Closed-loop stimulation using intracardiac impedance as a sensor principle: Correlation of right ventricular dP/dt(max) and intracardiac impedance during dobutamine stress test

Changes of the unipolar right ventricular impedance during the cardiac cycl e are related to the changing content Of blood (low impedance) and tissue ( high impedance) around the tip of the pacing electrode. During myocardial c ontraction, the impedance continuously increases reaching ifs maximum in la te systole. This impedance increase is thought to correlate with right vent ricular contractility, and thus, with the inotropic state of the heart. In the new Inos(2) DDDR pacemaker, integrated information from the changing ve ntricular impedance (VIMP) is used for closed-loop regulation of the rate r esponse. The aim of this study was to analyze the effect of increasing dobu tamine challenge on RV contractility and the measured impedance signals. In 12 patients (10 men, 68 +/- 12 years) undergoing implantation of an Inos(2 ) DDDR pacemaker (Biotronik), a right ventricular pigtail catheter was inse rted for continuous measurements of RV-dP/dt(max) and simultaneous VIMP sig nals during intrinsic and ventricular pac ed rhythm. Then, a stress test wi th a stepwise increase of intravenous dobutamine (5-20 mug/kg per min) was performed. To assess the relationship between RV contractility and measured sensor signals, normalized values of dP/dt(max) and VIMP were compared by linear regression. There was a strong and highly significant correlation be tween dP/dt(max) and VIMP for ventricular paced (r(2) = 0.93) and intrinsic rhythm (r(2) = 0.92), although the morphologies of the original impedance curves differed quite substantially between paced and intrinsic rhythm in t he same patient. Furthermore, VIMP correlated well with sinus rate (r(2) = 0.82), although there were at least four patients with documented chronotro pic incompetence. We conclude, that for intrinsic and ventricular paced rhy thms sensor signals derived from right ventricular unipolar impedance curve s closely correlate with dP/dt(max), and thus, with a surrogate of right ve ntricular contractility during dobutamine stress testing. Our results sugge st that "inotropy-sensing" via measurement of intracardiac impedance is hig hly accurate and seems to be a promising sensor principle for physiological rate adaptation in a closed-loop pacing system.