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The clinical utility of ventricular electrograms in comparison to atrial and ventricular electrograms in diagnosing the type of tachycardias recorded by an implantable defibrillator has not been addressed from the standpoint of a clinician's diagnostic accuracy and confidence in that diagnosis.
Fifty-two tachycardia episodes recorded from dual cham...
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Citations
... stored arrhythmia events triggering ICD therapy. 7 Correct diagnosis of arrhythmia treated by ICD is critical for guiding an appropriate therapeutic approach. ...
In patients known to be a high risk for sudden cardiac arrest, implantable cardioverter defibrillators (ICD) are a proven therapy to reduce risk of death. However, in patients without conventional indications for pacing, the optimal strategy for type of device, dual- versus single-chamber, remains debatable. The benefit of prophylactic pacing in this category of patients has never been documented. Although available atrial electrograms in a dual chamber system improve interpretation of stored arrhythmia events, allow monitoring of atrial fibrillation and may potentially reduce the risk of inappropriate shocks by enhancing automated arrhythmia discrimination, the use of dual-chamber ICDs has a number of disadvantages. The addition of an atrial lead adds complexity to implantation and extraction procedures, increases procedural cost and is associated with a higher risk of periprocedural complications. The single lead pacing system with ability to sense atrial signals via floating atrial electrodes (VDD) clinically became available in early 1980's but did not gain much popularity due to inconsistent atrial sensing and concerns about the potential need for an atrial lead if sinus node fails. Most ICD patients do not have indications for pacing at implantation and subsequent risk of symptomatic bradycardia seems to be low. The concept of atrial sensing via floating electrodes has recently been revitalized in the Biotronik DX ICD system (Biotronik, SE & Co., Berlin, Germany) aiming to provide all of the potential advantages of available atrial electrograms without the risks and incremental cost of an additional atrial lead. Compared to a traditional VDD pacing system, the DX ICD system uses an optimized (15 mm) atrial dipole spacing and improved atrial signal processing to offer more reliable atrial sensing. The initial experience with the DX system indicates that the clinically useful atrial signal amplitude in sinus rhythm remains stable over time. Future studies are needed to determine reliability of atrial sensing during tachyarrhythmias, particularly atrial fibrillation as well as clinical utility and cost-effectiveness of this technology in different populations of patients.
... 17 This is not to say that atrial electrograms cannot be useful, because they certainly can help when making a diagnosis, particularly when reviewed by expert readers. 18 So, we agree with the authors' conclusion that this system "provides an attractive alternative to an additional atrial lead if one wishes to obtain an atrial electrogram in ICD patients." 10 ...
Background:
Available atrial electrograms in implantable cardioverter-defibrillators (ICD) improve arrhythmia diagnosis, allow monitoring for atrial fibrillation and may reduce the risk of inappropriate therapies. A recently introduced ICD system using a single-lead with floating atrial electrodes provides diagnostic capability of a dual-chamber system without placing an additional lead. Data on long-term clinical performance of this system are limited.
Methods:
We retrospectively analyzed data from 35 consecutive patients implanted with Biotronik VR-T DX devices and Linox (Smart) DX leads.
Results:
Out of 35 patients (77% male, age 52±11.28 years), thirty two were followed for a mean of 432 ± 197 days (range 56-765). During implantation, average pre-amplified and amplified sinus P-wave amplitudes were 2.61±1.39 mV (range 0.9-6.8 mV) and 8.7±4.51 mV (1.4-18 mV), respectively. Despite statistically significant variations, the amplified P-wave amplitude measurements (calculated mean values over 3 months) remained within a clinically acceptable range during follow up (5.4 -8.7 mV). R-wave amplitude and ventricular pacing threshold measurements were stable over time. A total of 13 stored arrhythmia events (3 ventricular tachycardia, 8 supraventricular tachycardia, 2 atrial fibrillation) were reviewed. All of them showed readily interpretable atrial electrograms. Eight out of 10 (80%) supraventricular events were correctly classified by the device. Three patients received inappropriate ICD therapies.
Conclusion:
The single lead ICD system using a floating atrial dipole provides reliable recording of atrial signals during sinus rhythm and arrhythmias. Our data suggest that the system may offer diagnostic advantages of a dual chamber device without potential risks of an additional atrial lead. This article is protected by copyright. All rights reserved.
