Role of 'Myocardial Integrity'
The term 'myocardial integrity' is used to account for the disease conditions or induced changes in the myocardium that affect the short- and long-term outcomes from revascularization.
In diabetes, cardiovascular outcomes are related to the extent and severity of the diabetes, indicated by the type of therapy. In FREEDOM, it is unclear if the outcome differences with revascularization (PCI or CABG) are somehow related to the extent of microvascular myocardial disease, typical in the diabetic patient population with SIHD (Box 1).
An additional myocardial integrity component was evaluated in the STICH trial.[35,36] Although viability testing was made optional, 601 patients had viability testing performed, and 487 patients had a viable myocardium. After a median follow-up of 5.1 years, the patients with a viable myocardium had a lower death rate than those without a viable myocardium (p = 0.003), but after multivariate analysis, the difference was not statistically significant. The substudy of the STICH trial does not report on whether the viable myocardium was ischemic or not.[35,36]
At surgery, a more complete understanding of these myocardial integrity factors is necessary. Beyond the 10% of ischemia necessary to derive benefit from revascularization, the influence of the status of the myocardium prior to revascularization is increasingly important, as patients present for CABG with more complex, long-standing SIHD. The importance of this quantified functional anatomic approach to SIHD as a guide for revascularization was demonstrated by Choi et al. who documented that 85% of patients following MI had extensive collateral networks developed, even though they were not yet clinically apparent. With surgical revascularization, these networks become enormously influential to the heart's ability to move blood where it needs to, a type of revascularization remodeling.[63,64] The importance of recruitable collaterals in SIHD has recently been reviewed by Meier, where the coronary collateral circulation had an important impact on survival.[65,66]
At present, revascularizing nonischemic myocardium that is viable in SIHD will not likely change event rates. However, patients with increasing degrees of LV dysfunction are more likely to have combinations of normal, ischemic and nonviable myocardium. In the context of global multivessel revascularization and appropriate incomplete revascularization, the ability of surgical revascularization to provide multiple new sources of blood flow and perfusion, coupled with these myocardial integrity factors, may be prognostically important.
Future Cardiol. 2014;10(1):63-79. © 2014 Future Medicine Ltd.