Hydrodynamic function of second generation porcine bioprosthetic heart valves

Effects of Atrial Arrhytmias on the Regurgitation of a Monoleaflet Prosthetic Heart Valve

Many patients who receive a prosthetic heart valve also have or acquire cardiac arrhythmias. However, most in vitro studies of prosthetic valves examine them under normal rhythms. In this study, a monoleaflet prosthetic heart valve was tested in vitro under conditions that simulated normal sinus rhythm, first degree atrioventricular heart block, and atrial fibrillation (fixed and variable ventricular rates). Atrial contraction was simulated by an active atrial chamber. The timing between the atrium and ventricle was adjusted to simulate various types of arrhythmias. The closing, leakage, and total regurgitant volumes and fractions increased for each type of atrial arrhythmia when compared to normal sinus rhythm. The peak regurgitant flow increased for first degree atrioventricular heart block and atrial fibrillation with a fixed ventricular rate compared to normal sinus rhythm.

Hydrodynamic function of the second-generation mitroflow pericardial bioprosthesis

BACKGROUND

The hydrodynamic function of the smaller size Mitroflow Synergy stented pericardial bioprostheses has been studied in an in vitro fresh tissue aortic root model and compared with previous studies of free-sewn bioprostheses.

METHODS

Three valves of each of the sizes 19, 21, and 23 mm were sutured into fresh tissue aortic roots and tested in a pulsatile flow simulator using two different ventricular input impedance conditions. A high-speed camera was used to study the leaflet opening and closing configurations. Mean pressure difference as a function of root mean square forward flow, effective orifice area, regurgitant volumes, and total energy loss across the valves was measured.

RESULTS

Mean pressure difference with respect to root mean square forward flow decreased as the valve size increased. Thus effective orifice area increased as the valve size increased. The open leaflet configuration images showed that all three sizes of Mitroflow valves had a large circular orifice with minimal open leaflet deformation. All valves closed competently with no visible leakage and no closed regurgitant volume. The Mitroflow valves showed better effective orifice areas compared with previously tested frame-mounted porcine bioprostheses but lower effective orifice areas compared with porcine stentless bioprostheses; however, the open leaflet bending deformation was better than for any of the previously tested bioprosthetic valves.

CONCLUSIONS

The hydrodynamic function of the Mitroflow Synergy stented pericardial bioprosthesis shows potential for good in vivo hemodynamic performance. The good hemodynamic performance combined with relative ease of implantation technique makes the pericardial valve a good valve in the aortic position, particularly in older patients with small annuli.

Midterm evaluation of the Tissuemed (Aspire) porcine bioprosthesis: 493 patients, 506 bioprostheses

BACKGROUND

Valve durability has been a major concern with bioprostheses, and the Tissuemed (Aspire) porcine bioprosthesis was designed to provide a solution to structural valve failure. Because bioprostheses tend to fail by 8 years, the aim of our study was to determine its midterm durability and performance.

METHODS

We reviewed 506 prostheses that were implanted in 493 patients (287 men; mean age 73 +/- 6 years) between 1991 and 1999. Preoperatively 316 (68%) patients were in New York Heart Association class III or IV. There were 417 (85%) aortic, 61 (12%) mitral, 13 (2.6%) aortic and mitral, and two (0.4%) tricuspid procedures. Concomitant procedures were performed in 163 (33%) patients. Follow-up was complete in 488 (98.9%) patients with a total cumulative follow-up of 1,402 patient-years.

