Cardioplegic solution challenges.

A recent survey of the outcome in 8641 patients who underwent coronary artery bypass grafting operations in northern New England reported an overall mortality of 4.48%1, 65% of which could be directly attributed to postoperative heart failure. The conclusion drawn from these data is that in spite of the improvement in myocardial protection accomplished in past years, there is room for further improvement, in particular in high risk patient subsets. Although strategies that attenuate the systemic inflammatory effects of cardiopulmonary bypass (CPB) can indirectly enhance cardioprotection, only those directly targeted at the myocardium will be considered here. These direct strategies of myocardial preservation can be categorized as those involving aortic cross-clamping and cardioplegic arrest and those which are not cardioplegia-based. As far as cardioplegia is concerned, the available literature allows to summarize the state of the art as follows: cold crystalloid cardioplegia is associated with an excellent clinical outcome2, but blood cardioplegia offers superior cardioprotection in high risk situations, such as hypertrophied myocardium3, extended aortic cross-clamp times4, and evolving myocardial ischemia5. In this respect, a recent study by Tomasco et al.5 shows (by multivariate analysis) that the nonuse of blood cardioplegia in patients undergoing urgent or emergency bypass surgery is a predictive factor of increased mortality; antegrade delivery of cardioplegia is quite effective in many cases but retrograde coronary sinus perfusion is preferable in the presence of complete coronary occlusions with poorly collateralized myocardial areas6. Indeed, the nonuse of retrograde cardioplegia has been identified by multivariate analysis as one of the predictive factors of a poor outcome in patients with left ventricular dysfunction7; the controversy about cold versus warm blood cardioplegia is probably obsolete since there is increasing evidence that a tepid temperature (32-34 C) is an acceptable trade-off. It acts as a buffer against ischemic injury if cardioplegia delivery has to be transiently discontinued and, in addition, tepid bypass limits systemic vasodilation while improving cerebral protection. Indeed, temperature of cardioplegia might be less critical for adequate cardioprotection than the route of delivery; thus, in one study where the authors failed to detect differences between cold and warm blood cardioplegia in patients with poor left ventricular function8, the systematic use of retrograde cardioplegia in all patients may have masked the potential effect of temperature; the Buckberg s approach (which associates warm induction, intermittent cold blood cardioplegia and warm substrate-enriched initial blood cardioplegic reperfusion) is widely used and has shown its efficacy (with the caveat that a recent randomized trial failed to document any benefit of the terminal hot shot in low risk patients). We believe, however, that this technique can be simplified and made possibly more effective by using minimally diluted blood cardioplegia (that we have coined mini-cardioplegia9). Basically, this approach entails the continuous combined (antegrade/retrograde) delivery of arterial blood simply supplemented with a small volume of concentrated cardioplegia (in our practice, a mixture of potassium and magnesium). This solution is continuously added to the arterial tubing through an electrically-driven syringe pump, the flow rate of which is adjusted on-line to keep the heart arrested with the minimum amount of potassium. Along with a continuous mode of Address: Philippe Menasché, MD, PhD Department of Cardiovascular Surgery Hôpital Bichat 46, rue Henri Huchard 75018 Paris France Cardioplegic solution challenges