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Comparative Effectiveness Research 2015:5 73–79
Comparative Effectiveness Research Dovepress
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REVIEW
open access to scientific and medical research
Open Access Full Text Article
http://dx.doi.org/10.2147/CER.S62637
Off-pump versus on-pump coronary artery bypass
grafting: comparative effectiveness
Shahzad G Raja
Department of Cardiac Surgery,
Harefield Hospital, London, UK
Correspondence: Shahzad G Raja
Department of Cardiac Surgery,
Hareeld Hospital, Hill End Road,
Hareeld, Middlesex UB96JH, UK
Tel +44 18 9582 6511
Fax +44 18 9582 8992
Email drrajashahzad@hotmail.com
Background: Historically, coronary artery bypass grafting (CABG) with the use of cardio-
pulmonary bypass (CPB), referred to as on-pump CABG, has been regarded as the “gold
standard”. However, in recent years, it has been increasingly recognized that the systemic
inflammatory response associated with using CPB contributes substantially to postoperative
organ dysfunction. Intuitively, performance of CABG without CPB, referred to as off-pump
CABG, should translate into improved clinical outcomes. Interestingly, no single randomized
trial has been able to prove the superiority of off-pump CABG over on-pump CABG for all hard
outcomes, and off-pump CABG remains the subject of intense scrutiny as well as controversy.
The purpose of the review is to summarize the current best available evidence, comparing the
effectiveness of off- and on-pump CABG.
Methods: The English language scientific literature was reviewed primarily by searching
MEDLINE from January 2010 to December 2014 using PubMed interface to identify meta-
analyses and systematic reviews of randomized controlled trials as well as observational studies
using propensity score matching, comparing the effectiveness of off- and on-pump CABG.
Results: Current best available evidence from meta-analyses and systematic reviews of
randomized controlled trials as well as propensity score analyses suggests that off-pump CABG
is associated with fewer distal anastomoses, increased repeat revascularization rates, and poor
saphenous vein graft patency compared with on-pump CABG. No significant differences were
observed for other hard outcomes including mortality, myocardial infarction, and stroke.
Conclusion: Off-pump CABG compared to on-pump CABG is associated with similar short-,
mid-, and long-term mortality, comparable organ protection, and fewer distal anastomoses.
The concerns about the safety and efficacy of off-pump CABG are not substantiated by the
current best available evidence. However, the impact of learning curve on outcomes remains
a valid issue.
Keywords: cardiopulmonary bypass, coronary artery bypass grafting, off-pump coronary artery
bypass grafting, on-pump coronary artery bypass grafting, meta-analysis
Introduction
Coronary artery bypass grafting (CABG) remains the preferred treatment in patients
with complex coronary artery disease in the current era of tremendous upsurge in the
use of percutaneous interventions for the treatment of symptomatic coronary artery
disease. Traditionally, CABG has been performed with the aid of cardiopulmonary
bypass (CPB), enabling the construction of coronary anastomoses on a still heart in a
bloodless field.1 This on-pump CABG technique has remained the gold standard with
which all other surgical revascularization methods have been compared. However, con-
ventional on-pump CABG, despite its well-recognized safety and efficacy, is associated
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with a profound systemic inflammatory response secondary
to the use of CPB. This systemic inflammatory response to
CPB has the potential of causing myocardial ischemic injury,
neurocognitive deficits, strokes, as well as pulmonary, renal,
and hematologic complications.2
A rational way of counteracting the effects of this inflam-
matory response may be the avoidance of CPB itself. This
idea provided the catalyst for rejuvenation of off-pump
CABG – a technique that predates CPB but was rapidly
replaced by on-pump CABG soon after the invention of
the extracorporeal circulation.1 The initial enthusiasm that
off-pump CABG will result in superior outcomes has been
recently met with growing concern that it is associated with
incomplete revascularization, suboptimal graft patency, and
worse long-term survival compared with conventional on-
pump CABG.3 These concerns have fueled a lot of skepticism
about the place of off-pump CABG as a recognized treatment
option for coronary artery disease. The only means of
countering this skepticism is by comparing the effectiveness
of off- and on-pump CABG through the explicit and consci-
entious assessment of current best available evidence.
