Jp. Singh et al., LEFT-VENTRICULAR HYPERTROPHY IN HYPERTENSIVE PATIENTS IS ASSOCIATED WITH ABNORMAL RATE ADAPTATION OF QT INTERVAL, Journal of the American College of Cardiology, 29(4), 1997, pp. 778-784
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.