Utility of an Implantable Right Ventricular Oxygen Saturation-Sensing Pacemaker for Ambulatory Cardiopulmonary Monitoring

¹ From the Division of Cardiology, Department of Medicine, Queen Mary Hospital, University of Hong Kong
² From Medtronic Inc, Minneapolis

Mixed venous oxygen saturation (SvO₂) is a physiologic parameter reflecting cardiac output (CO) and tissue oxygen utilization. An implantable oxygen sensor incorporated in a right ventricular pacing lead has been developed to assess the feasibility of ambulatory monitoring of SvO₂ to predict cardiorespiratory parameters. Eight patients with a mean age of 62±2 years and sinoatrial disease received an SvO₂-driven dual-chamber rate-adaptive pacemaker capable of continuous SvO₂ measurement. During graded maximal exercise with measurement of oxygen consumption (VO₂), arterial oxygen saturation (SaO₂), and telemetered derived SvO₂ data, CO was assessed using the Fick principle. The accuracy of the derived CO was compared with CO measured directly by continuous-wave Doppler assessment of the ascending aortic flow. The maximum changes in SvO₂ and SaO₂ during exercise were 25±5 and 3±1%, respectively. SvO₂ was significantly correlated with Vo₂ (r=0.9±0.1, p<0.001), work done (r= 0.8±0.1, p<0.05), and minute ventilation (r=0.9±0.1, p<0.05). Doppler-derived CO was significantly correlated with CO estimated from SvO₂ measured (r=0.8±0.1, p<0.05) and is expressed as 46x derived CO +300. Although continuous SvO₂ sensing was originally developed to increase pacing rate during exercise, its use can be extended for monitoring cardiopulmonary performance on an ambulatory basis. This may be useful as a direct assessment of cardiopulmonary status in diseased states and also as an objective means to evaluate cardiac response to medical therapy in patients with heart failure.

Key Words: mixed venous oxygen saturation • pacing • intensive monitoring

Submitted on May 26, 1994
Accepted on August 4, 2007