Analysis of QT interval in patients with idiopathic mitral valve prolapse.

Analysis of QT interval from repeated recordings was made in 56 patients with documented idiopathic mitral valve prolapse (IMVP). The results were compared with a control of 62 healthy volunteers in whom mitral valve prolapse was excluded by both phonocardiography and echocardiography and with two other standard populations, those of Simonson and co-workers and of Ashman. After correction for age, the maximum QT interval of the patients with IMVP exceeded the 97.5 percentile of Simonson population in 51 of 56 patients compared with only three of 62 subjects of the control group. The difference between the QT interval of patients from the upper limits of the predicted mean values of Simonson was significant (P less than 0.002). The mean QTC interval in patients with IMVP was 0.48 +/- 0.035 second compared with 0.038 +/- 0.025 second in the control subjects. The difference between the mean QTC interval in patients with IMVP and the control subjects was significant (P less than 0.005). Spontaneous prolongation in the mean QT interval was noted in 43 of 56 patients with IMVP (76.6 percent) compared with only two of 62 control subjects (3 percent). The incidence of episodic arrhythmias was 72 percent in patients with marked QTC prolongation (mean, 0.58 second) compared with 22.6 percent in patients with lesser degree of QTC prolongation (mean, 0.46 second). The results suggest that QT abnormality is common in patients with IMVP and may play an important role in the genesis of cardiac arrhythmia.