Age-related effects of St Thomas' Hospital cardioplegic solution on isolated cardiomyocyte cell volume

Objectives: We tested the hypothesis that neonatal cells are more sensitive to cardioplegia-induced cell swelling than more mature cells and spontaneo us swelling in the absence of ischemia can be prevented by cardioplegia wit h a physiologic KCl product. Methods: Cell volumes of isolated ventricular myocytes from neonatal (3-5 days), intermediate (10-13 days), and adult (>6 weeks) rabbits were measured by digital video microscopy. After equilibrat ion in 37 degrees C physiologic solution, cells were suprafused with 37 deg rees C or 9 degrees C St Thomas' Hospital solution (standard or low Cl-) or 9 degrees C physiologic solution followed by reperfusion with 37 degrees C physiologic solution. Results: Neonatal cells swelled 16.2% +/- 1.8% (P < .01) in 37 degrees C St Thomas' Hospital solution and recovered during repe rfusion, whereas more mature cells maintained constant volume, In contrast, 9 degrees C St Thomas' Hospital solution caused significant age-dependent swelling (neonatal, 16.8% +/- 1.5%; intermediate, 8.6% +/- 2.1%; adult, 5.6 % +/- 1.1%). In contrast to more mature cells, neonatal cells remained sign ificantly edematous throughout reperfusion (8.1% +/- 1.5%). Swelling was no t due to hypothermia because 9 degrees C physiologic solution did not affec t volume, Lowering the KCl product of St Thomas' Hospital solution by parti ally replacing Cl- with an impermeant anion prevented cellular edema in all groups, Conclusion: In the absence of ischemia, neonatal cells were more s ensitive to cardioplegia-induced cellular edema than more mature cells, and edema observed in all groups was avoided by decreasing the KCl product of St Thomas' Hospital solution to the physiologic range. Differences in cell volume regulation may explain the sensitivity of neonatal hearts to hyperka lemic cardioplegic arrest and suggest novel approaches to improving myocard ial protection.