Pathophysiologic Substrate for Sustained Ventricular Tachycardia in Coronary Artery Disease

Sustained ventricular tachycardia (VT) in the presence of coronary artery disease (CAD) is almost always associated with prior infarction. Its mechanism is reentrant excitation and it can be initiated > 95% of the time. Disrupted and delayed endocardial activation and prolonged, fragmented electrograms recorded during sinus rhythm distinguish patients with VT from those with normal ventricles and those of prior infarction without VT. The extent of abnormalities of activation and number of abnormal, fragmented and late electrograms are greatest in patients with sustained VT. These abnormalities are associated with scar tissue separating the viable myocytes. Fragmented electrograms are due to discontinuous activation due to nonuniform anisotropy caused by the scar tissue. Patients with CAD demonstrate depressed excitability and prolonged relative refractory periods (ie, an upward shift in the strength-interval curve) at sites of infarction but effective refractory periods measured at 10 mA comparable to normals and dispersion of refractory periods. However the associated abnormalities of conduction and activation produce an abnormal dispersion of recovery. Intraoperative mapping of patients with CAD has shown that most of the abnormalities of endocardial activation and conduction are in the subendocardial layers and subendocardial resection of these areas cures VT and abolishes delayed, fragmented electrograms and split potentials and normalizes the electrograms recorded from the subjacent tissue. This supports the hypothesis that abnormalities of conduction are the critical pathophysiologic substrate of VT in CAD.