clinic.
... Real time MRI guided endograft treatment of aortic dissec-tion in swine relative to vital structures such as coronary artery ostia. Kuehne and colleagues [103] have reported preliminary experience deploying a passively-visualized nitinol-based aortic valve prosthesis from a transfemoral approach in healthy swine. Their work demonstrates the value of combined device and tissue imaging for precise placement of critical prostheses. ...
The often touted advantages of MR guidance remain largely unrealized for cardiovascular interventional procedures in patients. Many procedures have been simulated in animal models. We argue these opportunities for clinical interventional MR will be met in the near future. This paper reviews technical and clinical considerations and offers advice on how to implement a clinical-grade interventional cardiovascular MR (iCMR) laboratory. We caution that this reflects our personal view of the "state of the art."
Valvular heart disease remains as a major cause of morbidity and mortality in the aging population around the world. For patients with advanced, symptomatic disease, surgical open-heart valve replacement or repair remains the standard treatment with both excellent short- and long-term outcomes. However, there are many older patients that are not considered surgical candidates, especially those with comorbidities. Often medical management alone is not enough for these high-risk patients; thus, less-invasive transcatheter approaches for valve repair/implantation have been developed and are growing in use. This chapter will discuss advanced 3D imaging in such patients during the applications of such procedures.
Introduction:
Image-guided endovascular interventions, performed using the insertion and navigation of catheters through the vasculature, have been increasing in number over the years, as minimally invasive procedures continue to replace invasive surgical procedures. Such endovascular interventions are almost exclusively performed under x-ray fluoroscopy, which has the best spatial and temporal resolution of all clinical imaging modalities. Magnetic resonance imaging (MRI) offers unique advantages and could be an attractive alternative to conventional x-ray guidance, but also brings with it distinctive challenges.
Areas covered:
In this review, the benefits and limitations of MRI-guided endovascular interventions are addressed, systems and devices for guiding such interventions are summarized, and clinical applications are discussed.
Expert opinion:
MRI-guided endovascular interventions are still relatively new to the interventional radiology field, since significant technical hurdles remain to justify significant costs and demonstrate safety, design, and robustness. Clinical applications of MRI-guided interventions are promising but their full potential may not be realized until proper tools designed to function in the MRI environment are available. Translational research and further preclinical studies are needed before MRI-guided interventions will be practical in a clinical interventional setting.
Magnetic resonance image guidance for cardiovascular interventions has grown in recent years from a research tool to translation into clinical practice. The scope of improved visualization of cardiovascular anatomy, tissue characterization, physiologic information, and reduced ionizing radiation from cardiovascular magnetic resonance (CMR) is attractive compared to conventional fluoroscopic cardiac catheterization techniques. This is particularly relevant to a pediatric population who are more at risk from radiation, and more likely to need repeat interventions in the future.
Industry support has increased the development of interventional CMR systems. New generation scanners allow for faster scanning protocols, which translate into improved catheter visualization and tracking. The platforms for interacting with these images are also more intuitive. CMR conditional hardware in the form of catheters and guidewires is more available, although more work is still needed in this area.
These advances are balanced with the need to maintain safety issues in a CMR environment and any risks from heating. While there is some limitation in the available hardware options for sole CMR guidance, x-ray fused with CMR allows physiologic testing in the assessment of pulmonary avascular resistance as an example. There is now a growing body of early human experience or interventional cases, electrophysiology testing, and radiofrequency ablation in the CMR environment. These are discussed in the chapter.
Interventional cardiovascular MRI (or “iCMR”) is potentially revolutionary because of the exquisite tissue and blood imaging afforded to guide therapeutic procedures. By making small compromises in spatial or temporal resolution, and with little or no modifications to commercial high-performance MRI systems, images can be acquired and displayed almost instantaneously to operators. This may be useful simply to avoid ionizing radiation during conventional catheter-based procedures, especially in children. Perhaps more important, iCMR promises to enable more advanced procedures not otherwise possible without open surgical exposure.
