Hemodynamic and Antiectopic Effects of Long-term Dynamic Overdrive Pacing in Implanted VVI Pacemakers

Summary

Overdrive pacing has been found to suppress repetitive arrhythmias or focal automaticity. Dynamic overdrive is a type of overdrive pacing in which the pacemaker continuously adjusts the overdrive stimulation rate to the underlying rhythm. Our own animal experiments revealed a significant reduction of direct current and ischemia-induced premature ventricular beats (VPB). Furthermore the threshold for the direct current induction of ventricular tachycardias was significantly increased during dynamic overdrive pacing.

The aim of the study was to investigate the clinical reliability of long-term dynamic overdrive pacing in patients with symptomatic bradyarrhythmias, premature ventricular beats (7/10 patients with VPB ≥ Lown II°) and antiarrhythmic drug treatment. Therefore, 10 patients (all male) were treated with a DPG 1 pacemaker and a Helifix lead (Vitatron). The antiectopic effect of the dynamic overdrive pacing mode was controlled by repeated, 24-hour Holter ECGs (Ela Medical: Anatec) and the premature beat counter in the DPG 1.

Five out of ten patients had a VPB reduction of more than 80% and 5/10 patients a reduction of the Lown grade to ≥ II°. During long-term application of the ventricular dynamic overdrive pacing mode, 3/10 patients revealed a manifest myocardial failure. After successful recompensation these 3 and an additional 2 patients were hemodynamically investigated by right heart catheter in the supine position (25 W; 3 minutes). The hemodynamic parameters of cardiac output and mean pulmonary artery pressure were compared during 70 ppm (VVI mode) and dynamic overdrive mode. The ventricular dynamic overdrive pacing mode led to a 10 to 15% reduction of the stroke volume, whereas the cardiac output remained equal due to the increased heart rate. Our data show that patients with reduced left ventricular performance $(CO \downarrow ,\overline {PAP} \uparrow )$ at rest are particularly prone to develop myocardial failure during long-term ventricular dynamic overdrive pacing. In conclusion: Patients who might be candidates for ventricular dynamic overdrive require prior, careful investigation (Holter ECG; determination of the pump function). Atrial dynamic overdrive seems to have a better future, especially in dual chamber devices. Whether or not a significant reduction of premature beats also leads to prevention of tachycardia is still under discussion.