Assessment of Cardiac Baroreflex Function During Fixed Atrioventricular Pacing Using Baroreceptor-Stroke Volume Reflex Sensitivity

Baroreflex Sensitivity in Paced Patients. Introduction: The baroreceptor-heart rate (HR) reflex has prognostic value in cardiovascular medicine. However, it cannot be used in chronotropically incompetent or paced patients. In healthy subjects, the baroreceptor-stroke volume (SV) reflex, with power spectral analysis of SV and blood pressure (BP) variations in the low-frequency band, serves as an alternate measure of the baroreceptor-cardiac reflex. This study examined the baroreceptor-stroke volume (SV) reflex sensitivity in the supine and 60° upright positions in paced patients. Methods and Results: We studied 16 recipients of dual-chamber pacemakers paced at a fixed rate. The hemodynamics and baroreceptor-SV reflex sensitivity were measured during atrioventricular (AV) sequential pacing every 5 minute in the supine and 60° upright positions. Mean SV decreased from 42.0 ′ 20.1 mL in the supine to 36.6 ′ 16.1 mL in the upright position (P < 0.05), whereas BP and total peripheral resistance did not change. A significant fall in baroreceptor-SV reflex sensitivity from 29.2 ′ 18.0%/mmHg to 19.5 ′ 15.5%/mmHg was observed during upright tilt (P < 0.005). Conclusion: Fixed-rate AV sequential pacing did not blunt the decrease in baroreceptor-SV reflex sensitivity consistent with the arterial baroreflex gain response to upright posture. The decreased baroreceptor-SV reflex sensitivity occurring with the upright posture may reflect a baroreflex-induced inotropic effect secondary to vagal withdrawal and sympathetic activation.