Prosthetic heart valve evaluation by magnetic resonance imaging

Objective: To evaluate the potential of magnetic resonance imaging (MRI) for evaluation of velocity fields downstream of prosthetic aortic valves. Furthermore, to provide comparative data from bileaflet aortic valve prostheses in vitro and in patients. Methods: A pulsatile flow loop was set up in a 7.0 Tesla MRI scanner to study fluid velocity data downstream of a 25 mm aortic bileaflet heart valve prosthesis. Three dimensional surface plots of velocity fields were displayed. In six NYHA class I patients blood velocity profiles were studied downstream of their St. Jude Medical aortic valves using a 1.5 Tesla MRI whole-body scanner. Blood velocity data were displayed as mentioned above. Results: Fluid velocity profiles obtained from in vitro studies 0.25 valve diameter downstream of the valve exhibited significant details about the cross sectional distribution of fluid velocities. This distribution completely reflected the valve design. Blood velocity profiles in humans were considerably smoother and in some cases skewed with the highest velocities toward the anterior-right ascending aortic wall. Conclusion: Display and interpretation of fluid and blood velocity data obtained downstream of prosthetic valves is feasible both in vitro and in vivo using the MRI technique. An in vitro model with a straight tube and the test valve oriented orthogonally to the long axis of the test tube does not entail fluid velocity profiles which are compatible to those obtained from humans, probably due to the much more complex human geometry, and variable alignment of the valve with the ascending aorta. With the steadily improving quality of MRI scanners this technique has significant potential for comparative in vitro and in vivo hemodynamic evaluation of heart valve

Evaluation of an electronic warfarin nomogram for anticoagulation of hemodialysis patients

<p>Abstract</p> <p>Background</p> <p>Warfarin nomograms to guide dosing have been shown to improve control of the international normalized ratio (INR) in the general outpatient setting. However, the effectiveness of these nomograms in hemodialysis patients is unknown. We evaluated the effectiveness of anticoagulation using an electronic warfarin nomogram administered by nurses in outpatient hemodialysis patients, compared to physician directed therapy.</p> <p>Methods</p> <p>Hemodialysis patients at any of the six outpatient clinics in Calgary, Alberta, treated with warfarin anticoagulation were included. Two five-month time periods were compared: prior to and post implementation of the nomogram. The primary endpoint was adequacy of anticoagulation (proportion of INR measurements within range ± 0.5 units).</p> <p>Results</p> <p>Overall, 67 patients were included in the pre- and 55 in the post-period (with 40 patients in both periods). Using generalized linear mixed models, the adequacy of INR control was similar in both periods for all range INR levels: in detail, range INR 1.5 to 2.5 (pre 93.6% (95% CI: 88.6% - 96.5%); post 95.6% (95% CI: 89.4% - 98.3%); p = 0.95); INR 2.0 to 3.0 (pre 82.2% (95% CI: 77.9% - 85.8%); post 77.4% (95% CI: 72.0% - 82.0%); p = 0.20); and, INR 2.5 to 3.5 (pre 84.3% (95% CI: 59.4% - 95.1%); post 66.8% (95% CI: 39.9% - 86.0%); p = 0.29). The mean number of INR measurements per patient decreased significantly between the pre- (30.5, 95% CI: 27.0 - 34.0) and post- (22.3, 95% CI: 18.4 - 26.1) (p = 0.003) period. There were 3 bleeding events in each of the periods.</p> <p>Conclusions</p> <p>An electronic warfarin anticoagulation nomogram administered by nurses achieved INR control similar to that of physician directed therapy among hemodialysis patients in an outpatient setting, with a significant reduction in frequency of testing. Future controlled trials are required to confirm the efficacy of this nomogram.</p

Heart valve disease: investigation by cardiovascular magnetic resonance

Cardiovascular magnetic resonance (CMR) has become a valuable investigative tool in many areas of cardiac medicine. Its value in heart valve disease is less well appreciated however, particularly as echocardiography is a powerful and widely available technique in valve disease. This review highlights the added value that CMR can bring in valve disease, complementing echocardiography in many areas, but it has also become the first-line investigation in some, such as pulmonary valve disease and assessing the right ventricle. CMR has many advantages, including the ability to image in any plane, which allows full visualisation of valves and their inflow/outflow tracts, direct measurement of valve area (particularly for stenotic valves), and characterisation of the associated great vessel anatomy (e.g. the aortic root and arch in aortic valve disease). A particular strength is the ability to quantify flow, which allows accurate measurement of regurgitation, cardiac shunt volumes/ratios and differential flow volumes (e.g. left and right pulmonary arteries). Quantification of ventricular volumes and mass is vital for determining the impact of valve disease on the heart, and CMR is the 'Gold standard' for this. Limitations of the technique include partial volume effects due to image slice thickness, and a low ability to identify small, highly mobile objects (such as vegetations) due to the need to acquire images over several cardiac cycles. The review examines the advantages and disadvantages of each imaging aspect in detail, and considers how CMR can be used optimally for each valve lesion

Self-monitoring of oral anticoagulation: systematic review and meta-analysis of individual patient data

Background: Uptake of self-testing and self-management of oral anticoagulation has remained inconsistent, despite good evidence of their effectiveness. To clarify the value of self-monitoring of oral anticoagulation, we did a meta-analysis of individual patient data addressing several important gaps in the evidence, including an estimate of the effect on time to death, first major haemorrhage, and thromboembolism. / Methods: We searched Ovid versions of Embase (1980–2009) and Medline (1966–2009), limiting searches to randomised trials with a maximally sensitive strategy. We approached all authors of included trials and requested individual patient data: primary outcomes were time to death, first major haemorrhage, and first thromboembolic event. We did prespecified subgroup analyses according to age, type of control-group care (anticoagulation-clinic care vs primary care), self-testing alone versus self-management, and sex. We analysed patients with mechanical heart valves or atrial fibrillation separately. We used a random-effect model method to calculate pooled hazard ratios and did tests for interaction and heterogeneity, and calculated a time-specific number needed to treat. / Findings: Of 1357 abstracts, we included 11 trials with data for 6417 participants and 12 800 person-years of follow-up. We reported a significant reduction in thromboembolic events in the self-monitoring group (hazard ratio 0·51; 95% CI 0·31–0·85) but not for major haemorrhagic events (0·88, 0·74–1·06) or death (0·82, 0·62–1·09). Participants younger than 55 years showed a striking reduction in thrombotic events (hazard ratio 0·33, 95% CI 0·17–0·66), as did participants with mechanical heart valve (0·52, 0·35–0·77). Analysis of major outcomes in the very elderly (age ≥85 years, n=99) showed no significant adverse effects of the intervention for all outcomes. Interpretation: Our analysis showed that self-monitoring and self-management of oral anticoagulation is a safe option for suitable patients of all ages. Patients should also be offered the option to self-manage their disease with suitable health-care support as back-up. / Funding: UK National Institute for Health Research (NIHR) Technology Assessment Programme, UK NIHR National School for Primary Care Research