RESULTS

The 30-day mortality in this elderly population was 10% (95% confidence interval, 8 to 13), with no early valve-related deaths. Patients' survival at 8 years was 46% +/- 7%. This was influenced by the following factors: (1) the patient's age, being worse for those 70 years or older (p = 0.005); (2) those in New York Heart Association functional class III and IV (p = 0.004); (3) those in atrial fibrillation before the operation (p = 0.006); (4) those with poor left ventricular function (p = 0.009); and (5) those who had a previous cardiac operation (p = 0.003). Valve-related complications (expressed as percent per patient-year) were thromboembolism at 0.9%/patient-year; major hemorrhage at 1.4%/patient-year; bacterial endocarditis at 0.4%/patient-year; nonstructural dysfunction at 0.2%/patient-year, and reoperation at 0.2%/patient-year. At 8 years, freedom from thromboembolism was 93% +/- 7%, major hemorrhage, 90% +/- 4%, nonstructural dysfunction, 99% +/- 1%, structural valve failure, 100%, and reoperation, 99% +/- 1%. At follow-up, 98% of survivors were in New York Heart Association class I or II.

CONCLUSIONS

Our study suggests that at 8 years, the Tissuemed (Aspire) porcine bioprosthesis is durable and has satisfactory performance with low complication rates.

The effect of sizing on the in vitro hydrodynamic characteristics and leaflet motion of the Toronto SPV stentless valve

OBJECTIVES

We established an in vitro model to investigate the effects of valve sizing on the hemodynamic characteristics and leaflet motion of the Toronto SPV valve (St Jude Medical, Inc, St Paul, Minn).

METHODS

Nine valves were first implanted in fresh porcine aortic roots and then retested in glutaraldehyde-treated porcine aortic roots. Three valves were 1- to 2-mm oversized, 3 were 1- to 2-mm undersized, and there were 3 size-for-size implantations. The elasticities of the aortic roots and the composite roots were measured in the pressure range between 0 and 120 mm Hg, and the composite roots were then tested in a pulsatile flow simulator. The transvalvular gradient and regurgitation were measured and the effective orifice area and performance index were calculated for each root. Leaflet motion was recorded on videotape.

RESULTS

The external diameter of the fresh root increased by 35% as the hydrostatic pressure rose from 0 to 120 mm Hg, as compared with 11% for the glutaraldehyde-treated root. Valve implantation in the fresh root reduced the distensibility to 22% but did not change distensibility in the glutaraldehyde-treated root. The effective orifice area was dependent on the valve size, with the transvalvular gradient decreasing as the valve size increased. For the same size of valve the hydrodynamic parameters were slightly better if the valve was undersized by 1 mm. A significant difference in favor of the undersized valves was found in open-leaflet bending deformation.

CONCLUSION

Leaflet motion of the stentless porcine aortic valve in vitro is improved if the valve is slightly undersized, and this may be beneficial to the long-term durability of the prosthesis.

Early clinical experience with the Tissuemed porcine bioprosthesis

BACKGROUND

Tissuemed (Leeds, England) porcine bioprostheses are freshly mounted and dilated for correct functional sizing and commissural alignment, then fixed under low pressure. These valves closely approximate the natural leaflet geometry, reduce opening commissural bending stresses, and may provide a solution to structural valve failure from calcification and tears. To evaluate the performance of the bioprosthesis 207 Tissuemed bioprostheses were implanted in 203 patients, 114 men and 89 women (mean age 73 years; range 56 to 94 years), between 1991 and 1996. Preoperatively 66% of the patients were in New York Heart Association functional class III or IV. There were 175 aortic, 22 mitral, 2 tricuspid, and 4 multiple replacements. Concomitant procedures were performed in 26.1% (53 of 203) of patients. Follow-up was 99.5% (total cumulative follow-up 447.5 patient-years).

RESULTS

The 30 day mortality, influenced by age and valve position, was 11.8% with no early valve-related deaths. Patient survival at 5 years was 76% (standard error 3.3%). Valve-related complication rates (expressed as percent per patient-year and number of events) were thromboembolism 1.1% (5), hemorrhage 0.7% (3), bacterial endocarditis 0.2% (1), nonstructural valve failure 0.2% (1), and reoperation 0.5% (2). At 5 years freedom from valve-related events were as follows: thromboembolism 92.9% (standard error 2.7%), hemorrhage 96.1% (standard error 1.9%), endocarditis 98.1% (standard error 1.8%), nonstructural valve failure 99.2% (standard error 0.7%), structural valve dysfunction 100% (standard error 0.0%), and reoperation 98.1% (standard error 1.8%). At follow-up 73.8% of the patients were in New York Heart Association functional class I or II.

