Studies on electromechanical dissociation

To study the relationship between the electrical and the mechanical activities of the heart, we have developed a closed chest animal model in which the onset of electromechanical dissociation (EMD) could be predictably observed during cardiac arrest. Ventricular fibrillation, induced by a wire introduced into the right ventricle, was passively observed for successive periods of 60, 90 and 120 seconds, before external defibrillation was performed. When ventricular fibrillation lasted 120 seconds, EMD was consistently observed in each control animal. Adequate electrical activity persisted for more than 10 minutes in each dog. Pretreatment with the calcium antagonists verapamil and nifedipine delayed the onset of EMD, thereby providing myocardial protection during ventricular fibrillation. These observations indicate that the onset of EMD is predictable after ventricular fibrillation. This model can be used to study the effects of pharmacological interventions on the development of EMD.