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. 2011 Nov 28;14(2):188–193. doi: 10.1093/icvts/ivr071

Impact of off-pump to on-pump conversion rate on post-operative results in patients undergoing off-pump coronary artery bypass

Stefano Urso a,*, Justo Rafael Sadaba b, Matteo Pettinari c
PMCID: PMC3279983  PMID: 22159253

Abstract

A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was: In patients undergoing off-pump coronary artery bypass (OPCAB) surgery, does the off-pump to on-pump conversion rate have an impact on post-operative results? Altogether more than 420 papers were found using the reported search, of which 14 randomized controlled trials (RCTs) represented the best evidence to answer the clinical question. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes and results of these papers are tabulated and ordered according to the sample size. In the 14 RCTs reviewed, the off-pump to on-pump conversion rate incidence ranged from 0 to 13.3%. The most frequent causes of conversion were haemodynamic instability and intramyocardial-coronary target. A low conversion rate (<2%) was reported by five studies. Three of them did not show any difference in terms of mortality between the OPCAB and on-pump groups, one showed better survival of the OPCAB group at 5 years, and one reported better early survival of the OPCAB group. Three of these trials describe a high OPCAB experience and reported that patients undergoing OPCAB had a shorter post-operative stay and lower morbidity compared with patients undergoing on-pump coronary artery bypass grafting. Five RCTs showed a high conversion rate (>9%), and among them, one reported lower morbidity of the OPCAB patients, three were not able to show any benefit in terms of morbidity of the OPCAB, and one reported worse survival and patency graft rate of the OPCAB group. Four RCTs reported conversion rates ranging from 3.7 to 7.0%, describing a wide spectrum of results. We conclude that RCTs with a high off-pump to on-pump conversion rate were often associated with a lower experience in OPCAB of the surgeons participating in the trials. These studies were also mostly unable to show any benefit in terms of mortality or morbidity of OPCAB over the on-pump strategy. On the contrary, a low conversion rate is mostly reported by RCTs with a high structured experience in OPCAB. These trials were mostly able to show a benefit, in terms of morbidity and survival, of the OPCAB over the on-pump strategy.

Keywords: Off-pump, OPCAB, CABG, Coronary surgery, Myocardial revascularization

INTRODUCTION

A best evidence topic was constructed according to a structured protocol. This is fully described in the ICVTS [1].

THREE-PART QUESTION

In [patients undergoing off-pump CABG] does [the off-pump to on-pump conversion rate] have an impact [on post-operative results]?

CLINICAL SCENARIO

After starting your OPCAB programme, one of the referring cardiologists at your hospital suggests you abort your project because of the bad results reported by the ROOBY trial in terms of survival. You want to check the literature for evidence on this issue.

SEARCH STRATEGY

The MEDLINE database was searched from January 1966 to May 2011. The medical subject headings keywords included OPCAB, off-pump, off-pump, beating heart. Only randomized clinical trials with a sample population of 100 or more patients were included in this review.

SEARCH OUTCOME

More than 420 papers were found using the reported search. From these, 14 papers were identified. That provided the best evidence to answer the question. These are presented in Table 1.

Table 1:

Best evidence papers

Author, date and country, study type (level of evidence) Patient group Outcomes Key results Comments
ROOBY trial: Shroyer et al., N Engl J Med 2009 [5], USA Multicentre controlled, single-blind, randomized trial (level 1b)

  • 2203 patients scheduled for urgent or elective CABG

  • Exclusion criteria: valve disease, need of immediate surgery, small target vessels, diffuse coronary disease, extremely high risk profile

 30-day survival Overall mortality: off-pump 1.6%; on-pump mortality 1.2% (P = 0.47)

  • No differences were shown in terms of 30-day mortality between the two groups

  • At 1 year of follow-up, patients in the off-pump group had higher cardiac mortality

  • Follow-up angiograms in 1371 patients grafts revealed that the overall rate of graft patency was lower in the off-pump group than in the on-pump group (82.6 vs. 87.8%, P < 0.01)
1-year survival

  • Overall mortality: off-pump 4.1%; on-pump 2.9% (P = 0.15)

  • Cardiac mortality: off-pump 2.7%; on-pump 1.3% (P = 0.03)
Off-pump to on-pump conversion rate 12.4% Causes not specified
Experience in OPCAB ‘Participating surgeons were required to document that they had performed at least 20 off-pump including some in which complete revascularization was performed for all vascular territories of the heart’
BACHAS 1 and BACHAS 2 trials: Angelini et al., Lancet 2002 [2], J Thorac Cardiovasc Surg 2009 [18], UK Single centre, observer-blinded randomized, clinical trials (level 1b)

