Algorithm to Distinguish between Different Tachycardias Caused by Pacemakers/Defibrillators

While pacemakers, implanted cardiac defibrillators (ICDs), and cardiac resynchronization therapy (CRT) devices have saved countless lives, these devices can sometimes cause arrhythmias. The most common is pacemaker-mediated tachycardia (PMT); more rare, is tracking of sinus or atrial tachycardia. While all systems have algorithms to detect and stop PMTs, the algorithms cannot distinguish between the two conditions. Differentiation is important, because subsequent programming of pacemaker function and other medical treatments depends on it. For example, if atrial tracking were misdiagnosed as PMT, subsequent programming choices would decrease the maximum tracking rate and diminish the patient's exercise capacity.

Bruce Lerman and James Ip at the Weill Cornell Medical College/New York-Presbyterian Hospital have developed an algorithm for differentiating between these two tachycardias, based on the readings from the device following the standard first step in terminating an episode of PMT - namely, extending the device's postventricular atrial refractory period (PVARP) .

The sequence of atrial sensed (As), atrial refractory (Ar), ventricular paced (Vp), and ventricular sensed (Vs) events are recorded, and the following determinations are made:

If the reading is The tachycardia was Vp-Ar-Vs (V-A-V) atrial tachycardia with intact AV conduction Vp-Ar-As-Vs (V-A-A-Vs) PMT with intact AV conduction Vp-Ar-As-Vp (V-A-A-Vp)
Atrial tachycardia with complete heart block OR PMT with complete heart block, which can be distinguished using the atrial rate - a slower atrial rate following PVARP extension is specific for PMT

The response to PVARP extension (V-A-A-V vs V-A-V) is a specific method for differentiation and can be used in conjunction with observations of atrial rate for distinguishing between the two mechanisms of pacemaker-facilitated tachycardia.