Report:

Sinus rhythm 64/min 1

Pacemaker rhythm 62/min 1

Failure to sense (interpolated) 3

R-on-T pacing 2

Concealed retrograde conduction 3

Comment:

The two rhythms, so to speak, pass through each other in a prolonged handover of the ventricles! The PR intervals become longer during the interpolated bigeminy, attesting to concealed retrograde passage of the pacemaker impulses into the AV junction. It is called concealed because it is only manifest by its effect on the subsequent beat - not per se. The sinus beats are themselves interpolated between the paced ones, but they make no visible impression on the latter: pacemaker-ventricular intervals are rarely measurable by surface electrocardiography, anyway.

The double interpolation constitutes yet another form of ‘semiventricular’ tachycardia.

More of the same is shown beloe (Fig 54a). Surprisingly often (and always for the paper roll) the red stripe indicates that “the end is nigh”. It may well be that sick patients consume more and more ECG paper as they get sicker.

Fig 54a. More episodes of double interpolation.

Fig 55. Modified lead V5. 70 year old man with ischæmic and peripheral vascular disease, fitted with a temporary pacemaker following cardioversion from atrial tachycardia with block. An episode of bigeminy was interpreted (incorrectly, by myself) as escape-capture bigeminy and the pacemaker slowed down in order to prove it. The correct diagnosis was revealed.