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Ann Thorac Surg 1995;60:1093
© 1995 The Society of Thoracic Surgeons
Division of Cardiothoracic Surgery, University at Buffalo, State University of New York, 100 High St, Buffalo, NY 14203
Introduced as method of prevention of ischemia by continuous delivery of normothermic blood cardioplegia, so-called warm heart surgery continues to evolve into different techniques, including the one described by Kaukoranta and associates. In their study, patients undergoing coronary artery bypass grafting received either mildly hypothermic or normothermic blood cardioplegia, apparently delivered at retrograde flows of 128 mL/min. Cardioplegic interruptions of 8.3% ± 1.1% and 5.1% ± 0.8% of ischemic time (cardioplegia off during the period of aortic cross-clamping) occurred in the mildly hypothermic and normothermic groups, respectively.
Decreased myocardial oxygen consumption and smaller transcardiac pH differences were observed 30 minutes after aortic declamping in the mildly hypothermic compared with the normothermic groups. However, there were no differences at 60 minutes. Creatine kinase-MB levels during the first 8 hours were higher in the normothermic group and no different thereafter (see Fig 3). These initial differences may be due to low retrograde cardioplegic flows, as mentioned by Kaukoranta and associates in the Comment section. I consider these flows inadequate for the normothermic group. Also, cardioplegic interruptions were used for visualization during construction of the distal anastomoses, which may account for these differences. Aerobic myocardial protection requires that flow not be interrupted. Recent technology allows for visualization of the anastomotic site without the need for cardioplegic interruptions.
Although heart rate was higher and left ventricular stroke work index was decreased in the normothermic group, there were no other hemodynamic differences between the two groups. Importantly, right ventricular failure, a major concern during retrograde cardioplegia, was not observed. Similarly, the incidence of neurologic events was not different between groups.
My extensive experience with retrograde continuous normothermic blood cardioplegia and normothermic systemic perfusion is in agreement with Kaukoranta and associates' findings in all types of cardiac procedures. The ability to administer different concentrations of blood:crystalloid mixtures minimizes potassium and volume overload. Newer devices deliver normothermic cardioplegia and cool it when needed, or deliver potassium with magnesium to blood without the need for crystalloid solutions. All these have increased the versatility and safety of the normothermic myocardial protection method. To my knowledge, aspartate and glutamate, as administered by Kaukoranta and associates, have not been reported during the infusion of continuous normothermic blood cardioplegia. Their value and potential side effects remain to be defined.
Some degree of hypothermia adds to the versatility of this type of myocardial protection. However, the need to cool the heart to very low temperatures has been questioned, and ``not all is well the colder the heart is.'' Rather, the development of a strategy for myocardial protection, using any or all techniques currently available for a particular situation, preventing ischemia by perfusion with normothermic (or near normothermic) blood whenever possible, remains the major contribution of warm heart surgery.
Finally, in understanding discrepancies in surgical results, one has to call a ``spade a spade'' in the details of the myocardial protection used. In this manner, surgeons may more effectively evaluate the voluminous and somewhat conflicting literature on the results of normothermic blood cardioplegia.
Related Article
Ann. Thorac. Surg. 1995 60: 1087-1093.
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