Time-Warping Analysis of the T-Wave Peak-to-End Interval to Quantify Ventricular Repolarization Dispersion During Ischemia

Variations in the dispersion of ventricular repolarization can be quantified by T-wave time-warping based index,
$d_w$
. However, the early phase of the T-wave can be affected by ST-segment changes during ischemia. We hypothesized that restricting
$d_{w}$
to the T-wave peak-to-end (
$T_{pe}$
) would circumvent this limitation while still quantifying variations in repolarization dispersion. A total of 101 ECG recordings from patients undergoing coronary occlusion, together with their control recordings, were analyzed. A series of
$d_{w}$
values was calculated by quantifying the
$T_{pe}$
morphological variations between the T-waves at different occlusion stages and a baseline T-wave. We introduced a normalized version of
$d_w$
,
$\mathcal {R}_d$
, reflecting variations of
$d_w$
during occlusion relative to control recordings (
$\mathcal{R}_d = 1$
corresponds to the same level of variation). The
$d_w$
series followed a gradually increasing trend with occlusion time, reaching median [range]
$\mathcal {R}_d$
values of 9.44 [1.01, 80.74] at the occlusion end.
$\mathcal {R}_d$
at occlusion end was significantly higher than threshold values of 1, 2, 5, and 10 in 94.1%, 85.11%, 64.4% and 48.5% of patients, respectively. The spatial lead-wise analysis of
$d_w$
showed distinct distributions depending on the occluded artery, suggesting a relation with the ischemia location. The relative variation
$\mathcal {R}$
with ischemia of index
$d_w$
(9.4) is greater than that of the T-wave amplitude (7.7),
$T_{pe}$
interval (2.7) and T-wave width (3.0). In conclusion,
$d_w$
tracks ischemic-induced variations in repolarization dispersion in a more robust manner than classical indexes, avoiding the impact of ST segment elevation/depression or early T-wave distortions, thus warranting further clinical studies.