Changes in spontaneous sinus node rate after ventricular pacing as an estimate of autonomic tone: clinical applications.

Rapid ventricular pacing (VP) reproduces neurohumoral variations associated with ventricular tachycardia. This study was set up to analyse the mechanisms that cause changes in sinus heart rate after rapid VP and to find the clinical factors that adapt sinus heart rate to VP, and the clinical value of the method. Rapid VP was performed in 356 patients aged 15 to 86 years, in increments of 10 beats, at progressively faster rates every 10 s up to 200 beats.min-1. Group I comprised 122 patients with no underlying heart disease; group II comprised 234 patients with an underlying heart disease. The sinus heart rate (HR) was initially accelerated (SR1), in comparison with the basal sinus HR, for 2 to 5 s (90.5 beats.min +/- 21 vs 71 +/- 19 in group I, 89.5 +/- 26 vs 76 +/- 16 in group II). Five seconds later, there was a decrease in HR (SR2) which was slower than the basal HR (62 beats.min +/- 22 in group I, 75 +/- 15 in group II). The variations in HR, defined as SR1-SR2/SR1, were significantly higher in group I than group II: 31 +/- 18% vs 19 +/- 15%, (P < 0.001). With the injection of 2 mg atropine in 14 group I patients the variations in HR were suppressed after ventricular pacing. When oral beta-blockers were administered to 21 group I patients, there were still significant changes in HR. The changes in HR were reproducible during electrophysiological study.(ABSTRACT TRUNCATED AT 250 WORDS)