Patient

• 64-year-old man
• Assurity^TM + DR dual-chamber pacemaker (Abbott) for complete atrioventricular block
• AMS episode stored in the device memory

Tracing

• atrial pacing and ventricular pacing
• premature atrial contraction followed by an extended AV delay so as not to exceed the maximum synchronous rate (130 beats/minute)
• atrial arrhythmia
• each short atrial cycle decrements the filtered atrial rate by 39 ms
• acceleration of the ventricular pacing rate
• AMS when the filtered atrial rate interval falls below the atrial tachycardia detection interval
• slowing of the ventricular pacing rate

 Comments

• management of pacemaker patients with atrial arrhythmia episodes is complex given the different types of mechanisms known to trigger atrial arrhythmias and the risk of runaway ventricular pacing due to sensing of a rapid atrial rhythm
• the device can be programmed to respond to atrial arrhythmia by switching to an asynchronous mode in order to avoid high-rate ventricular pacing which can compromise hemodynamic stability
• mode switching is the ability of the pacemaker to automatically switch from an atrial tracking mode (DDD or VDD) to a non-atrial tracking mode (DDI or VDI)
• upon termination of the atrial tachyarrhythmia, mode switching reverts to the programmed synchronous pacing mode
• the ideal mode switching algorithm has the following characteristics: fast triggering to avoid prolonged rapid ventricular pacing during the initial detection phase of the arrhythmia; ability to quickly revert to a synchronous mode at the end of the arrhythmia episode; good atrial arrhythmia diagnostic capabilities even in the presence of atrial signals of varying amplitude and rate; ability to avoid mode switching in response to crosstalk, noise or sinus tachycardia
• the fallback algorithm used by Abbott^TM pacemakers features certain specificities that are important to know
• automatic mode switching (AMS) uses a filtered, not actual, atrial rate based on a comparison of the current atrial rate with a continually updated average rate
• automatic mode switching (AMS) to DDI(R) or VVI(R) mode occurs when the filtered atrial rate surpasses the atrial tachycardia detection rate (ATDR)
• the device measures the actual PP interval at each cycle and calculates a filtered atrial rate interval (FARI) according to the following rule: if the actual PP interval is ≤ FARI, the FARI is decremented by 39 ms; if the actual PP interval is > FARI: the FAI is incremented by 23 ms
• atrial activities sensed in the PVARP, contrary to signals in the blanking period, are taken into account in the calculation of the FARI
• mode switching occurs as soon as the filtered atrial interval falls below the atrial tachycardia detection interval
• during mode switching, the pacing rate corresponds to the AMS base rate (programmable independently of the base rate) or the rate indicated by the sensor (rate response)
• the return to synchronous mode is only possible if the atrial rate falls below the maximum synchronous rate (FARI > the maximum synchronous rate interval) and not below the atrial tachycardia detection rate