  • BACHAS 1: 200 patients undergoing CABG

  • Exclusion criteria: LVEF ≤ 30%, recent MI; supraventricular arrhythmia; previous CABG; renal or respiratory impairment; previous stroke, TIA, or coagulopathy, CAD of branches of the circumflex artery distal to the first obtuse marginal branch

  • BACHAS 2: 201 patients

  • Exclusion criteria: the same ones of BACHAS 1, minus recent MI and CAD of branches of the circumflex artery distal to the first obtuse marginal branch

 30-day survival

  • BACHAS 1: overall mortality: off-pump 0%; on-pump 2% (P = N.S)

  • BACHAS 2: overall mortality: off-pump 0%; on-pump 0% (P = N.S)

 

  • No difference in terms of early, mid- or long-term mortality between off-pump and on-pump group

  • Early and mid-term outcomes showed the following risk differences with off-pump compared with on-pump surgery: atrial fibrillation –25% chest infection –12%; inotropic requirement –18%; transfusion of red blood cells –31%, and hospital stay longer than 7 days –13%

  • Long-term outcomes showed the likelihood of graft occlusion was no different between off-pump (10.6%) and on-pump (11.0%) groups (odds ratio, 1.00; 95% confidence interval, 0.55–1.81; P > 0.99)
75-month survival BACHAS 1 and 2 were pooled together: no difference in survival between the 2 groups (hazard ratio, 1.24; 95% CI, 0.72–2.15; P = 0.44)
Off-pump to on-pump conversion rate

  • BACHAS 1: 0%

  • BACHAS 2: 0%

  • In BACHAS 1, two patients did not receive off-pump because of cross-over
Experience in OPCAB ‘BHACAS trials were carried out in a single centre by a single academic surgical team. This surgical team has documented innovations in OPCAB technique, their performance and that of residents learning OPCAB, and other aspects of their experience with OPCAB over more than a decade’
Prague-4 Trial: Straka, Widimsky et al., Ann Thorac Surg 2004 [11], Circulation 2004 [19], Czech Republic Single centre, observer-blinded randomized (level 1b)

  • 388 patients undergoing elective isolated CABG

  • Exclusion criteria: concomitant surgery, and emergency

 30-day survival Overall mortality: off-pump 2.0%; on-pump 1.1% (P = 0.39)

  • No difference in clinical outcomes, mortality and morbidity between the two groups

  • The patency of arterial coronary bypass grafts done on the beating heart was equal to grafts done on pump
Off-pump to on-pump conversion rate 9.8% Causes: small or intramuscular arteries (n = 14), haemodynamic instability (n = 6)
Experience in OPCAB ‘All surgeons had experience with the off-pump technique, which was adopted in this centre in 1996’
Best Bypass Surgery trial: Møller et al., Circulation 2010 [14], Denmark Single centre, randomized, observer-blinded, clinical trial (level 1b) 341 patients with 3-vessel disease, >54 years old and EuroSCORE ≥ 5 Exclusion criteria: previous heart surgery, left ventricular ejection fraction (EF) ≤30%, unstable preoperative condition 30-day survival Overall mortality: off-pump 3.4%, on-pump 6.7% (P = 0.21)

  • Early overall mortality in on-pump group was almost double than in off-pump group with no statistical difference

  • The number of patients with myocardial infarction was nearly doubled in the on-pump group (15 versus 9) with no statistical difference

  • The mean number of grafts per patient did not differ significantly between the groups (3.22 in off-pump group and 3.34 in on-pump group; P = 0.11). Fewer grafts were performed to the lateral part of the left ventricle territory during off-pump surgery (0.97 versus 1.14 after on-pump surgery; P = 0.01)
Off-pump to on-pump conversion rate 4.5% Causes: unstable haemodynamic (n = 3), intraoperative transoesophageal echocardiography showing aortic valve disease requiring repair (n = 1), intraoperative recognition of left ventricular aneurysm requiring surgical repair (n = 1), not operated on by a trial surgeon because of logistics (n = 2), and anaesthesiologist unwilling to participate in off-pump surgery (n = 1)
Experience in OPCAB ‘Each of the 3 participating surgeons performed at least 50%of their CABG procedures as off-pump procedures in their normal activity’
MASS III trial: Hueb et al., Circulation 2010 [4], Brazil Single centre, observer-blinded randomized, clinical trials (level 1b)

