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.