THE VO2 TO WORK RATE RATIO - USEFULNESS T O ASSESS CARDIOPULMONARY EXERCISE CAPACITY IN MINUTE VENTILATION VVI-R PACING

This study was designed to assess the effect of acute minute ventilati on sensing, rate-responsive pacing on cardiopulmonary exercise capacit y in 27 patients (mean age 60 years) with chronotropic incompetence. T he exercise protocol consisted of bicycle exercise in semisupine posit ion with breath-to-breath analysis of gas exchange. At the anaerobic t hreshold heart rate increased from 75 +/- 9 in the VVI-mode to 113 +/- 21 beats/min in the VVI-R-mode (p < 0.001), oxygen uptake from 9.3 +/ - 3.4 to 10.9 +/- 4.3 ml/kg/min (p < 0.001) and work rate from 52 +/- 20 to 65 +/- 24 watts (p < 0.001). Compared to 41 normal subjects, VVI -R pacing increased oxygen uptake up to 75% and work rate up to 79% of normal values, while heart rate increased similarly in both groups. T he VO2 to work rate ratio (dVO2/dWR), calculated as the slope of the r elation of oxygen uptake to work rate below the anaerobic threshold, i mproved from 7.9 +/- 2.3 to 10.2 +/- 2.4 ml/min/watts (p < 0.001) in t he VVI-R-mode; so it did not differ from normal values. Thus, acute re spiratory dependent rate-responsive pacing results in substantial impr ovement in cardiopulmonary exercise capacity in patients with chronotr opic incompetence. The VO2 to work rate ratio demonstrated to be a rel iable parameter for assessing this improvement.