Atrioventricular block masked by posteroseptal bypass tract located in coronary sinus aneurysm

Area of Science:

• Cardiology
• Electrophysiology
• Cardiac Anatomy

Background:

• Atrial fibrillation with ventricular preexcitation signifies a high-risk cardiac arrhythmia.
• Catheter ablation of accessory pathways is a common treatment.
• Electrocardiography provides limited anatomical precision for accessory pathways.

Observation:

• A rare case presented with an accessory pathway located within a coronary sinus aneurysm.
• Antegrade atrioventricular conduction obscured an underlying atrioventricular nodal block.

Findings:

• Precise localization of the accessory pathway was achieved despite the unusual anatomical location.
• The coronary sinus aneurysm served as the substrate for the bypass tract.
• Coexisting atrioventricular nodal block was unmasked after identifying the accessory pathway.

Implications:

• This case expands the understanding of accessory pathway substrates.
• It emphasizes the importance of detailed anatomical assessment in complex arrhythmias.
• Coronary sinus aneurysms should be considered in the differential diagnosis for challenging ablation cases.