THE RELATIONSHIP BETWEEN TEMPERATURE AND CALCIUM IN ACUTE CELL-DAMAGEAFTER EXPOSURE TO RADIOFREQUENCY OR THERMAL-ENERGY IN ISOLATED NEONATAL AND ADULT-RABBIT CARDIAC MYOCYTES

Radiofrequency (RF) ablation is a nonsurgical technique using catheter -directed RF energy for treating cardiac arrhythmias in children and a dults. Previous reports have suggested that sequestration of calcium ( Ca2+) by the sarcoplasmic reticulum may partially protect mature cardi ac myocytes from the effects of RF energy. The purposes of this study were to determine whether differences exist between neonatal and adult myocyte responses to RF energy and if myocyte damage is a Ca2+-depend ent process. Because immature myocardium is functionally deficient in sarcoplasmic reticulum, we hypothesized that immature myocytes would b e more susceptible to damage induced by RF energy. Isolated ventricula r myocytes were obtained from neonatal and adult New Zealand White rab bits by enzymatic dissociation, then placed in a perfusion chamber des igned to deliver RF energy or a heated perfusate solution. Measurement s of bath temperature, cell morphology, and contractile response to el ectrical stimuli were recorded. RF energy application associated with increased perfusate temperature resulted in cell death, but not when t he temperature rise was inhibited. Thus, the acute damage to cells exp osed to RF energy appears to be mediated by thermal energy. After expo sure to thermal energy, neonatal cells underwent contracture at lower temperatures than did adult cells. Perfusion with solutions containing low Ca2+ concentrations, comparable to intracellular diastolic Ca2+ l evels, had a protective effect for both neonatal and adult myocytes. T hese findings indicate that acute cell damage after exposure to RF ene rgy is mediated by a Ca2+-dependent process. Furthermore, immature myo cardium is particularly susceptible to RF-mediated cell damage, possib ly secondary to reduced Ca2+ sequestration by the sarcoplasmic reticul um.