ECG Reviews
2:1 Atrioventricular (AV) Block ECG Review
2:1 atrioventricular block is a form of second-degree AV nodal block and occurs when every other P wave is not conducted through the AV node to get to the ventricles, and thus every other P wave is not followed by a QRS complex.
2:1 AV block can possibly be from either second-degree AV nodal block type I (Wenkebach) or second-degree AV nodal block type II. This distinction is crucial, as the former is usually benign, whereas the later requires implantation of a permanent pacemaker.
A general rule to remember is that if the PR interval of the conducted beat is prolonged and the QRS complex is narrow, then it is most likely second-degree AV nodal block type I (Wenkebach). Alternatively, if the PR interval is normal and the QRS duration is prolonged, then it is most likely second-degree AV nodal block type II, and a pacemaker is probably warranted.
Recall that second-degree AV nodal block type I (Wenkebach) is an issue in the AV node itself, which is subject to sympathetic and parasympathetic tone, whereas second-degree AV nodal block type II is an “infranodal” conduction disease of the His-Purkinje system, meaning that altering AV nodal conduction would have no effect.
Various maneuvers can be employed to distinguish between the two potential rhythms when an ECG reveals 2:1 AV nodal block:
Carotid sinus massage or adenosine: This slows the sinus rate, allowing the AV node more time to recover, thus reducing the block from 2:1 to 3:2 and unmasking any progressing prolonged PR intervals that would indicate second-degree AV nodal block type I (Wenkebach).
Atropine administration: This enhances AV nodal conduction and could eliminate second-degree AV nodal block type I (Wenkebach), as it is due to slowed AV nodal conduction.
Exercise ECG testing: This enhances AV nodal conduction and could also eliminate second-degree AV nodal block type I (Wenkebach), as it is due to slowed AV nodal conduction.
ECG Examples:
- 2:1 Atrioventricular (AV) Block ECG (Example 1)
- 2:1 Atrioventricular (AV) Block ECG (Example 2)
- 2:1 Atrioventricular (AV) Block ECG (Example 3)
References:
1. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric, 6e
2. Surawicz B, et al. AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram. Circulation. 2009; doi:10.1161/CIRCULATIONAHA.108.191095.