Reentry formation during ventricular fibrillation

Sudden cardiac death caused by ventricular fibrillation (VF) is the leading cause of death in the industrialized world. It is thought that multiple unstable reentrant spiral waves are the underlying cause of VF. According to the "restitution hypothesis", reentrant waves form due to a cellular instability resulting in alternans leading to conduction block. Alternans are thought to occur when the slope of the restitution curve (i.e., the relationship of APD to its preceding diastolic interval DI) is >1. A video imaging system capable of recording transmembrane potential with high temporal and spatial resolution was used to study the mechanisms of reentry formation during VF in isolated pig hearts. Restitution curves were constructed during steady state pacing at progressively shorter pacing intervals. The slope of the restitution curves was >1 for DIs<82 msec. During VF, reentrant waves frequently formed in regions where impulse propagation was impaired in previous beats. First, impulse propagation slowed, conduction block occurred but no reentry was initiated. Second, the impulse propagated in the retrograde direction forming reentry in the region where black had occurred. These events were not associated with APD alternans despite the fact that during VF DI values were always less than 82 ms.