Contemporary coronary artery bypass grafting
Since its first description in the 1960s coronary artery bypass grafting (CABG) increased dramatically over the following three decades in developed countries. The numbers of CABG operations then gradually decreased with the widespread use of percutaneous coronary intervention (PCI), initially with balloon angioplasty and then with the improving technologies of bare metal and drug eluting stents. In contrast, in many developing countries, and starting from a particularly low base, the number of CABG operations is continuing to increase. Currently there are around 3/4 of million CABG operations performed worldwide each year.
For over 20 years there has been considerable controversy over the relative merits of CABG versus stents in terms of patient survival. In an analysis of 15 trials of PCI versus CABG involving around 9000 patients there was no obvious difference in survival between CABG and PCI [
1]. However, one of the reasons for this finding was unquestionably because of the nature of the patients enrolled into the trials. Only around 5% of all potentially eligible patients were recruited into the trials and the vast majority of patients actually had single or double vessel disease which did not involve the proximal anterior descending coronary artery [
1]. In such a population it was therefore entirely predictable that there would be no difference in survival between CABG and PCI. However, the findings in these randomized trials were at considerable variation with many registries often containing tens of thousands of patients, propensity matched for baseline characteristics, which showed a significant survival advantage for CABG [
2]. The most likely explanation for the different findings between trials and registries is almost certainly because registries enrolled patients taken from everyday clinical practice and who have much more severe coronary disease than those entered into the trials. Whereas trial patients had to be deemed potentially suitable for PCI many patients in registries had disease of such severity that it precluded PCI whereas, in contrast, there are very few patients who are technically ineligible for CABG in trials or registries.
In 2014 a very significant body of evidence has now accumulated to show a clear and distinct survival advantage for CABG over PCI as well as marked reductions in myocardial infarction and the need for repeat revascularization. The 5-year analysis of the SYNTAX Trial has now been published for both 3-vessel coronary disease [
3] and left main stem disease [
3]. For 3-vessel coronary artery disease CABG produces a clear survival advantage of 5.4% at 5 years with marked reductions in myocardial infarction and repeat revascularization and without an increased incidence of stroke [
3]. Furthermore, as the severity of coronary artery disease increases, patients with intermediate (23-32) and high (> 32) SYNTAX scores have respective survival benefits with CABG of 7% and 9% [
3]. A recent meta-analysis of contemporary trails of PCI versus CABG in 3-vessel disease that includes the SYNTAX analysis confirms this marked reduction in mortality for patients with CABG in contrast to PCI [
5].
Many studies have suggested that the benefits of CABG are further enhanced in patients with diabetes and this has been recently confirmed in the FREEDOM Trial and two independent meta-analysis of CABG versus PCI in patients with diabetes [
6,
7].
For patients with left main disease the situation is somewhat different. Overall in the analysis of 705 patients from the SYNTAX Trial with left main there was no difference in overall between CABG and PCI [
4]. In a subgroup analysis, patients with the lower (< 23) and intermediate (23-32) SYNTAX scores had a lower mortality and risk of stroke with PCI versus CABG [
4]. Indeed, it was only in patients with left main with high SYNTAX scores (> 32) where there appeared to be a survival advantage of CABG as well as a marked reduction in the need for repeat revascularization. Overall for left main as opposed to 3-vessel disease there was an increased risk of stroke with CABG versus PCI. These findings are almost certainly real because they are entirely consistent with the results of the Precombat Trial, which also showed no significant differences in outcomes in terms of survival or myocardial infarction in left main disease in 600 patients randomized to PCI or CABG [
8]. Again, in the Precombat Trial the only advantage of CABG was in reduction in repeat revascularization but additionally there was no increased incidence of stroke with CABG versus PCI. A definitive answer to the optimal mode of revascularization for left main disease will be the Excel and Noble Trials that have either competed or are near to completion of enrolment.
Optimising CABG: arterial grafts and off-pump CABG
Two important developments have taken place over the past 30 years with respect to the performance of CABG. In 1986 the Cleveland Clinic reported in a landmark paper the survival benefit of the internal mammary artery (IMA) when placed to the left anterior descending in terms of reducing subsequent death, myocardial infarction, recurrent angina and the need for repeat revascularization [
9]. The benefits of the IMA are almost certainly due to its high production of nitric oxide which not only enhances the patency of the IMA but also helps protect the native coronary circulation against the development of further disease [
10]. Consequently many authors have investigated the benefits of a second IMA and although there has only been one randomized trial to date, the ART Trial, that has completed recruitment but awaits ten-year outcomes data [
11], there is very strong circumstantial evidence of improved survival with a second IMA [
12]. More recently, two independent groups produced meta-analyses reporting that in propensity matched patients a second IMA graft resulted in a marked reduction in the hazard ratio for death [
13,
14]. Furthermore, the preliminary results of the ART Trial showed the use of a second IMA did not increase the risk of death, myocardial infarction, stroke or repeat revascularization at 1 year but did report an increased incidence of sternal wound breakdown but mainly and predominantly in patients with diabetes [
11]. Despite strong evidence in favor of a second IMA, fewer than 5% of patients in the USA and fewer than 10% of patients in Europe currently receive this option.
With regards to the radial artery, there is now convincing evidence that its patency is superior to that of saphenous veins beyond one year as long as the radial artery is used in patients with at least a 70% stenosis in the native coronary artery [
15]. There is now also evidence that the use of a radial artery rather than saphenous vein in addition to an IMA may result in superior long-term survival in comparison to vein grafts [
16].
Off pump surgery was introduced into clinical practice in the 1980s and for a while saw a great surge in popularity before there was genuine appreciation of its more challenging technical aspect. This then led to a flurry of publications suggesting that off pump surgery actually resulted in inferior outcomes compared to conventional on pump CABG [
17]. However, recently two large randomized trials, the Coronary Trial [
18] and the GOPCABGE [
19] have both reported that at one year of follow-up there is no difference in any major outcome in terms of mortality, stroke, repeat revascularization or new renal injury between the two techniques. Nevertheless some enthusiasts continue to argue that in higher risk patients there is a significant reduction in all course mortality and stroke with the use of off pump surgery. Two very large propensity matched registries [
20,
21] have both described similar findings of reduction in mortality and all major aspects of morbidity with off pump surgery. It should also be noted that off pump surgery is probably optimal when it is performed with a true no touch aortic technique which has also been shown to significantly reduce the risk of stroke [
22,
23].
Summary
Today’s best evidence suggests that CABG is definitely a markedly superior revascularization strategy for patients with multi-vessel disease in terms of survival, reduction of myocardial infarction and need for repeat revascularization and without a significant increase in the risk of stroke. In contrast, CABG only has a benefit in most patients with left main disease who are in the higher risk tertiles whereas for lower and intermediate tertiles (mainly ostial or mid-shaft lesions with perhaps one or two vessel disease) PCI offers similar survival with a lower incidence of stroke but with a higher risk of repeat revascularization. There is now robust and consistent evidence that many patients would benefit from the use of a second internal mammary artery and possibly also a radial artery. For off pump surgery the evidence is conflicting but for most patients there seems to be no obvious benefit over on pump surgery except perhaps in patients in the highest risk categories.
Compliance with ethics guidelines
David P. Taggart declares that he has no conflict of interest. This manuscript is a mini-review and does not involve a research protocol requiring approval by the relevant institutional review board or ethics committee.
Higher Education Press and Springer-Verlag Berlin Heidelberg
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