Complete AV Dissociation

Report:

Pacemaker rhythm 80/min 3

Sinus rhythm, non-conducted, 85/min 3

Complete AV dissociation 3

Left atrial abnormality (LAA) 1

Comment:

The paced complexes have the typical LBBB/LAD appearance, indicating pacing from the apex of the right ventricle. The pacemaker is set at 80/min, presumably to improve the cardiac output; the usual pre-set pacemaker rate is 70/min. Perhaps this is no ordinary VVI pulse generator – it may be a VVIR unit.

There is some sinus arrhythmia. The atria and the ventricles beat without any relationship to each other: there is a complete AV dissociation. There is also a presumption of AV block, but it would require a considerably slower pacing rate to be sure of whether it’s even second degree, let alone complete.

The first two paced beats appear to be followed by retrogradely conducted P waves. This is an illusion: the sinus P waves spuriously elevate the terminal QRS and the T waves seem to take off from a negative trough. Marriott comments on this deceptive P wave polarity, adding wisely (as always) that it only deceives those that have some advanced knowledge of electrocardiography and know about retrograde conduction15!