Balloon sizing and transcatheter closure of acute atrial septal defects guided by magnetic resonance fluoroscopy: assessment and validation in a large animal model.

PURPOSE

To quantitatively assess atrial septal defects (ASDs) with small shunts using MRI followed by transcatheter closure monitored by MR fluoroscopy.

MATERIALS AND METHODS

Acute ASDs were created in 14 pigs under x-ray fluoroscopy. Six animals were studied in order to select MR-compatible delivery systems and imaging strategies. ASDs in eight animals were examined with balloon sizing under MR fluoroscopy, flow measurements, and contrast media injections, after which transcatheter closure was performed under MR fluoroscopy. The delivery system was assembled from commercially available materials.

RESULTS

The ratio of pulmonary to systemic flow (Qp/Qs) was reduced from 1.23 +/- 0.15 before ASD closure to 1.07 +/- 0.11 after ASD closure (P < 0.001). In two out of eight animals Qp/Qs was close to 1.0 before closure despite the presence of defects >15 mm. The ASDs were measurable with MR balloon sizing in all of the animals. Balloon sizing was identical with MR (16.9 +/- 2.3 mm) and x-ray fluoroscopy (17.1 +/- 1.3 mm). The in-house-assembled delivery system allowed successful placement of closure devices under MR guidance.

CONCLUSION

Assessment and closure of small shunts with MR fluoroscopy is feasible. A barrier to the rapid implementation of transcatheter closure in patients is uncertainty about the MR safety of guidewires and device delivery systems.