Rate Responsive Pacing Using the Evoked QT Principle. A Physiological Alternative to Atrial Synchronous Pacemakers

Abstract

We have evaluated clinically a rate-responsive pacemaker which uses the evoked QT principle as indicator of physiological demand. This pacemaker is microprocessor-based and fully programmable noninvasively through radiofrequency coupling to an external microcomputer. To date this system has been implanted in 15 patients. With this QT sensing pacemaker the rate response to exercise was smooth and progressive, and gradually returned to the basic paced rate after termination of activity. Physiologic rate responsive pacing resulted in significant improvement in exercise tolerance and a 40% increase in cardiac output when compared to fixed-rate pacing in 8 patients. This initial experience confirms the possibility of obtaining a physiological response to exercise using a pacing system dependent only on a unipolar electrode which is independent of the problems of atrial activity and sensing. Rate responsive pacing might prove to be a useful alternative to atrial synchronous systems, and particularly advantageous in those patients whose sinoatrial function is abnormal or who suffer from atrial arrhythmias.

Closed Loop Stimulation is Effective in Improving Heart Rate and Blood Pressure Response to Mental Stress: Report of a Single‐Chamber Pacemaker Study in Patients with Chronotropic Incompetent Atrial Fibrillation

“…In the past, one of the most interesting systems permitting rate‐adaptive pacing in response to both physical and mental stress was the QT‐sensing. These pacemakers increase the pacing rate when the QT interval shortens and indirectly detect changes in the circulating catecholamine level dues to the increased metabolic demand 11–14 …”

Clinical Evaluation of Peak Endocardial Acceleration as a Sensor for Rate Responsive Pacing

“…Numerous parameters have been investigated for controlling the pacemaker rate like oxygen saturation, 1 venous pH, 2 QT interval, 3,4 body motion, 5 respiratory rate, 6 stroke volume, 7 central venous temperature, 8–10 and minute ventilation 11 . To date only some of these indicators are used and none can be claimed to be definitively physiological.…”

Autonomic Nervous System‐Controlled Cardiac Pacing: A Comparison Between Intracardiac Impedance Signal and Muscle Sympathetic Nerve Activity

“…6,[10][11][12][13] Among present pacemaker sensors, only the QT-based rate adaptive pacing may be regarded as a closed-loop sys-tem. 14,15 This particular realization, however, may lead to positive feedback of the pacing rate on the sensed signal, making the system potentially unstable.…”