SAI QRST (Spatial Angle Index) Calculator

Spatial Angle Index (SAI QRST): Explanation and Clinical Context SAI QRST is a quantitative ECG-derived index that measures the spatial angle between the QRS complex and T wave vectors in three-dimensional space. It reflects the degree of heterogeneity in ventricular depolarization and repolarization. Higher values of SAI QRST indicate greater electrical instability and are associated with increased risk of ventricular arrhythmias and sudden cardiac death.

This index is calculated from vectorcardiographic data, using the areas under the QRS complex and T wave and the angle between them. Clinical studies suggest that SAI QRST above 145 mV·ms is associated with higher arrhythmic risk in post-myocardial infarction and cardiomyopathy patients. It provides incremental prognostic value beyond traditional ECG markers and is useful for risk stratification in both ischemic and non-ischemic cardiomyopathy.