In recent times, MRI guidance and cardiovascular intervention have become intricately entwined. Detailed, accurate physiological information using combined invasive and MRI data is becoming the clinical gold standard. Image fusion is being used to improve interventional techniques. Immediate post-interventional physiological feedback from MRI has become feasible. Recent advances have seen the advent of successful interventional percutaneous catheterization in patients using only MRI guidance. MRI has also played a key role in multimodality data acquisition for patient-specific biophysical modeling. This advance, in particular, may hold the key to targeted cardiovascular treatments and interventions at the patient level. This chapter aims to describe the rationale behind the use of cardiovascular MR for these applications explain the processes involved and understand the current limitations.
In selected patient populations with valvular heart disease, minimally invasive surgical and transcatheter procedures are becoming an alternative to standard open surgical approaches. Because these procedures are characterized by limited or no direct exposure of the operative field, pre-procedural planning and intraoperative decision making rely heavily on image guidance.
Standard two-dimensional imaging with conventional angiography and echocardiography is integral part of the procedures, and novel three-dimensional (3D) imaging approaches are increasingly used for pre- and intraoperative visualization. Pre-procedural 3D imaging provides detailed understanding of the operative field for surgical/interventional planning, while subsequent integration of imaging during the procedure allows real-time guidance. These images are also used as inputs to computational modeling, which is fundamental to device design.
This chapter describes the role of advanced imaging for interventional guidance of valvular procedures and their input to computational models, based on the emerging experience with computed tomography and other modalities allowing 3D imaging, including C-arm computed tomography, echocardiography, and magnetic resonance imaging.
Real-time magnetic resonance imaging (rtMRI) is a compelling modality for guidance of surgical interventions. An effective toolkit for planning and guidance of surgery using rtMRI includes continuously updated images with excellent soft tissue contrast, devices that are visible in the images, interactively adjustable imaging parameters, simultaneous imaging and display of multiple intersecting oblique planes, and the ability to measure blood flow and perfusion. MRI has the benefit of not exposing the patient, physician, or staff to ionizing radiation from X-rays. This chapter describes the initial experience in the development of minimally invasive surgical implantation of an aortic valve in the beating heart, using continuously updated rtMRI. The potential benefits of this approach include reduction of patient trauma from open heart surgery using cardiopulmonary bypass, and the ability to implant a more robust device than can be delivered by catheter-based methods. Since the heart is a moving target, the surgeon is guided by continuously updated images, rather than those previously acquired as in stereotactic procedures.
The use of MR guidance for endovascular intervention is appealing because of its lack of ionizing radiation, high-contrast visualization of vessel walls and adjacent soft tissues, multiplanar capabilities, and potential to incorporate functional information such as flow, fluid dynamics, perfusion, and cardiac motion. This review highlights state-of-the-art imaging techniques and hardware used for passive tracking of endovascular devices in interventional MR imaging, including negative contrast, passive contrast, nonproton multispectral, and direct current techniques. The advantages and disadvantages of passive tracking relative to active tracking are also summarized.
MRI-or combined X-ray and MRI (XMR)-guided catheterization was introduced as an alternative to X-ray-guided catheterization to reduce radiation exposure and offer more comprehensive anatomical, hemodynamic and physiological data. However, developments have been slow to come into routine clinical practice. We report a 10-year experience of solely MRI-guided and XMR catheterization in patients at our institution, review the developments in clinical MRI-guided and XMR catheterization and discuss future perspectives. This includes further results from our clinical trial on MRI-guided cardiac interventions.
Magnetic resonance imaging is now established as the gold standard for the diagnosis and management of a range of diseases. In cardiology, the technique's high spatial and temporal resolution makes it possible to quantify and characterize anatomical structures with great precision. Consequently, it has played a key role in evaluating the results of translational research. This article contains a review of the application of magnetic resonance imaging in animal models, from the smallest species to the animal used most frequently in cardiovascular translational research – the pig. The different contrast media available are discussed, and a systematic guide to the cardiac studies that give the best anatomical and physiological results is presented.
Chronic totally occluded coronary arteries are frequently found in symptomatic patients undergoing diagnostic coronary angiography. However, the presence of such an artery has a significant impact on choice of revascularization treatment. This case report shows the potential of preprocedural multislice computed tomography coronary angiography in guiding percutaneous revascularization of chronic totally occluded coronary arteries. Heart Metab. 2007;34:30-32.