  • 308 patients referred for isolated coronary bypass surgery for the first time and an off-pump procedure was deemed technically feasible

  • Exclusion criteria: emergency or concomitant major surgery, ventricular aneurysm requiring repair and end left ventricular EF <40%

 30-day survival Overall mortality: off-pump 0.6%; on-pump 0% No difference was found between groups in the primary composite end point at 5-year follow-up. Although OPCAB surgery was related to a lower number of grafts and higher episodes of atrial fibrillation, it had no significant implications related to long-term outcomes
60-month survival Overall mortality: off-pump 8.4%; on-pump 5.2% (P = 0.18)
Off-pump to on-pump conversion rate 1.9% Causes: haemodynamic instability (n = 3)
Experience in OPCAB ‘The procedure was performed by surgeons experienced in both on-pump and off-pump bypass surgery’
Légaré, et al., Circulation. 2004 [12] and Karolak et al., Am Heart J 2007 [20], Canada Single centre, randomized, clinical trial (level 1b)

  • 300 patients requiring isolated CABG surgery at a single institution

  • Exclusion criteria: emergency procedure (requiring immediate surgery), concomitant major cardiac procedures, EF <30% and reoperation

 In hospital survival Overall mortality: off-pump 1.3%; on-pump 0.7% (P = 1) No differences in short-term mortality or morbidity outcomes between on-pump and off-pump groups
45.6 months survival Overall mortality: off-pump 6.7%; on-pump 3.3% (P = 0.18)
Off-pump to on-pump conversion rate 13.3% Causes: of haemodynamic instability (n = 14), inadequate visualization of target vessel (n = 5), or inability to place the stabilizer because of obesity (n = 1)
Experience in OPCAB No data
Octopus trial: Nathoe et al., N Engl J Med 2003 [15], The Netherlands Multicentre controlled, single-blind, randomized trial (level 1b)

  • 281 patients referred for isolated coronary bypass surgery for the first time

  • Exclusion criteria: emergency or concomitant major surgery, recent Q-wave myocardial infarction and poor left ventricular function

 In hospital survival Overall mortality: off-pump 0%; on-pump 0% No statistically significant difference in cardiac outcome, symptoms or quality of life at 1 year between patients who underwent on-pump surgery and those who underwent off-pump surgery
12-month survival Overall mortality: off-pump 1.4%; on-pump 0%
Off-pump to on-pump conversion rate 7.0% Causes not specified
Experience ‘Surgery was performed by surgeons experienced in both on-pump and off-pump bypass surgery’
Hernandez et al., Ann Thorac Surg 2007 [6], USA Single centre, randomized, clinical trial (level 1b)

  • 204 patients aged 40–80 years requiring elective or urgent CABG

  • Exclusion criteria: patients requiring concomitant valve or carotid artery surgery, emergency operation, reoperation, heavily calcified ascending aorta, deep intramyocardial LAD, preoperative inotropic agent (e.g. dobutamine, epinephrine, amrinone, milrinone, or dopamine >3μg kg−1 min−1) or cardiac-assist device

 In hospital survival Overall mortality: off-pump 0%; on-pump 1%

  • No significant difference in short-term mortality

  • Incidence of stroke was higher in on-pump group (2.9%) than in off-pump group (0%)

  • Off-pump group presented 55% reduction in the risk for demonstrating troponin release within the first 24 h after surgery

  • There was no difference in neurocognitive deficit at discharge or at 6 months between the two groups
Off-pump to on-pump conversion rate 1% Causes not specified
Experience in OPCAB No data
Smart trial: Puskas et al., J Thorac Cardiovasc Surg 2003 [3], J Am Med Assoc 2004 [7], Ann Thorac Surg 2011 [8], USA Single centre, observer-blinded randomized, clinical trial (level 1b)

  • 197 patients undergoing elective CABG

  • Exclusion criteria: cardiogenic shock requiring emergency surgery or pre-operative intra-aortic balloon pump

 In hospital survival Overall mortality: off-pump 3.1%; on-pump 2.0% (P = 0.64)

  • There were no significant differences between the groups in the incidence of death, myocardial infarction, stroke, recurrent angina, readmission for cardiac or non-cardiac events, or percutaneous reintervention during hospitalization, at 30 days, or at 1-year follow-up

