Radial artery versus saphenous vein graft for coronary artery bypass grafting—long-term outcomes

I read with great interest the article by Gaudino et al. [1] comparing differences in long-term outcomes when radial artery (RA), right internal thoracic artery (ITA) or saphenous vein graft (SVG) were used to complement the left ITA-to-left anterior descending graft. The authors [1] emphasized that randomized trials failed to confirm an association between the use of multiple arterial grafting for coronary artery bypass grafting (CABG) and improved long-term outcomes compared to the use of a single arterial grafting. However, the authors [1] underlined that in a pooled analysis of individual patients data from 5 randomized trials, the use of RA as the second conduit was associated with a significant reduction in the risk of cardiac events and a survival benefit at 10 years compared to the use of SVG [2]. Those data are presented in Table 4 (Post Hoc Outcomes in a Study of the Association of RA vs SVG With Cardiovascular Outcomes Among Patients Undergoing CABG) of that pooled analysis [2]: RA group—outcome death: 128/534 patients (24.0%); SVG group—outcome death: 134/502 patients (26.7%), P = 0.01 (altogether, 262 events/deaths and 1036 patients). This means that there is only a 10% relative reduction (24% vs 26.7%) in death rate in favor of the patients with RA graft versus patients with SVG. Gaudino et al. [3] are currently conducting ROMA study. The primary hypothesis of the ROMA trial is that in patients undergoing primary isolated non-emergent CABG, the use of 2 or more arterial grafts compared with a single arterial graft will be associated with a reduction in the composite outcome of death from any cause, any stroke, post-discharge myocardial infarction and/or repeat revascularization. The authors [3] also wrote: ‘Because of the known increase in graft attrition rate after the 5th postoperative year, we expect to see a linearized rate of death of 2% between 5 and 10 years postoperatively and estimate that the overall 10-year mortality will be 18–20%. We consider a 20% relative risk reduction in mortality to be clinically meaningful and sufficient to change practice. To detect a 20% relative reduction (from 18% to 14.4%) in 10-year mortality, with 80% power at 5% alpha, the sample size must include 3650 patients or 631 events’. How so, that for detection of 20% relative reduction of mortality we need a sample size of 3605 patients and 631 events and, on the other hand, for 10% relative reduction of mortality, a smaller sample of 262 events/deaths and 1036 patients [2] was large enough? Testing RA artery patency up to 20 years following surgery, Gaudino et al. [4] showed that for targeted coronary artery stenosis <90%, RA and SVG have around 45% of probability of graft failure at 10 years, and at 20 years, probability of graft failure was 72.5% for SVG and 80.4% for RA (P = 0.95). For targeted coronary artery stenosis >90%, RA graft patency was superior—87.3% [ITA (81.5%), SVG (51%)]. If we assume that long-term outcome is connected with better graft patency [1], than, would not it be irrelevant which second graft we use to graft targeted coronary artery with stenosis <90%?