High-Grade Atrioventricular Block

Definition and Characteristics

High-grade atrioventricular (AV) block is a condition where two or more consecutive P waves at a normal frequency are not conducted to the ventricles, with evidence of some residual AV conduction still present, generally considered to be of intra- or infra-Hisian location, as defined by the American Heart Association and the American College of Cardiology 1, 2, 3, 4
The hallmark feature of high-grade AV block is ≥2 consecutive P waves that fail to conduct to the ventricles, with some conduction remaining, unlike complete (third-degree) AV block 1, 3
High-grade AV block is typically unresponsive to atropine but may improve with catecholamines, according to the American Heart Association 1

The American College of Cardiology recognizes different types of AV block, including:

High-grade AV block is associated with a high risk of progression to complete heart block, significant morbidity and mortality, and a less reliable ventricular escape mechanism compared to nodal AV blocks, as stated by the American College of Cardiology and the American Heart Association 1, 4
High-grade AV block has significant clinical implications, including a high risk of progression to complete heart block and associated morbidity and mortality, especially when symptomatic or associated with structural heart disease 1, 4
High-grade AV block is associated with a slower and more unpredictable ventricular escape rhythm compared to AV nodal block, as described by the American College of Cardiology 1

The treatment of high-grade AV block typically involves permanent pacemaker implantation, evaluation of reversible causes (medication effects, electrolyte disturbances), and close monitoring while preparing for pacemaker implantation, as recommended by the American College of Cardiology and the American Heart Association 1, 6