Author + information
- Received April 26, 1996
- Revision received October 8, 1996
- Accepted December 4, 1996
- Published online March 15, 1997.
- Jagmeet P Singh, MD, DMA,* (, )
- Jim Johnston, BScA,
- Peter Sleight, MD, FRCP, FACCA,
- Rosemary Bird, BScA,
- Kathryn Ryder, MRCP, DPhilA and
- George Hart, DM, FRCPA
- ↵*Dr. Jagmeet Singh, Framingham Heart Study, 5 Thurber Street, Framingham, Massachusetts 01701.
Objectives. This study sought to examine whether the responses of the QT interval to changes in the heart rate were altered in left ventricular hypertrophy (LVH).
Background. The QT interval has been shown to have a delayed adaptation to sudden changes in heart rate in normal subjects. Abnormalities in the adaptation of the QT interval to changes in the RR interval may facilitate the development of ventricular arrhythmias.
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 visual control using a validated algorithm with automatic QT measurements at 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 adaptive response of the QT interval was measured as the ratio of the slope from 10% to 90% of the QT change relative to the RR interval change (dQT/dRR10–90). Steady state adaptation was also studied as the percent 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/dRR10–90was 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 percent 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 different (5.71 ± 0.5 vs. 4.6 ± 0.3, p = 0.43), than that in control 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 serious ventricular arrhythmias.
(J Am Coll Cardiol 1997;29:778–84)
☆ Dr. Singh was supported by The Norman Collisson Research Foundation and Gibson Trust, Oxford, England, United Kingdom. The Department of Cardiovascular Medicine is funded by the British Heart Foundation, London, England, United Kingdom.
- Received April 26, 1996.
- Revision received October 8, 1996.
- Accepted December 4, 1996.
- The American College of Cardiology