Poor discrimination of atrial tachycardia by a dual chamber defibrillator

Patient

This 59-year-old man received a Lumax 540 HF-T triple chamber defibrillator in the context of ischemic cardiomyopathy with conduction disorder. An event report (yellow color) was issued in the context of a classified VT1.

Main programmed settings

VF zone (250 ms limit), VT1 zone (360 ms limit)
8/12 cycles in the VF zone and 32 cycles in the VT1 zone were needed for the diagnosis
Maximum sensitivity programmed at 0.8 mV
VF zone: ATP one shot, followed by 8 shocks of maximum strength (40 J); VT1 zone: monitor only without programmed therapy
Effective discrimination in the VT1 zone (SMART discrimination)
Pacing mode: DDD biventricular at 50 bpm

Trace

Remote tracing

The 4 channels available are 1) the markers with the time intervals, 2) the atrial (A) sensing channel, 3) the right ventricular (RV) sensing channel, and 4) the left ventricular (LV) sensing channel.

1:1 tachycardia; however, the atrial activity was sensed intermittently, as it fell in the post ventricular sensing atrial blanking period;
mode switch (MSW, DDI) because 5 of 8 atrial cycles were classified Ars, and the average atrial rate measured on the last 4 cycles was >160 bpm;
more reliable atrial sensing with 1:1 rhythm;
monitor VT1 classification; discrimination in the PP = RR arm (average PP and RR during the initial classifications = 353 and 348 ms, respectively; in the PP = RR arm, the first analysis is stability (this rhythm was stable, with an 8 ms measurement of stability for a 24 ms threshold). The second analysis is the stability of PP (stable during episode). Since PR was stable, no monotonous change is observed. The last analysis is sudden onset, which was fulfilled at 24% for a threshold programmed at 20%. The device therefore diagnosed VT1;
monitor zone only without delivery of therapy;
spontaneous termination of the tachycardia after a ventricular event (favors an atrial tachycardia).

Programmer tracing

the programmer tracing allows a scrutiny of the onset of the tachycardia, which initially started with an atrial extrasystole (in favor of an atrial tachycardia).

Comments

This patient presented with multiple episodes of 1:1 tachycardia detected in the monitor zone. Programming in the monitor zone may enable 1) the recording of the episodes, 2) the clarification of the origin of the arrhythmia, and 3) depending on the diagnosis and on the tolerance of the rhythm, the programming of therapies. This episode began with an atrial extrasystole and ended with a ventricular event, both in favor of a supraventricular origin.

Initially, the atrial electrograms were miscounted because some of them fell in the post-ventricular atrial blanking period. Later, the defibrillator sensed the 1:1 ratio. The discrimination between 1:1 VT and 1:1 atrial tachycardia is probably the most challenging for double or triple chambers defibrillators. Indeed, the RR and PP cycles are regular, the PR intervals are fixed, and the defibrillator detects a sudden onset, thus diagnosing VT.

Pacing & Defibrillation

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