Mechanical testing of human cardiac tissue: some implications for MRI safety.
OBJECTIVE
The effects of aging on tissue strength and its ability to withstand forces associated with MRI have not been investigated. This study aimed to determine the forces required to cause partial or total detachment of a heart valve prosthesis in patients with age-related degenerative diseases exposed to MRI.


METHODS
Eighteen tissue samples excised during routine heart valve replacement surgery were subjected to a suture pull-out test using a tensile materials testing machine. Five preconditioning cycles were applied before commencing the final destructive test. The test was complete when the sample ruptured and the suture was pulled completely free from the tissue. Results were compared with previously calculated magnetically induced forces at 4.7 T.


RESULTS
All tissue samples displayed a basic failure pattern. Mean forces required to cause initial yield and total rupture were 4.0 N (+/- 3.3 N) and 4.9 N (+/- 3.6 N), respectively. Significant factors determining initial yield were stenosed calcific tissue (p < .01), calcific degeneration (single pathology) (p < .04) and tissue stiffness (p < .01). Calcific degeneration (p < .03) and tissue stiffness (p < .03) were also significant in determining maximum force required to cause total rupture.


CONCLUSIONS
Specific age-related degenerative cardiac diseases stiffen and strengthen tissue resulting in significant forces being required to pull a suture through valve annulus tissue. These forces are significantly greater than magnetically induced < 4.7 T. Therefore, patients with degenerative valvular diseases are unlikely to be at risk of valve dehiscence during exposure to static magnetic field < or = 4.7 T.
Edwards
Maria-Benedicta
MB
United Kingdom Heart Valve Registry, Department of Cardiothoracic Surgery, Hammersmith Hospital, UK.
Draper
Edward R C
ER
Hand
Jeffrey W
JW
Taylor
Kenneth M
KM
Young
Ian R
IR
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D001021:Aortic Valve / Q000473:pathology / Q000601:surgery; D004869:Equipment Safety; D005260:Female; D006349:Heart Valve Diseases / Q000175:diagnosis / Q000601:surgery; D006350:Heart Valve Prosthesis; D019918:Heart Valve Prosthesis Implantation / Q000295:instrumentation; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D008943:Mitral Valve / Q000473:pathology / Q000601:surgery; D011475:Prosthesis Failure; D013314:Stress, Mechanical; D016896:Treatment Outcome