Abstract: A pacemaker for tachycardia control which comprises a detector for sensing the onset of a tachycardia, a generator responsive to the detector for issuing a stimulating pulse to the heart for arresting the tachycardia, a second detector for sensing the response of the heart to the stimulating pulse and if the tachycardia was not arrested, for determining if the pulse was issued at an incorrect early or late time relative to the tachycardia beat, and a controller for the stimulating pulse generator responsive to the second detector whereby, when the tachycardia is not arrested, to cause a subsequent stimulating pulse to be issued at an adjusted later or earlier time relative to the tachycardia beat.

Abstract: An apparatus for the investigation and/or control of tachycardia comprising an implantable pacemaker having a short (typically 180 ms or lower) refractory period and providing in use, output pulses in response to external stimuli applied to the skin of the patient, and an external stimulus generator comprising means for generating the external stimuli. In the control of tachycardia, the implanted unit provides output pulses in response to natural heart beats. These output pulses are detected by the external stimulus generator through electrodes thereon held in contact with the skin. The external generator determines the pulse rate of the detected pulses and, if above a preset level, generates the external stimuli of an appropriate characteristic in time and number to cause the implanted unit to issue output pulses to arrest the tachycardia. The apparatus may also be used to induce a tachycardia, enabling non-invasive electrophysiological studies to be made.