The Commonest Cause of a Pause

Report:

Sinus tachycardia 100/min 1

Atrial-sensing ventricular pacemaker rhythm 1

Blocked SVEB 6

Left atrial abnormality (LAA) 1

Right bundle branch block 1

Comment:

There is a subtle but definite change in the T wave of the last paced beat before the pause: it is more peaked in lead 2 rhythm strip. The pacemaker may have failed to sense this P wave, or the latter may be within the pacemaker’s PVARP.

The sinus escape P wave just beats the pacemaker to the ventricles, its PR interval being shorter than the programmed (sensing) AV interval. This is not obvious from the trace itself; the difference may be in milliseconds and we do not know which lead the pacemaker electrode is “looking” at.

Below (Fig 100a) is another example, from a different patient; the T wave is dimpled in the V1 rhythm strip. This time the escape is paced atrial P wave, followed by a native atrial wave P’ in the next cycle and then resumed sinus rhythm.

As Marriott said: “The commonest causes of pauses are blocked APCs”53.

Fig 100a.

Fig 101. 88 year old man several days after aortic valve replacement.