The Late Electrophysiological Consequences Of Posterior Wall Isolation In Patients With Atrial Fibrillation

Area of Science:

• Cardiology
• Electrophysiology
• Surgical Innovation

Background:

• Atrial fibrillation (AF) ablation commonly uses various lesion sets, including the 'box set' to isolate the posterior heart wall.
• The efficacy of posterior wall isolation (PWI) and the necessity of complete bidirectional block for long-term sinus rhythm maintenance remain unclear.
• This study investigates the long-term integrity of the 'box set' lesion created by epicardial High Intensity Focussed Ultrasound (HIFU) for AF ablation.

Purpose of the Study:

• To assess the long-term effectiveness of the 'box set' lesion in maintaining sinus rhythm after surgical AF ablation.
• To determine the correlation between posterior wall and pulmonary vein isolation and the success of AF abolition.
• To evaluate the necessity of complete bidirectional block for successful long-term outcomes.

Main Methods:

• 101 patients who underwent HIFU AF ablation over 4 years prior were screened; 17 underwent late electrophysiological study.
• Patients were categorized into ongoing AF (n=11) or normal sinus rhythm (NSR, n=6) groups based on clinical history and 7-day Holters.
• Electrophysiological studies utilized a transseptal approach, mapping catheters, and voltage mapping to assess posterior wall (PW) and pulmonary vein (PV) isolation and scar formation.

Main Results:

• All patients with ongoing AF showed absence of PW+PV isolation with fractionated electrograms on the posterior wall.
• In the 6 patients with long-term freedom from AF, PW+PV isolation was confirmed in 4 (67%).
• One patient in NSR had prolonged conduction across the box set lesion, while others showed either dissociated potentials or complete electrical silence in the ablated area.

Conclusions:

• Successful long-term sinus rhythm restoration after AF ablation is strongly correlated with pulmonary vein and posterior wall isolation or delayed conduction.
• These findings support the importance of achieving complete block within the 'box set' lesion for effective AF management.
• The results are timely given the increasing use of hybrid ablation techniques that incorporate this lesion set.