64 year old man implanted with a tiple chamber defibrillator Consulta CRT-D in the context of an ischemic cardiomyopathy with complete AV block; shortness of breath during exercise.
Stress test realized during the consultation (squats) with the telemetry wand placed over the device ; atrial detection recently programmed at 0.8mV in the context of a ventriculo –atrial crosstalk ; at rest the atrial sensing is around 1.2mV ; the first line correspond to and ECG derivation with superimposed markers ; the second line correspond to the bipolar RV EGM, the third line correspond to the bipolar atrial EGM and the foutrh line correspond to the far-field RV coi / LV tip EGM;
This tracing illustrates the importance of a functional atrial lead for optimal resynchronization. This patient has a intermittent episodes of atrial undersensing. The analysis of the atrial EGM demonstrates a large variability of the atrial signal amplitude with the breathing. In a patient with a preserved atrioventricular conduction, atrial undersensing during is associated with the reappearing of spontaneous ventricles but no sudden drop of the heart rate and thus without significant symptoms. In contrast, in patients with a complete atrioventricular block (as in this case), the atrial undersensing causes a sudden dropin the heart rate and is often poorly tolerated. Atrial undersensing during exercise is the first cause of sudden rate drop during exercise, and is much more common than the 2:1 behavior, the ventricular oversensing or the loss of capture by the two ventricular leads (which are the other causes of sudden drop rate during exercise). In addition, the lack of adequate monitoring of the P-waves during exercise may also have a pro-arrhythmogenic effect if an atrial pacing is given during the vulnerable atrial period.
