Effects of atrioventricular and interventricular delays on gas exchange during exercise in patients with heart failure

Abstract

Cardiac resynchronization therapy (CRT) has been an important treatment for heart failure. However, it is controversial as to whether an individualized approach to altering AV and VV timing intervals would improve outcomes. Changes in respiratory patterns and gas exchange are dynamic and may be influenced by timing delays. Light exercise enhances the heart and lung interactions. Thus, in this study we investigated changes in non-invasive gas exchange by altering AV and VV timing intervals during light exercise. Patients (n = 20, age 66 ± 9 years) performed two walking tests post-implantation. The protocol evaluated AV delays (100, 120, 140, 160 and 180 milliseconds), followed by VV delays (0, -20 and -40 milliseconds) while gas exchange was assessed. There was no consistent group pattern of change in gas exchange variables across AV and VV delays (p > 0.05). However, there were modest changes in these variables on an individual basis with variations in VE/VCO2 averaging 10%; O2 pulse 11% and PETCO2 5% across AV delays, and 4%, 8% and 2%, respectively, across VV delays. Delays that resulted in the most improved gas exchange differed from nominal in 17 of 20 subjects. Gas exchange measures can be improved by optimization of AV and VV delays and thus could be used to individualize the approach to CRT optimization.