CONCLUSIONS

There were no early valve-related deaths, no episodes of structural valve failure, and valve-related complications compared favorably with other porcine series. There was overall clinical improvement in patient symptoms. Our experience suggests that the Tissuemed porcine bioprosthesis is a safe and reliable heart valve providing good clinical improvement in patient symptoms. Long-term clinical follow-up is, however, essential to complete the evaluation.

Medtronic intact porcine bioprosthesis: 10 years' experience

BACKGROUND

The Medtronic Intact porcine bioprosthesis experience was evaluated over a period of 10 years to determine the influence of structural valve deterioration by valve position in various age groupings.

METHODS

From 1986 to 1996 inclusive, at three centers, 1,272 patients had the prosthesis implanted in 1,296 procedures. The mean age of the population was 67 years (range, 9 to 91 years). There were 836 aortic valve replacements (AVR) (64.5%), 333 mitral valve replacements (MVR) (25.7%), and 110 multiple valve replacements (MR) (8.5%).

RESULTS

The early mortality was 7.3% (94 of 1,296 procedures). The early mortality with concomitant procedures (primarily coronary artery bypass grafting) was 9.8% (52 of 528) and without, 5.5% (42 of 768). The late mortality was 4.25%/patient-year. The linearized rate of major thromboembolism was 0.86%/patient-year. The rate of reoperation was 1.19%/patient-year and valve-related mortality, 1.06%/patient-year. There were 36 cases of structural valve deterioration for aortic valve replacement (16), mitral valve replacement (15), tricuspid valve replacement (2), and multiple valve replacement (3). The freedom from structural valve deterioration for aortic valve replacement was in patients 21 to 40 years, 62.5%+/-25.8% at 7 years; 41 to 50 years, 75.0%+/-15.3% at 7 years; 51 to 60 years, 91.0%+/-4.5% at 8 years; 61 to 70 years, 98.7%+/-0.7% at 10 years; and older than 70 years, 98.3%+/-1.0% at 10 years (p < 0.05). The freedom from structural valve deterioration for mitral valve replacement was for patients 41 to 50 years, 91.7%+/-8.0% at 7 years; 51 to 60 years, 85.9%+/-9.9% at 8 years; 61 to 70 years, 86.3%+/-6.8% at 8 years; and older than 70 years, 93.9%+/-4.8% at 8 years (not significant).

CONCLUSIONS

The Medtronic Intact porcine bioprosthesis has acceptable freedom from structural valve deterioration in both the aortic and mitral positions approaching 10 years of evaluation.

Medtronic Intact porcine bioprosthesis: clinical performance to seven years

The clinical performance of the Medtronic Intact porcine bioprosthesis was evaluated in 1,084 patients (mean age 66.4 years, range 9 to 91 years) who had a total of 1,099 implantations between 1985 and 1992, inclusive. There were 709 aortic valve replacements, 297 mitral valve replacements, and 80 multiple valve replacements. Concomitant procedures were performed in 432 (39.3%). The age group distribution (years) was 35 or younger in 20 patients, 36 to 50 in 64, 51 to 64 in 274, 65 to 69 in 225, 70 or older in 500. The total follow-up time was 2,741 patient-years (mean, 2.5 years) and was 97.5% complete. The early mortality rate was 7.1% and late mortality was 3.9% per patient-year. The overall patient survival at 7 years was 70% +/- 3%. The freedom from major thromboembolism was 94% +/- 1% at 7 years (p = not significant for valve positions). The freedom from reoperation at 7 years was 93% +/- 1%; freedom from valve-related mortality was 89% +/- 2%. The freedom from structural valve deterioration at 7 years was 97% +/- 1% (aortic valve replacement 97% +/- 1%; mitral valve replacement 97% +/- 2%). The freedom from structural valve deterioration among age groups was not different for the overall population, aortic valve replacement, or mitral valve replacement. Hemodynamic assessment revealed obstructive properties for aortic valve replacement sizes of 21 and 23 mm and for mitral valve replacement sizes of 25 and 27 mm.(ABSTRACT TRUNCATED AT 250 WORDS)

