When a pacemaker fires, a small spike is seen on the ECG. An atrial pacemaker will generate a spike followed by a P wave and a normal QRS complex. Figure 1 shows the ECG of a patient with an atrial pacemaker that was placed to address a problem in the sinoatrial (SA) node.

What information from the ECG trace indicates the position of the ventricular pacemaker?

QRS complexes are broad with a LBBB morphology, indicating the presence of a ventricular pacing electrode in the right ventricle.

Can pacemaker cause T wave inversion?

In patients with pacemakers, nonpaced ECGs frequently show large T-wave inversion in the inferior and anterior leads. These deep negative T waves typically represent “cardiac memory” (a transient abnormality) rather than ischemia.