ST-segment elevation during cardiac electrophysiologic surgery.
Explore the source record for details and available documents.
Adolescent↗
Biomedical subjects
R P Cochran
Publications and source records attributed to R P Cochran.
Comparison of viscoelastic properties of suture versus porcine mitral valve chordae tendineae.
Recent reports have advocated the use of polytetrafluoroethylene (PTFE) suture for replacement or reinforcement of ruptured or elongated mitral valve chordae tendineae. The mechanical properties of PTFE (Gore-Tex) and other sutures were determined and compared to those of porcine mitral valve chordae. The results were analyzed to assess how closely chordal mechanical function may be simulated by synthetic suture materials. Chordae tendineae and suture samples were tested in uniaxial tension using an INSTRON Model 1000 at strain rates of 5 and 10 mm/min. The stress (g/mm2) was plotted versus strain, and the elastic modulus determined as the slope of the curve. Chordae tendineae exhibited a nonlinear viscoelastic stress/strain behavior. The elastic modulus of both suture types tested was significantly higher than that of the chordae. However, the PTFE suture did exhibit some viscoelastic characteristics (hysteresis and creep) that begin to approach the chordal behavior. Chordal viscoelastic behavior results from the inherent composite structure (collagen, elastin, endothelium, water, and ground substance). As yet, no synthetic materials are able to imitate this behavior with the appropriate tensile strength and fatigue resistant characteristics. At present, PTFE appears to be the best synthetic alternative for chordal replacement, due to its limited viscoelastic capabilities. Nevertheless, the need to more nearly approximate the mechanical behavior of mitral valve chordae tendineae with synthetic material warrants further investigation.
Animals↗
Repair of sternal dehiscence using a Harrington compression system.
Explore the source record for details and available documents.
Debridement↗
Cryopreservation does not alter antigenic expression of aortic allografts.
Cryopreserved aortic homografts are reportedly viable, but no cross-matching or immunosuppression is utilized. Alterations of the antigenic expression by cryo-preservation must be assumed. We designed a protocol to test this premise. Fisher 344 rats served as recipients in all cases. Lewis rats, a mildly disparate strain, were utilized as donors. Four cohorts of animals were utilized. Group I (N = 11) served as a "first set" control. All animals received a syngeneic skin graft. After 28 days an allogeneic skin graft was placed; rejection was seen at 10.3 +/- 0.5 days. Group II (N = 16) first received allogeneic skin grafts with a similar "first set" rejection pattern of 10.4 +/- 0.47 days. A second skin graft was placed and demonstrated an accelerated rejection response of 6.06 days +/- 0.25 days. Group III (N = 17) received two leaflets from a "fresh" Lewis heart valve inserted into a subcutaneous pouch. Allogeneic skin grafts in this group demonstrated a similar second set rejection at 7.05 +/- 0.82 days. Group IV (N = 22) also underwent implantation of heart valve leaflets, except "cryopreserved" Lewis leaflets were implanted into the subcutaneous pouch. An allogeneic skin graft was placed and demonstrated a second set rejection at 7.18 +/- 0.39 days. A one-way analysis of variance shows no significant difference in Groups III and IV, but a significant difference with respect to Group I (P less than 0.00001). Cryopreservation does not alter the antigenic expression in this model, and at present we strongly recommend that at least ABO compatibility be utilized in all patients undergoing aortic homograft implantation.
Animals↗
Bovine pericardium: a source of pulmonary venous obstruction in the Mustard procedure.
Following Mustard's popularization of the intraatrial baffle procedure for transposition of the great arteries, debate has persisted regarding the ideal materials to use. Reports of xenograft (i.e., bovine pericardium) as a suitable prosthetic material made it an appealing choice. We report our recent experience with 2 patients in whom bovine pericardium was used for atrial augmentation, with subsequent pulmonary venous obstruction. For this reason, we have abandoned this material as an acceptable prosthetic in the Mustard procedure.
Animals↗
False inferior pseudoaneurysm: two-dimensional and Doppler echocardiographic findings.
