Question:

A 68-year-old man with a history of permanent atrial fibrillation comes to the office for follow-up. He has been having symptoms due to ineffective ventricular rate control despite aggressive medical therapy. On examination, the patient's heart rate is 125/min and irregular. ECG shows atrial fibrillation with rapid ventricular response. A catheter-based radiofrequency ablation of the atrioventricular node with placement of a permanent ventricular pacemaker is planned. The ablation tip should be positioned at which of the following locations?

Between the tricuspid valve and the inferior vena cava opening

Interatrial septum near the opening of the coronary sinus

Left atrium near the opening of the pulmonary veins

The posterior border of the fossa ovalis

Upper part of crista terminalis near the superior vena cava opening

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Explanation:

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The atrioventricular (AV) node controls the rate at which atrial impulses are conducted to the ventricles. In patients with atrial fibrillation, continuous stimulation of the AV node can sometimes lead to a rapid ventricular rate, which can cause hemodynamic instability and (if persistent) tachycardia-induced cardiomyopathy. In order to prevent these complications, patients with a rapid ventricular response sometimes undergo radiofrequency ablation of the AV node. The AV node is located on the endocardial surface of the right atrium, near the insertion of the septal leaflet of the tricuspid valve and the orifice of the coronary sinus.

(Choices A and D) The isthmus between the inferior vena cava and the tricuspid annulus is the site of radiofrequency ablation for atrial flutter. The fossa ovalis is the name given to the foramen ovale (fetal opening between the right and left atria) once it is closed. However, neither option refers to the location of the AV node.

(Choice C) The pulmonary vein ostia are often the origination site of the aberrant electrical activity that triggers atrial fibrillation, and catheter ablation of these trigger sites (pulmonary vein isolation) can be used to prevent recurrent atrial fibrillation. However, this patient has already developed permanent atrial fibrillation and is undergoing an ablation procedure involving the AV node.

(Choice E) The sinoatrial node is located in the upper anterior right atrium at the opening of the superior vena cava.

Educational objective:
The atrioventricular node is located on the endocardial surface of the right atrium, near the insertion of the septal leaflet of the tricuspid valve and the orifice of the coronary sinus.