Paradoxical pacing spikes during a wide complex tachycardia in biventricular defibrillator. What is the mechanism? Is it undersensing due to troubleshooting?

Figures

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  FIGURE 1. The 12‐lead electrocardiogram of the patient shows a wide complex tachycardia at the rate of 115 bpm. Leads I, II, and III are in zoom. A small deflection—the P wave—is seen regularly before some QRS and is marked with red vertical arrows

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  FIGURE 2. Leads I, II, and III during the wide complex tachycardia. It is apparent that the presence of a P wave is related to the pacing spike inscribed in the QRS. Red vertical arrows refer to the P waves and blue horizontal to the pacing spikes, respectively

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  FIGURE 3. Chest X‐ray showing the position of the defibrillator lead at a high septal position far away from the exit site of the tachycardia (red asterisk). A red asterisk illustrates the exit of the ventricular tachycardia circuit on the cardiac silhouette. The dotted red line refers to the distance the electrical impulse covers from the exit site till being sensed by the tip of the defibrillator lead. This propagation time is prolonged and in the meanwhile sensed AV interval has expired. As a result, ventricular pacing ensues despite QRS onset