TIME-DOMAIN SIGNAL-AVERAGED ELECTROCARDIOGRAM IN NONISCHEMIC VENTRICULAR-TACHYCARDIA

The prevalence of late ventricular potentials (LVPs) defected by signa l averaged ECG (SAECG) is variable in nonischemic heart diseases. In i diopathic dilated cardiomyopathy, the prevalence increases from about 25% to 70%-90% in cases of spontaneous sustained ventricular tachycard ia (VT), is not significantly correlated with hemodynamic and Holter d ata, and has a good positive predictive value for induced and spontane ous sustained VT. However, its predictive value for cardiac death has not been established. In primary hypertrophic cardiomyopathy, LVPs are rare (about 20%), not correlated to hemodynamic data, enhanced in cas es of spontaneous sustained VT (up to 77%), and have a good predictive value of induced VT. LVP-SAECG are frequent in arrhythmogenic right v entricular dysplasia (ARVD) (70%-80%). They can identify patients with VT and an unapparent or limited form of this disease, or ARVD with fe w ventricular arrhythmias. The prevalence (26%-37%) of LVPs in mitral valve prolapse is clearly higher than in normal individuals or in othe r valvular diseases and is enhanced in cases of spontaneous and induce d VT. Its significance remains speculative. After surgical repair of t etralogy of Fallot, LVPs can identify a group of patients with higher probability of induced and spontaneous risk of VT. The usefulness and significance of LVPs in other nonischemic cardiac diseases have not to date been established. In ''true'' idiopathic VT, without proved stru ctural cardiac disease, the prevalence of LVPs does not exceed that ob served in normal individuals (0%-5%), but in ''apparent'' idiopathic V T the prevalence of LVPs rises to 20%-40%. In these latter cases more invasive techniques must be used to discover a limited form of myocard iopathy.