Primary T Wave Changes

Report:

Ventricular pacemaker rhythm 60/min 3

1:1 retrograde conduction 2

Primary T wave changes V1-3 5

Comment:

T waves concordant with the QRS complex are no more expected in paced beats than in LBBB: their orientation is due to a myocardial factor rather than abnormal ventricular conduction. In routine reporting, the repolarisation changes secondary to IVCDs of any kind – opposite the main QRS vector – are ignored.

In this case, the cause of the paradoxical T wave inversion in the anteroseptal leads is known, both from the angiography and the sinus rhythm trace shown below (Fig 4a), with LAHB. The sinus rhythm is slower than the paced one, reflecting the rate hysteresis of the pacemaker. The T wave changes are relatively more marked, and extend to V4-5. This demonstrates that the pacemaker, to an extent, masks the repolarisation changes seen in normal conduction. Sometimes, again like LBBB, it masks them completely. But not in this case.

The matter is complicated by the fact that both LBBB and pacemaker rhythm may cause T wave inversion in the same leads after the conduction has normalised5. In those cases, however, the T inversion is usually shallower and the QT interval longer.