Study of QRS-loop parameters and conventional ST-T indexes for identification of ischemic and healthy subjects

Several studies have shown the usefulness of the vectorcardiogram (VCG) and the electrocardiogram (ECG) for the detection of cardiac ischemia. We computed a set of VCG and ECG parameters to identify ischemic patients from healthy subjects. The study groups consisted of 80 ischemic patients and 52 healthy subjects. For both populations, five VCG parameters computed on QRS-loop were analyzed, i.e.: (a) Volume, (b) Planar Area, (c) Ratio between Area and Perimeter, (d) Perimeter, and (e) Distance between Centroid and Loop. Likewise, three conventional ECG ST-T parameters were calculated, i.e: (f) ST Vector Magnitude, (g) ST segment level and, (h) T-wave amplitude. Results indicate that VCG and ECG parameters have significant differences between healthy and ischemic subjects. The QRS-loop parameter with the best global performance was Volume, which reached a Sensitivity (Se)=64.5%, a Specificity (Sp)=74.6%, and an Area Under Relative Operating Characteristic Curve (AUC)= 0.77. The best ST-T index was STVM, which obtained Se= 73.2%, Sp=73.9%, and AUC=0.79. However, when all QRS-loop and ST-T parameters were combined, we obtained Se=90.9%, Sp=93.7% and AUC=0.97. In conclusion, the inclusion of QRS-loop parameters improves the conventional ST-T analysis in the identification of ischemic patients.