Junctional Rhythm

Excerpt

The sinoatrial node (SA) is the default pacemaker and is located subepicardially and is crescent in shape. The atrioventricular node (AV) is a subendocardial structure situated in the inferior-posterior right atrium. It sits within an anatomic region bordered posteriorly by the coronary sinus ostium, superiorly by the tendon of Todaro, and anteriorly by the septal tricuspid valve annulus. This anatomic region is also commonly referred to as the triangle of Koch. The sinoatrial nodal artery supplies blood to the sinoatrial node, it branches off the right coronary artery in 60% of cases, whereas in 40% of cases, it comes from the left circumflex coronary artery. The blood supply to the AV node is from the AV nodal branch of the right coronary artery (90%) or the left circumflex artery (10%) depending on the right or left dominant blood supply to the heart. The first septal perforator of the left anterior descending artery also supplies blood to the AV node. A junctional rhythm is where the heartbeat originates from the AV node or His bundle, which lies within the tissue at the junction of the atria and the ventricle (see Image. Junctional Rhythm). Generally, in sinus rhythm, a heartbeat is originated at the SA node. This electrical activity then travels through the atria to the AV node from where it reaches the Bundle of His from where the electrical signals travel to the ventricles through the Purkinje fibers.

The terminology used to identify the type junctional rhythm depends on its rate and is as follows:

1. Junctional bradycardia: rate below 40 beats per minute

2. Junction escape rhythm: rate 40 to 60 beats per minute

3. Accelerated junctional rhythm: rate of 60 to 100 beats per minute

4. Junctional tachycardia: rate above 100 beats per minute