POSSIBLE MECHANISM OF ECG FEATURES IN PATIENTS WITH IDIOPATHIC VENTRICULAR-FIBRILLATION STUDIED BY HEART MODEL AND COMPUTER-SIMULATION

The possible contribution of localized conduction delay and abnormal a ction potentials to ventricular fibrillation (VF) was studied by apply ing an anisotropic cardiac computer model to clinical cases of the Bru gada-type electro-cardiogram (EGG), which shows right bundle branch bl ock (RBBB), a normal QT interval, ST-segment elevation, and late r' in leads V-1 and V-2. The anisotropic heart model was composed of 50,000 discrete units with a spatial resolution of 1.5 mm and was mounted in a human torso model. The longitudinal/transverse conduction velocity ratio was 3:1. For the normal EGG, a conduction velocity of 0.75 mis w as required. In the abnormal area of the right anterior epicardial wal l, the conduction velocity was set at 0.2 m/s, with decreasing action potential amplitude and 10% prolonged action potential duration. The E CG features of ST-segment elevation and Brugada-type right bundle bran ch block pattern were simulated. The action potential duration was abl e to change dynamically with coupling interval of stimulation, with a ratio of 9% for normal ventricular muscle and 50% for Purkinje fibers. Five successive stimuli were applied to the left lateral epicardium 3 00 ms after the first sinus excitation, and sustained VF was induced w ith the transmural conduction delay at the right anterior ventricle as a block increasing the vulnerability. At the initiation of VF, reentr y circuits were shown around the border zone of the right epicardium a nd were very heterogeneous around the conduction delayed area and sept al area. In an area with the characteristics of nontransmural conducti on delay sustained VF was prevented, and the pattern of transient righ t bundle branch block appeared on the simulated ECG and body surface p otential maps. The late r' wave was calculated in the precordial leads and right anterior site on the body surface potential maps. These res ults suggest that increased multipolarity in the border zone between t he Purkinje fibers and delayed conduction area in the right ventricle might play an important role as a functional block for the persistence of VF.