Limitations of testing methods for evaluation of dual chamber versus single chamber adaptive rate pacing

As new modes of cardiac pacing are developed, it is important to determine if these modes offer additional benefits over already existing options. Comparisons between dual (DDDR) and single chamber ventricular (VVIR) rate-modulated pacing using standard exercise protocols have produced conflicting results. 1–4 Exercise duration alone does not appear to accurately reflect differences in cardiac efficiency and tissue perfusion. Similarly, maximal oxygen uptake tends to reflect exercise duration rather than cardiac performance. 5 This study was designed to compare the DDDR and VVIR pacing modes using measures of exercise duration and maximal oxygen uptake, as well as less frequently used parameters, including anaerobic threshold time, maximal carbon dioxide production, respiratory exchange ratio, cardiac output, and the ratio of cardiac output to oxygen uptake.