A logical and comprehensive approach to evaluating
clinically relevant research incorporates many different types
of evidence (including randomized controlled trials [RCTs],
nonrandomized controlled trials, and experimental data) and
analyzes the information’s content for consistency, coherence,
and clarity.4 It has long been recognized that not all research
designs are equal in terms of the risk of error and bias in
their results. When seeking answers to specific questions,
some research methods provide better evidence than that
provided by other methods. That is, the validity of the results
of research varies as a consequence of the different methods
used. For example, when evaluating the effectiveness of an
intervention, the RCT is considered to provide the most reli-
able evidence.5 It is considered the most reliable evidence
because the processes used during the conduct of an RCT
minimize the risk of confounding factors influencing the
results. As a result of this, the findings generated by RCTs
are likely to be closer to the true effect than that generated
by other research methods.5 However, the conduct of RCTs
is costly and often inefficient due to the large number of
participants needed to estimate the treatment effects with
adequate precision.6 Furthermore, conducting RCTs may
not be feasible or even ethical for all clinical questions of
interest, and restrictive selection criteria can limit the external
validity of their results.7
Observational studies are often a practical alternative to
efficiently obtain estimates of the effectiveness of treatment
in nonexperimental, routine-care settings. Nonetheless,
the lack of randomization and other RCT design elements
renders observational studies susceptible to biases, includ-
ing confounding (and particularly confounding by factors
that affect treatment choice and are also causally associated
with the outcome), selection, and differential ascertain-
ment bias.8 Proposed as a potential solution to the problem
of confounding of the treatment–outcome association, a
propensity score expresses the probability of having been
treated with an intervention based on variables measured at
or before the time of treatment.9,10 Analyses using propensity
score methods attempt to emulate randomized comparisons,
because they allow contrasts between patient groups that are
on average similar on all observed confounders.
A rational approach to comparing the effectiveness of
two treatment strategies will be to take into consideration
evidence from RCTs as well as propensity score-matched
observational studies. In recent years, with the increasing
popularity of systematic reviews, these are starting to replace
the RCT as the best source of evidence.5 This review article
attempts to assess the comparative effectiveness of off- and
on-pump CABG by evaluating the current best available
evidence from most up-to-date systematic reviews and
meta-analyses of RCTs as well as propensity score-matched
observational studies.
Methods
Search methodology
The English language scientific literature was only reviewed
primarily by searching MEDLINE from January 2010 to
December 2014 using PubMed interface.11 Keywords used
in the search included MeSH terms: meta-analysis, CPB,
extracorporeal circulation, coronary artery bypass surgery,
CABG, and off-pump coronary artery bypass. In addition,
non-MeSH terms such as systematic review, CABG, on-pump
coronary artery bypass surgery, OPCAB, off-pump coronary
artery bypass surgery, and beating heart coronary artery
surgery were also used. The “related articles” function was
used to broaden the search, and all abstracts, studies, and cita-
tions scanned were reviewed. The reference lists of articles
found through these searches were also reviewed for relevant
articles. In addition, links on Web sites (e-library, CINAHL
[Cumulative Index to Nursing and Allied Health Literature],
DARE [Database of Abstracts of Reviews of Effectiveness],
and EMBASE) containing published articles were searched
for relevant information. The author of this article chose
systematic reviews and meta-analysis of RCTs only relevant
to the topic. The search was done in stages so as to achieve
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75
Off-pump versus on-pump CABG
the search strategy with a high sensitivity (meaning that it
has the highest likelihood of retrieving all relevant articles).
Similar search terms were combined using the Boolean
operator “OR” to find all abstracts that contained information
about a particular search term. These individual terms were
then combined using the Boolean operator “AND” to find
articles that contained information on all the search terms.
This is a well-recognized method for performing sensitive
searches and has been described in detail in the British
Medical Journal.12
Inclusion criteria
All meta-analyses or systematic reviews of blinded or
unblinded RCTs as well as propensity score-matched
observational studies comparing off-pump CABG on the
beating heart with conventional on-pump CABG on CPB
using cardioplegic arrest, recruiting adult human patients
undergoing multivessel bypass grafting, and reporting
impact of these two techniques on any clinical outcome
published between January 2010 and December 2014 were
included. Meta-analyses reporting on the outcomes of
hybrid revascularization procedures, robotically assisted
surgery, using circulatory assist devices, or comparing
off-pump CABG with drug-eluting stents were excluded.
