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At least 181 records · Page 10Linked to original sources
PubMed2006

Hemolysis, high-intensity transient signals (HITS) and hemodynamic results after aortic valve replacement with the Medtronic Hall Easy-Fit heart valve prosthesis.

BACKGROUND AND AIM OF THE STUDY: Previous studies have shown a correlation between type, orientation and valve size of mechanical heart valve prostheses and the incidence of high-intensity transient signals (HITS). The study aim was to investigate the presence of HITS and hemolysis and the impact of valve size and hemodynamic parameters following aortic valve replacement (AVR) using the new Medtronic Hall Easy-Fit prosthesis. METHODS: A total of 150 patients (120 males, 30 females; mean age 62 +/- 8 years; range: 32-78 years) underwent AVR (n = 94; 63% concomitant procedures) with the Easy-Fit valve in its optimal orientation. Patients were investigated at between three and 36 months after AVR using transcranial Doppler examination of the right and left middle cerebral artery, and the incidence of HITS was determined. For evaluation of hemolysis, serum lactate dehydrogenase (LDH), hemoglobin and bilirubin were measured. These parameters were related to valve size. Transthoracic echocardiography was performed in all patients. RESULTS: Among the patients, 112 (75%) showed no or low HITS (34% none, 41% < 30/h), while only 38 (25%) had elevated HITS (range 31-100/h, 14%; range > 100/h, 11%). Statistical analysis showed a linear association between the HITS count and valve size. A positive correlation between valve size and LDH was observed; hemoglobin and bilirubin showed normal values. CONCLUSION: The valve size-dependent increase in LDH after AVR corresponds with the observation that the presence of HITS increases with valve size. In light of these findings, the surgical approach to implant the largest size Easy-Fit valve possible should be discussed, given the excellent hemodynamic results provided by the valve, even in smaller sizes.

Adult↗
PubMed1999

Isolated tricuspid valve surgery for severe tricuspid regurgitation following prior left heart valve surgery: analysis of outcome in 34 patients.

BACKGROUND AND AIMS OF THE STUDY: Patients with symptoms of right heart failure due to severe tricuspid regurgitation following a prior operation on left heart valves present a difficult problem. The outcome of tricuspid surgery in this setting is not well defined. We describe a single-center experience of isolated tricuspid valve surgery after prior left heart valve surgery, and analyze potential risk factors for a poor outcome. METHODS: Thirty-four patients who underwent isolated tricuspid valve operation for severe tricuspid regurgitation following prior valvular surgery for left-sided valve disease between 1980 and 1997 were identified. Charts were reviewed for clinical, echocardiographic, catheterization and surgical data. Follow up of survivors was conducted by telephone to ascertain functional status. RESULTS: Three patients died in hospital (early mortality rate, 8.8%). At a follow up of 71 +/- 39 months, 13 patients were alive and 21 reached an end-point (three cardiac reoperations, 18 deaths). Event-free actuarial survival at five years was 41.6 +/- 9.2%. Patients who were alive at follow up had a mean NYHA functional class of 2.1 +/- 0.6 compared with 3.4 +/- 0.5 preoperatively; 85% of survivors were symptomatically improved. Predictors of poor outcome were: increased age at the time of tricuspid surgery (p = 0.0007) and higher number of prior cardiac operations (one versus two or three, p-value 0.01, relative risk 3.4). Pulmonary artery systolic pressure, left ventricular ejection fraction, right ventricular function and size, annulus diameter, tricuspid valve pathology, and valve replacement versus repair were not predictive of outcome. CONCLUSIONS: Isolated tricuspid valve surgery for severe tricuspid regurgitation following prior surgery for left-sided heart valve disease can be performed with acceptable early mortality. There remains a high late mortality that is predicted only by age and the number of previous cardiac operations. However, in this selected group of severely symptomatic patients, significant improvement in symptoms are achieved in the survivors.

Adolescent↗
PubMed2004

Mechanical heart valve cavitation: valve specific parameters.