This chapter will address recent developments in MR guided cardiac catheterization and give the reader a better understanding of this novel technique. The rationale behind the development of MR guided cardiac catheterization will be explained with respect to improved anatomical information, increased physiological information and reduced x-ray exposure. In addition, the technical requirements and MR guided cardiac catheterisation will be discussed. Finally, animal and human studies using MR guided cardiac catheterisation will be discussed.
IntroductionInterventional MRI systemsAdvantages of MR-guided proceduresMR instrumentation and visualization strategiesSafety issuesXMR guidanceFuture perspectivesConclusion
AcknowledgmentsReferences
MR guidance has been used recently to navigate endovascular catheters and deliver stents in large (aorta and pulmonary) and small (coronary, renal, and femoral) arteries, place ASD closure devices, deliver pulmonary valve stents, guide cardiac RF ablations, and perform intramyocardial injections. However, MR visualization of a stent lumen is still a problem and requires more attention. Because of technical limitations and safety concerns associated with the prototype devices used, limited numbers of clinical studies have been performed. Considerable development is necessary to overcome the challenges and take advantage of the benefits that MR has to offer for endovascular interventions. In this article we review the current state of the art and address the topic partly by referring to our own experiments and presenting our recent illustrations. J. Magn. Reson. Imaging 2005. © 2005 Wiley-Liss, Inc.
Real-time magnetic resonance imaging is attractive to guide minimally invasive treatment of structural heart disease not only because it can spare radiation but also because soft tissue imaging may add value. Interventional cardiovascular magnetic resonance imaging will allow simple as well as novel non-surgical treatments of structural heart disease in children. Real-time MRI tools already are available. Catheter tools are emerging. A handful of pediatrics hospitals are installing investigational systems now to explore this promising technology.
We read with interest the report of all-cause mortality in patients with Fidelis leads as compared with those with nonadvisory leads ([1][1]). Among 1,030 Fidelis patients (Minneapolis, Minnesota) and 1,641 Quattro patients (Minneapolis, Minnesota) over a mean follow-up period of 34.4 and 39.9
Real-time magnetic resonance imaging (rtMRI) is considered attractive for guiding transarterial aortic valve implantation (TAVI). Compared with X-ray fluoroscopy, rtMRI offers unrestricted scan plane orientation and an unsurpassed soft-tissue contrast with simultaneous device visualization,
The rapid expansion of less invasive surgical and transcatheter cardiovascular procedures for a wide range of cardiovascular conditions, including coronary, valvular, structural cardiac, and aortic disease has been paralleled by novel three-dimensional (3-D) approaches to imaging. Three-dimensional imaging allows acquisition of volumetric data sets and subsequent off-line reconstructions along unlimited 2-D planes and 3-D volumes. Pre-procedural 3-D imaging provides detailed understanding of the operative field for surgical/interventional planning. Integration of imaging modalities during the procedure allows real-time guidance. Because computed tomography routinely acquires 3-D data sets, it has been one of the early imaging modalities applied in the context of surgical and interventional planning. This review describes the continuum of applications from pre-operative planning to procedural integration, based on the emerging experience with computed tomography and rotational angiography, respectively. At the same time, the potential adverse effects of imaging with X-ray-based tomographic or angiographic modalities are discussed. It is emphasized that the role of imaging guidance in this context remains unclear and will need to be evaluated in clinical trials. This is in particular true, because data showing improved outcome or even non-inferiority for most of the emerging transcatheter procedures are still lacking.
To assess the feasibility and effectiveness of rapid right ventricular pacing with a magnetic resonance (MR)-compatible pacemaker lead during MR-guided aortic valvuloplasty.
This study was approved by the institutional animal research committee. Seven pigs were investigated. All experiments were performed with an interventional 1.5-T MR system. Interventions were monitored with a steady-state free precession real-time imaging sequence. An MR-compatible pacemaker lead was placed in the right ventricular apex with MR guidance before valvuloplasty. After positioning the balloon in valve position, valvuloplasty was performed with rapid right ventricular rapid pacing at a heart rate of 180 beats per minute to minimize cardiac output.
