A comparison of external rate responsive pacemakers with identical implanted units.

Seven patients with previously implanted accelerometer-based DDDR pacemakers had an identically programmed external pacemaker taped onto their chest. Both units underwent a simultaneous test to set the sensitivity of the accelerometer. The units were then programmed to record the pacing rates for a 15-minute period. The patients underwent an exercise course that included walking and stairs. After the exercise, the patients sat for 3 minutes and the pacing rates from the test were telemetered. The pacing rate was compared at 2 minutes, 4 minutes, peak, and 3 minutes postexercise. The mean standard deviation (SED) for the external pacemaker was 97.9 at 3.53 ppm, 102 at 10.6 ppm, 106 at 8.94 ppm, and 71.3 at 2.29 ppm at 2, 4, peak, and decay, respectively. The mean SED for the implanted pacemaker was 98.1 at 5.76 ppm, 100 at 10.2 ppm, 104 8.24 ppm, 72.4 at 2.88 ppm at 2, 4, peak, and decay, respectively. Difference between pacemakers in ppm was 0.286, 2.0, 2.71, and 1.14 at 2, 4, peak, and decay, respectively. A 95% confidence interval in ppm was -5.28 to 5.85, -10.1 to 14.1, -7.30 to 12.7, and -1.89 to 4.17 at 2, 4, peak, and decay, respectively. In all patients there was a high confidence correlation between the implanted and external unit. An external unit can be used to predict the rate response of an accelerometer-based pacemaker without any adjustments to the pacing parameters.