The rationale for including meta-analyses or systematic
reviews published from January 2010 onward was only to
ensure that the meta-analyses included ROOBY, DOORS,
CORONARY, and GOPCABE trials, the four large multi-
institutional trials that first reported the outcomes in 2009,
2012, and 2013.13–16
Data extraction and validation of the
studies
The articles found by the search strategy (Figure 1) were then
appraised. The appraisal of each article was performed in a
structured format, using critical appraisal checklists. These
are widely available in several formats and aid in assessing
the article for methodological and analytical soundness and
help uncover any significant methodological flaws.17 The
following information was extracted from each study: first
author, year of publication, included studies, number of
patients operated on with each technique, and key outcomes
(Table 1).
Results
Evidence from meta-analysis of RCTs
In-hospital mortality
Sá et al18 published a meta-analysis of 47 RCTs including
a total of 13,524 patients (6,758 for off-pump and 6,766
for on-pump CABG). The in-hospital or 30-day mortality
498 Studies identified from
database(s) search 29 Studies identified through references and related
articles
Studies outside January 2010–December 2014
period (n=282)
Title or abstract not appropriate (n=120)
Narrative reviews excluded (n=58)
Systematic reviews of OS (n=36)
Systematic reviews comparing OPCAB with strategies
other than on-pump CABG (n=14)
Outdated systematic reviews (n=9)
527 Studies identified in initial
search
245 Studies identified and
screened for retrieval
125 Studies retrieved for more
detailed evaluation
Eight latest meta-analyses
deemed appropriate and included
Figure 1 Search strategy.
Abbreviations: OS, observational studies; OPCAB, off-pump coronary artery bypass; CABG, coronary artery bypass grafting.
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Raja
showed no statistical significant difference between off-
pump CABG compared to on-pump CABG (random-effect
model: risk ratio [RR] 0.938, 95% confidence interval [CI]
0.731–1.203, P=0.612).
Mid-term mortality
Chaudhry et al19 in their recently published meta-analysis
reported that off-pump CABG confers similar overall mid-
term survival when compared with on-pump CABG (hazard
ratio [HR] 1.06, 95% CI 0.95–1.19, P=0.31). Zhang et al20
also confirmed that off-pump CABG does not increase 1-year
mortality compared to on-pump CABG.
Mid-term major cardio- and cerebrovascular events
Takagi et al published a meta-analysis of eight large RCTs
including 10,954 patients randomized to off-pump or on-
pump CABG. A pooled analysis demonstrated no statisti-
cally significant difference in off- and on-pump CABG in
the random-effects model for mid-term major cardio- and
cerebrovascular events (HR 1.10, 95% CI 0.93–1.29, P for
effect =0.27; P for heterogeneity =0.03).21
Graft patency
Zhang et al22 reported an increased risk of occlusion of all
grafts (RR 1.35, 95% CI 1.16–1.57) and saphenous vein grafts
(SVGs) (RR 1.41, 95% CI 1.24–1.60) in the off-pump CABG
group, whereas there was no significant difference in graft
occlusion of left internal mammary artery (RR 1.15, 95% CI
0.83–1.59) and radial artery (RR 1.37, 95% CI 0.76–2.47)
grafts between off- and on-pump CABG.22 This was a meta-
analysis of 12 RCTs, for a total of 3,894 and 4,137 grafts
performed during off- and on-pump CABG, respectively.
Repeat revascularization
Takagi et al23 published a meta-analysis to determine whether
repeat revascularization rates are increased following
off-pump CABG. Pooled analysis of 12 RCTs demonstrated a
statistically significant 38% increase in repeat revasculariza-
tion rates with off-pump relative to on-pump CABG in the
fixed-effects model (odds ratio [OR] 1.38, 95% CI 1.09–1.76,
P=0.008) at $1 year. In general, exclusion of any single
trial from the analysis did not substantively alter the overall
result of this analysis. There was no evidence of significant
publication bias.
Long-term survival
The most recently published pooled analysis of five RCTs
(1,486 patients) demonstrated a statistically nonsignifi-
cant 14% increase in mortality at $5 years with off-pump
relative to on-pump CABG (HR 1.14, 95% CI 0.84–1.56,
P=0.39).24
Evidence from meta-analysis of propensity
score-matched observational studies
Kuss et al25 published a systematic review and meta-analysis
of 35 propensity score analyses accounting for a total of
123,137 patients. The estimated overall OR was ,1 for
all outcomes, favoring off-pump surgery. This benefit was
statistically significant for mortality (OR 0.69; 95% CI
0.60–0.75), stroke, renal failure, red blood cell transfusion
(P,0.0001), wound infection (P,0.001), prolonged ventila-
tion (P,0.01), inotropic support (P=0.02), and intra-aortic
balloon pump support (P=0.05). The OR for myocardial
infarction, atrial fibrillation, and reoperation for bleeding
were not significant.