Positioning of the pacemaker lead with MR guidance was feasible in all swine (sensing, 6 mV +/- 1; threshold, 1 V +/- 0.5). The lead could be seen on steady-state free precession images without inducing any artifacts. Rapid right ventricular pacing was feasible in all swine, and balloon stability at the time of inflation was achieved with no balloon movement. Aortic valvuloplasty was successfully accomplished in all experiments.
Rapid right ventricular pacing with an MR-compatible pacemaker lead is feasible and effective.
Percutaneous intervention for valvular heart disease is becoming a reality and is one of the fastest growing fields in interventional cardiology. As exposure and visualization are critical for surgical repair or replacement, adequate imaging is crucial for transcatheter interventions where direct visualization is not possible. X-ray and ultrasound are the fundamental modalities for imaging in this situation, although magnetic resonance related imaging is under development. In this review, we describe the use of fluoroscopic, computed tomographic, and echo imaging for rapidly evolving percutaneous valve technologies with a focus on providing clinical pearls and perspective on each imaging tool.
Growth factor-dependent cell proliferation can cause in-stent neointimal hyperplasia. The study aim was to evaluate whether oral everolimus inhibits the intimal proliferation associated with the implantation of prosthetic pulmonary valved stents.
Prosthetic pulmonary valves were implanted in 12 pigs (mean bodyweight 25 kg) using a transcatheter technique. Tricuspid valves were prepared from a titanium-coated polymer and sewn into a self-expanding nitinol stent (diameter 20 mm). Valved stents were implanted in the pulmonary position, where they remained for three months. In six animals, treatment with 2 mg/kg everolimus (Certican; Novartis) per day was started three days before implantation and continued throughout the course of the experiment. The other six pigs acted as controls. Adjuvant anticoagulation treatment consisted of acetylsalicylic acid and oral clopidogrel. After three months, hemodynamic valve function was investigated at catheterization and with MRI. At postmortem investigation the valved stents were explanted and subjected to macroscopic, histological and electron microscopic examination.
There were no adverse side effects due to everolimus treatment. The overall mean everolimus plasma level during the study was 4.2 +/- 2.4 ng/ml. MRI revealed intact valve function with a regurgitation fraction of 7.3 +/- 4.2% in controls and 4.3 +/- 3.1% in the everolimus group (p <0.01). On macroscopic inspection and histological examination, the everolimus group showed only a thin tissue coverage of the stent struts. The valve cusps were free from intimal thickening, and electron microscopy showed a thin continuous cellular coating. In contrast, substantial neointimal formation was noted in controls. Tissue neogenesis was pronounced at the base of the valve, extended to the valve cusps, and caused valve thickening and foreshortening.
The oral administration of everolimus effectively inhibits tissue neogenesis in pulmonary valved stents in pigs.
The authors performed this study to report their initial preclinical experience with real-time magnetic resonance (MR) imaging-guided atrial septal puncture by using a MR imaging-conspicuous blunt laser catheter that perforates only when energized.
The authors customized a 0.9-mm clinical excimer laser catheter with a receiver coil to impart MR imaging visibility at 1.5 T. Seven swine underwent laser transseptal puncture under real-time MR imaging. MR imaging signal-to-noise ratio profiles of the device were obtained in vitro. Tissue traversal force was tested with a calibrated meter. Position was corroborated with pressure measurements, oximetry, angiography, and necropsy. Intentional non-target perforation simulated serious complication.
Embedded MR imaging antennae accurately reflected the position of the laser catheter tip and profile in vitro and in vivo. Despite having an increased profile from the microcoil, the 0.9-mm laser catheter traversed in vitro targets with similar force (0.22 N +/- 0.03) compared with the unmodified laser. Laser puncture of the atrial septum was successful and accurate in all animals. The laser was activated an average of 3.8 seconds +/- 0.4 before traversal. There were no sequelae after 6 hours of observation. Necropsy revealed 0.9-mm holes in the fossa ovalis in all animals. Intentional perforation of the aorta and atrial free wall was evident immediately.
MR imaging-guided laser puncture of the interatrial septum is feasible in swine and offers controlled delivery of perforation energy by using an otherwise blunt catheter. Instantaneous soft tissue imaging provides immediate feedback on safety.