A synthetic leaflet heart valve with improved opening characteristics

A new geometry for the design of polyurethane leaflet heart valves has been investigated. The geometry termed the 'alpharabola' has a radius of curvature that increases from the centre of the leaflet at the free edge towards the base of the valve and perimeter of the leaflet. The hydrodynamic function and leaflet opening characteristics of the new valve design have been compared to a valve with a spherical leaflet geometry using the same material. The pressure and flow required to open alpharabola leaflets in steady flow tests was markedly lower than for spherical leaflets. Under pulsatile flow conditions with the valve leaflets fully open, the pressure drop across the alpharabola and spherical leaflets was similar, but much lower than in a porcine bioprosthesis. High speed photography showed that the alpharabola leaflets opened in less than 30 ms with the leaflet opening initiating in the base of the leaflet where the radius of curvature was larger. The synthetic leaflet valve has demonstrated short term durability in accelerated fatigue tests to 100 million cycles.

Geometry of homograft valve leaflets: effect of dilation of the aorta and the aortic root

With the increasing interest in aortic homografts as either a free-sewn valve or whole-root replacement, the effect of internal pressure and dilation of the aorta and aortic root on valve leaflet geometry has been studied. Seven aortic homograft roots were studied, six that had been stored in antibiotics and one that had been cryopreserved. The diameter of the aorta was determined as a function of internal pressure and correlated with the stress-strain characteristics of the aortic wall. Three-dimensional leaflet surface geometry was measured in the "neutral" position, and the leaflet was characterized by its radius of curvature and angle of inclination, using a cylindrical model. The diameter of the aorta increased by between 30% and 50% as the dilation pressure increased from 0 to 120 mm Hg. This was consistent with the stress-strain data obtained from strips of the aortic wall in the circumferential direction. The angle of inclination of the leaflet increased from 20 to 80 degrees and the radius of curvature increased from 4 to 17 mm as the internal pressure increased from 0 to 80 mm Hg. The open leaflet configuration showed a triangular orifice with low bending strains for a dilated root, but increased bending strains with reduced dilation pressure. These are important considerations when implanting a free-sewn homograft into the aortic root.

A model of the geometrical changes in aortic valve leaflets in response to leaflet extension and variable boundary conditions

The function, deformation and performance of heart valve leaflets are dependent on the material properties and the geometry of the leaflet. As the leaflet acts as a constrained membrane the geometry is dependent on the boundary condition applied to the leaflet and any permanent extension of the leaflet. Both of these factors are varied during the preparation of frame-mounted porcine bioprosthetic heart valves and surgical insertion of free-sewn valves. This can result in abnormal geometry and function. A mathematical model has been developed which describes these changes in geometry of a cylindrical leaflet as a function of the diameter of the aortic root (boundary conditions) and the length (or permanent extension) of the leaflet. Both the angle of inclination and the radius of curvature of the cylindrical leaflet were reduced with increased leaflet length or decreased aortic diameter. Agreement was found between the model predictions and experimental observations in porcine bioprosthetic heart valves, where abnormal leaflet geometries are produced by non-physiological boundary conditions and permanent set of the leaflets by fixation with glutaraldehyde. The general solutions developed in this model allow leaflet geometries to be predicted for a range of conditions in free-sewn and frame-mounted valves.