Relation between aortic cross-clamp time and mortality--not as straightforward as expected

Due to modern techniques of cardio protection, less attention has been paid to aortic cross-clamp (XCL) times. However, patients with impaired cardiac contractile function are still at increased perioperative risk, which may be partially due to an increased susceptibility to myocardial ischemia. We tested whether XCL times are associated with perioperative mortality in patients with preserved versus poor left ventricular function.

We determined predictors of operative mortality on all patients undergoing cardiac surgery with aortic cross-clamping in our institution between 1990 and 2003. We excluded patients with markedly prolonged XCL times (>120 min, n=1426) in order to limit the effect of intraoperative technical difficulties and their known association with poor outcomes. Of the included patients (n=27,215), 99.8% received antegrade, retrograde, or combined blood cardioplegia.

Overall mortality was 2.2%. Multivariable analysis revealed that XCL time was an independent predictor of mortality for patients with LVEF >40% (odds ratio 1.014 per min of XCL, CI 1.01-1.02). However, XCL time was not a predictor in patients with LVEF <40%, mainly due to high mortality in patients with short XCL times. Mortality of patients with an LVEF <40% was the same or higher at cross-clamp times of 1-30 min than at 91-120 min.

Despite modern techniques of cardio protection, XCL time remains an independent predictor of mortality in patients with preserved preoperative contractile function. The unexpected lack of risk prediction by aortic cross-clamp time in patients with low ejection fraction appear to be due to a high mortality rate when XCL times were short.