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.