Use of a multi-stage exercise test to assess the responsiveness of rate-adaptive pacemakers in dogs

Objectives: To assess the ventricular rate response of rate-adaptive (VVIR) pacemakers in dogs using a multi-stage exercise test. Methods: The rate-responsiveness of VVIR pacemakers was assessed in seven dogs with complete atrioventricular (AV) block and implanted with various models of pulse generators (six motion sensors and one automatic dual-sensor rate-response pacemaker). Response activity was assessed with a multi-stage exercise test on a treadmill. Atrial and ventricular rate were analysed retrospectively at the end of the test and the AV ratio was calculated after each minute of exercise. Results: During exercise, the mean (sd) AV ratio recorded in all paced dogs was 1.7 (0.5) (expected physiological ratio 1.0), although a variety of individual performances was observed. A poor response (AV ratio 2.8 [0.2]) was obtained with the automatic dual-sensor pacemaker, suggesting that this type of rate-responsive device may not be indicated for implantation in dogs with complete AV block. The overall AV ratio for the six dogs implanted with motion sensors was 1.4 (0.2), showing a better performance of these pacemakers during exercise. Clinical Significance: This multi-stage exercise test represents an easy and repeatable method for assessing the accuracy of rate-responsive sensors and offers valuable information for the correct setting of VVIR pacemakers in dogs.