A comparative study on the behavior of three different automatic mode switching dual chamber pacemakers to intracardiac recordings of clinical atrialfibrillation

Automatic mode switching (AMS) allows patients with dual chamber pacemakers who develop paroxysmal AF to have a controlled ventricular rate. The aim o f this study was to (1) compare the rate-controlled behavior of three AMS a lgorithms in response to AF, in terms of speed and stability of response an d resynchronization to sinus rhythm, and (2) compare the influence of pacem aker programming on optimal mode switching. We studied 17 patients (12 men, 5 women; mean age 59 +/- 15 years) who developed AF during electrophysiolo gical study. Unfiltered bipolar atrial electrograms during sinus rhythm and AF were recorded onto high fidelity tapes and replayed into the atrial por t of three dual chamber pacemakers with different mode switching algorithms (Thera, Marathon, Metal. The Thera pacemaker uses rate smoothing, and mode switches occur when mean sensed atrial rate exceeds the predefined AMS rat e (MR). Marathon mode switches after a programmable number of consecutive r apid atrial events (NR). Meta DDDR monitors the atrial rare by a counter fo r atrial cycles faster than the programmed AMS rate. It increases or decrea ses the counter if the atrial cycle length is shorter or longer than the pr ogrammed AMS interval, respectively. Mode switch occurs when the AF detecti on criteria are met (CR). A total of 260 rhythms were studied. NR was signi ficantly faster than MR and CR (latency 2.5 +/- 3 s vs 26 +/- 7 s vs 15 +/- 22 s, respectively, P < 0.0001). During sustained AF, MR resulted in the m ost stable and regular ventricular rhythm compared to NR or CR. In CR, vent ricular rate oscillated between AMS and atrial tracking (cycle length varia tions: 44 +/- 2 s vs 346 +/- 109 s vs 672 +/- 84 s, P < 0.05). At resumptio n of sinus rhythm, MR resynchronized after 143 +/- 22 s versus 3.4 +/- 0.7 s for NR and 5.9 +/- 1.1 s for CR, resulting in long periods of AV dissocia tion when a VVI/VVIR mode is used after AMS. programming of atrial refracto ry periods did not affect AMS response, although the speed of AMS onset can be adjusted by programming of onset criteria in the Meta DDDR. AMS algorit hms differ in their ability to handle recorded clinical atrial arrhythmias. The rapid-responding algorithm exhibits rate instability, whereas slow res ponding algorithm shows a long delay in response and risk of AV dissociatio n. Thus different instrumentation of AMS may have clinical implications in patients with dual chamber pacemakers who develop AF.