Normothermic Ischemia in Coronary Revascularization

Warm heart surgery-continuous perfusion with normothermic blood cardioplegia-was introduced as an alternative to conventional intermittent hypothermic perfusion for myocardial protection. Interruption of global coronary flow, however, greatly facilitates the performance of distal coronary anastomoses and is the method that has evolved with many surgeons using warm blood cardioplegia for coronary revascularization. We present results (mean +/- SD) in 720 patients undergoing coronary bypass surgery protected with intermittent warm blood cardioplegia and exposed to normothermic ischemia but with electromechanical arrest. An average of 3.2 +/- 0.9 grafts were constructed per case with an average aortic cross clamp time of 61.8 +/- 22.2 minutes. Cardioplegia was interrupted a total of 28.5 +/- 12.4 min per operation. The percent time off cardioplegia (PTOC) expressed as a proportion of the cross clamp was 48.2 + 18.6%. The longest single time off cardioplegia (LTOC) was 11.4 +/- 4.0 min per patient. Calculated mean cardioplegia delivery during the cross clamp period was 75 ml/min. PTOC and LTOC were divided into quartiles (PTOC: 62%; LTOC: 13 min) and related to prespecified composite outcome of mortality, enzymatic myocardial infarct and low output syndrome. PTOC was protective (event rate/quartile 16.1%, 17.2%, 9.4%, 10.6%, p = 0.07) and longer LTOC (event rate/quartile 13.5%, 10.3%, 10.9%, 19.0%, p = 0.046) borderline harmful. The data suggest that when necessary multiple periods of normothermic myocardial ischemia in the presence of electromechanical arrest are well tolerated and potentially protective provided that any single ischemic interval is < 13 min.