What is happening in this electrogram?
This is part of a stored episode on the patient’s dual chamber ICD.
What is the rhythm?
What therapies were delivered?
Why were therapies delivered?
Are the therapies appropriate?
What if any programming changes should be considered?
Answer:
Inappropriate therapy for AV-nodal reentrant tachycardia (AVNRT). The rhythm is AV-nodal reentrant tachycardia at approximately 176bpm. Note the1:1 AV association of the P and R waves indicative of nearly simultaneous atrial and ventricular depolarization. The rate is between 140 and 280 bpm, and in this example, the QRS complex is narrow. The patient was asymptomatic during this episode and recalls the painful shock.
The therapies that were delivered are antitachycardia pacing (ATP), which were not successful given AVNRT is a supraventricular tachycardia, followed by a 36J shock. The therapies were delivered because the rate fell into the programmed VT therapy zone of 171bpm. The P waves were not being sensed as they were falling into a banking period being so close to the R wave. Given the device was not detecting the P waves, the rate branch that was applied was V>A. The V>A rate branch discriminator states if there are more Vs than As, deliver therapy.
The device functioned appropriately based on how it was programmed, but cardioversion for AVNRT is not ideal unless the patient is hemodynamically unstable. Unfortunately, AVNRT is a common cause of inappropriate ICD therapies. The Electrophysiologist was contacted, and the device was reprogrammed to a higher VT therapy zone to avoid another shock for this rhythm. A consult for an AVNRT ablation was scheduled.
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