Subthalamically induced paroxysmal ventricular tachycardia after complete heart block

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Abstract
Several weeks after atrioventricular conduction in dogs had been chronically blocked by injected formalin, stimulation of the Hl field of Forel increased the rate of ventricular contractions from less than 60/min. as high as 280/min. This tachycardia typically started abruptly about 15 sec. after diencephalic stimulation was begun and persisted up to 2 min. after it stopped. The return to the basal rate was abrupt; subsequent brief periods of ventricular tachycardia sometimes occurred spontaneously. The rate of ventricular tachycardia was independent of the atrial rate, and was not due to re-establishment of atrioventricular conduction. The effect could be reproduced by re stimulation. A change in the configuration of the QRS complex, suggesting a change of ventricular pacemaker, occurred at the onset of the ventricular tachycardia. During the paroxysms systolic and diastolic arterial pressure (measured directly) increased; stroke volume (calculated from measurements with an ultrasonic flowmeter on the aorta) decreased. Spontaneous activity, treadmill exercise, startle, excitement, or infusion of epinephrine, norepi-nephrine, or isopropyl nor epinephrine increased the ventricular rate only about 50%.