Algorithm-Facilitated Pacemaker-Mediated Tachycardia Mimicking Refractory Septic Shock

Algorithms that minimize right ventricular pacing, such as atrioventricular (AV) hysteresis, prolong the AV delay to promote intrinsic conduction. With intact ventriculoatrial (VA) conduction, this can facilitate pacemaker-mediated tachycardia (PMT).

A 62-year-old woman with a dual-chamber pacemaker presented with respiratory failure and hypotension at a paced rate of 110 beats/min, treated for presumed sepsis with escalating vasopressors. Interrogation showed an upper tracking rate of 130 beats/min, AV hysteresis ON, and postventricular atrial refractory period (PVARP) (225 milliseconds) shorter than VA conduction (360 milliseconds), producing a 550-millisecond endless-loop PMT (∼109 beats/min) that escaped device detection. Disabling hysteresis and extending PVARP terminated it, allowing vasopressor weaning.

When PVARP is shorter than the VA interval, a long AV delay converts retrograde conduction into a slow re-entrant circuit that escapes device diagnostics and mimics sinus tachycardia.

Suspect slow PMT in paced patients with fixed tachycardia near 100-110 beats/min when AV hysteresis is active. Disabling hysteresis and extending PVARP beyond VA conduction is diagnostic and lifesaving.