When Ventricular Safety Standby Does Not Work

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A 52‐year‐old female with a dual chamber pacemaker for high‐degree atrioventricular (AV) block was seen in the implantable cardioverter defibrillator (ICD) clinic complaining of palpitations. She had been upgraded to a cardiac resynchronization therapy (CRT‐D) 1 year prior due to pacing‐induced cardiomyopathy using the original pacemaker right ventricular (RV) lead as the pace/sense lead in the CRT‐D device while capping the new defibrillator DF‐1 pace/sense lead. Device interrogation showed that instead of true biventricular pacing, she was ventricular pacing via the ventricular safety standby (VSS) mode (Fig. 1, Panel A). In addition, there was a threshold increase in the RV pace/sense lead from 1.25 V @ 0.5 ms (3 months’ prior) to 3.0 V @ 0.5 ms associated with a nominal increase in impedance 430–510 Ω. Chest X‐ray showed no change in lead position or signs of damage to any lead.
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