January 1, 1990Circulation
Paradoxical effects of exercise on the QT interval in patients with polymorphic ventricular tachycardia receiving type Ia antiarrhythmic agents.
Why the study?
Does exercise testing reveal abnormal QT interval responses in patients who developed polymorphic ventricular tachycardia from type Ia antiarrhythmic agents?
Population
22 patients
Comparison
Exercise testing performed in the absence of all… vs Control patients matched for age, sex, and heart…
Design
Case-control
Authors
Discussion
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Implication
Exercise QTc prolongation may mark type Ia proarrhythmia susceptibility; hypothesis-generating for risk stratification pending validation.
Key Points
- To determine whether patients who develop polymorphic ventricular tachycardia from type Ia antiarrhythmic agents exhibit abnormal QT interval adaptation during exercise in the absence of medication.
- Evaluated exercise testing off all antiarrhythmic medications in 11 case patients with documented type Ia drug-induced polymorphic ventricular tachycardia and 11 control patients matched for age, sex, and heart disease.
- Measured resting and 3-minute exercise QT, RR, and corrected QT (QTc, calculated via Bazett's method) intervals in both cohorts.
- Baseline resting QT (410 ± 13 vs 386 ± 11 msec) and QTc (438 ± 10 vs 438 ± 4 msec) intervals showed no significant differences between case and control groups.
- During exercise, the QTc interval paradoxically increased in case patients compared to controls (482 ± 8 vs 431 ± 5 msec; p < 0.001), reflecting blunted absolute QT shortening (to 357 ± 11 vs 310 ± 9 msec; p = 0.06).
- A QTc interval increase greater than 10 msec with exercise occurred in 10 of 11 case patients compared to 1 of 11 control patients (p < 0.001).
Structured PICO
Does exercise testing reveal abnormal QT interval responses in patients who developed polymorphic ventricular tachycardia from type Ia antiarrhythmic agents?
P
Population
22 patients (11 case patients with newly documented polymorphic ventricular tachycardia in response to type Ia antiarrhythmic agents, and 11 control patients matched for age, sex, and heart disease)
I
Intervention
Exercise testing performed in the absence of all antiarrhythmic drugs
C
Comparator
Control patients matched for age, sex, and heart disease
O
Outcome
Response of the QT, RR, and QTc intervals to exercise testing at rest and at 3 minutes of exercisesurrogate
Patients with a history of proarrhythmia from type Ia antiarrhythmic agents exhibit a paradoxical prolongation of the QTc interval during exercise testing even in the absence of drugs.
Cite This Study
Kadish et al. (1990) studied this question.