Drop in percentage CRT
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We observe an alert for percentage of biventricular pacing below 95%. Often this is caused by onset of atrial fibrillation. However, we see no epsodes of mode switch, the time in mode switch is 0 seconds, the AF curves are flat and also on the real-time EGM there is no evidence for atrial fibrillation. The atrial lead has adequate sensing (>1mV) and we clearly see atrial events on the atrial channel (on the real-time EGM). However on the real time EGM, we do see two premature ventricular complexes (PVCs) with cycles <600 ms. These ventricular events are sensed and therefore decrease the %CRT (%biV) counter and trigger the alert. Even if these RV events were to trigger LV pacing, these beats will not be resynchronized as the LV pacing spike is much to late to be effective.
For CRT to be effective, the patient needs to receive at least 90/95 % CRT with full biventricular (or at least LV) capture. The alert can thus have clinical consequences which may occur sooner or later depending on the patient. Whether clinical action is required depends on the patient’s sensitivity to the loss of CRT. Most often, the patient can endure a couple of days without perfect CRT without becoming symptomatic. Intensified remote monitoring, for example a planned check-up one week later, may reduce the amont of unnecessary clinical interventions. PVCs are common and they may come and go in certain patients. While the trigger is often not known for these patients, common triggers for PVCs are alterations in general status (fever, a fall, holiday, etc), medication changes or direct cardiac triggers (ischemia, progression of cardiopathy). When there is no direct cause to be identified and the patient reports a stable context, it may be decided to attempt to suppress the PVCs using medication. Betablockers are most often used and are efficient in decreasing PVC burden. In some cases more aggressive medication may be attempted such as flecainide and amiodarone. Only in rare cases, does a high PVC burden require invasive procedures such as radiofrequency ablation.
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