Table 1 Current best available evidence (meta-analyses of RCTs) comparing off-pump and on-pump coronary artery bypass grafting
Author (ref) Year No of RCTs Total patients No OPCAB No CPB Key outcome
Sá et al18 2012 47 13,524 6,758 6,766 Similar 30-day mortality; similar MI; 20.7%
reduction in stroke after OPCAB
Chaudhry et al19 2014 5 1,486 744 742 Similar mid-term survival
Takagi et al21 2014 8 10,954 5,481 5,473 Similar mid-term MACCE
Zhang et al22 2014 12 8,031* 3,894* 4,137* Reduced SVG patency after OPCAB;
similar LIMA and RA patency
Takagi et al23 2013 12 11,594 5,811 5,783 38% increase in RR rates after
off-pump CABG
Takagi et al24 2014 5 1,486 744 742 Statistically nonsignicant 14% increase in
long-term mortality after off-pump CABG
Note: *No of grafts analyzed (no of patients 11,594).
Abbreviations: CABG, coronary artery bypass grafting; CPB, cardiopulmonary bypass (on-pump); LIMA, left internal mammary artery; MACCE, major adverse
cardiovascular and cerebrovascular events; MI, myocardial infarction; OPCAB, off-pump coronary artery bypass; RA, radial artery; RCT, randomized controlled trial;
RR, repeat revascularization; SVG, saphenous vein graft; No, number.
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Off-pump versus on-pump CABG
Discussion
Current best available evidence in the form of meta-analyses
and systematic reviews of RCTs as well as propensity score-
matched studies confirms comparable impact of off- and
on-pump CABG on short-, mid-, and long-term mortality as
well as major cardio- and cerebrovascular events with fewer
distal anastomoses, poor SVG patency, and increased repeat
revascularization rates after off-pump CABG.18–25
Since its renaissance nearly 2 decades ago, off-pump
CABG has remained a subject of intense scrutiny. It has
been compared with the gold standard on-pump CABG in
numerous RCTs as well as large retrospective observational
studies.26 However, inability of small, prospective, RCTs that
have lacked sufficient sample size to demonstrate differences
in early and long-term outcomes coupled with mispercep-
tions and misconceptions about incomplete revascularization,
reduced long-term graft patency, and increased need for repeat
revascularization resulting in inferior long-term survival have
prompted opponents of off-pump CABG to demand abandon-
ment of this technique.3 On the other hand, proponents of
off-pump CABG claim that larger observational studies that
are better powered to statistically compare outcomes have
shown more favorable in-hospital outcomes and equivalent
long-term outcomes with off- and on-pump CABG.26
In the current era of evidence-based medicine, the logical
approach to comparing the effectiveness of two therapeutic
strategies, ie, off- and on-pump CABG, is to evaluate the
best available evidence. At present, evidence from systematic
reviews and meta-analysis is regarded as the gold standard.5
This comparative effectiveness review of off- and on-pump
CABG evaluated the current best available evidence and
found comparable effectiveness of off- and on-pump CABG
for hard outcomes.
Fewer distal anastomoses coupled with poor SVG pat-
ency are well-recognized criticisms of off-pump and also
reported by the current best available evidence.3,22 Incomplete
revascularization and poor graft patency translate into
increased repeat revascularization and are associated with
worse long-term survival.24 Grafting of vessels on the lat-
eral and inferior aspects is no longer impossible due to the
availability of modern stabilizers, heart positioning devices,
and intracoronary shunts. Hence, it is imperative that any
future RCTs reporting incomplete revascularization after
off- and on-pump CABG must provide an explanation for
failure to completely revascularize.26 Moreover, the future
trials comparing the effectiveness of off- and on-pump
CABG must include a myocardium at risk score, which is
a potentially valuable tool to aid in determining the true
significance of the non-revascularized territory, because
there is a recognized hierarchy of effect, depending on
which vessels are left ungrafted and how much myocardium
is at risk.27 Furthermore, it is equally important to understand
that completeness of revascularization and number of grafts
should not be used synonymously. In many centers, off-pump
CABG is offered to patients who only require one or two
grafts, whereas, all else equal, the same patient requiring four
or five grafts will not be considered for off-pump CABG.
