Exercise testing for assessment of the significance of ST segment depression observed during episodes of paroxysmal supraventricular tachycardia

Sixteen patients who had manifested ST segment depression during episodes of paroxysmal supraventricular tachycardia (PSVT) were studied with exercise testing in order to detect coronary artery disease and myocardial ischaemia. No ST segment depression was observed during exercise testing in 15 out of the 16 patients tested. Paroxysms of supraventricular tachycardia associated with ST segment depression occurred during exercise testing in three cases. The ST segment depression was immediately apparent, remained constant throughout the supraventricular tachycardia and was almost instantly abolished following conversion to sinus rhythm. Patients with heart rates greater than 250 beats min-1 during PSVT had marked ST segment depression associated with the tachycardia. These results suggest that coronary artery disease and myocardial ischaemia are not involved in the genesis of ST segment depression during PSVT. Tachycardia per se may be the cause of ST segment depression by altering the slope of phase 2 of the ventricular action potential. Retrograde atrial activation may also induce ST segment shifts in some of the cases.