Rate-adaptive pacing using intracardiac impedance shows no evidence for positive feedback during dobutamine stress test.
BACKGROUND
The Inos2 DDDR pacemaker senses unipolar intracardiac impedance signals for adapting heart rate to meet the haemodynamic needs of physical activity. Theoretically, such pacing devices could be limited by positive feedback since increase in beating frequency per se enhances contractility. We have addressed this problem in patients with chronotropic incompetence who were subjected to a pharmacological stress test.


RESULTS
Twelve patients with chronically implanted Inos2 DDDR pacemakers were studied using the standard protocol of stress echocardiography. Most of the patients reached the programmable maximum closed-loop rate during the incremental dobutamine challenge. The time courses for increase in as well as for recovery of heart rate were not different from control patients receiving routine diagnostic stress echocardiography.


CONCLUSIONS
In patients implanted with the Inos2 DDDR pacemaker acute stimulation with intravenous dobutamine leads to a robust increase in paced heart rate without any evidence of positive feedback.
Department of Pharmacology and Toxicology, Medical Faculty, University of Technology, Dresden, Germany. Christ@rcs.urz.tu-dresden.de
Torsten
T
Christ
Matthias
M
Schier
Arne
A
Brattström
Gerhardt
G
Muth
Andreas
A
Hartmann
Dobromir
D
Dobrev
Ursula
U
Ravens
D002304:Cardiac Pacing, Artificial; D002316:Cardiotonic Agents / Q000494:pharmacology; D004280:Dobutamine / Q000494:pharmacology; D025401:Echocardiography, Stress; D005246:Feedback; D005260:Female; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic; D009200:Myocardial Contraction; D010138:Pacemaker, Artificial
D002316:Cardiotonic Agents; D004280:Dobutamine