A more logical way to address the issue of completeness
of revascularization is to use the index of completeness of
revascularization (number of grafts performed divided by the
number of grafts needed [number of graftable vessels with
angiographically significant stenoses]).26
Tangentially mentioned is the fact that some patients
are selected for off-pump CABG because of their high risk
status and these patients are intentionally offered incomplete
revascularization as a “lesser of two evils” or “perfection is
the enemy of good” strategy.
Similarly, any RCT comparing graft patency after off-
and on-pump CABG must provide information about the
mode of conduit harvesting as well as the experience of
conduit harvester and principal operator, important but often
unrecognized confounders. Interestingly, all concerns about
suboptimal graft patency in recent years have been predomi-
nantly attributed to ROOBY trial.13 This trial demonstrated
that the patency rate of the off-pump arm was lower than
that of the on-pump arm on 12-month angiography, and the
1-year composite adverse outcome rate (death from any
cause, nonfatal myocardial infarction, and any reintervention
procedure) was higher for off-pump than that for on-pump
CABG. Such findings can be explained on the basis that the
53 participating surgeons enrolled on average only eight
patients per year during the study period and had unaccept-
ably high conversion rates to on-pump surgery (12%) and
incomplete revascularization (18%). Moreover, in 60% of
the cases, a resident was the primary surgeon again raising
concerns about the relative inexperience translating into
poor graft patency. Another unrecognized confounder that
contributed to poor graft patency in the ROOBY trial was
the concomitant use of endoscopic vein harvesting (EVH)
in 1,471 patients (on-pump =907 and off-pump =564).13 The
incidence of a patient having one or more occluded SVGs
on follow-up angiography was 41.3% in the EVH group,
compared with 28.0% in the open vein harvesting group
(P,0.0001). Overall, SVG patency in the EVH group was
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Raja
74.5%, which was significantly worse than the 85.2% rate in
the open vein harvesting group (P,0.0001).28 Since ROOBY
trial was recruiting at a time when EVH was not being widely
practiced, the poor vein graft patency secondary to EVH can
be attributed to learning curve and relative inexperience of the
vein harvesters. Poor conduit quality, a consequence of the
learning curve for EVH, has been shown to be a predictor of
early graft failure, blunted positive remodeling, and greater
negative remodeling.29
The unique technical challenges of off-pump CABG fuel
the perception that adoption of this myocardial revascular-
ization strategy may lead to poorer outcomes during each
surgeon’s “learning curve”.30 Interestingly, those who perceive
off-pump CABG as an inferior revascularization strategy
with a steep learning curve propose it as a preferred option
for high-risk patients.3 There is no doubt that despite the
substantial learning curve associated with off-pump CABG,
early outcomes of off-pump CABG in high-risk patients
are better than those of conventional on-pump CABG.31
However, these superior outcomes in high-risk patients can
only be achieved if off-pump is offered to high- and low-
risk patients alike. In the current era, increasing number of
patients with high-risk profile is being referred for CABG.
In view of changing the patients’ profile, it will be prudent to
acknowledge that off-pump CABG is a valuable technique in
the armamentarium of cardiac surgeons and is here to stay.26
This further emphasizes the need for recognition of off-pump
CABG as a subspecialty with structured training program
to ensure that myocardial revascularization surgeons of the
future can negotiate the learning curve for off-pump safely
and perform CABG for high-risk patients as proficiently as
for low-risk patients. There is ample evidence to validate
that the learning curve in off-pump CABG can be safely
negotiated with appropriate patient selection, individual-
ized grafting strategy, peer-to-peer training of the entire
team, and graded clinical experience (preoperative planning,
adequate exposure, proximal anastomoses to the aorta, and
distal anastomoses initially to anterior wall vessels, followed
by inferior wall vessels and then lateral wall vessels).32 In
fact, centers with established off-pump training programs
have consistently shown that off-pump CABG can be safely
and successfully taught to trainees without jeopardizing
outcomes.33,34
Currently, off- and on-pump CABG have comparable
outcomes. The concerns about the safety and efficacy of
off-pump CABG are not substantiated by the current best
available evidence. However, the impact of learning curve
on outcomes remains a valid issue.
Disclosure
The author reports no conflicts of interest in this work.
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22. Zhang B, Zhou J, Li H, Liu Z, Chen A, Zhao Q. Comparison of graft
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