Evaluation of left atrial lesions after initial and repeat atrial fibrillation ablation: lessons learned from delayed-enhancement MRI in repeat ablation procedures

Abstract

Background: We evaluated scar lesions after initial and repeat catheter ablation of atrial fibrillation (AF) and correlated these regions to low-voltage tissue on repeat electroanatomic mapping. We also identified gaps in lesion sets that could be targeted and closed during repeat procedures.

Methods and results: One hundred forty-four patients underwent AF ablation and received a delayed-enhancement MRI at 3 months after ablation. The number of pulmonary veins (PV) with circumferential lesions were assessed and correlated with procedural outcome. Eighteen patients with AF recurrence underwent repeat ablation. MRI scar regions were compared with electroanatomic maps during the repeat procedure. Regions of incomplete scar around the PVs were then identified and targeted during repeat ablation to ensure complete circumferential lesions. After the initial procedure, complete circumferential scarring of all 4 PV antrum (PVA) was achieved in only 7% of patients, with the majority of patients (69%) having <2 completely scarred PVA. After the first procedure, the number of PVs with complete circumferential scarring and total left atrial wall (LA) scar burden was associated with better clinical outcome. Patients with successful AF termination had higher average total left atrial wall scar of 16.4%+/-9.8 (P=0.004) and percent PVA scar of 66.2+/-25.4 (P=0.01) compared with patients with AF recurrence who had an average total LA wall scar 11.3%+/-8.1 and PVA percent scar 50.0+/-24.7. In patients who underwent repeat ablation, the PVA scar percentage was 56.1%+/-21.4 after the first procedure compared with 77.2%+/-19.5 after the second procedure. The average total LA scar after the first ablation was 11.0%+/-4.1, whereas the average total LA scar after second ablation was 21.2%+/-7.4. All patients had an increased number of completely scarred pulmonary vein antra after the second procedure. MRI scar after the first procedure and low-voltage regions on electroanatomic mapping obtained during repeat ablation demonstrated a positive quantitative correlation of R(2)=0.57.

Conclusions: Complete circumferential PV scarring difficult to achieve but is associated with better clinical outcome. Delayed-enhancement MRI can accurately define scar lesions after AF ablation and can be used to target breaks in lesion sets during repeat ablation.

Figure 1

A) Correlation of Circumferential PVA Scar from First Ablation Procedure and Recurrence. B) Patients with PVA Isolated Following Initial and Repeat Ablation Procedures.

Figure 2

3D MRI model of the LA following failed PVAI (1) and repeat successful PVAI (2). After the initial failed ablation, all four PV’s showed incomplete PVA scar as evident by lack of continuous scar (orange/white) around each pulmonary vein ostia (white outline). Gap lesions of healthy myocardium (blue) were identified and targeted (yellow arrows) prior to repeat ablation. Following the successful repeat procedure, all four PVA had continuous scar lesions.

Figure 3. Increased Posterior Wall Scar Formation

The first column (left) represents posterior wall scar (orange/white) following the first procedure in three different patients. The second column (right) represents the scar formation following the second ablation procedure. The repeat procedure induced significantly more posterior wall scarring during the second debulking procedure. This was associated with increased total LA wall scar in each patient.

Figure 4. Identification of Gap Lesions following Procedure Failure

In our patient series, five patients had recurrence of AF following the second procedure. All patients had significant gap lesions on their follow up MRI. Below is an example of two patients who experienced significant gap lesions (blue tissue, marked by yellow arrow) on their right pulmonary veins.

Figure 5

Correlation between DE-MRI following a failed ablation procedure with the electroanatomical map (EAM) obtained during the repeat procedure for three patients. The images on the left demonstrate PA (top) and AP (bottom) views of the DE-MRI color model scar patterns. The images on the right are the EAM obtained during repeat procedure. There is a strong a correlation in the size and distribution of MRI scar (red tissue) with low voltage regions (<0.1mV; red) of the EAM.

Figure 6. Quantitative Correlation between DE-MRI Scar and Low-Voltage Tissue on Electroanatomical Mapping

Figure 7. Recovery of Electrical Potentials that Correlate with Incomplete Scar Lesions

In this patient example, the upper left picture demonstrates incomplete PVA scarring of the left superior pulmonary vein. This vein demonstrated recovery of previously isolated electrical potentials that correlated with the lack of complete anatomical scarring.

Figure 8. Complete Anatomical and Electrical Isolation

Patients who demonstrated complete anatomical scar on DE-MRI had no recovery of electrical potentials on repeat exam. In this example, the upper left picture demonstrates a lesion with complete anatomical scarring of the right superior pulmonary vein. This vein demonstrated no recovery of electrical potentials on repeat electrophysiology study.