Spontaneous automaticity arising from a successfully ablated Mahaim fiber

Area of Science:

• Cardiology
• Electrophysiology
• Cardiac Electrophysiology

Background:

• Atriofascicular accessory pathways, such as Mahaim fibers, can cause supraventricular tachycardias.
• Left bundle branch block (LBBB) morphology during tachycardia suggests ventricular activation originating from the left ventricle.
• Spontaneous automaticity in accessory pathways is an uncommon but recognized phenomenon.

Observation:

• A 22-year-old woman presented with arrhythmias exhibiting variable LBBB morphology.
• Electrophysiologic study identified an atriofascicular fiber responsible for antidromic reciprocating tachycardia.
• The Mahaim fiber demonstrated spontaneous automaticity during the study.

Findings:

• Successful ablation of the accessory pathway targeting Mahaim potentials at the tricuspid annulus was performed.
• Post-ablation, slow automatic ventricular rhythms with LBBB morphology persisted.
• These slow rhythms were observed immediately after ablation and during long-term follow-up, albeit sporadically.

Implications:

• This case highlights the potential for abnormal automaticity in remnant accessory pathway tissue after ablation.
• The findings suggest that distal portions of the Mahaim fiber can exhibit automaticity, leading to slow ventricular rhythms.
• Understanding this mechanism is crucial for managing complex arrhythmias and unexpected post-ablation findings.