Six Years Follow-Up of an Implanted SvO2 Sensor in the Right Ventricle

INTRODUCTION: Mixed venous oxygen saturation (SvO(2)) is a standard invasive measure used in the management of congestive heart failure patients. The reliability of a long-term SvO(2) sensor remains unproven. METHODS: Nine patients (NYHA Class I/II, n=2/7) were implanted with a dual chamber pacemaker modified to utilize a right ventricular SvO(2) lead (Medtronic Inc., Models 8007/4327A IPG/Lead). Invasive studies compared sensor SvO(2) to reference (Optical Swan-Ganz catheter) at 0, 3 and 9 months. Symptom limited tests (Bike(max)) with metabolic assessment and arterial oxygen saturation measurements performed 1-7 days, 3.5 and 9.5 months post-implant allowed for cardiac output calculations. Long-term sensor performance was confirmed by submaximal tests, Bike(subm) in years 1-3, and Walk(in-place) every 6 months for the duration of follow-up. RESULTS: Sensor SvO(2) readings were stable over time when compared to the Swan-Ganz Catheter. Non-invasive CO measured during Bike(max) was in normal ranges for this patient population, 3.7+/-0.9 l/min at rest and 8.4+/-2.2 l/min at peak-exercise. Resting SvO(2) values from Bike(subm) and Walk(in-place) did not change significantly over time (P>0.1 vs. 1 year) and neither did the change from rest to peak exercise during Bike(subm) (P>0.05 vs. 1 year) or Walk(in-place) (P>0.05 vs. 4 year). CONCLUSION: While limited in size, this small pilot study suggests that long-term monitoring of SvO(2) by implanted devices may be feasible. The clinical value remains to be proven in future studies.