Background:
Tachycardia diagnoses from implantable device recordings ultimately depend upon analysis of captured electrograms (EGMs). The degree to which atrial EGMs improve tachycardia discrimination, dependent upon the level of expertise of the medical professional involved, remains uncertain.
Objective:
To determine if atrial EGM recordings improve tachycardia discrimination and whether this improvement, if any, varies for professionals with different levels of training.
Methods:
Expert-adjudicated supraventricular tachycardia (SVT) and ventricular tachycardia (VT) dual-chamber EGMs (DEGMs) from the RATE Registry were provided to EP specialists (EPS), EP fellows (EPF), and nurse practitioners or physician assistants (NPPA). Each participant diagnosed 112 EGMs presented in random sequence (61 VTs, 51 SVTs) as "SVT", "VT", or "Uncertain" in two stages. First, participants analyzed ventricular EGMs (VEGMs) alone (atrial channel covered). Then, the tracings were randomized and reanalyzed with atrial EGMs exposed. The diagnostic accuracy of VEGMs alone vs. DEGMs was assessed for each group.
Results:
For all three groups, diagnostic accuracy improved significantly (>20% for VTs, >15% for SVTs, all p values < 0.01) when DEGMs were provided. EPS diagnosed VTs more accurately than EPF and NPPA (VEGM: 73.1±7.6% vs. 58.7±15.5% and 56.1±14.1%, p < 0.01; DEGM: 98.0±2.7% vs. 90.8±16.0% and 80.3±7.4%, p < 0.01). EPF diagnosed VTs more accurately than NPPA only when DEGMs were provided. There was no significant intergroup difference in SVT diagnoses.
Conclusions:
Dual-chamber EGMs are superior to ventricular EGMs alone for tachycardia discrimination at all levels of expertise. The level of training affects diagnostic accuracy with and without atrial EGMs.
During recent years, dramatic progress has been made in implantable cardioverter defibrillator (ICD) technology that has led to further reduction in generator size, improved ease of implantation, improved battery longevity, and reduction of inappropriate and unnecessary ICD therapies. Notable new technologies include the wide utilization of DF-4/IS-4 connectors, single lead dual chamber ICD system with floating atrial bipoles, novel shock reduction strategies, remote monitoring, the subcutaneous ICD system, and magnetic resonance imaging conditional ICD and resynchronization devices.
During the past 25 years, the implantable cardioverter-defibrillator (ICD) has evolved from the treatment of last resort to the gold standard for patients at high risk for lifethreatening ventricular tachyarrhythmias. Patients at high risk include those who survived life-threatening ventricular tachyarrhythmias, and patients with cardiac diseases who carry an increased risk for these tachyarrhythmias. We performed a clinical assessment during implantation and follow-up of our patients in Rotterdam.
Part I Prognosis and follow-up of patients with an ICD In Chapter 1, the clinical benefit of ICD therapy, survival, and adverse events of patients who received an ICD at the Erasmus MC Rotterdam are described. Our data confirm the benefit from ICD implantation, especially for those patients with a poor left ventricular function. In Chapter 2, defibrillation efficacy testing is investigated. The role of a second defibrillation threshold test after implantation appears questionable. With the advances in ICD technology, defibrillation thresholds are low and stable, which changed the mode of death in ICD patients from instantaneous arrhythmic death to heart failure. Our data demonstrate that despite the advanced ICD technology, a subset of patients may require a second defibrillation efficacy test to confirm a poor prognosis. The feasibility of remote monitoring of ICD therapy is discussed in Chapter 3. The expanding indications for ICD therapy and the complexity of current devices have a high impact on follow-up policy. Currently, the quality of medical supervision only depends on scheduled regular follow-up visits, which is time consuming and expensive. Too long follow-up intervals may have the disadvantage of a delay in the awareness of changes of the clinical course of the underlying disease or in the technical status of the device. Transmission of stored ICD data can overcome this problem and thus offers the potential to improve patient care. Finally, a case of Twiddler’s syndrome, which was detected by home monitoring is presented in Chapter 4.
