In vitro assessment of the Lenz effect on heart valve prostheses at 1.5 T.

PURPOSE: Increasing numbers of patients with cardiac valve prostheses are being referred for magnetic resonance imaging (MRI) despite concerns about the potential for functional valve impedance due to Lenz forces. This study aims to determine, in vitro, the occurrence of Lenz forces on 9 heart valve prostheses at 1.5 T and assess the risk of impedance of valve function. MATERIALS AND METHODS: A specially designed hydro-pneumatic system was used to record pressure changes across the valve indicative of any MR induced alteration in leaflet performance. Nine cardiac valve prostheses were exposed to the B0 field at 1.5 T. Each valve was advanced through the B0 field and continuous signals from high frequency pressure transducers were recorded and pressure drops across the valve were assessed using time correction superimposition. The delta p across the valve was assessed as a marker of any MRI induced alteration in leaflet performance. RESULTS: All prostheses produced sinusoidal waveforms. Profiles were asymmetrical and there was no consistency in complex shape and valve type/sub-group. Irregularities in pressure profiles of 4 prostheses were detected indicating resistance of the occluder to the B0 field. CONCLUSION: This study provides empirical evidence of the Lenz Effect on cardiac valve prostheses exposed to the MR B0 field causing functional valve impedance and increasing the risk of valvular regurgitation and reduced cardiac output. Thus, it is essential to consider the potential for the Lenz Effect when scanning cardiac valve implant patients in order to safeguard their wellbeing.

Anticoagulant management of pregnancy following heart valve replacement in the United Kingdom, 1986-2002.

BACKGROUND AND AIM OF THE STUDY: Patients with mechanical heart valves require anticoagulation which is associated with significant maternal mortality (1-4%) and fetal complications (31%) in pregnancy. The study aim was to identify anticoagulant protocols and outcomes for pregnant women undergoing heart valve replacement (HVR) in the United Kingdom. METHODS: Women aged between 18 and 45 years and registered with the United Kingdom Heart Valve Registry (UKHVR) each completed a questionnaire, and their obstetric notes were reviewed. The data analyzed included valve type (mechanical, bioprosthetic, homograft), valve site (mitral, aortic, tricuspid, pulmonary), anticoagulation at confirmation of pregnancy, between 6-12 weeks and from 12 weeks to term, delivery, maternal and fetal outcomes, and cause of death. The summary statistics and a descriptive review of the findings are reported. RESULTS: Of 2,532 women eligible for the study, 922 responded. Among these women, 72 became pregnant, with 60 pregnancies in the mechanical valve (MV) group and 45 in the tissue valve (TV) group. Three anticoagulation regimes were used during early pregnancy: unfractionated heparin (UFH), low-molecular-weight heparin (LMWH) or warfarin. All women received warfarin in the second trimester and heparin for delivery. Live births were recorded in 30% of MV pregnancies and in 60% of TV pregnancies. Miscarriage rates differed markedly (37% MV versus 2% TV). Fetal outcome was poorest in the warfarin-only group, with embryopathy occurring at a dose level of 6 mg. The maternal outcomes did not differ significantly among groups. High-dose heparin during the first trimester and for delivery was effective for the majority of mechanical valves. CONCLUSION: The study results illustrate the diverse and uncertain manner in which UKHVR patients are managed during pregnancy. A national notification system would record much-needed prospective information on anticoagulation and pregnancy outcomes, thus aiding evidence-based management.

Composite aortic valve graft replacement: mortality outcomes in a national registry.

BACKGROUND: Composite aortic valve and root replacement (CVG) is a complex surgical procedure, but excellent center-specific outcomes are reported. We sought to report outcomes in a national cohort. METHODS AND RESULTS: The United Kingdom Heart Valve Registry was interrogated for 1962 first-time CVG (and 37,102 aortic valve replacements [AVR] as a reference group) procedures from 1986 to 2004. We analyzed 30-day mortality, long-term survival (97.2% complete follow-up), and examined available risk factors for mortality using univariate and multivariate logistic regression analysis and causes of death. CVG patients were younger, received larger valve sizes and were more likely to be emergent than AVR patients. Overall 30-day mortality was 10.7% (CVG) and 3.6% (AVR). For CVG, multivariate analysis identified advanced age (> 70 years), concomitant coronary artery surgery, impaired left ventricular function, urgent or emergency status, prosthetic valve size < or = 23 mm and hospital activity volume < or = 8 procedures per annum as significant factors for 30-day mortality. Kaplan-Meier, 1-year, 5-year, 10-year and 20-year survival were 85.2%, 77.1%, 70% and 59.3%, respectively. The conditional (post-30-day) survival was similar to the AVR cohort. CONCLUSIONS: These Registry data provide a unique national insight into CVG outcomes. After a higher initial mortality risk, CVG has equivalent conditional longer-term survival to AVR.

Mechanical testing of human cardiac tissue: some implications for MRI safety.

PURPOSE: 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. CONCLUSION: 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.

Assessment of magnetic field (4.7 T) induced forces on prosthetic heart valves and annuloplasty rings.

