This ECG was reported as dual chamber pacing.

What do you think?There is obvious atrial pacing, but is there ventricular pacing?Let us look closer at the tracing:

There is an atrial stimulus artefact (Ap) followed by a P wave and a prolonged AV delay.There is also a prolonged QT interval which must be mentioned.Because of the prolonged AV delay and QT interval, the atrial stimulus artefact at rest is close to the preceding T wave. If rate adaptive pacing is programmed ON, then with exercise, the atrial pacing rate increases with physiological demand, and the stimulus artefact may become embedded in the T wave. In this situation, atrial systole may occur with closed AV valves and the patient may describe this as walking into a brick wall.There is also a ventricular ectopic present.Because of its close association to a stimulus artefact, some may confuse this for ventricular pacing. However, the timing as shown below makes this an atrial stimulus artefact occurring immediately before the ectopic.

Remember that with atrial pacing, a ventricular ectopic may not be sensed as shown below.

Between the atria and ventricles, there is an electrical barrier at the AV node. Therefore, a ventricular ectopic must be conducted retrograde and depolarize the atria order to inhibit the atrial output and this usually does not happen and results in an atrial stimulus artefact in the ectopic QRS.This is not pacemaker malfunction!Harry Mond