Nathan S. Burgon 1, Robert S. Oakes 1, Eugene G. Kholmovski PhD 3, Sathya Vijayakumar MS 3, Eric N. Fish 1, Joshua J.E. Blauer 2, Rob S. MacLeod PhD 2, Nassir F. Marrouche MD 1, and Edward V.R. DiBella PhD 3

1 Division of Cardiology, University of Utah School of Medicine. Salt Lake City, Utah.

2 Scientific Computing Institute, University of Utah. Salt Lake City, Utah.

3 Utah Center for Advanced Imaging Research, University of Utah. Salt Lake City, Utah.

Background. Using delayed enhancement cardiovascular MRI, it is possible to detect changes that are associated with atrial fibrillation (AF). Quantification of these changes may provide a way to triage patients to the most effective treatment options. The purpose of this study was to assess the inter- and intraobserver agreement of the detection and quantification method.

Methods. Delayed enhancement MRI (DE-MRI) scans were obtained on a total of forty-three patients with atrial fibrillation who presented to the University of Utah for radio frequency catheter ablation of the arrhythmia. All scans were acquired on a 1.5 Tesla Avanto clinical scanner using a TIM phased-array receiver coil. DE-MRI’s were acquired 15 minutes following gadolinium contrast agent injection (dose = 0.1 mmol per kg of body weight). For the interobserver agreement, two blinded reviewers experienced in reviewing DE-MRI of the LA independently performed 2D segmentation of the DE-MRI slices. The endocardial and epicardial contours of the LA were traced manually with care to avoid the pulmonary veins. The size of the fibrotic area within the LA wall, as depicted by DE-MRI, was then determined data was quantified using a semi-automated algorithm by a third individual. The limits of agreement (LOA) were calculated by Bland-Altman analysis. The difference between the amount of enhancement detected from the segmentation of observer 1 and observer 2 was taken and plotted against the average detected enhancement from the segmentations observers 1 and 2. The average difference and 95% confidence interval were then determined. The intraobserver agreement was calculated from a subset of 10 patients which were segmented twice by the same reviewer in a manner similar to that described for the interobserver variability.

Results. DE-MRI results were quantified by determining a fraction of LA wall with abnormal (i.e. elevated) enhancement. The average difference for the interobserver agreement was -0.9% (Limits of Agreement [LOA] = -7.9% to 6.1% of LA wall). The average difference for the intraobserver agreement was 0.49% (LOA = -4.96% to 5.95% of LA wall).

Conclusion. The quantification of DE-MRI enhancement method is a reproducible method for detecting regions of the LA which may represent changes due to the disease process in patients with atrial fibrillation. DE-MRI holds great promise to be used for pre-procedural planning and patient triage.