Real-time MR imaging (rtMRI) is now technically capable of guiding catheter-based cardiovascular interventions. Compared with x-ray, rtMRI offers superior tissue imaging in any orientation without ionizing radiation. Translation to clinical trials has awaited the availability of clinical-grade catheter devices that are both MRI visible and safe. We report a preclinical safety and feasibility study of rtMRI-guided stenting in a porcine model of aortic coarctation using only commercially available catheter devices.
Coarctation stenting was performed wholly under rtMRI guidance in 13 swine. rtMRI permitted procedure planning, device tracking, and accurate stent deployment. "Active" guidewires, incorporating MRI antennas, improved device visualization compared with unmodified "passive" nitinol guidewires and shortened procedure time (26+/-11 versus 106+/-42 minutes; P=0.008). Follow-up catheterization and necropsy showed accurate stent deployment, durable gradient reduction, and appropriate neointimal formation. MRI immediately identified aortic rupture when oversized devices were tested.
This experience demonstrates preclinical safety and feasibility of rtMRI-guided aortic coarctation stenting using commercially available catheter devices. Patients may benefit from rtMRI in the future because of combined device and tissue imaging, freedom from ionizing radiation, and the ability to identify serious complications promptly.
Over the last 10 years, a number of technological advances have allowed real-time magnetic resonance imaging to guide cardiac catheterization, including improved image quality, faster scanning times, and open magnets allowing access to the patient. Potential advantages include better soft tissue imaging to improve catheter manipulation and additional functional information to assist with interventional decision-making, all without exposure to ionizing radiation. MRI-guided diagnostic catheterization, balloon dilation, stent placement, valvar replacement, atrial septal defect closure, and radiofrequency ablation all have been shown feasible in animal models. MRI-guided catheterization has the potential to replace the current X-ray-based diagnostic and interventional procedures for children with congenital heart disease, avoiding all radiation exposure while improving soft tissue imaging.
Interventional cardiovascular magnetic resonance imaging (iCMR) refers to catheter-based therapeutic procedures using MRI rather than conventional radiographic guidance. iCMR promises to further blur the distinction between medical and surgical therapeutics by permitting surgical-quality “exposure” in minimally invasive procedures. Catheter-based procedures conducted without x-rays may be useful in avoiding or reducing radiation exposure to children1 and clinical staff,2 in avoiding nephrotoxic radiocontrast,3 and in reducing staff musculoskeletal injury4 from x-ray–protective lead aprons. More important, iCMR is exciting because it should permit an entirely new range of procedures otherwise attainable only with open surgical exposure. iCMR requires “real-time” imaging, which for our purposes means image acquisition and display to clinicians, completely refreshed 1 to 10 frames per second, depending on the application, within a short delay (approximately 250 ms).
Clinical investigational procedures have begun at several centers. The chief limitation to clinical translation, at present, appears to be the availability of clinical-grade catheter devices. This brief review will survey interventional cardiovascular imaging, treatment, and patient handling considerations; unique iCMR catheter design requirements; proof-of-concept animal and clinical experiments conducted to date; and novel applications we can expect in the near future.
MRI is possible because water protons, ubiquitous in tissue and blood, have magnetic moments (or “spins”) that align in a magnetic field like compass needles. These spins have a characteristic resonance frequency at which they absorb electromagnetic radiation, a frequency that varies with the intensity of the surrounding magnetic field. Exposed to radio waves, spins become energized at these characteristic frequencies and afterward emit radio signals (“relax”), a process that can be detected with sensitive radio hardware. Pictures of tissues inside the magnet bore are created by “encoding” the position of proton spins in space by using small magnetic field changes (gradients). The positions correspond to known emitted …
MRI guidance of percutaneous transluminal balloon angioplasty (PTA) of aortic coarctation (CoA) would be desirable for continuous visualization of anatomy and to eliminate x-ray exposure. The aim of this study was (1) to determine the suitability of MRI-controlled PTA using the iron oxide-based contrast medium Resovist (ferucarbotran) for catheter visualization and (2) to subsequently apply this technique in a pilot study with patients with CoA.
