Alteration of the QT/RR Relationship in Patients with Idiopathic Ventricular Tachycardia

It has been shown that alterations in QT/RR relationship may be associated with arrhythmogenesis in several clinical settings. In the present study the QT/RR relationship was studied in 20 patients with idiopathic ventricular tachycardia (12 men and 8 women, aged 41±14 years) compared to 20 normal subjects (9 men and 11 women, aged 39 ± 13 years). All the patients were off any antiarrhythmic drugs and had no evidence of intraventricular conduction defects. The QT intervals and their preceding RR intervals were measured on electrocardiogram strips from 24-hour Holter tapes at hourly intervals. The differences in the maximum, minimum, and mean of either the QT interval or its corrected values between patients with idiopathic ventricular tachycardia and normal subjects were not statistically significant. There was a significant correlation between the QT and RR intervals in normal subjects (γ= 0.73 ± 0.12, P < 0.05) and in patients with idiopathic ventricular tachycardia (γ= 0.80 ± 0.10, P < 0.05). However, the linear regression line of the QT interval against the RR interval were significantly (P < 0.001) altered in patients with idiopathic ventricular tachycardia (QT = 0.24 + 0.18 RR) compared to normal subjects (QT = 0.27 ± 0.12 RR). We conclude that although there is no significant change in the QT interval and its corrected values, the QT/RR relationship is significantly altered in patients with idiopathic ventricular tachycardia as compared to normal subjects. This may be of importance in the pathogenesis of idiopathic ventricular tachycardia in these patients.