The role of cardioplegic solution buffering in myocardial protection. A biochemical and histopathological assessment.
The advantages of buffering cardioplegic solutions to improve adenosine triphosphate preservation and postarrest hemodynamic function have been previously promoted. We evaluated the benefit of histidine buffering (195 mmol/L) in a low sodium (27 mEq/L) cardioplegic solution (Roe's) in a canine model of multidose cardioplegic arrest. Four solutions, two unbuffered (K+ = 10 mEq/L and K+ = 30 mEq/L) and two buffered (K+ = 10 mEq/L and K+ = 30 mEq/L), were tested in four groups of dogs for a 4 1/2 hour arrest period followed by 1 hour of reperfusion. Use of the unbuffered solution resulted in a drop in myocardial adenosine triphosphate from 29 +/- 1 mmol/kg (mean +/- standard error of the mean) (K+ = 30 mEq/L) and 28 +/- 2 mmol/kg (K+ = 10 mEq/L) to 8 +/- 2 mmol/kg and 7 +/- 2 mmol/kg, respectively, during the arrest period. In both buffered groups, adenosine triphosphate remained at preischemic levels during the entire arrest period. Myocardial glycogen followed the same pattern as adenosine triphosphate in the buffered groups. Lactate production was markedly elevated in all groups during ischemia. Postarrest hemodynamic function, as assessed by intraventricular isovolumic developed pressure measurements, was better (p less than 0.05) in the buffered low-potassium group than in the other three groups. The extent of myocardial necrosis, measured by triphenyl tetrazolium staining and confirmed by electron microscopy, was minimal (2% +/- 1% of biventricular mass) in the buffered low-potassium group, significantly greater (7% +/- 2% and 10% +/- 2%) in the unbuffered high-potassium and low-potassium groups, respectively, and highest (35% +/- 9%) in the buffered high-potassium group. These findings indicate that significant buffering capacity (similar to that of blood) in a crystalloid cardioplegic solution can be effective in preserving myocardial adenosine triphosphate stores, improving postarrest contractile function, and minimizing myocardial necrosis, provided the combination of high extracellular potassium and high pH levels is avoided.