Ischemia-related depolarization changes detected in body-surface ambulatory ECG recordings

It is well known that myocardial ischemia causes changes in the the ST-segment of the ECG. Unfortunately, not all ischemic states are reflected by the ST-level. Recent studies show that myocardial ischemia alters not only the repolarization phase, but it also affects the depolarization phase of the heart, subsequently altering electrical conduction patterns, and giving rise to ischemia-dependent changes in the QRS complex. These changes could be utilized in formulating clinical diagnosis. From the European ST-T data base the authors analyzed all 8 patients with single-vessel LAD occlusion, for which a modified lead III and V₃ or V₄ were available. The authors calculated the time-frequency distributions during the averaged QRS complex, using the continuous wavelet transform. From these distributions, an intra-QRS subband energy index was calculated by integrating the coefficients across the QRS complex, for four overlapping subbands: LF (24-35 Hz), MF (30-45 Hz), HF (40-60 Hz), and HHF (50-80 Hz). Finally, each subband index was normalized (% of total QRS energy), trended across the 120-min recording, then low-pass filtered with a cosine window of length 2 min 20 sec, and plotted. In all 8 patients ST and T changes were accompanied by intra-QRS changes in all subbands during the ST episode. The authors observed a relative drop in the energy in subband LF, while the MF index went up. HF first dropped, during the first half of the ST episode, then increased towards the end of the episode. HHF typically decreased-due to loss of fine structure in the depolarization wavefront