Effect of amyl nitrite inhalation on the abnormal T loop of vectorcardiogram.

The effect of amyl nitrite (AN) on the vectorcardiographic T loop was studied in 17 cases who had negative T waves in the left chest leads of ECG. Thirty sec after AN inhalation the maximum T vector was displaced to the left and anteriorly in 15 and to the left and posteriorly in 2 cases. The magnitude of maximum spatial T vector was decreased and the spatial T loop became more circular. Changes in the amplitude of T loop projected to the scalar lead X were closely related with changes in the heart rate which would represent the sympathetic tone.