Mechanical conversion of post-ischaemic ventricular fibrillation: effects on function and myocyte injury in isolated rat hearts.

Ventricular fibrillation (VF) and ventricular tachycardia (VT) are common phenomena during reperfusion. In experimental research many hearts have to be excluded from haemodynamic evaluation because of severe arrhythmias. Theoretically, electroconversion or mechanical conversion (MC) might be used to convert VF or VT. MC induces a physical shock analogous to a chest thump. The aim of this study was to investigate the efficacy of MC in isolated, perfused rat hearts, and to see whether MC itself induced myocardial cell injury and functional impairment. Langendorff-perfused rat hearts (n = 89) from several experimental series subjected to 30 min of global ischaemia and 60 min of reperfusion were retrospectively analysed. Left ventricular systolic (LVSP), end-diastolic (LVEDP), and developed (LVDP) pressures, coronary flow (CF), and heart rate (HR) were measured. If VF or VT continued for 1 min during reperfusion, MC was attempted by a flick of the forefinger to the right ventricle. If VF or VT still occurred, MC was repeated. Hearts that did not have regular beating after 20 min of reperfusion were excluded. Release of cardiac troponin T (cTnT) was measured before ischaemia and after 20 min of reperfusion. Forty-four out of 89 hearts had VF or VT during reperfusion. Thirty-five hearts were converted, 18 of which were converted by one or two MCs only. The higher the total number of MCs employed, the more cTnT was released. After 20 min of reperfusion, LVEDP, LVDP and CF were better in hearts with a higher number of MCs and with increased release of cTnT. After 60 min of reperfusion, LVEDP was still improved in hearts with more cTnT release, whereas LVSP was lower, and LVDP and CF were independent of the number of MCs. There was no consistent correlation between release of cTnT and heart dysfunction. In conclusion, MC effectively converted VF or VT. MCs increased post-ischaemic myocardial cell damage, as judged from increased cTnT release. Post-ischaemic dysfunction was partly attenuated in hearts with multiple MCs, and did not correlate with release of cTnT. We feel that MCs should not be used in isolated, perfused hearts.