  • Graft patency was similar between the two groups

  • Mean total hospitalization cost per patient was significantly less for OPCAB
60-month survival On-pump 81.8%, off-pump 92.9% (P = 0.02)
84-month survival On-pump 73.7%, off-pump 83.7% (P = 0.09)
Off-pump to on-pump conversion rate 1% Causes: intramyocardial coronary artery (n = 1)
Experience in OPCAB Surgical procedures were performed by a single experienced OPCAB practitioner, who routinely performs more than 90% of his isolated coronary cases using OPCAB
Muneretto et al., Ann Thorac Surg 2003 [9], Italy Single centre, randomized, clinical trial (level 1b)

  • 176 patients receiving isolated CABG on an elective basis

  • Exclusion criteria: >75 years of age, presence of chronic obstructive pulmonary disease, creatinine clearance <60 ml/min, combined carotid disease, symptomatic peripheral arterial disease, severe atherosclerotic disease of the ascending aorta and history of cerebrovascular accidents

 In hospital survival Overall mortality: off-pump 3.4%; on-pump 2.3% (P = NS) Off-pump patients had a considerable reduction of ventilation time, ICU stay, post-operative stay and atrial fibrillation rate
15 months survival Overall mortality: off-pump 1.2%; on-pump 2.3% (P = NS)
Off-pump to on-pump conversion rate 9.1% Causes: intramyocardial or calcified vessels (n = 8)
Experience in OPCAB No data
Fattouch et al., J Thorac Cardiovasc Surg 2009 [10], Italy Single centre, observer-blinded randomized, clinical trial (level 1b)

  • 128 patients with STEMI undergoing urgent CABG

  • Exclusion criteria: mechanical complications of myocardial infarction; cardiopulmonary resuscitation required before surgery; life-saving procedures; onset of cardiac shock in >24 h; ischaemic mitral valve regurgitation more than moderate; and concomitant cardiac surgical procedures

 In hospital survival Overall mortality: off-pump 1.6%; on-pump 7.7% (P ≤ 0.04) Off-pump surgery reduced early mortality and morbidity in patients with ST-segment elevation myocardial infarction in respect to the on-pump
36-month survival No cardiac-related late deaths occurred
Off-pump to on-pump conversion rate 1.6% Causes: haemodynamic instability (n = 1)
Experience in OPCAB No data
Masoumi et al., Asian Cardiovasc Thorac Ann 2008 [16], Iran Single centre, randomized, clinical trial (level 1b) 124 patients with an EF of 35% or less who were referred for isolated first-time CABG. Exclusion criteria: single-graft CABG In hospital survival Overall mortality: off-pump 0%; on-pump 6.45% (P ≤ 0.045) There were significantly fewer incidences of mortality, low cardiac output events, arrhythmias, renal failure and gastrointestinal haemorrhage in the off-pump group compared with on-pump group
Off-pump to on-pump conversion rate 4.8% Causes not specified
Experience in OPCAB No data
Lingaas et al., Ann Thorac Surg 2006 [13], Norway Single centre, observer-blinded randomized, clinical trial (level 1b)

  • 120 patients with stable angina pectoris and moderate or good left ventricular function eligible for coronary bypass surgery

  • Exclusion criteria: EF <30% or serum creatinine concentration >200 mmol/l or dialysis

 30-day survival Overall mortality: off-pump 1.6%; on-pump 1.6% (P = NS) No differences between off-pump and on-pump groups in terms of survival, cardiac function expressed as functional class, exercise ECG, MRI of the heart and graft patency
12-month survival No mortality events
Off-pump to on-pump conversion rate 9.1% Causes: haemodynamic instability or inaccessible target (n = 5), to facilitate revision of grafts after intra-operative coronary angiography (n = 2)
Experience in OPCAB ‘Four participating surgeons with varying experience in on-pump and off-pump coronary surgery, including one surgeon in training, performed the operations’
Khan et al., N Engl J Med 2004 [17], UK Single centre, observer-blinded randomized, clinical trial (level 1b)

  • 104 patients with isolated, first-time coronary-artery surgery and who required at least three grafts were eligible

  • Exclusion criteria: age <30 years or >80 years; additional surgical procedures; stroke within the preceding 6 months; carotid-artery stenosis; myocardial infarction in the preceding 3 months; EF <20%; pregnancy and breast-feeding; and a history of complications after diagnostic angiography

 30-day survival Overall mortality: off-pump 0%; on-pump 0% Graft-patency rate was lower at 3 months in the off-pump group than in the on-pump group
Off-pump to on-pump conversion rate 3.7% Causes: electrical instability (n = 1) and intramyocardial LAD (n = 1)
Experience in OPCAB ‘In the two years preceding the study, the surgeons performed 13% of their coronary work off-pump’
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RESULTS

In the 14 randomized controlled trials (RCTs) reviewed, the off-pump to on-pump conversion rate ranged from 0 to 13.3%. The most frequent causes of conversion were haemodynamic instability and intramyocardial-coronary target.