The MRI contrast-to-noise ratio and artifact behavior of Resovist-treated balloon catheters was optimized in in vitro and animal experiments (pigs). In 5 patients, anatomy of the CoA was evaluated before and after intervention with high-resolution respiratory-navigated 3D MRI and multiphase cine MRI. Position monitoring of Resovist-treated catheters was realized with interactive real-time MRI. Aortic pressures were continuously recorded. Conventional catheterization was performed before and after MRI to confirm interventional success. During MRI, catheters filled with 25 micromol of iron particles per milliliter of Resovist produced good signal contrast between catheters and their background anatomy but no image distortion due to susceptibility artifacts. All MRI procedures were performed successfully in the patient study. There was excellent agreement between the diameters of CoA and pressure gradients as measured during MRI and conventional catheterization. In 4 patients, PTA resulted in substantial widening of the CoA and a decrease in pressure gradients. In 1 patient, PTA was ineffective.
The MRI method described represents a potential alternative to conventional x-ray fluoroscopy for catheter-based treatment of patients with CoA.
Endovascular recanalization (guidewire traversal) of peripheral artery chronic total occlusion (CTO) can be challenging. X-ray angiography resolves CTO poorly. Virtually "blind" device advancement during x-ray-guided interventions can lead to procedure failure, perforation, and hemorrhage. Alternatively, MRI may delineate the artery within the occluded segment to enhance procedural safety and success. We hypothesized that real-time MRI (rtMRI)-guided CTO recanalization can be accomplished in an animal model.
Carotid artery CTO was created by balloon injury in 19 lipid-overfed swine. After 6 to 8 weeks, 2 underwent direct necropsy analysis for histology, 3 underwent primary x-ray-guided CTO recanalization attempts, and the remaining 14 underwent rtMRI-guided recanalization attempts in a 1.5-T interventional MRI system. Real-time MRI intervention used custom CTO catheters and guidewires that incorporated MRI receiver antennae to enhance device visibility. The mean length of the occluded segments was 13.3+/-1.6 cm. The rtMRI-guided CTO recanalization was successful in 11 of 14 swine and in only 1 of 3 swine with the use of x-ray alone. After unsuccessful rtMRI (n=3), x-ray-guided attempts were also unsuccessful.
Recanalization of long CTO is entirely feasible with the use of rtMRI guidance. Low-profile clinical-grade devices will be required to translate this experience to humans.
Interventional cardiovascular magnetic resonance imaging (iCMR) is potentially revolutionary because of the exquisite tissue and blood imaging afforded to guide therapeutic procedures. By making small compromises in spatial or temporal resolution, and with little or no modifications to commercial high-performance magnetic resonance imaging (MRI) systems, images can be acquired and displayed almost instantaneously to operators. This may be useful simply to avoid ionizing radiation during conventional catheter-based procedures, especially in children. Perhaps more important, iCMR promises to enable more advanced procedures not otherwise possible without open surgical exposure.
Background— The design of a percutaneous implantable prosthetic heart valve has become an important area for investigation. A percutaneously implanted heart valve (PHV) composed of 3 bovine pericardial leaflets mounted within a balloon-expandable stent was developed. After ex vivo testing and animal implantation studies, the first human implantation was performed in a 57-year-old man with calcific aortic stenosis, cardiogenic shock, subacute leg ischemia, and other associated noncardiac diseases. Valve replacement had been declined for this patient, and balloon valvuloplasty had been performed with nonsustained results.
Methods and Results— With the use of an antegrade transseptal approach, the PHV was successfully implanted within the diseased native aortic valve, with accurate and stable PHV positioning, no impairment of the coronary artery blood flow or of the mitral valve function, and a mild paravalvular aortic regurgitation. Immediately and at 48 hours after implantation, valve function was excellent, resulting in marked hemodynamic improvement. Over a follow-up period of 4 months, the valvular function remained satisfactory as assessed by sequential transesophageal echocardiography, and there was no recurrence of heart failure. However, severe noncardiac complications occurred, including a progressive worsening of the leg ischemia, leading to leg amputation with lack of healing, infection, and death 17 weeks after PHV implantation.
Conclusions— Nonsurgical implantation of a prosthetic heart valve can be successfully achieved with immediate and midterm hemodynamic and clinical improvement. After further device modifications, additional durability tests, and confirmatory clinical implantations, PHV might become an important therapeutic alternative for the treatment of selected patients with nonsurgical aortic stenosis.
Received September 5, 2002; revision received October 18, 2002; accepted October 20, 2002.