Several aspects of mechanical heart valve cavitation, in particular of "severe" vapor cavitation, have been investigated in order to describe the phenomenon of cavitation itself and to classify various mechanical heart valves with respect to their tendency to cavitation. Furthermore, following the results of the measurements, a model for determination of time-dependent physical properties and dynamics of cavitation bubbles, such as size, pressure and temperature was developed. In order to classify the cavitation tendency of mechanical valves, a pulsatile hydraulic-driven circularly mock loop was used. Besides measurements of the relevant hemodynamic parameters, the leaflet velocities of the valves were also determined. In addition, numerous high-resolution pressure measurements, in particular the pressure drops necessary for the initiation of cavitation (local atrial pressure drop), were performed. For the investigation of bubble dynamics, a second pulsatile electro-magnetically-driven tester was used. The influence of density, viscosity and temperature of the fluid on the onset of cavitation was investigated. Cavitation events were recorded with a digital high-speed video camera (up to 40,500 frames/sec) for all investigated heart valves and under different conditions. A critical local upstream pressure drop (located within the model atrium after valve closure) of 450 mmHg was found for all valves as well as a valve specific correlation between left ventricular pressure gradient and local upstream pressure drop. Also, a valve dependent correlation between left ventricular pressure gradient and the local upstream pressure drop was provided. Finally, valve specific parameters were found to predict the cavitation tendency for a specific heart valve. The implementation of a suitable theoretical model allowed conclusions on bubble physics. High pressures (up to 800 bar) and temperatures (up to 1,300 degrees C) at bubble collapse have been determined. The influence of fluid parameters such as density, viscosity and temperature on the onset of cavitation is negligible within physiological range. Critical regions for cavitation for all mechanical heart valves were detected. All mechanical heart valves investigated show cavitation under different conditions (dp/dt) associated with high pressures and temperatures at bubble collapse. Cavitation bubble occurrence depends on valve design and location.

Biophysical Phenomena↗
PubMedDate not supplied

Surface analysis of bileaflet prosthetic heart valve leaflet leading edge.

In 1991 and 1992, two patients presented with persistent clinical hemolysis after mitral valve replacement with bileaflet valves, in the absence of paravalvular leaks. When each valve was replaced, the hemolysis disappeared. The first valve was not examined in the laboratory owing to its loss, but it looked normal. The second valve was tested and found to have normal hemodynamics and a normal appearance by light microscopy (LM) and scanning electron microscopy (SEM), but fringe pattern interferometry (FPI) showed its leading leaflet edges to be flatter and rougher than another St. Jude Medical valves (SJMV). This led the authors to collect 17 bileaflet valves (14 SJMV and 3 Carbomedics) for examination of their surface characteristics to see if there was any correlation with hemolysis. All valves were examined by LM, SEM, and FPI. However, only FPI indicated the presence of notable differences in surface roughness and convexity of the leading leaflet edges. Further, convexity of an edge tended to vary inversely with its roughness, and the flat inlet surfaces of most leaflets were consistently less rough than the adjacent edge. The authors' hemolytic valve had one of the flattest and roughest edges of the series. Roughness of the leading edge may contribute to hemolysis by presenting an abrasive surface to the antegrade flow of blood, and by forming the sides of the gap between the leaflets, through which blood is squeezed during closed regurgitation, generating substantial shear forces and causing hemolysis. FPI is a noncontact, sensitive modality, useful in screening pyrolytic carbon surfaces but, unlike other current methods, it is reproducible, does not require modification of the surface, and causes no alteration of the surface texture.

Anemia, Hemolytic↗
PubMed2001

Prosthetic heart valves: why biological?

The replacement of heart valves only became feasible after the development of the heart-lung machine in 1953. Two groups of prosthetic heart valves were subsequently developed: biological valves that do not require anticoagulation and mechanical valves that require life-long anticoagulation with Coumadin. The incidence of heart surgery and the demographics of patients who require heart valve surgery vary worldwide; these factors influence the choice of prosthetic valve for the individual patient and are briefly reviewed. Improved biological tissue-fixation methods are also increasing the durability of biological prosthetic valves and will further favor the implantation of biological valves in the future.