A low conversion rate (<2%) was reported by five studies: the BACHAS trials [2], the Smart trial [3], the Mass III [4], the study published by Fattouch et al. [5] and the study published by Hernandez et al. [6]. The first three of them (BACHAS trials [2], Smart trial [3] and Mass III [4]) describe a high structured experience in OPCAB. In the remaining studies [3, 6–10], no data about experience in off-pump are available.

Among these five RCTs, three [2, 4, 6] did not show any difference in terms of early, mid- or long-term mortality between the OPCAB and on-pump groups, one showed better survival of the OPCAB group at 5 years [3], and one [10] reported a lower early mortality in patients with ST-segment elevation myocardial infarction undergoing OPCAB in comparison to the on-pump group. Three RCTs described lower post-operative morbidity (rate of atrial fibrillation, chest infection, transfusion of red blood, inotropic requirement [2], stroke [6]) and lower hospital stay [2, 3] in patients undergoing OPCAB).

Both studies analysing the bypasses functionality (BACHAS trials [2], Smart trial [3]) reported no differences in long-term graft patency.

Five RCTs presented a high conversion rate (>9%): the ROOBY Trial [5], the Prague-4 Trial [11], and the studies published by Legare et al. [12], Muneretto et al. [9], and Lingass et al. [13]. Among them, the ROOBY Trial [5] is the largest RCT (2203 patients), the one documenting the poorest experience in OPCAB by the surgeons participating in the trial, and the one associated with the second highest conversion rate (12.4%).

Among this group of RCTs only the ROOBY Trial [5] documented a worse early survival of the OPCAB group. None, except one [5], documented a benefit in term of reduction of the morbidity in the OPCAB group.

Among the 3 trials exploring graft patency [5, 11, 13] only the ROOBY trial [5] showed a lower overall rate of graft patency of the OPCAB group.

Four RCTs showed an intermediate conversion rate, ranging from 3.7 to 7.0%: the Best Bypass Surgery Trial [14], Octopus trial [15] and the studies published by Masoumi et al. [16] and Khan et al. [17].

In this group, only the Best Bypass Surgery Trial [14] reported a high experience in OPCAB of the surgeons participating in the trial.

The Best Bypass Surgery Trial, which is also the largest study of this group (341 patients), showed that the on-pump early overall mortality and incidence of myocardial infarction nearly doubled those of the off-pump group (no statistical significant in both cases). It also showed no differences in terms of graft numbers between the two groups.

The Octopus trial [15] reported no difference with regards to cardiac outcomes and early survival and quality of life between the OPCAB and on pump groups.

Masoumi et al. [16] have analysed only patients with severe left ventricle dysfunction. This trial was able to show lower mortality, low cardiac output events, arrhythmias, renal failure and gastrointestinal haemorrhage in the off-pump group compared with the on-pump group.

Khan et al. [17] showed a lower graft-patency rate at 3 months in the off-pump group than in the on-pump group.

CLINICAL BOTTOM LINE

We conclude that RCTs with a high off-pump to on-pump conversion rate (>9%) were often associated with a low experience in OPCAB of the surgeons participating in the trials. These studies were also mostly not able to show any benefit in terms of mortality or morbidity of OPCAB over the on-pump strategy.

On the contrary, a low conversion rate (<2%) is mostly reported by RCTs with a high structured experience in OPCAB. These trials were mostly able to show a benefit in terms of morbidity, and in two cases of survival, of the OPCAB over the on-pump strategy. No trials with a low conversion rate were able to document a significant difference in terms of graft patency between the on-pump and the OPCAB groups.

RCTs with an intermediate conversion rate reported a wide spectrum of results.

The results of this review may be jeopardized by the fact that the outcomes of the trials included were strongly influenced by their statistical power.

Conflict of interest: none declared.

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