There are many different lesion
sets that are used for the surgical ablation of atrial fibrillation (AF). One
such pattern is the ‘box set’, a single ring of scar delivered anterior to the
pulmonary veins, which aims to electrically isolate the posterior wall from the
rest of the heart. However it remains unclear whether posterior wall isolation
(PWI) is an effective lesion set for maintenance of sinus rhythm and whether it
is necessary to achieve complete bidirectional block. We investigated the
long-term integrity of the ‘box set’ lesion created during surgical AF ablation
by epicardial High Intensity Focussed Ultrasound (HIFU). All patients had
documented persistent or recurrent paroxysmal AF prior to surgery. We
correlated this with subsequent success or failure in the abolition of atrial
With regional ethical and R&D
approval, 101 patients who had previously undergone HIFU AF ablation greater
than 4 years ago were screened for inclusion in the study. 17 patients agreed to late
electrophysiological study: 11 with on-going AF and 6 in normal sinus rhythm.
Clinical history and 7-day holters
were used to define the NSR group. We performed a diagnostic EP study using a
transseptal approach in fully anticoagulated patients (INR>2.0 and ACT
maintained at >300s). A catheter was placed in the coronary sinus (CS) and a
circular multipolar mapping catheter was used to map the left atrium and
pulmonary veins. Patients in atrial fibrillation were cardioverted. We recorded
whether posterior wall (PW) and pulmonary vein (PV) isolation had been achieved
at the surgical procedure. In selected cases we recorded a voltage map using
either CARTO (Biosense- Webster) or NavX (St Jude Medical) to identify areas of ablation scar.
All 11 patients with AF had absence
of PW+PV isolation with fractionated electrograms recorded across the PW. In
the 6 patients with long-term freedom from AF, PW+PV isolation was confirmed in
4 (67%) and in 1 there was prolonged conduction across the box-set lesion with
CS to PW activation time of around 200ms versus 45ms from mid-CS to left atrial
appendage. Of the 4 patients with confirmed PW+PV isolation, 1 had dissociated
spontaneous atrial potentials within the box set area and the other 3 had
electrical silence throughout with inability to capture the posterior wall
pacing at 10mA at multiple sites.
There appears to be a clear
correlation between the successful restoration of long-term sinus rhythm and
isolation / delayed conduction from the pulmonary veins and posterior wall.
Given the advent of hybrid atrial fibrillation ablation techniques designed to
deliver this lesion set, these findings are timely and highly relevant.
Credits: Edward J. Davies; Ian Lines; Malcolm Dalrymple-Hay; Guy A Haywood