Sinus node dysfunction and impairment of global atrial conduction time after high rate atrial and ventricular pacing in dogs.

It has been shown in animals and humans that AF shortens the atrial refractory period and impairs its rate adaptation. The aim of the study was to evaluate the effects of high rate pacing on sinus node function and intraatrial conduction. Eight dogs were subjected to rapid atrial pacing (AP) at a rate of 400 beats/min for 16 days. After a complete recovery of left ventricular function, they underwent rapid ventricular pacing (VP) at 240 beats/min of equal duration. Sinus node recovery time (SNRT) was measured after pacing at 150, 160, and 170 beats/min. P wave duration was measured on a surface ECG recorded at a paper speed of 200 mm/s. Measurements were performed at baseline, immediately after AP or VP, and four weeks after termination of AP or VP. SNRT immediately after AP and VP was significantly prolonged at all three pacing rates (P < 0.03). P wave duration increased significantly after either type of pacing (AP: 74.3 +/- 6.4 ms, VP: 70.0 +/- 3.8 ms) compared with baseline values (60.6 +/- 6.2 ms, P < 0.05). Rapid AP and VP induces sinus node dysfunction and prolongs intraatrial conduction time. The effects of sustained AP and VP on sinus node function and atrial myocardium returned toward control values 4 weeks after cessation of pacing. The authors hypothesize that reversible electrical remodeling occurs both in the sinus node and in the atrial myocardium.