Complete atrioventricular block due to myocardial infarction

ECG 13A: Sinus rhythm with ST segment elevation in the inferior territory with reciprocity in leads I, aVL, V2 and V3;

ECG 13B: Second tracing obtained a few minutes later; atrioventricular dissociation with persistence of ST segment elevation; complete AV block due to inferior infarction;

Comments: The incidence of complete atrioventricular block in the setting of an acute infarction has considerably decreased since the use of reperfusion techniques (thrombolysis or emergency angioplasty) although remains nonetheless non-negligible (approximately 3 to 5%). Depending on the location of the infarction (anterior or inferior/posterior), the evolving and anatomical morphological characteristics of the block differ from one another.

For the inferior/posterior infarction, the site of the block is generally located at the atrioventricular node, the ventricular rate remains relatively normal (between 40 and 60 beats/minute), and the QRS complexes are narrow. The conduction disorder is most often spontaneously regressive within a few days due to the reversible nature of the conduction pathways (inflammatory and/or edematous).

In case of anterior infarction, the block occurs most often as a result of a irreversible necrosis of the two branches of the bundle of His. The QRS complexes are wide, the escape rhythm rate is slow (less than 40 beats/minute) and often unstable. The block represents extensive necrosis accompanied by high mortality (> 70%) due to heart failure. The complete AV block pattern may be preceded by a bundle branch block, a bifascicular block or a second-degree AV block type 2.

There is a sub-section in the new European recommendations for post-infarction AV block. There is no indication for definitive pacing (class III) if an AV block occurring in the aftermath of an infarction regresses spontaneously. In the rare cases where the complete AV block becomes permanent (after several weeks), a pacemaker should be implanted.

This patient underwent an angioplasty of the first segment of the right coronary artery with good results and the placement of a temporary pacing catheter; the conduction disorder regressed after 2 days, after which the catheter was removed.

Take-home message: Depending on the location of the infarction (anterior or inferior/posterior), the anatomical and evolving morphological characteristics of the AV block are opposite. The prognosis is often highly altered in the setting of a post-infarction anterior AV block, with very high mortality. Conversely, the conduction disorder is most often spontaneously resolved within a few days in the setting of an inferior infarction. The indications for definitive pacemaker implantation are therefore very rare.