Ventricular arrhythmia with postural dependency

Ventricular arrhythmias associated with recumbency were noted in a 17-year-old man with mild idiopathic myocarditis. These arrhythmias were refractory to several anti-arrhythmic drugs. Frequent ventricular arrhythmias were reproducibly recorded in the supine position and in a 15 degree tilt from the horizontal, while they were completely abolished in positions tilted more than 30 degrees from the horizontal, at which time sinus rate increased to more than 70 beats/min. The ventricular arrhythmias were suppressed during treadmill exercise and markedly aggravated when the underlying sinus rate was decreased during sleep or lying flat in bed. The arrhythmias were entirely abolished by atropine 1 mg. Furthermore, they were suppressed during atrial pacing at the rates of 80 and 90 bpm. Ventricular tachycardia could not be induced by programmed right ventricular stimulation. The appearance of postural arrhythmias in this patient correlated with relative bradycardia suggesting that they may be related to enhanced vagal nerve activity.