Anterior Infarction: “Trifascicular” Block

Report:

Sinus rhythm 99/min

First degree AV block

PR interval 0.28”

Right bundle branch block

Left anterior hemiblock

Axis –85o

Extensive acute anterior infarction

Comment:

The term “trifascicular” is a misnomer – irresistible to some – because the AV block is almost invariably situated not in a fascicle but within the AV node. The longer the PR interval, the more remote the likelihood of its “fascicular” provenance becomes.

Of course, a purist may have trouble diagnosing the LAHB itself59, especially if the LAD had been present earlier, associated with, or due to, inferior infarction (Fig 84a).

A feature of this tracing is the absence of reciprocal changes in the inferior leads despite impressive ST segment elevation in the anterior leads. This can be ascribed to (i) natural resolution of reciprocal changes over 20 hours since admission, (ii) new or increased LAHB, with deeper S waves in all three inferior leads and (iii) old inferior infarction, still ascertainable on the admission ECG (below, Fig 84a).