The feasibility of utilizing the systolic pre-ejection interval as a determinant of pacing rate

Abstract

Rate-modulated pacing modes adjust the stimulus rate by responding to sensed alterations in physiologic indexes of metabolic demand. This study was designed to determine whether right ventricular pre-ejection interval, measured in patients by a prototype pacemaker system capable of tracking intraventricular volume, changes predictably with exercise and, if so, whether it can be used in an algorithm to vary heart rate appropriately. This system utilizes intraventricular electrical impedance measurements of injected microampere currents to determine intracavitary volume changes. Five pacemaker-dependent patients underwent temporary insertion of a tripolar electrode connected to an external device that sensed cardiac signals, generated an impedance wave form and produced stimuli at rates dependent on pre-ejection interval. Pre-ejection interval did not change as a result of variations in pacing rate itself (347 +/- 41 ms at 70 beats/min versus 321 +/- 19 ms at 130 beats/min), but consistently decreased during graded exercise (by 23% from baseline). During rate-modulated pacing based on pre-ejection interval, heart rate significantly increased during exercise compared with ventricular demand pacing (by 46 +/- 6 versus 7 +/- 6 beats/min, respectively), and increased appropriately during burst exercise. Thus, the pre-ejection interval appears to be a specific, reliable physiologic determinant of pacing rate during exertion, which may be applicable in implantable rate-modulated pacemakers.

A Method to Calculate Tissue Impedance Through a Standard Bipolar Pacing Lead

“…This device incorporated a tripolar lead from which a low level alternating current passed from the distal electrode to the pacemaker can. Relative changes in RV volume were derived from the changes in impedance measured between the two ring electrodes situated in the RV (Ruitter et al 1992;McGoon et al 1989).…”

Rate-Responsive Cardiac Pacing: Technological Solutions and Their Applications

“…One of the disadvantages of this sensor type is the slow response to effort. Numerous attempts have been made to improve response time and to allow diversification of the rhythm and pacing frequency distribution to achieve a nearly physiological distribution of heart rate in a human undertaking various forms and degrees of intensity of exercise [ 82 , 83 , 84 , 85 ].…”

The measurement of impedance to assess myocardial contractility and rhythm stability

“…The right ventricular PEI is measured from the onset of the sensed intrinsic R wave, or from the pacing spike, to the point of maximum change in the impedance curve indicative of ventricular volume change . The PEI has been shown to be a reliable indicator of metabolic need and has been used in the PRECEPT (Cardiac Pacemakers Inc., St Paul, MN, USA) pacemaker for heart rate modulation (Ruitter et al 1992, McGoon et al 1989. Although the PEI parameter is a time period and not an actual volume measurement PEI and stroke volume are closely related and PEI gives an indirect indication of the contractility of the myocardium (Ruitter et al 1992.…”