Effects of duration of ventricular fibrillation and heart massage on haemodynamic responses after defibrillation in dogs.

The purpose of this study was to investigate the effects of duration of ventricular fibrillation (VF), and of closed chest manual cardiac massage during VF on the recovery of the circulation. 24 open chest episodes and 50 closed chest episodes were studied. Longer duration of VF resulted in slower recovery. The critical recovery time was 60 to 90 s, beyond which no recovery occurred spontaneously. Heart massage improved recovery in nearly all cases. This indicates that the favourable effect of heart massage is not only confined to carotid flow to the brain but also that it has a favourable effect on the contractility of the heart, probably by the generation of coronary flow. Changes in coronary flow during spontaneous recovery were similar to those in reactive hyperaemia. The maximum mean coronary flow during recovery was 1.7 to 6 times the steady state values. When the duration of VF was longer than 60 s the recovery of the circulation was often worsened by a pronounced transient bradycardia, occasional ventricular tachycardia or frequent ventricular premature excitations.