A 73-year old man with a history of dilated cardiomyopathy and left bundle branch block was implanted with a triple-chamber Boston Scientific Autogen CRT-D. Interrogation revealed a PMT episode.
This EGM shows an example of an anti-PMT algorithm intervention during exercise-induced sinus tachycardia in a patient where the maximal tracking rate has been programmed too low. The final part of the EGM shows a remarkable sustained loss of biventricular stimulation (alternans between right ventricular stimulation and biventricular detection). This episode illustrates the limitations of programming left ventricular detection since it can result in inhibition of left ventricular stimulation. When a premature left ventricular contraction is detected by the right ventricular lead with sufficient delay, left ventricular stimulation could occur within the vulnerable period. This algorithm has been designed to avoid stimulating during this vulnerable period. The downside is that this phenomenon can be result in a loss of resynchronization especially during exercise in patients with left bundle branch block. Tachycardia and delayed left ventricular depolarization during spontaneous activation could lead to isolated right ventricular stimulation on the next cycle while left ventricular pacing is inhibited due to the refractory period.
In this patient, it is necessary to increase the maximum tracking rate. Regarding left ventricular sensing, it is either possible to disable or to decrease the left ventricular refractory period.