The noninvasive differentiation of true aneurysm from pseudoaneurysm is sensitively and specifically accomplished with two-dimensional echocardiography. Recent reports suggest that Doppler flow patterns may further enhance the specificity of the diagnosis of pseudoaneurysm. We present a patient with ventriculographic and two-dimensional echocardiographic features of an inferior pseudoaneurysm. Doppler examination, however, failed to show phasic flow characteristic of a small communicating orifice between two larger chambers. At surgery, a large posterolateral true aneurysm was found. Thus the addition of Doppler flow patterns to imaging information may help to distinguish pseudoaneurysms from true aneurysms.
Cardiac Catheterization↗
The effect of anterior chordal replacement on mitral valve function and stresses. A finite element study.
During the past 10 years chordal replacement with expanded polytetrafluoroethylene (ePTFE) suture has become an acceptable mitral valve repair technique. Unfortunately, its effect on the mechanical function of the valve is unclear. The purpose of this study was to test whether replacement of ruptured anterior leaflet chordae with ePTFE suture restores mitral valve function and stresses to normal ranges. To answer this question, the authors' existing finite element model of the mitral valve was modified to simulate six different valve conditions: 1) normal, 2) rupture of anterior chordae, 3) replacement using two 4-0 ePTFE sutures, 4) replacement using four 4-0 ePTFE sutures, 5) replacement using two 5-0 ePTFE sutures, and 6) replacement using four 5-0 ePTFE sutures. Physiologic pressures representing ventricular systole from the onset of isovolumic contraction to peak left ventricular pressure were applied to each model. It was found that after rupture, coaptation was impaired and stresses increased dramatically in chordae adjacent to the rupture site. Replacement with two ePTFE sutures restored proper coaptation and lowered stresses to near normal. Using four sutures also restored coaptation and lowered stresses even further. There was minimal difference between 4-0 and 5-0 suture. In conclusion, the replacement of ruptured anterior leaflet chordae with ePTFE suture restores both mitral valve function and stresses to normal ranges.
Biomechanical Phenomena↗
Cardiac disease and the patient with burns.
Cardiac disease has many manifestations that may complicate burn care. A review of 2477 consecutive acute burn admissions was conducted to determine the types and incidence of cardiac complications in this patient population. Nearly one half of patients with a prior cardiac history manifested some form of cardiac dysfunction, most frequently arrhythmias. Eight percent had an in-hospital myocardial infarction. Only 6% of patients without a prior cardiac history manifested cardiac dysfunction. The in-hospital mortality rate after myocardial infarction for both groups was 3.5 to 4 times that of patients without burns. Except for patients with prosthetic valves, for whom anticoagulation and infection prophylaxis are required, burn care of the cardiac patient is expectant with selective use of invasive monitoring and therapy as determined by the patient's clinical course.
Adult↗
Replacement of mitral valve posterior chordae tendineae with expanded polytetrafluoroethylene suture: a finite element study.
BACKGROUND AND AIMS: Expanded polytetrafluoroethylene (ePTFE) suture has been used clinically for replacement of ruptured mitral valve chordae tendineae. The purpose of this study was to assess mitral valve function after posterior chordal replacement with ePTFE suture. METHODS: A three-dimensional finite element computer model of the mitral valve was used, which incorporated geometry, regional tissue thickness, collagen fiber orientation, and anisotropic material properties for the leaflets, interface, and chordae tendineae. To simulate chordal rupture, four marginal and four basal chordae were removed from the posterior leaflet. Chordal replacement was simulated using two elements with the physical and material properties of 2-0 ePTFE suture. Systolic loading pressures were applied. RESULTS: The chordal rupture model demonstrated posterior leaflet prolapse, abnormal stress concentrations, potential regurgitation, and elevated chordal stress. Conversely, the chordal replacement model corrected the prolapse and returned chordal stress to normal levels. However, stress concentrations were shown at suture attachment points. CONCLUSIONS: This integrated mitral valve finite element model provides a tool to investigate the performance of the valve system. In this study, we have shown that 2-0 ePTFE suture replacement of ruptured posterior chordae tendineae returns the valve to a near normal state, in terms of leaflet stress and coaptation, and chordal stresses.
