Relation between power spectrum time course during ventricular fibrillation and electromechanical dissociation. Effects of coronary perfusion and nifedipine

To relate the evolution of ventricular fibrillation (VF) to the haemodynamic recovery after cardioversion, we characterized the differences in the ECG power spectrum (PS) time course, among different types of VF: under control conditions, with previous administration of nifedipine and on cardiopulmonary bypass (CPB). In the first few seconds VF showed a PS with a narrow peak between 8 and 15 Hz and its higher harmonics, suggesting some organization and regularity. In the following 40 seconds, the arrhythmia accelerated slightly, maintaining an organized spectrum. Afterwards, the PS became slow and irregular, losing its initial characteristics after 60 seconds. Conversely, VF on CPB maintained its organized PS, over a prolonged period. Previous administration of 0.32, 0.64 mg kg-1 of nifedipine maintained the initial characteristics of the PS for 90 and 150 seconds. Similar results were obtained with previous autonomic blockade. In another group of dogs, defibrillation was performed after successive periods of VF, to study electromechanical dissociation (EMD). In all control dogs, EMD was observed after 90 seconds of VF. Pretreatment with nifedipine postponed EMD until 120-150 seconds and was not observed in dogs on CPB. The PS time course during VF seems a reliable method of analyzing and quantifying the different types of VF. It could be related with the onset of EMD, reflecting the metabolic alterations that happen during VF. Nifedipine could delay the ischaemic effects during VF and increase the possibility of successful cardiac resuscitation.