BACKGROUND: The impact of diffuse atrial fibrosis detected by T1 mapping on the 
clinical outcome after atrial fibrillation (AF) ablation is unknown.
OBJECTIVE: This study aimed to validate and assess the impact of post-contrast 
cardiac magnetic resonance (CMR) imaging atrial T1 mapping on the clinical 
outcome after catheter ablation for AF.
METHODS: CMR imaging was performed in 3 groups by using a clinical 1.5-T 
scanner: controls, patients with paroxysmal AF, and patients with persistent AF. 
A T1 mapping sequence was used to calculate the post-contrast T1 relaxation time 
(T1 time) at the interatrial septum as an index of diffuse atrial fibrosis. A 
subset underwent left atrial endocardial bipolar voltage mapping for 
electrophysiologic correlation. After AF ablation, patients underwent clinical 
review and 7-day Holter monitoring at 6-month intervals.
RESULTS: One hundred thirty-two patients (20 controls, 71 (63%) patients with 
paroxysmal AF, and 41 (37%) patients with persistent AF) underwent CMR imaging. 
Post-contrast atrial T1 time was significantly shorter in AF groups (237 ± 42 
ms) than in controls (280 ± 37 ms) (P < .001). Post-contrast atrial T1 time 
correlated with mean septal voltage (R2 = .48; P < .001) and global left atrial 
voltage (R(2) = .41; P < .001). A diagnosis of AF, AF duration, and left 
ventricular end-diastolic volume independently predicted shortened post-contrast 
atrial T1 time. The single procedure success rate was 74% at 12 ± 5 months 
postablation. Post-contrast atrial T1 time was the only predictor of arrhythmia 
recurrence in multivariate analysis (P = .015). A post-contrast atrial T1 time 
of >230 ms was associated with freedom from AF in 85% relative to 62% with a 
post-contrast atrial T1 time of <230 ms (P = .01).
CONCLUSION: Post-contrast atrial T1 time as measured using CMR imaging provides 
an index of atrial fibrosis that correlates with tissue voltage, presence of AF, 
and clinical outcomes after catheter ablation.