12 lead ECG

• wide QRS tachycardia
• a careful analysis of the tracing allows demonstrating a small-amplitude pacing artifact from V3 to V5
• it is therefore a pacemaker-mediated tachycardia
• interruption of the tachycardia

EGM recorded simultaneously

• EGM analysis confirms the diagnosis of pacemaker-mediated tachycardia
• succession of VP-AS cycles (ventricular pacing, atrial sensing) with prolongation of the AV delay so as not to exceed the maximal tracking rate
• diagnosis of PMT made by the device after 8 consecutive VP-AS cycles
• intervention of the anti-PMT algorithm with a prolongation of the post-ventricular atrial refractory period (PVARP) to 400 ms on one cycle
• atrial activity is sensed in PVARP (AR) and does not synchronize ventricular pacing

Comments

• a pacemaker-mediated tachycardia (PMT) is the term used to define pacemaker-driven tachycardia, most often at the maximum pacing rate with repeated ventricular pacing – retrograde atrial conduction sequences
• the electrocardiographic diagnosis of pacemaker-mediated tachycardia is based on the demonstration of a tachycardia with ventricular pacing (wide QRS with pacing artifact) and retrograde atrial conduction (negative P’ waves in the inferior leads)
• this diagnosis can sometimes be difficult (artifacts and P’ waves difficult to identify) but should be systematically evoked in the presence of a regular tachycardia with wide QRS in an implanted patient
• the maintenance of a PMT results from the sensing of a retrograde P’ wave, outside of refractory periods, leading to the triggering of an often prolonged AV delay, which again promotes retrograde conduction after ventricular pacing
• the cycle is repeated indefinitely unless there is appearance of a retrograde block or the intervention of a specific pacemaker algorithm
• the first pacemakers were not protected against this type of runaway and the tachycardia could last indefinitely, generating an occasionally very disabling symptomatology
• a PMT of prolonged duration may be poorly supported with a symptomatology ranging from simple sensation of malaise or palpitations to cardiac decompensation in patients with an underlying heart disease
• dedicated algorithms have been designed by the different manufacturers to automatically diagnose a PMT and to break active PMT episodes
• interruption of the tachycardia following intervention of the algorithm is strongly suggestive of a PMT and eliminates the hypothesis of sinus tachycardia or atrial tachycardia
• PMT management involves the programming of a specific interruption algorithm, the programming of a PVARP longer than the retrograde conduction time (sometimes difficult because limiting in terms of monitoring atrial activity 1/1 during exercise), the prevention of episodes by suppressing triggering factors (pacing or sensing defects, oversensing, etc.)