Myocardial function is normal after rapid cooling of the in vivo neonatal heart

Rapid cooling (RC) on cardiopulmonary bypass (CPB) has been reported to be injurious to the neonatal myocardium when compared with slow cooling (SC). However, previous studies have been performed on isolated heart preparations using asanguineous perfusates and may not represent clinically valid conclusions. In this study, the effect of RC versus SC on post-CPB cardiac function in an in vivo neonatal heart model using a blood perfusate was investigated. Thirteen neonatal piglets underwent median sternotomy. Left ventricular ultrasonic dimension transducers were placed in the minor and major axis diameters, and an intraventricular micromanometer was placed. Baseline left ventricular pressure-dimension data were obtained during transient vena caval occlusion. Animals were then placed on CPB (blood prime; mean hematocrit, 25%) with the prime temperature at either 18 degrees C (RC) or 37 degrees C (SC) and perfusion cooled either quickly (RC) or gradually (SC) such that within 2 minutes of cooling the average myocardial temperature was 23.5 degrees C in the RC group versus 33.8 degrees C in the SC group (p = 0.0001). Animals were cooled to 20 degrees C, rewarmed to 37 degrees C, and then weaned from CPB. Left ventricular pressure-dimension data were obtained 30 minutes after CPB and compared with baseline. The slope (MW) and x-intercept (Vo) of the linear stroke work-end-diastolic volume relationship were used as load-insensitive indices of left ventricular function at baseline and after CPB. There was no statistically significant difference in baseline versus postbypass MW or Vo in the RC or SC groups.(ABSTRACT TRUNCATED AT 250 WORDS)