Ambulatory Holter ECGs
Ambulatory Holter ECG recordings were obtained in a standard fashion with a portable tape recorder, and simulated V1 to V5 leads. Holter ECG recordings were analyzed on a DelMar Reynolds AccuPlus (model 403) MARS Holter Analysis Workstation (GE Medical Systems Information Technologies, Inc., Milwaukee, USA). Arrhythmia frequency recordings were normalized to 24 h and did not include a complete 24-h period of uninterrupted and interpretable rhythms, owing to noise or a loss of signal. In patients with more than one Holter ECG recording, the study closest in time to the CMR was analyzed. Ventricular tachycardia (VT) is defined as a cardiac arrhythmia with three or more consecutive complexes emanating from the ventricles with a heart rate of greater than 100 bpm. NSVT is defined as VT with three or more beats, that spontaneously ends in less than 30 seconds. SVT is defined as VT lasting more than 30 seconds and/or requiring termination due to hemodynamic compromise in less than 30 seconds.16 Patients with VAs were divided into monomorphic (VAs with a single QRS morphology) and polymorphic groups (VAs with multiple QRS morphologies).16, 17 A downsloping shift of 0.1 mV or more from the isoelectric baseline of the ST-segment, that occurred at least 0.08 s after the junction (J)-point, was defined as ST-segment depression. VAs burden was defined as the number of VAs divided by the total beats.