Is automatic mode switching effective for atrial arrhythmias occurring at different rates? A study of the efficacy of automatic mode and rate switching to simulated atrial arrhythmias by chest wall stimulation

Automatic mode switching (AMS) is a useful means to avoid rapid ventricular response during atrial fibrillation (AF), but AMS cannot occur if the dete cted atrial rate during AF is below the mode switching criteria. This may b e the result of antiarrhythmic medications, or when the atrial events fall within the atrial blanking period, or if the atrial amplitudes during AF ar e too small to be sensed. We hypothesize that the addition of an automatic rate switching (ARS) algorithm may complement AMS response during AF with d ifferent detected atrial rates. We studied the Marathon DDDR pacemaker (Mod el 294-09, Intermedics Inc.) with the AMS and ARS algorithms that are indep endently programmable but can also operate in combination. AF sensed above the AMS rate (160 beats/min) will lead to VDIR pacing, whereas AF below AMS rate will be tracked at an interim rate as dictate by the ARS, at a ventri cular response that is 20 beats/min above the sensor indicated rate. Atrial tachyarrhythmias were simulated by chest wall stimulation (CWS). CWS was a pplied to 33 patients (16 men, 17 women, mean age 69 +/- 11 years) with a M arathon DDDR pacemaker using an external pacer to simulate AF occurring at two rate levels: above the AMS rate (programmed at 160 beats/min) at 180 be ats/min and below the AMS rate at 120 beats/min. The maximum, minimum, and mean ventricular rates during CWS in DDDR mode with AIMS alone, ARS alone, and their combination were compared. During CWS at 120 beats/min, the AIMS plus ARS setting showed a mean ventricular rate of 79 +/- 3 beats/min and 1 24 +/- 14 beats/min in the AIMS setting alone (P < 0.01). With CWS at 180 b eats/min, the mean ventricular rate in the AMS plus ARS setting compared to the AMS setting alone was not significantly different. However, the variat ion in ventricular pacing rate was 7 +/- 14 beats/min in the AMS plus ARS s etting and 40 +/- 42 beats/min in the AIMS setting (P < 0.05). In conclusio n, AMS is effective for simulated atrial tachyarrhythmias sensed above the AIMS rate. Combined AIMS with ARS is useful to handle simulated atrial tach yarrhythmia at a slower rate and to avoid rate fluctuation during AMS. Ther e is also a possibility that this can be applied to the naturally occurring atrial tachyarrhythmias.