Part II Rhythm discrimination by the ICD
The primary goal of the ICD is to detect and subsequently terminate ventricular tachyarrhythmias. The secondary goal is to deliver therapy only when necessary. Inappropriate therapy due to atrial tachyarrhythmias is the most common adverse event in ICD patients. In this second part of the thesis, rhythm discrimination by the ICD is investigated. Chapter 5 describes a confusing stored ICD electrogram. This electrogram demonstrates an apparent induction of ventricular tachycardia after appropriate pacing by the ICD. However, accurate analysis demonstrated an artefact representing a ventricular premature beat initiating the ventricular tachycardia. The initial clinical experience with a new dual-chamber algorithm, SMART, is discussed in Chapter 6. This new algorithm is based on comparison of atrial and ventricular rates, which divide tachyarrhythmias into 3 rate branches. Next, applicable single- and dual-chamber arrhythmia discriminators are applied in order to classify the tachyarrhythmia. In our series, the SMART algorithm achieved a sensitivity of 100%, with a positive predictive value of 95.6% for all ventricular arrhythmias. The majority of misclassified episodes appeared to be atrial tachyarrhythmias with stable atrioventricular conduction. In Chapter 7, the evolution of timing-based detection algorithms in ICDs is studied. Over the last 25 years, ICDs base arrhythmia discrimination on timing-based detection criteria in order to avoid inappropriate therapy for atrial tachyarrhythmias. Original single-chamber detection criteria have been implemented as such in dualchamber devices. Atrial signals can be reliably recognized with atrial leads and improved arrhythmia discrimination algorithms based on atrial signals were developed. However, this did not reduce the incidence of inappropriate therapy over time with the development of algorithms as was proven with comparative studies. Chapter 8 evaluated whether clinical characteristics can predict inappropriate therapy due to atrial tachyarrhythmias. We identified a history of atrial tachyarrhythmias and recurrent slow ventricular tachycardias, rate < 170 bpm, as independent predictors of inappropriate therapy. Whether device selection should depend on the knowledge of a history of atrial tachyarrhythmias still is open for debate, as inappropriate therapy equally occurs in patients with single- and dualchamber devices. The results of our prospective, randomized study comparing the performance of tachyarrhythmia detection algorithms in single- and dual-chamber devices are presented in Chapter 9. During a mean follow-up of 12 months, the investigators classified 653 tachyarrhythmia episodes with stored electrograms: 391 episodes were ventricular tachyarrhythmias and 262 epsiodes were atrial tachyarrhythmias.
Overall, no significant difference in tachyarrhythmia detection, atrial or ventricular, between single- and dual-chamber devices was observed. Not sinus tachycardia or atrial fibrillation were a problem, but atrial tachyarrhythmias with stable N:1 atrioventricular conduction remain a problem for both devices. In Chapter 10, a systematic approach for the analysis of stored electrograms is proposed. Stored electrograms in ICDs have not only improved our patient management, but also contributed to our understanding of tachyarrhythmias. Stored electrograms are usually visually analyzed, but the analysis can also be performed in a methodological way by application of blocks containing physiologic information.
Part III Single-chamber, dual-chamber or biventricular devices In Chapter 11, we studied factors influencing appropriate therapy and survival in ICD patients with single- and dual-chamber devices, in an era that dual chamber devices were only implanted for patients with bradycardia indication. Survival analysis demonstrated no significant difference between patients with single- and dualchamber devices for mortality and for event-free rate of appropriate therapy. A tendency to less inappropriate interventions was observed in a small series of dual chamber devices. In addition, it was observed that a history of atrial fibrillation contributed to appropriate therapy. Resynchronization therapy by means of biventricular pacing is a novel therapy for patients with heart failure and severely diminished left ventricular function associated with intracardiac conduction delay. In Chapter 12, we present a brief review of early trials evaluating the therapeutic effect of biventricular pacing. Furthermore, we propose a method to select the optimal right and left ventricular pacing sites together with a technique of left ventricular lead positioning. The incidence of ventricular tachyarrhythmias in ICD patients with resynchronization therapy is presented in Chapter 13. Event-free survival was analyzed for patients with either a primary or a secondary prevention indication for ICD therapy. Ventricular tachyarrhythmias are very common for congestive heart failure patients with a secondary prevention indication. Patients with primary prophylaxis have an annual event rate of 10%, even when they tend to have a worse heart failure class. The decision-making process to implant an ICD in heart failure patients for primary prophylaxis of sudden cardiac death has presently become a clinical decision, based on low left ventricular ejection fraction plus heart failure.
Since it has been shown that adverse events are more frequent with dual-compared to single-chamber ICDs in patients with heart failure, and since the importance of prevention of unnecessary right ventricular pacing and the success of biventricular pacing have been demonstrated in numerous studies, the need for dual-chamber ICD systems has to be reassessed. The development of these systems was accompanied by expectations of improved hemodynamics in patients with bradycardia, a reduced incidence of atrial fibrillation, inappropriate therapies, and bradycardia-associated ventricular tachyarrhythmias.