Anisotropy↗
Discrepancies between labeled and actual dimensions of prosthetic valves and sizers.
BACKGROUND AND AIMS: The hemodynamic performance of a mechanical or stented bioprosthetic valve is primarily determined by the diameter of its orifice. Thus, in aortic or mitral valve replacement, assessment of the native annular size and selection of the correspondingly sized prosthetic valve is necessary to achieve maximum hemodynamic performance. The purpose of this study was to determine the actual dimensions of aortic and mitral valve sizers and their corresponding prostheses, and to determine whether they differed from their marked dimensions. METHODS: Mechanical and stented bioprosthetic valves and sizers were obtained from the manufacturers (CarboMedics, St. Jude, Medtronic-Hall, Starr-Edwards, Carpentier-Edwards, and Medtronic-Hancock), and the diameters were measured. RESULTS: For the mechanical models, both aortic and mitral sizers were larger than their marked size by 0.5 mm to 1.0 mm. The aortic valves were all smaller than their corresponding sizers, but the relationship of the mitral valves to corresponding sizers varied with the manufacturer. For the bioprosthetic models the aortic and mitral sizers were true to marked size, the aortic valves were close to marked size and the mitral valves were smaller than marked size. CONCLUSIONS: These differences make optimal sizing difficult at best, particularly if more than one manufacturers' product is used in an institution. These differences may or may not impact valve performance in an individual surgeon's hands. However, the wide range of variations across prosthetic type and manufacturer obligate the surgeon to be aware of these variances to achieve maximum hemodynamic performance for each patient.
Aortic Valve↗
Variations in annuloplasty ring and sizer dimensions may alter outcome in mitral valve repair.
BACKGROUND AND AIMS: Sizing the mitral annulus remains one of the more subjective areas of annuloplasty surgery. We compared the dimensions of annuloplasty rings to annuloplasty sizers and to human mitral valve annuli to determine whether any discrepancies exist that might impact repair results. METHODS: The anterior and posterior length of rigid rings, flexible rings, and corresponding sizers were measured. The ratio of the anterior length to the total length was calculated (A/T ratio) and compared to normal human ratios. RESULTS: Nearly all rings had A/T ratios between 30% and 35% (except for the 32-mm rigid ring at 37.5%). For both rigid and flexible rings, the ring A/T ratios and the sizer A/T ratios differed significantly (except for the 28-mm rigid ring and sizer). In comparison to the average human A/T ratio (36.6%), the ratio for most rings was significantly lower. CONCLUSIONS: The mismatch between rings and sizers results in three possible scenarios: the length of the anterior portion of the ring can be equal to, smaller than, or larger than the anterior portion of the sizer. The clinical implications are that the valve could become stenotic when the ring is implanted or that the anterior portion of the annulus could be altered (stretched or buckled). We feel that to assure improved long-term results, more accurate matching of sizers to rings is essential and that better matching to normal human anatomical ratios would be ideal.
Heart Valve Prosthesis↗
Methods of pseudosinus creation in an aortic valve-sparing operation for aneurysmal disease.
Explore the source record for details and available documents.
Aortic Aneurysm↗
Stress variations in the human aortic root and valve: the role of anatomic asymmetry.
The asymmetry of the aortic valve and aortic root may influence their biomechanics, yet was not considered in previous valve models. This study developed an anatomically representative model to evaluate the regional stresses of the valve within the root environment. A finite-element model was created from magnetic-resonance images of nine human valve-root specimens, carefully preserving their asymmetry. Regional thicknesses and anisotropic material properties were assigned to higher-order elastic shell elements representing the valve and root. After diastolic pressurization, peak principal stresses were evaluated for the right, left, and noncoronary leaflets and root walls. Valve stresses were highest in the noncoronary leaflet (538 kPa vs right 473 kPa vs left 410 kPa); peak stresses were located at the free margin and belly near the coaptation surfaces (averages 537 and 482 kPa for all leaflets, respectively). Right and noncoronary sinus stresses were 21% and 10% greater than the left sinus. In all sinuses, stresses near the annulus were higher than near the sinotubular junction. Stresses vary across the valve and root, likely due to their inherent morphologic asymmetry and stress sharing. These factors may influence bioprosthetic valve durability and the incidence of isolated sinus dilatation.
