Symptoms and electrocardiographically documented rhythm preceding spontaneous shocks in patients with implantable cardioverter-defibrillator.

During a follow-up of 24 +/- 20 months after treatment with an implantable cardioverter-defibrillator (ICD), 101 of 241 patients (42%) received > or = 1 spontaneous ICD shocks with documentation of the rhythm leading to shock by Holter or telemetry monitoring or stored electrograms by the device. Sustained ventricular tachycardia (VT) or ventricular fibrillation (VF) was documented in 67 of the 101 patients (66%) with electrocardiographically documented shocks, nonsustained VT in 4 patients (4%), supraventricular tachyarrhythmias in 41 patients (41%), and normal sinus or pacemaker rhythm in 10 patients (10%). No, mild (palpitations and/or mild dizziness) and severe symptoms (presyncope/syncope) preceded spontaneous ICD shocks in 20 (30%), 33 (49%) and 27 (42%) of the 67 patients, respectively, with electrocardiographically documented VT or VF, and in 23 (56%), 16 (39%) and 1 (2%) of the 41 patients, respectively, with electrocardiographically documented supraventricular tachyarrhythmias. Three of the 4 patients with nonsustained VT had mild symptoms, and 1 patient with nonsustained VT had presyncope. None of the 10 patients with spurious discharges during normal sinus or pacemaker rhythm had symptoms preceding the ICD shocks. It is concluded that (1) most patients with either electrocardiographically documented VT/VF or a non-VT/VF rhythm preceding spontaneous ICD shocks have no or mild symptoms preceding the shock, and (2) severe symptoms preceding ICD shocks suggest sustained VT or VF as the underlying rhythm, although severe symptoms rarely occur in patients with supraventricular tachyarrhythmias or nonsustained VT.