T wave width alterations during Valsalva Maneuver in diabetic patients

In this work we analyzed the T wave width evolution on an ECG database containing 27 records coming from diabetic patients performing the Valsalva Maneuver (VM). The objective is to assess whether the maneuver is accompanied with early signs of ischemia and if those are measurable by T wave shortening. The hypothesis for this T wave shortening is that endocardial action potentials reduce their duration at the very beginning of global ischemia generated by the VM while epicardial action potentials duration remains unchanged so reducing the overall T width. The absence of significant ST changes evidence no severe ischemia. We found a mean T wave shortening in 27 ms with standard deviation of 2.5 ms (p < 10^-5) during VM as compared to the control situation (before VM). Delineation of T wave is done automatically. Since the T onset delineation had not been validated in manually annotated databases, several thresholds have been swept, looking for the best display of T wave width shortening.