Abstract
Background
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).Case summary
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.Discussion
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.Take-home messages
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.