A young patient with Danon disease receives two ICD shocks: why?

We report the case of an 18-year-old man with Danon disease, a genetic disorder inclunding a severe hypertrophic cardiomyopathy with very broad QRS, who had an implantable cardioverter defibrillator for primary prevention. Nine months after implantation, he received two inappropriate shocks due to R-wave double counting during sinus tachycardia. We discuss how to avoid such inappropriate therapy.