A possible mechanism for pacemaker-induced T-wave changes.

The genesis and the significance of pacemaker-induced T-wave changes remain unclear. Changes in body surface potential mapping (BSM) were observed and compared with resting thallium-201 myocardial scintigraphy (T1-SC) findings before, during and after ventricular pacing (VP) in 10 patients with various bradyarrhythmias. All studies were performed with the patients taking no medication. In all patients, isoarea QRST maps showed a characteristic abnormal dipolar pattern with positive values distributed over the upper chest and negative values over the lower chest during VP at a physiological rate for 14 days or more. These abnormalities were preserved almost completely after pacing was terminated; and coincided with deep T-wave inversions in leads II, III, aVF and V4-6. In three patients, BSM performed before VP showed normal QRST isoarea maps with positive values distributed over the left lower chest. All patients in whom resting T1-SC was performed during chronic VP showed transient perfusion defects in the posteroinferior (seven cases) or inferolateral (one case) left ventricular wall. In three patients, T1-SC was performed before VP and showed a normal distribution. Both the pacing-induced perfusion defects and the T-wave abnormalities remained unchanged 2 h after ceasing VP, were attenuated 7 days later and disappeared within a month. These findings suggest that chronic ventricular pacing may produce myocardial ischaemia, and that it persists for a certain period after the cessation of pacing, resulting in post-pacing T-wave inversion.