Bioprosthesis↗
PubMed2006

Heart valve replacement: which valve for which patient?

The ideal heart valve substitute would show no deterioration or thrombogenicity, offer no resistance to blood flow, and be easy to implant. However, such a valve does not exist and we must accept compromises in some of these qualities based on our patients' needs. In selection of cardiac valve prosthesis, valve-related factors such as durability, thrombogenicity, and fluid dynamics should be carefully matched to patient-related factors such as age, size, life expectancy, comorbidities, plans for pregnancy, and lifestyle. In addition, surgeon- or operation-related factors should be considered. Technical aspects of implantation, ease of reoperation, and operative mortalities may tip the risk and benefit balance in a particular direction. We review currently available heart valve prostheses and the clinical factors that are involved in selection of a heart valve substitute.

Age Factors↗
PubMed1983

Penetration of netilmicin into heart valves, subcutaneous and muscular tissue of patients undergoing heart surgery.

In 57 patients undergoing heart surgery concentrations of netilmicin in plasma, heart valves, muscle, and subcutaneous tissue were determined after a 5 min intravenous bolus injection of 1.5 mg/kg body weight. Within 8 h netilmicin serum concentration declined from 3 micrograms/ml to 1 microgram/ml. In heart valves the concentrations during heart surgery were high enough to inhibit most staphylococci, Klebisiella, Enterobacter and Escherichia coli strains. No different serum and tissue concentrations in patients with and without extracorporal circulation could be found.

Adipose Tissue↗
PubMed1994

Numerical simulation of unsteady laminar flow through a tilting disk heart valve: prediction of vortex shedding.

Heart valves induce flow disturbances which play a role in blood cell activation and damage, but questions of the magnitude and spatial distribution of fluid stresses (wall shear stress and turbulent stress) cannot be readily addressed with current experimental techniques. Therefore, a numerical simulation procedure for flow through artificial heart valves is presented. The algorithm employed is based on the Navier-Stokes equations in generalized curvilinear coordinates with artificial compressibility for coupling of velocity and pressure. The algorithm applies a finite-difference technique on a body-conforming composite grid around the heart valve disk on which the numerical simulations are performed. Steady laminar flow over a backward-facing step and unsteady laminar flow inside a square driven cavity are computed to validate the algorithm. Two-dimensional, time-accurate simulation of flow through a tilting disk valve with a steady upstream Reynolds number as high as 1000 reveals the complex behavior of 'vortex shedding'. By scaling the results at the Reynolds number of 1000 to peak systolic flow conditions, the maximum value of shear stress on the valve disk is estimated to be 770 dyn cm-2. The 'apparent' Reynolds stress associated with vortex shedding is estimated to be as high as 3900 dyn cm-2 with a vortex shedding frequency of about 26 Hz. The 'apparent' Reynolds stress value is of similar magnitude as reported in experiments but would not be expected to damage blood cells because the spatial scales associated with vortex shedding are much larger than blood cell dimensions.

Algorithms↗
PubMed1991

Static and dynamic stresses during valve closure of a bileaflet mechanical heart valve prosthesis.

The effect of contact geometry and component compliance on the magnitude, distribution, and state of various types of stresses on a bileaflet mechanical heart valve prosthesis during valve closure was analyzed using an Edwards-Duromedics mitral valve as example. Static and dynamic stresses developing on both the leaflet and pivot ball during valve closure were modeled using finite element analysis (FEA). Uniform contact between the leaflet and housing as well as between the pivot ball and pivot slot can significantly reduce both static and dynamic stresses around the contact area. The level of the dynamic flexural stresses can be an order of magnitude higher than that of the static stresses. When both the radial and axial compliance of the housing are taken into consideration, peak dynamic stress was more than 40% less than that generated through the impact between a moving leaflet and a non-compliant rigid housing.

Compliance↗