Role of Coronary Anatomy

Up to now, understanding of the anatomic conditions that constitute a survival benefit from coronary revascularization versus lone medical therapy has been largely based on milestone studies performed during the 1970s. Soon after CABG was introduced in 1969, three randomized trials compared surgical revascularization with lone medical therapy: the VA-Study, the ECSS, and the CASS. Although these studies are outdated in many aspects, including a low use of arterial conduits and limited means of phar-macologic risk factor modification or of platelet inhibition, it is unlikely that they will ever be replicated. In concert with analyses of large registry databases, the early studies established the conditions in which CABG improves survival compared with medical therapy (Table 6-3).

A meta-analysis of all published randomized trials of CABG versus lone medical treatment for coronary artery disease identified left main disease (diameter stenosis > 50%), multivessel disease, and involvement of the proximal left anterior descending coronary artery (LAD) as significant predictors of a survival benefit from CABG.24 In the cumulative experience of seven studies, the VA-study being the first, surgical

Table 6-3. Conditions in Which CABG Improves Survival Compared with Medical Therapy

Left main coronary artery disease

Triple- or double-vessel disease involving the proximal LAD Triple- or double-vessel disease in the presence of severe angina or large areas of ischemia on functional testing Triple-vessel disease associated with impaired left ventricular function

LAD, left anterior descending coronary artery.

revascularization for left main disease was associated with a 65% relative reduction in mortality compared with lone medical therapy.24 Notably, in left main disease, there was a survival benefit of surgery irrespective of the presence or absence of spontaneous or inducible symptoms or signs of ischemia or reduced left ventricular function. The same is also true for triple- or double-vessel disease involving the proximal LAD.25

In all other conditions, the indication for surgical coronary revascularization depends on a combination of anatomic and clinical criteria. If triple-vessel disease is associated with impaired left ventricular function (left ventricular ejection fraction [LVEF] <50%), surgical revascularization improves survival irrespective of LAD involvement.26,27 In the presence of severe angina or large areas of ischemia on functional testing, surgical revascularization of triple- or double-vessel disease is also indicated for both symptomatic and prognostic reasons, even in the absence of left ventricular dysfunction.20,21

Coronary revascularization has never been shown to confer a survival benefit in patients with single-vessel disease. This is also true for isolated proximal LAD stenoses. The meta-analysis by Yusuf showing a survival benefit from surgery in patients with LAD involvement must be interpreted with the notion that this result was obtained in a cohort consisting predominantly of patients with multivessel disease.24 More recently, the randomized MASS trial compared lone medical treatment with plain balloon angio-plasty or CABG in 214 patients with symptomatic, isolated, high-grade stenosis of the LAD.28 During a 5-year follow-up, there was no appreciable difference among the three treatment arms in either death or MI. Although the power to detect small differences in event rates was low in MASS, the results were consistent with the current judgment that there is no prognostic indication for coronary revascularization in stable single-vessel disease.

No study has ever demonstrated that the risk of subsequent MI can be reduced in patients with stable angina by either bypass surgery or PCI. Concerning PCI, the recently published COURAGE trial confirmed this old notion in the setting of contemporary PCI and medical therapy.29 The degree of stenosis is a notoriously poor predictor of subsequent events. Although the risk of subsequent MI is higher with high-grade stenoses than with low-grade stenoses, the latter are by far more frequent. Therefore, most infarctions are triggered by low-grade stenoses. The current means of identifying vulnerable plaques are limited. Several techniques for assessing the vulnerability of plaques appear promising, including intravascular ultrasound, optical coherence tomography, intracoronary thermography, and pal-pography. Nevertheless, the prognostic impact of the findings obtained by these methods has not been established by prospective studies.

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