Time-resolved mr venography pre catheter-based ablation for atrial fibrillation

Objective

The purpose of this study was to evaluate Time-resolved MR venography (TR-MRV) of the pulmonary venous circulation using the time-resolved angiography with interleaved stochastic trajectories (TWIST) method of time-resolved MRA (TR-MRA) and compare it with the more commonly used conventional Contrast enhanced magnetic resonance angiography (CE-MRA) approach in atrial fibrillation patients referred for pre-ablation pulmonary vein mapping.

Background

Catheter-based ablation of the pulmonary veins prevents recurrence of atrial fibrillation in 70-80% of patients during the first year of follow-up^1,2. CE-MRA depicts the left atrium and pulmonary veins with high spatial resolution, enabling accurate measurement of pulmonary vein ostia to be made with depiction of their relationship to other structures.^1,3 Conventional CE-MRA however requires timing of contrast enhancement and produces images with overlap of venous and arterial structures, potentially obscuring pulmonary vein ostia. TR-MRA is an alternative to conventional CE-MRA and has been used successfully in other vascular territories.⁴ Such an approach may be particularly advantageous in the pulmonary circulation with its rapid arteriovenous transit time, allowing acquisition of pure pulmonary venous phase images with a simpler imaging protocol.

Material and methods

26 patients (15 males; age 60.0 ± 12.7y) referred for pre-ablation pulmonary vein mapping underwent both conventional CE-MRA and TR-MRV with TWIST. Imaging was performed on a 1.5 Tesla (MAGNETOM Avanto, Siemens Healthcare) MRI scanner. Source partition and MIP images were evaluated. Quantitative Analysis: Pulmonary vein ostium orthogonal dimensions were measured using double oblique multiplanar reformatting. Qualitative Analysis: For qualitative analysis, both source partition images and MIP images were assessed by two observers. Pulmonary vein conspicuity was scored on a scale of 1-4 (1=poor, 2=fair, 3=good, 4=excellent). The number of pulmonary veins (3 veins= common ostium, 4 veins = normal, 5 veins=accessory vein) was recorded.

Results

Orthogonal venous diameters were comparable for both TR-MRV and conventional CEMRA (1.34cm ± 0.37 vs 1.38cm ± 0.36, respectively); see Table 1. Visualization of pulmonary vein anatomy and variant anatomy was also similar for both techniques (fig 1).

Table 1 Comparison of the mean pulmonary diameter ± standard deviation (maximum; minimum values for TWIST and Conventional CE-MRA respectively.

Figure 1

Comparison of accessory vein and common ostium detecting ability using a bar graph to quantify differences between conventional CE-MRA and TWIST TR-MRA. However, TWIST was superior in detecting common ostiums and slightly better than the conventional CE-MRA technique at identifying patients with both common ostiums and accessory veins. Finally, CE-MRA was slightly better overall for visualizing the pulmonary veins but had a greater margin of error. The TWIST technique, on the other hand, had slightly worse overall results but was more consistent in yielding high quality visualizations of the veins. The CE-MRA was able to identify the focal ostial stenosis present in one patient during the qualitative analysis while the TWISE was not.

Conclusion

We have demonstrated that TR-MRV using TWIST produces comparable anatomic images and pulmonary venous dimensions to the more widely used CEMRA technique. TR-MRV improves arterio-venous separation producing high resolution pulmonary venous phase images without arterial overlap.