Inappropriate shock caused by P- and T-wave oversensing in a subcutaneous implantable cardiac defibrillator in a patient in sinus rhythm

Figures

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  Figure 1. Electrocardiogram in the emergency department revealed sinus tachycardia at a rate of 106 beats/min, left atrial enlargement, poor R-wave progression, right-axis deviation, and low voltage in the limb leads.

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  Figure 2. Review of the patient’s electrogram (EGM) shows the same morphology of the P, QRS, and T wave at the 0-second mark. Then at 3 seconds of the EGM his P wave and then T wave become sensed, leading to tachycardia detection. This ultimately led to activation of the implantable cardiac defibrillator and the patient was shocked. After discharge the patient remained in sinus rhythm with intermittent oversensing of his T wave, but it did not meet the threshold for tachycardia detection.

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  Figure 3. a: The patient’s presenting sensing electrogram (EGM) vector. Note larger P waves and slewed QRS; the conditional zone was set at 180 beats/min (bpm) and shock zone at 240 bpm. b: The patient’s modified sensing vector with new conditional shock zone setting of 200 bpm and shock zone of 250 bpm. As can be seen within the new EGM, P-wave, QRS, and T-wave morphology are distinctly different.