Current Assessment of CABG Clinical Outcomes: Short- & Long-term Mortality
As a specialty, cardiothoracic surgeons have tracked the remarkable decline in acute mortality of CABG over the past 25 years. Ferguson et al., in a trend analysis of the decade 1990–1999 from the Society of Thoracic Surgeons (STS) database, documented that there was a significant decline in risk-adjusted mortality over the decade, despite a documented increase in the predicted risk of mortality (PROM) in this surgical population over the same time interval. More recently, El Bardissi et al. documented a 24.4% relative risk reduction in observed CABG mortality from 2000–2009. Even more recently, however, the STS database has documented no further decline in observed mortality, but rather a plateauing over the past several years, at 1.8–2.0%.
The El Bardissi study also demonstrated that the STS National Database PROM remained stable at 2.3%, distinct from the decade between 1990 and 1999, where the predicted risk increased substantially. Clinically, CABG patients have more comorbidities including hypertension, diabetes and obesity, and a greater extent and complexity of ischemic heart disease. This latter complexity is documented by increased anatomic severity and more preoperative myocardial dysfunction from prior myocardial injury, some related to prior revascularization interventions. In other regional analyses, however, the PROM for CABG has declined, as documented by the Michigan Society of Cardiothoracic Surgery (2006–2010). Given this stable and even declining PROM, it is paradoxical that there has not been an equal, if not greater, decline in the risk-adjusted operative mortality, at either the regional or national level, during this same time interval.
Observational data from NY, USA, the STS and other databases have, for years, supported the use of CABG in patients with three- and two-vessel disease with proximal left anterior descending disease, based on these acute outcomes and tracking registry patients over time.[15,18–20] However, none of these registries have data on medical therapy for patients with ischemic heart disease, such that only the intervention itself could be tracked over time and compared (e.g., percutaneous coronary intervention [PCI] vs CABG in NY, USA). Only the Duke studies were able to account for medical therapy, as well as revascularization for SIHD.
Randomized Trials: CABG versus PCI in SIHD
More recently, randomized controlled trial data from the BARI-2D, SYNTAX,[22,23] FREEDOM and ASCERT trials parallel the findings from these observational studies. This data synergy has changed the information matrix for decision-making in SIHD revascularization. BARI-2D was an optimal medical therapy (OMT) versus intervention trial in diabetic patients. These results strongly supported CABG over PCI in diabetic multivessel disease patients, both for long-term mortality and a decreased incidence of late myocardial infarction (MI). SYNTAX identified a mortality benefit from CABG at 4 and 5 years and a reduced incidence of MI at 5 years, in patients with intermediate and high SYNTAX tercile three-vessel disease, in high tercile two-vessel disease patients with LAD disease and in left main patients with three-vessel disease. The FREEDOM trial identified a survival benefit at 5 years in multivessel diabetic patients, as well as freedom from MI at 5 years. Using a different and more controversial methodology, the ASCERT trial demonstrated better survival with CABG in a noncontemporary cohort of patients. Therefore, two new principle benefits of CABG, demonstrated in the observational analyses and confirmed by these trials, are:
Long-term freedom from MI.
More correctly, these two benefits accrue from CABG performed according to the conventional anatomy-driven strategy for CABG, used in both SYNTAX and FREEDOM.
The uncertainty of these findings relates to:
The documented incidence of acute incomplete anatomic revascularization, which in the SYNTAX trial was 37% for CABG and 43% for PCI;
The late functional incomplete revascularization in CABG trials, where 20–25% of grafts are occluded at the 12–18-month protocol-specified angiographic evaluation, as was the case in the PREVENT IV trial.[27,28]
These rates of incomplete anatomic revascularization and vein graft attrition were higher than anticipated, but demonstrated no impact on late mortality or MI incidence in these evaluations. The relationship between these short- and long-term technical shortfalls and long-term outcomes remains unclear.
Future Cardiol. 2014;10(1):63-79. © 2014 Future Medicine Ltd.