Clinical study of late potentials. Comparison of late potentials in myocardial infarction, cardiomyopathy and idiopathic ventricular tachycardia.

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Abstract
Late potentials (LPs) were studied using the signal averaging technique in 80 patients with myocardial infarction (MI), idiopathic cardiomyopathy (CM) and idiopathic ventricular tachycardia (IVT). In MI, LP duration was 28.4 .+-. 12.6 ms in the sustained VT group (I; 8 cases); 18.6 .+-. 9.0 ms in the nonsustained VT group (II; 11 cases); and 14.4 .+-. 8.6 ms in the non-VT group (III; 21 cases); (p < 0.05 in I vs II, p < 0.01 in I vs III and not significant in II vs III). In CM, it was 33.7 .+-. 13.0 ms in group I (6 cases); 20.1 .+-. 5.9 ms in group II (12 cases); and 7.1 .+-. 9.2 ms in group III (14 cases); (p < 0.01 in I vs II, I vs III and II vs III). The LP duration in IVT (8 cases) was 15.6 .+-. 10.4 ms, which was significantly shorter than that of group I in MI and CM (p < 0.05 vs MI and p < 0.01 vs CM). Late potential duration was also compared between a pacing-inducible VT group and a non-inducible VT group. The mean value of LP duration in the inducible VT groups of MI was significantly longer than that in the non-inducible group (27.8 .+-. 3.9 ms in 4 cases vs 17.3 .+-. 2.5 ms in 4 cases, p < 0.05). However, there was no significant difference in LP duration between the inducible and non-inducible groups of CM (22.0 .+-. 11.0 ms in 5 cases vs 22.2 .+-. 13.6 ms in 5 cases). In IVT, it was 21.0 .+-. 4.7 ms in 4 cases and 12.8 .+-. 11.3 ms in 4 cases (n.s.). In conclusion, LP duration was closely related to sustained VT in MI and CM, but not in IVT, and then related to inducibility of VT by pacing in MI, but not in CM. It is therefore proposed that the pathophysiological significance of LPs is different in each underlying disease.