Beat-to-beat variations of the electrocardiogram in survivors of sudden death without structural heart disease.

Aim: We sought to determine whether survivors of sudden death without structural heart disease have beat-to-beat electrocardiographic (ECG) characteristics at the microvolt and at the millisecond level that differ from normal subjects.

Methods: We studied patients at our implantable cardioverter defibrillator clinic who had been resuscitated from ventricular fibrillation with no evidence of underlying structural heart disease. Continuous 10-minute high-resolution unfiltered digital surface ECGs at 1000-Hz sampling rate were acquired in these subjects and in a group of healthy volunteers.