PURPOSE: To assess the magnetic field interactions on 11 heart valve prostheses and 12 annuloplasty rings subjected to a 4.7 T MR system. MATERIALS AND METHODS: Ex vivo testing was performed to evaluate translational and rotational forces using previously described techniques. RESULTS: Seventeen out of 23 prostheses showed zero interaction with the magnetic field. Translational forces with deflection angles of 2-20 degrees were demonstrated in six prostheses. Only two heart valves and two annuloplasty rings demonstrated rotational forces. The Carpentier Edwards (CE) Physio Ring, which contains Elgiloy, demonstrated deflection angles three times greater than those previously measured at 1.5 T. Furthermore, there was a direct relationship between increasing prosthesis size and increasing translational force. All heart valve prostheses attracted to the magnetic field were slightly paramagnetic/weakly ferromagnetic. CONCLUSION: Twenty-three heart valve prostheses evaluated for MRI are considered safe in static fields up to 4.7 T based on current safety criteria. However, the CE Physio Ring appeared to develop an increasing magnetism upon re-entry into the MR system. We conclude that prostheses made from Elgiloy may not be acceptable for patients in an MR environment of > or =4.7 T. Further investigations are required to confirm the safety of Elgiloy.

Is 30-day mortality an adequate outcome statistic for patients considering heart valve replacement?

BACKGROUND: In-hospital mortality is widely used by clinicians as a benchmark measure of outcome for determining risks/benefits of cardiac surgery. Patients, however, may wish to have information on estimated longer-term outcomes. Mortality risk by 1 year after the operation may be a more meaningful outcome statistic. We therefore undertook to determine 30-day and 365-day postoperative mortality rates in a large series of consecutive patients who have undergone heart valve replacement (HVR) surgery in the United Kingdom since 1986. METHODS: Data on 80,757 patients registered on the UK Heart Valve Registry were analyzed. Kaplan-Meier actuarial survival analysis was calculated to determine 30-day (group 1) and 365-day (group 2) mortality. Cox proportional hazards were calculated for each group to identify significant risk factors for mortality less than 1 year. RESULTS: Thirty-day mortality represents around half (56%) of the 365-day mortality. This ratio was robust for most subdivisions of the total population. Cox proportional hazards demonstrated female sex, age older than 70 years, single tricuspid valve replacement, multiple valve replacement regardless of type of valve, and subsequent valve operation as significant risk factors of early mortality (group 1). However, men were at significantly greater risk of late mortality (group 2). All other factors remained significant with the exception of subsequent valve operation, which was dropped from the model (group 2). CONCLUSIONS: The robustness of these data would allow cardiologists and cardiac surgeons to provide preoperative patients with a reasonably accurate estimate of survival rates at 1 year after valve replacement surgery in addition to the customary short-term 30-day outcome.

Outcomes in nonagenarians after heart valve replacement operation.

BACKGROUND: Changes in the age profile of the United Kingdom population and improvements in preoperative and postoperative care have resulted in increasing numbers of very elderly patients undergoing heart valve replacement (HVR) operations. Although HVR operations in nonagenarians are relatively uncommon, the demand for cardiac operations in this age group may increase over time. Outcomes after HVR operations in nonagenarians have not been well described yet. Therefore, the aim of this study was to determine outcomes in terms of early mortality and long-term survival in 35 nonagenarians after HVR operation. METHODS: Data from the United Kingdom Heart Valve Registry were analyzed and nonagenarian patients were identified. Additional analyzed data include gender, valve position, valve type, valve size, operative priority, follow-up time, and date and cause of death. Kaplan-Meier actuarial curves were calculated to determine accurate 30-day mortality and long-term survival. RESULTS: On average five HVR operations are performed annually in the United Kingdom in nonagenarians with equal numbers of males and females. Aortic valve replacement with a bioprosthetic valve was the most common operation and 86% were elective admissions. Fourteen patients died within the review period; mean time to death was 402 days. Overall 30-day mortality was 17%, which was higher for males compared with females; females also displayed better long-term survival. CONCLUSIONS: HVR operations in nonagenarians carry a significantly higher risk of early mortality and reduced long-term survival. Despite increases in the age profile of the population, elective HVR operation with patients aged 90 years or older is likely to remain an infrequent surgical procedure reserved for very carefully selected patients.

Translational and rotational forces on heart valve prostheses subjected ex vivo to a 4.7-T MR system.

PURPOSE: To assess the magnetic field interactions on 60 heart valve prostheses subjected to a 4.7 T MR system. It addresses the question of whether heart valves deemed safe at 1.5 T may pose safety hazards as patients are exposed to increased static magnetic fields. MATERIALS AND METHODS: Ex vivo testing was performed to evaluate translational and rotational forces on 60 heart valves using previously described techniques. RESULTS: Translational forces were detected on 58 heart valves ranging from 0.5 degrees to 7.5 degrees. Seven valves exhibited paramagnetic/weakly ferromagnetic behavior, and 51 valves exhibited diamagnetic behavior. Rotational forces were observed for 46 valves. CONCLUSIONS: Criteria previously used for safety assessment of heart valve prostheses and expressed in terms of magnetic forces suggest the forces observed in this study are compatible with the safe use of these valves in magnetic resonance (MR) systems with static fields up to 4.7 T.