To date, the surgical approach is the only option to replace the aortic valve. Percutaneous pulmonary valve replacement has recently opened new perspectives on transcatheter replacement of cardiac valves. We report our experience of aortic valve replacement through a percutaneous technique in lambs.
A bovine jugular vein containing a valve was dissected and sutured into a stent. Twelve lambs were divided into 3 groups. In the first, a valved stent was implanted in the descending aorta after creation of an aortic insufficiency. In the second, the valve was implanted in the native position. In the third, we inserted a valved stent in the native position using an orientation mechanism. All valves were successfully delivered and functioned perfectly in short-term evaluation. All experiments in group 2 failed: 1 valve obstructed the coronary artery orifices, 1 stent was responsible for a major mitral valve insufficiency, and the third implant migrated prematurely. A paraprosthetic leak occurred in the last animal in this group. Animals in group 3 had successful implantation of the valved stent. The orientation mechanism allowed perfect alignment of the device without any damage to the coronary circulation or to mitral valve function.
Nonsurgical implantation of an aortic valve is possible in lambs in the descending aorta and in the native position. An orientation mechanism is obviously needed to avoid obstruction of the coronary orifices. With further improvements, this technique should be feasible in humans.
The design of a percutaneous implantable prosthetic heart valve has become an important area for investigation. A percutaneously implanted heart valve (PHV) composed of 3 bovine pericardial leaflets mounted within a balloon-expandable stent was developed. After ex vivo testing and animal implantation studies, the first human implantation was performed in a 57-year-old man with calcific aortic stenosis, cardiogenic shock, subacute leg ischemia, and other associated noncardiac diseases. Valve replacement had been declined for this patient, and balloon valvuloplasty had been performed with nonsustained results.
With the use of an antegrade transseptal approach, the PHV was successfully implanted within the diseased native aortic valve, with accurate and stable PHV positioning, no impairment of the coronary artery blood flow or of the mitral valve function, and a mild paravalvular aortic regurgitation. Immediately and at 48 hours after implantation, valve function was excellent, resulting in marked hemodynamic improvement. Over a follow-up period of 4 months, the valvular function remained satisfactory as assessed by sequential transesophageal echocardiography, and there was no recurrence of heart failure. However, severe noncardiac complications occurred, including a progressive worsening of the leg ischemia, leading to leg amputation with lack of healing, infection, and death 17 weeks after PHV implantation.
Nonsurgical implantation of a prosthetic heart valve can be successfully achieved with immediate and midterm hemodynamic and clinical improvement. After further device modifications, additional durability tests, and confirmatory clinical implantations, PHV might become an important therapeutic alternative for the treatment of selected patients with nonsurgical aortic stenosis.
To assess the feasibility of using magnetic resonance (MR) imaging to guide stent deployment in the pulmonary valve and artery and evaluate, after stent deployment, the position and morphology of and blood flow through the stent.
Angiography and 1.5-T MR imaging were performed in a dual-imaging suite. Nitinol stents were placed in the pulmonary valve and main pulmonary artery in five pigs by using MR imaging guidance. For interactive MR imaging monitoring of catheter manipulation and stent delivery, balanced fast field-echo and T1-weighted turbo field-echo sequences were used. Visualization of the delivery system was based on T2* (with air as the contrast material) or T1 (with gadodiamide as the contrast material). After stent deployment, the position and morphology of and flow through the stent were verified with multiphase multisection balanced fast field-echo and velocity-encoded cine MR imaging. Findings at angiography and postmortem examination also helped verify stent placement. The paired Student t test was used for data analysis.
The stent was successfully deployed in all animals. The stent was placed distal to the pulmonary valve in four animals and across the pulmonary valve in one animal. The position and morphology of the stent were clearly depicted on balanced fast field-echo images. In the animal with the stent placed across the pulmonary valve, the pulmonary regurgitant fraction was 37%; this was not seen in the animals with stents placed distal to the pulmonary valve. No complication (eg, stent migration, intramural injury, or vascular perforation) was noted during the intervention. Findings at angiography and postmortem examination confirmed the position of the stents.
MR imaging has the potential to guide stent placement in the pulmonary valve or artery and to evaluate flow volume within the stent lumen after the intervention.