Physiological Pacing

Report:

Pacemaker rhythm 70/min 7

AV sequential pacemaker 2

100% capture 1

Comment:

The patient had a DDD (“universal”) pacemaker, now the commonest type implanted1.

In this example, both the atria and the ventricles are paced, mimicking the natural sequence of atrial-ventricular activation. This sequence has, through the American love of scientific sounds, come to be called synchrony, however undesirable the latter would be in its true meaning of being at the same time, simultaneous, rather than sequential.

Atrial systole may contribute 20-25% to the ventricular filling. This is of special importance in patients with non-compliant ventricles.

Should the patient's own P waves occur at a faster rate, the ventricle would still be paced, at the new rate, as the atrial lead has both sensing and pacing capacities. If the native PR interval were shorter than the programmed AV interval, the heart would now be paced from the sinus node with a normal QRS – there would be no visible evidence of an electronic pacemaker.

One of the patient’s pre-implantation ECGs is shown below (Fig 1a). Interestingly, it was reported as normal by both the computer and the Cardiologist, despite the (admittedly discrete) 2:1 AV block and ST/T changes consistent with LVH or ischæmia.