Ventricular fibrillation: the importance of being coarse?

Ventricular fibrillation (VF) has been classified electrocardiographically as "fine amplitude" or "coarse amplitude" VF. It has been suggested that coarse VF represents increased "synchronization" of myocardial activation which could result in lower thresholds for defibrillation. To test the "synchronization" differences between coarse VF and fine VF, we induced VF in ten normal anaesthetized dogs. Standard limb lead and His bundle electrograms were recorded simultaneously with 12 bipolar epicardial electrograms (eight dogs) and six lead ECG (two dogs). Activation "synchronization" was assessed by calculating the standard deviations (SD) of electrogram activation times during one coarse VF and one fine VF cycle. Less synchronization during VF was indicated by a 50% larger SD (CVF: 29.3 +/- 1.1 msec, FVF: 32.6 +/- 1.6 msec) compared to ventricular pacing (21.2 +/- 1.6 msec) and 500% larger than sinus rhythm (6.5 +/- 0.5 msec). Coarse VF and fine VF did not differ. In addition, the 6-lead ECG recorded during early VF had episodes of coarse VF and fine VF occurring simultaneously. The amplitude of all electrograms diminished over 15 minutes until only fine VF could be recorded. We conclude that coarse VF does not reflect greater synchronization of activity than fine VF early in fibrillation (five minutes). Rather, differences are due to lead orientation. Later in the fibrillation bout, fine VF probably reflects metabolically induced degeneration of cellular excitability.