Single-chamber ICDs should be used restrictively and with great caution in patients with (sinus-) bradycardia and heart failure, since a relevant proportion of these patients is at risk of hemodynamic deterioration. Even if the proportion of patients with proven pacemaker syndrome is so small that it does not reach the level of statistical significance in large studies, a small percentage of patients with hemodynamic deterioration due to VVI pacing is still clinically (and economically) intolerable. Since the development of bradycardia or symptomatic chronotropic incompetence (e.g., due to amiodarone) is difficult to predict, it seems reasonable to use the indication for dualchamber systems liberally. However, the systematic prevention of unnecessary right ventricular pacing is crucial if dual-chamber ICDs are used.
If advanced tachycardia discrimination algorithms and careful, individual programming are used, dual-chamber ICDs are superior in the prevention of inappropriate therapies. Additionally, dualchannel electrograms allow a more reliable interpretation of stored tachycardia episodes. In summary, dual-chamber systems represent a valuable improvement of ICD therapy but require thorough programming to convey their advantage.
Many ICD carriers experience inappropriate shocks, but the relative merits of dual- /single-chamber devices for arrhythmia discrimination still remain unclear. We explored possible advantages of the atrial data provided by dual-chamber implantable defibrillators (ICD) for discrimination of real-life supraventricular/ventricular tachyarrhythmias (SVT/VT).
100 dual-chamber traces from 24 ICD were blindly reviewed in dual-chamber and simulated single-chamber (with/without discriminator data) reading modes by five electrophysiologists who determined chamber of origin and provided Likert-scale "confidence" ratings. We assessed 1) intra/interobserver concordance; 2) diagnostic accuracy, using expert diagnoses as a reference standard; 3) ROC curves of sensitivity/specificity of "likelihood perception" scores, generated by combining chamber-of-origin diagnostic judgments with Likert-scale "confidence" ratings. We also assessed diagnostic accuracy of automated discrimination by all possible dual-/single-chamber algorithm configurations.
Interobserver concordance was "substantial" (modified Cohen kappa-test values for dual-/single-chamber, 0.79/0.68); intraobserver concordance "almost complete" (kappa ≥ 0.89). Dual-chamber mode provided best diagnostic sensitivity/specificity (99%/92%) and highest reader confidence (p<0.001). Area under ROC curves of sensitivity/specificity values for the "likelihood perception" score (representing electrophysiologists' perceptions of the likelihood that an episode was of ventricular origin) was highest in dual-chamber mode (0.98 vs. 0.93 for both single-chamber modes; p<0.001). Regarding automated discrimination, all four dual-chamber configurations conferred 100% sensitivity (specificity values ranged 39%-88%), whereas single-chamber configurations appeared inferior (best sensitivity/specificity combination, 89%/64%).
Availability of the atrial channel helps in reducing inappropriate ICD therapies by providing relevant advantages in terms of both appropriate cardiologist's post-hoc discrimination of SVT/VT (improving program tailoring) and automated arrhythmia discrimination.
With wider indications for implantable cardioverter defibrillator therapy, more patients at lower risk for ventricular tachyarrhythmia receive this treatment. To maintain the ratio of benefit versus side-effects at an acceptable level, the risk of inappropriate implantable cardioverter defibrillator therapy has to be minimized.
Implantable cardioverter defibrillators require the activation of enhanced detection criteria. These can avoid inappropriate therapy of sinus tachycardia (gradual onset) and atrial fibrillation (irregular rate) while other regular supraventricular tachycardias may be misclassified even with combinations of criteria (QRS morphology, abrupt onset, regular rate). Carefully programmed, dual-chamber implantable cardioverter defibrillators provide better ventricular tachyarrhythmia/supraventricular tachycardias discrimination. Key issues are long tachycardia detection (18 cycles or more), deactivation or restrictive programming of safety therapy despite supraventricular tachycardia classification, and restriction of shock therapy to high tachycardia rates (>or=250 bpm). Further developments are necessary to reduce the incidence of inappropriate therapy due to lead failure that is more frequent in physically active patients.
With optimized programming, the rate of inappropriate ventricular tachyarrhythmia detection is significantly reduced. Particularly the prevention of inappropriate shocks has important implication for the quality of life and acceptance of implantable cardioverter defibrillator treatment.
