Sequential magnetic resonance monitoring of pulmonary flow with endovascular stents placed across the pulmonary valve in growing Swine.
BACKGROUND
Patients with endovascular stent implantation for the treatment of right ventricular outflow tract obstruction are often left with incomplete relief of the obstruction and significant pulmonary regurgitation. A noninvasive and reproducible method for monitoring such patients is desirable. MRI in the presence of a stent, however, has to overcome the problem of potential metallic artifacts.


RESULTS
Under x-ray fluoroscopic guidance, endovascular nitinol stents were placed across the pulmonary valve in 6 young pigs to induce pulmonary regurgitation. Five additional pigs served as controls. Initial MRI was performed after 2 days (13.5+/-1.8 kg) and follow-up after 3 months (32+/-2.9 kg). Pulmonary flow volumes and regurgitant fraction were quantified by velocity-encoded cine (VEC) MRI through (VEC-TS) and distal to (VEC-DS) the stent. VEC-TS was compared with VEC-DS and volumetric measurements of left and right ventricular stroke volumes provided by cine MRI ("gold standard"). Antegrade and retrograde pulmonary flow volumes by VEC-TS were slightly but significantly less than those with VEC-DS and cine MRI. Excellent correlations (r>0.97) for phasic pulmonary flow volumes as measured by VEC-TS and VEC-DS were shown. Pulmonary regurgitant fraction increased from 32.8+/-15% to 49.6+/-17% (P<0.05) over the course of 3 months with VEC-TS.


CONCLUSIONS
MRI demonstrates the progression of pulmonary regurgitation in growing swine. VEC MRI has the ability to quantify pulmonary blood flow inside the lumen of nitinol stents. MRI appears to be ideally suited for monitoring patients with endovascular nitinol stents in the pulmonary artery or pulmonary valve position.
Kuehne
T
T
Department of Radiology, Division of Pediatric Cardiology, University of California, San Francisco, USA.
Saeed
M
M
Reddy
G
G
Akbari
H
H
Gleason
K
K
Turner
D
D
Teitel
D
D
Moore
P
P
Higgins
C B
CB
D000497:Alloys; D000818:Animals; D016477:Artifacts; D001783:Blood Flow Velocity; D001835:Body Weight; D002302:Cardiac Output; D004195:Disease Models, Animal; D018450:Disease Progression; D004562:Electrocardiography; D005500:Follow-Up Studies; D006339:Heart Rate; D006352:Heart Ventricles / Q000503:physiopathology; D018810:Magnetic Resonance Angiography / Q000379:methods; D019028:Magnetic Resonance Imaging, Cine; D011651:Pulmonary Artery / Q000254:growth & development / Q000503:physiopathology*; D011652:Pulmonary Circulation / Q000502:physiology; D011665:Pulmonary Valve Insufficiency / Q000503:physiopathology*; D015607:Stents; D013552:Swine; D014654:Vascular Patency
D000497:Alloys; C013616:nitinol