Copyright © 1992 by the European Society of Cardiology.
© 1992 The European Society of Cardiology
Paradoxical early lengthening and subsequent linear shortening of the QT interval in response to exercise
Department of Cardiology, Harefield Hospital Harefield, Middx, U.K.
Received 2 July 1991; revised 7 May 1992; .
Correspondence: J. G. Coghlan, Dept. of Cardiology, Harefield Hospital, Harcfield, Middx UB9 6JY, U.K.
Abstract
The QT responses to exercise during ventricular pacing were evaluated in 12 patients in whom permanent pacemakers were implanted/or complete heart block. The initial response of the QT to exercise was a paradoxical lengthening during the first minute of exercise (mean 4·8 ms P<0·01). Thereafter, the QT was found to shorten in a linear fashion in response to increasing exercise, both in terms of exercise duration (r=0·787; P<0·001) and atrial rate (r = 0·712; P<0·001). The total QT shortening with exercise was small (20 ms for a mean increase in atrial rate of 60 beats . min1) and displayed substantial inter-individual variability (931 ms).
These results explain some of the limitations of the QT pacemaker, and provide insights in to the dynamics of the QT response, which may help tailor the programming of these systems to the individual patient.
Key Words: Rate adaptive pacing QT exercise