Comparison of left atrial area marked ablated in electroanatomical maps with scar in MRI.

BACKGROUND: Three-dimensional electroanatomic mapping (EAM) is routinely used to mark ablated areas during radiofrequency ablation. We hypothesized that, in atrial fibrillation (AF) ablation, EAM overestimates scar formation in the left atrium (LA) when compared to the scar seen on late-gadolinium enhancement magnetic resonance imaging (LGE-MRI). METHODS AND RESULTS: Of the 235 patients who underwent initial ablation for AF at our institution between August 2011 and December 2012, we retrospectively identified 70 patients who had preprocedural magnetic resonance angiography merged with LA anatomy in EAM software and had a 3-month postablation LGE-MRI for assessment of scar. Ablated area was marked intraprocedurally using EAM software and quantified retrospectively. Scarred area was quantified in 3-month postablation LGE-MRI. The mean ablated area in EAM was 30.5 ± 7.5% of the LA endocardial surface and the mean scarred area in LGE-MRI was 13.9 ± 5.9% (P < 0.001). This significant difference in the ablated area marked in the EAM and scar area in the LGE-MRI was present for each of the 3 independent operators. Complete pulmonary vein (PV) encirclement representing electrical isolation was observed in 87.8% of the PVs in EAM as compared to only 37.4% in LGE-MRI (P < 0.001). CONCLUSIONS: In AF ablation, EAM significantly overestimates the resultant scar as assessed with a follow-up LGE-MRI.

Irregular ventricular activation results in QT prolongation and increased QT dispersion: a new insight into the mechanism of AF-induced ventricular arrhythmogenesis.

INTRODUCTION: Atrial fibrillation (AF) has been shown to be associated with increased risk of ventricular arrhythmias. We have previously shown reverse electrical remodeling of the ventricles following successful restoration of sinus rhythm in patients with persistent AF. The purpose of this study was to assess the relative role of irregular ventricular activation in mediating the previously observed changes. METHODS AND RESULTS: Twenty-two patients referred for an invasive electrophysiologic study were randomized to 30 minutes of regular or irregular atrioventricular (AV) sequential pacing at 100 beats per minute (bpm) with a programmed AV interval of 100 ms. Irregular pacing was triggered from prerecorded digital signal with a mean rate of 100 bpm, and a standard deviation of 150 ms (25% of the mean rate). In the regular pacing group, QT and QTc decreased from 448 ± 102 ms and 453 ± 105 ms to 428 ± 109 ms and 442 ± 104 ms, respectively (P < 0.001 for QT interval and P < 0.001 for QTc interval). There was no significant change in QT dispersion. In the irregular pacing group, QT and QTc increased from 477 ± 104 ms and 486 ± 78 ms to 489 ± 106 ms and 500 ± 106 ms (P < 0.01 for QT interval and P = 0.03 for QTc interval). In addition, there was a significant increase in QT dispersion from 50 ± 22 ms to 66 ± 22 ms (P = 0.001). Since the rate and pacing sites were similar between the groups, we attribute the repolarization changes in the irregular pacing group to the irregular activation of the ventricles. CONCLUSION: The detrimental effects of irregular pacing go beyond the hemodynamic changes and include electrical remodeling that favors an arrhythmogenic substrate.

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

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.