Abstract
A 79-year-old man implanted with a cardiac resynchronization therapy defibrillator (CRT-D) was admitted for acute exacerbation of chronic heart failure. Hemodialysis had been initiated due to progressive chronic renal failure one month previously. He had lost consciousness during hemodialysis and cardiopulmonary resuscitation was started. Electrocardiography indicated ventricular tachycardia of 175 /min, but CRT-D and automated external defibrillator (AED) (HeartStart FR2, Philips Medical Systems, USA) did not indicate shock delivery. We switched the FR2 AED to manual mode, then manually charged and delivered a shock. A single defibrillation was successful, and the patient awoke. This patient had been implanted with a CRT-D mainly for cardiac resynchronization therapy to treat chronic heart failure. As ventricular tachycardia was suppressed with drugs, the rate threshold of CRT-D ventricular tachycardia was set high to prevent inappropriate shocks. We considered that the CRT-D did not deliver shocks because the ventricular tachycardia rate was below the threshold of the CRT-D. Furthermore, the AED also did not deliver a shock. Automated external defibrillators (AEDs) do not indicate shock delivery depending on waveforms and the rate of ventricular tachycardia. Healthcare providers should understand the characteristics of automatic analysis by AEDs and CRT-D, and consider switching an AED to the manual mode if necessary.
