Ann Thorac Surg 2001;71:876
© 2001 The Society of Thoracic Surgeons
Invited commentary
Shukri F. Khuri, MDa
a Surgical Service, VA Boston Healthcare System Harvard Medical School, 1400 Veterans of Foreign Wars Parkway, West Roxbury, MA 02132, USA
e-mail: shukri.khuri{at}med.va.gov
Numerous controversies about the type and methods of delivery of cardioplegic solutions continue to prevail, despite a voluminous literature of experimental studies published over the past 15 years. This fact alone underscores the need for more sensitive tools with which reliable online assessments of the adequacy of myocardial protection can be obtained. This experimental study by Warner and colleagues demonstrates the value of employing an online metabolic monitor to settle, at least experimentally, an important controversy related to the merits of single versus multidose cardioplegia in the infant heart. Prolonged aortic clamping of the infant heart resulted in progressive myocardial tissue acidosis in the anterior left ventricular wall when cardioplegia was administered through a single dose; it also resulted in post-reperfusion cardiac dysfunction. In contrast, multidose administration of the same solution completely prevented acidosis in that wall, and preserved post-reperfusion cardiac function. One of the limitations of this study, however, is the use of a single electrode, placed in the anterior wall, with the assumption that the distribution of the cardioplegic solution in the heart was homogeneous, and that the pH in the anterior wall was representative of pH in the other walls. Clinical studies, which employed the electrode described in this study intraoperatively in adult patients, have shown a variable and an unpredictable heterogeneity in the distribution of the cardioplegic solution administered during the period of aortic clamping. This heterogeneity is manifested by significant and often marked differences between the myocardial pH levels observed in the anterior and posterior walls of the left ventricle, with the posterior wall demonstrating increased vulnerability to the onset of acidosis. These differences, which have been observed even in the absence of coronary artery disease, underscore the importance of monitoring myocardial pH in both the anterior and the posterior walls of the left ventricle.
In addition to demonstrating the value of myocardial pH measurement in the assessment of the adequacy of myocardial protection, this study is one of the first clinically-relevant experimental studies which show the adverse impact of myocardial acidosis during the period of aortic clamping on post-reperfusion cardiac function. There is now compelling evidence from myocyte culture studies that acidosis is a primary trigger for apoptosis. This finding, together with the adverse impact of myocardial tissue acidosis demonstrated in this study, suggest that future myocardial protection strategies should be based on the prevention of regional myocardial acidosis—an approach which will be aided by the development of tools for the on-line assessment of myocardial pH.
