First Degree AV Block

Report:

Sinus rhythm 72/min

First degree AV block (PR 0.42”)

VEBs

SVEBs, blocked

Left axis deviation –60o

Old inferior and anterior infarction

Junctional escape beats (last and first) QRS complex

Comment:

There is some variation in the long PR intervals: the third and the eighth sinus beats have slightly shorter intervals than the beats between them. The eighth beat’s P wave is delayed, without obvious cause, perhaps reflecting a sinoatrial exit block or a concealed SVEB somewhere along the way.

The first and the last QRS are associated with nonconductable atrial waves; the first may be a blocked sinus wave and the last may be retrograde, but there is no certainty here. It is equally uncertain where the first QRS comes from; it may be the last in a long Wenckebach sequence. The VEBs are preceded by sinus P waves which cannot be conducted either: there is no time before the onset of the VEBs.

The second last P wave is clearly a premature SVEB; its conduction, too, is doomed by the proximity to the preceding QRS (VEB) complex. The last P wave probably comes from the same source as its associated QRS, the junctional escape beat.

The left axis is in this case due to both the inferior infarction and a LAHB: there are no secondary R waves there, but there is one in aVR, quite delayed with respect to the R wave below, in aVL; V6 is an RS complex. These are all the signs of LAHB.

Below (Fig 86a) is the patient’s post-pacemaker ECG; four atrial waves are paced and one is an atrial pseudofusion beat. This is acceptable. But is pacing itself acceptable therapy for first degree AV block alone? It can be: a long AV interval can not only deprive the patient of effective atrial transport, it can behave like a pacemaker syndrome, with P waves in the wrong place56. Of course, in this case the patient got a fat QRS complex as a trade-off for atrial transport. If he lives long enough, and has the insurance or money, someone may synchronise his QRS for him.