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Although myocardial cooling is standard practice for protecting the immature heart from ischemic injury during cardiac surgery, controversy exists regarding the optimal cooling rate. It has been proposed that rapid cooling may induce calcium release from the sarcoplasmic reticulum, thereby inducing myocellular injury and contractile dysfunction. We tested the hypothesis that the magnitude of the responses to cooling in newborn myocytes would not be affected by the rate of cooling. Ventricular myocytes were isolated from newborn piglets (5-8 days old), field stimulated (0.5 Hz) and contractions recorded using a video edge detection system. Following baseline recordings at 34°C, individual cells were cooled either rapidly (over 3 minutes) or slowly (over 15 minutes) to 20°C. These cooling rates and the target temperature were based on myocardial temperatures previously recorded during initiation of cardiopulmonary bypass using rapid or slow cooling protocols. Control cells were maintained at 34°C (n=10) or at 20°C(n=7) for the duration of the experiment. In all 4 groups, contractile function was compared 15 minutes after baseline (time 0) recordings. At baseline, there was no difference in contraction percentage (CP) or relaxation half-time (RT1/2) among the rapid cooling (R; n=7), the slow cooling (S; n=17), or the control 34°C groups. As shown in the Table (mean±SEM), cooling-induced increases in CP and RT1/2 were not significantly different in R, S or Control 20°C groups. Rewarming cells from both the R (n=4) and S (n=11) groups to 34°C after the same duration of cooling produced a comparable return toward baseline(CP=7.8±3.3% in R vs. 7.1±1.1% in S group; RT1/2=188±46 ms in R vs. 127±15 in S group; p=NS). These results support the hypothesis that in neonatal myocytes, the rate of cooling from 34°C to 20°C does not affect the magnitude of the cold-induced changes in these indices of contraction or relaxation. We conclude that when clinically relevant rates of myocardial cooling are used, there is no difference in the effects of rapid versus slow cooling rates on contractile function in ventricular myocytes isolated from newborn piglets.
El-Khouri, H., Haddock, P., Miller, J. et al. Effects of Cooling Rate on Contractile Function of Ventricular Myocytes Isolated from Newborn Piglets ♦ 107.
Pediatr Res43
(Suppl 4), 21 (1998). https://doi.org/10.1203/00006450-199804001-00128
