LEFT-VENTRICULAR HYPERTROPHY IN HYPERTENSIVE PATIENTS IS ASSOCIATED WITH ABNORMAL RATE ADAPTATION OF QT INTERVAL

Objectives. This study sought to examine whether the responses of the QT interval to changes in the heart rate were altered in left ventricu lar hypertrophy (LVH). Background. The QT interval has been shown to h ave a delayed adaptation to sudden changes in heart rate in normal sub jects. Abnormalities in the adaptation of the QT interval to changes i n the RR interval may facilitate the development of ventricular arrhyt hmias. Methods. Consecutive newly diagnosed hypertensive subjects, not taking any medications, were age and gender matched for LVH (n = 21) versus no LVH (n = 16). QT interval dynamics were analyzed under visua l control using a validated algorithm with automatic QT measurements a t the end of the T wave. A computerized Holter system was developed to study the QT interval response to changes in the RR interval. The ada ptive response of the QT interval was measured as the ratio of the slo pe from 10% to 90% of the QT change relative to the RR interval change (dQT/dRR(10-90)). Steady state adaptation was also studied as the per cent shortening and lengthening of the QT interval during acceleration and deceleration of heart rate. Results. The adaptive response of the QT interval measured as dQT/dRR(10-90) was increased in the LVH group compared with that in the control subjects during both acceleration ( 0.33 +/- 0.06 vs, 0.18 +/- 0.02, p = 0.02) and deceleration phases (0. 23 +/- 0.04 vs. 0.16 +/- 0.02, p = 0.03). In the LVH group, the percen t lengthening of the QT interval was greater (7.6 +/- 0.7 vs. 5.1 +/- 0.2, p = 0.03), whereas the percent shortening was not significantly d ifferent (5.71 +/- 0.5 vs. 4.6 +/- 0.3, p = 0.43), than that in contro l subjects. Conclusions. The QT interval response to changes in the RR interval is rapid and exaggerated in LVH. These abnormalities of the QT interval response demonstrate that there are altered repolarization dynamics in patients with LVH that may make them vulnerable to seriou s ventricular arrhythmias. (C) 1997 by the American College of Cardiol ogy.