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J Thorac Cardiovasc Surg 2008;135:139-146
© 2008 The American Association for Thoracic Surgery

Cardiopulmonary Support and Physiology

Nonischemic myocardial acidosis adversely affects microvascular and myocardial function and triggers apoptosis during cardioplegia

Division of Cardiothoracic Surgery, Department of Surgery, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Mass.

Presented in part at the American Heart Scientific Sessions 2006, Chicago, Ill, November 12-15, 2006.

Received for publication May 2, 2007; revisions received July 10, 2007; accepted for publication July 16, 2007.

^_* Address for reprints: Frank W. Sellke, MD, Division of Cardiothoracic Surgery, BIDMC, LMOB 2A, 110 Francis St, Boston, MA 02215. (Email: fsellke{at}caregroup.harvard.edu).

Objectives: We investigated whether the degree of nonischemic myocardial acidosis during a period of cardioplegic arrest differentially affects the recovery of microvascular/left ventricular function, the profile of Bcl₂-family protein expression, and the occurrence of apoptosis.

Methods: Isolated hearts from donor rabbits were perfused with oxygenated diluted blood on a modified Langendorff apparatus. The hearts were arrested for 60 minutes with cold (15°C ± 0.5°C) diluted-blood cardioplegic solution (hematocrit: 18%–25%) administered continuously under nonischemic conditions (flow rate; 10 mL/min). The myocardial pH was adjusted and measured continuously with a glass electrode system. Myocardial pH was maintained at 7.2, 6.5, or 6.2, respectively (n = 6 per group) during 60 minutes of arrest. Hearts were then reperfused for 120 minutes with oxygenated diluted blood.

Results: Recovery of left ventricular and microvascular endothelial function was better with a myocardial pH of 7.2 than with a pH of 6.5 or 6.2 (P < .05). There were no significant differences in total Bcl₂, phospho-Bcl₂-serine 70, phospho-Bad-serine 112, and phospho-Bad-serine 136 levels among groups. Myocardial pH of 7.2 also induced less caspase 3 activation and apoptotic cells (terminal deoxynucleotidyl transferase–mediated dUTP nick end labeling) than a pH of 6.5 or 6.2 (P < .05). Regression analysis demonstrated that a significant relationship existed between the recovery of endothelial microvascular (r ² = 0.38, P =.004) or left ventricular (r ² = 0.37, P =.007) function and myocardial pH.

Conclusion: Severe acidosis during cardioplegic arrest, independent of ischemia, adversely affects recovery of microvascular and left ventricular function and increases indices of apoptosis. This effect on apoptosis may influence long-term outcome after cardiac surgery.