Atrial Pacing failure

Patient

A 72-year-old man received an Adapta dual chamber pacemaker for management of sinus node dysfunction; programming in AAIR⇔DDDR mode; his symptoms reappeared in the form of near syncope and fatigue.

Trace

The first channel is lead II of the surface ECG with the markers superimposed, the second shows the atrial EGM and the third is lead II with the intervals superimposed;

atrial pacing without capture on the atrial EGM channel; sensing of spontaneous atrial events is labeled AR as they fall in the post-atrial pacing refractory period; spontaneous conduction to the ventricle (VS);
continuation of this sequence AP-AR-VS; compared with the beginning of the tracing, the AP-AR interval has gradually increased (from 162 to 217 ms); however, the AR-VS interval has remained fixed (approximately 200 ms), indicating that the spontaneous atrial events are conducted to the ventricle;

Comments

This tracing shows an atrial capture defect. The atrial output amplitude was programmed at 2.5 V / 0.4 ms in this patient. Without apparent cause, the pacing threshold surpassed this value (3 V / 0.4 ms), while sensing remained appropriate (> 2 mV) and the pacing impedance was normal (500 ohms). An increase in the output amplitude to 4 V / 0.4 ms eliminated the dysfunction. In a second stage, the pacing threshold stabilized near 1.6 V / 0.4 ms, allowing a long-term programming at 2.8 / 0.4 ms and guaranteeing acceptable safety margin and energy consumption.

Pacing & Defibrillation

ECG

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