Adult↗
Nondestructive analysis of mitral valve collagen fiber orientation.
Collagen is the most abundant and highest modulus component in mitral valve (MV) tissue. MV leaflet and chordal collagen ultrastructure were analyzed by small angle light scattering (SALS) and polarized light microscopy (PLM) to provide collagen fiber architecture mapping. It was hypothesized that structural arrangement strongly influences MV tissue mechanical properties and thus physiologic function.
Actin Cytoskeleton↗
Mechanical properties of basal and marginal mitral valve chordae tendineae.
The authors determined the stress/strain characteristics of basal and marginal mitral valve chordae tendineae. The chordae exhibit a nonlinear stress/strain behavior typical of biologic materials, with a discrete transition in the tensile elastic modulus. The post-transition moduli for both basal and marginal chordae are greater than the pretransition values by a factor of approximately 10. In addition, the stress carried by the marginal chordae is higher than that supported by the basal ones at all recorded strains, indicating the marginal chordae are stiffer than the basal chordae. The authors determined the number and distribution of chordal insertions, and found a marginal to basal insertion ratio of almost 2 to 1. The implication is that it may be possible surgically to remove basal chordae without seriously compromising mitral valve function.
Animals↗
Porcine aortic leaflet arrangement may contribute to clinical xenograft failure.
Clinical experience with the first generation porcine xenograft shows significant deterioration and mechanical failure after 7-8 years post-implantation. Although many mechanisms of valve failure have been identified, the inherent differences between porcine and human aortic valves have not been emphasized. To determine if these differences are significant, the authors studied the anatomy of the aortic valve in 10 post-mortem porcine hearts. The authors found that the non-coronary leaflet was the smallest and the right leaflet was the largest based on the dimensions of area, perimeter, weight, and attached edge length (p < 0.05). These results differ from reported analyses of human aortic valves, in which the smallest cusp is generally the right the largest is the non-coronary. The authors believe that these differences between the human and porcine aortic valves may result in atypical mechanical stresses and the disruption of blood flow patterns in the sinuses of Valsalva, and may decrease the long-term stability of the porcine bioprostheses. In other words, the failure found with porcine bioprostheses after 8 years of implantation might be expected from the inherent structure (and associated fluid dynamics) of the porcine aortic valve positioned in the human aortic root.
Animals↗
Collagen synthesis is upregulated in mitral valves subjected to altered stress.
Mitral regurgitation (MR) and abnormal ventricular wall motion (AVWM) are two cardiac conditions that may increase mitral valve (MV) stresses. Theoretically, increased stress could induce damaging MV tissue alterations. These alterations may impair the preferred option of repair, and mandate replacement. It is hypothesized that MV collagen synthesis is upregulated in response to MR and AVWM. To test this hypothesis in a pilot study, an ischemic sheep model (n = 8) was employed. Four sheep underwent selective coronary artery ligation to infarct a papillary muscle, which resulted in MR. Two other sheep underwent similar coronary ligation to create AVWM. As controls, two sheep underwent sham surgery (no ligation). Sheep were killed 4 and 8 weeks post operatively and their MVs were sectioned. Sections were stained with an antibody (SP1.D8, University of Iowa) to procollagen I (precursor to collagen I). The percent area of procollagen stain present present was measured by image analysis (Optimas Corporation) and used as an indicator of collagen synthesis. Procollagen results indicated that MV collagen synthesis was upregulated by factor of 1.8 in both the MR and AVWM groups versus controls. In addition, results showed greater upregulation in anterior leaflets compared with posterior leaflets in both infarct groups. These results indicate that MV collagen synthesis is upregulated in response to MR and AVWM.
Animals↗