Patient - EN
64-year-old man implanted with a triple-chamber defibrillator Consulta CRT-D for ischemic cardiomyopathy with complete AV block; shortness of breath during exercise.
Graph and trace
Stress test performed during the consultation (squats) with the telemetry wand placed over the device; atrial sensing recently programmed at 0.8mV in the context of ventriculo-atrial crosstalk; at rest, atrial sensing is around 1.2mV; the first line corresponds to an ECG lead with superimposed markers, the second line to the bipolar RV EGM, the third line to the bipolar atrial EGM and the fourth line to the far-field RV coil / LV tip EGM;
- normal function AS-BV (shortening of the AV delay: rate adaptive AV delay); significant variations in atrial signal amplitude with breathing;
- at peak exercise (less than one minute after the previous tracing), persistent variation in atrial signal amplitude; first undersensed P wave;
- the next P wave is sensed (AS-BV cycle); pseudo 2:1 behavior pattern: one P-wave out of 2 is not sensed; sudden drop in heart rate explaining the patient’s symptoms;
- prolonged episode of atrial undersensing with atrial pacing at the minimal rate (rate responsive algorithm not activated, DDD mode);
- transient recovery of atrial sensing (according to breathing cycles);
- alternation of sensed and undersensed P-waves with atrial pacing.
NID old - EN
3098
Exercise and increased respiratory movements are often associated with an intermittent alteration of atrial sensing. Atrial undersensing during exercise can lead to a pattern at times closely resembling that observed during a 2:1 block. The markers allow making the differential diagnosis with absence of repetitive AS-BV-AR cycles evocative of 2:1 block.
This tracing illustrates the importance of the proper functioning of the atrial lead for optimal resynchronization. This patient presents an intermittent atrial undersensing. Atrial EGM analysis revealed a large variability in the amplitude of atrial signals in conjunction with the respiratory rhythm. In a patient with preserved atrioventricular conduction, an atrial undersensing during exercise is associated with a reappearance of spontaneous ventricles without a sudden fall in rate and therefore without significant symptomatology. Conversely, in a patient with complete atrioventricular block (as in this tracing), atrial undersensing results in a sudden drop in rate, very often symptomatic. Atrial undersensing is much more frequent than 2:1 behavior, ventricular oversensing or loss of capture of the 2 leads which constitute the other causes of a sudden drop in rate during exercise and should therefore be investigated in priority in this setting. In addition to the lack of proper monitoring of P-waves during exercise, atrial undersensing may have a pro-arrhythmogenic effect if atrial pacing occurs in an atrial vulnerable period with a risk of induction of an atrial arrhythmia.