Modulation of the Q-T interval by the autonomic nervous system.

Recent investigations have clarified some of the effects of the autonomic nervous system on duration and spatial distribution of the Q-T interval in humans. The use of atrial pacing to fix heart rate or 24-hour continuous electrocardiographic recording to develop a regression formula for individual patients has provided a means to interpret the effects of an intervention that alters both the heart rate and the Q-T interval. Drugs that affect the autonomic nervous system can influence Q-T interval directly or by changing rate. Bazett's formula to correct for rate may be misleading after certain drug interventions. For example, the Q-T interval during sinus rhythm or atrial pacing and the ventricular effective refractory period shorten after atropine plus propranolol, but corrected Q-T interval using Bazett's formula does not change. No change occurs in the Q-T interval during sinus rhythm or atrial pacing, or in ventricular effective refractory period after administration of propranolol although corrected Q-T interval using Bazett's formula markedly shortens. Q-T interval during sinus rhythm and atrial pacing and ventricular effective refractory period decrease after atropine but correct Q-T interval lengthens.(ABSTRACT TRUNCATED AT 250 WORDS)