[Ross procedure versus mechanical aortic valve replacement in young adults]. / Ross-mutét vagy mechanikus mubillentyu beültetés fiatalkori aorta vitiumos betegeknél.

UNLABELLED: Clinical and echocardiographic data of young adults undergoing aortic valve replacement either by pulmonary autograft or mechanical prosthesis were analysed. Between 1995 and 2002 thirty-four consecutive patients (age 26.2 +/- 5.3 years) underwent aortic valve surgery by the authors (17 Ross procedures and 17 mechanical prostheses). Reasons for not doing a Ross procedure were size mismatch (3); anomalous coronaries (2); thin pulmonary sinuses (2); severe hypertension (2); poor LV function (2); active endocarditis (1); lack of suitable homograft (2) and the patient's request (3). There was no early mortality detected, although all patients were followed up (64.4 +/- 26.8 months). Two late deaths occurred in the prosthetic valve group (1 sepsis secondary to endocarditis, 1 end-stage heart failure). During the follow-up time there were two cases of endocarditis and two anticoagulant-related complications in the mechanical valve group. In the Ross group, one patient required reoperation for early endocarditis secondary to an infected homograft. The only late complication after the Ross procedure was a minor pulmonary embolism. Echocardiography showed a competent autograft in all but one patient. LV end diastolic dimensions and wall thickness were significantly smaller in the autograft patients (p = 0.049 andp = 0.017, respectively). CONCLUSIONS: Freedom from anticoagulation-related complications and unrestricted lifestyle as well as the more complete LV mass regression make the autograft a superior valve substitute in young adults; however it is not suitable for everyone.

Biocompatibility of acellular human pericardium.

BACKGROUND: Previous studies have shown successful decellularization of human pericardium without affecting the major structural components and strength of the matrix. The aim of this study was to assess the biocompatibility and reseeding potential of the acellular human pericardial scaffold. MATERIALS AND METHODS: Pericardia were treated sequentially with hypotonic buffer, sodium dodecyl sulfate, and a nuclease solution. The presence of cellular attachment factors after decellularization was evaluated using immunohistochemistry. The scaffold was seeded with dermal fibroblasts and cellular attachment to and numbers of cells penetrating were assessed over time. Biocompatibility was also evaluated following subcutaneous implantation into a mouse model for three months. RESULTS: After decellularization, the scaffold stained positively for fibronectin, but collagen IV and laminin staining was reduced. Seeded fibroblasts attached to the mesothelial surface and were visualized in the tissue within a week of seeding. The majority of fibroblasts in the tissue were viable and there was evidence of remodeling of the matrix. Analysis of the explanted tissues from mice showed that fresh/frozen and glutaraldehyde-fixed pericardia were encapsulated with a thick layer of inflammatory cells and fibrous tissue. In contrast, the decellularized scaffold was infiltrated with myofibroblasts, CD34+ cells and macrophages, indicating a healthy repair process. Compared with the glutaraldehyde-fixed tissue, the calcium content of the fresh/frozen and decellularized pericardia was negligible. CONCLUSIONS: The pericardial scaffold was biocompatible in vitro and in the mouse model in vivo.

Amplitude modulation drive to rectangular-plate linear ultrasonic motors with vibrators dimensions 8 mm x 2.16 mm X 1 mm.

In this paper, to exploit the contribution from not only the stators but also from other parts of miniature ultrasonic motors, an amplitude modulation drive is proposed to drive a miniature linear ultrasonic motor consisting of two rectangular piezoelectric ceramic plates. Using finite-element software, the first longitudinal and second lateral-bending frequencies of the vibrator are shown to be very close when its dimensions are 8 mm x 2.16 mm x 1 mm. So one single frequency power should be able to drive the motor. However, in practice the motor is found to be hard to move with a single frequency power because of its small vibration amplitudes and big frequency difference between its longitudinal and bending resonance, which is induced by the boundary condition variation. To drive the motor effectively, an amplitude modulation drive is used by superimposing two signals with nearly the same frequencies, around the resonant frequency of the vibrators of the linear motor. When the amplitude modulation frequency is close to the resonant frequency of the vibrator's surroundings, experimental results show that the linear motor can move back and forward with a maximum thrust force (over 0.016 N) and a maximum velocity (over 50 mm/s).

Development and characterization of an acellular human pericardial matrix for tissue engineering.

This study aimed to produce an acellular human tissue scaffold with a view to recellularization with autologous cells to produce a tissue-engineered pericardium that can be used as a patch for cardiovascular repair. Human pericardia from cadaveric donors were treated sequentially with hypotonic buffer, SDS in hypotonic buffer, and a nuclease solution. Histological analysis of decellularized matrices showed that the human pericardial tissue retained its histioarchitecture and major structural proteins. There were no whole cells or cell fragments. There were no significant differences in the hydroxyproline (normal and denatured collagen) and glycosaminoglycan content of the tissue before and after decellularization (p > 0.05). There were no significant changes in the ultimate tensile strength after decellularization (p > 0.05). However, there was an increased extensibility when the tissue strips were cut parallel to the visualized collagen bundles (p = 0.005). No indication of contact or extract cytotoxicity was found when using human dermal fibroblasts and A549 cells. In summary, successful decellularization of the human pericardium was achieved producing a biocompatible matrix that retained the major structural components and strength of the native tissue.

Combined severe pectus excavatum correction and aortic root replacement in Marfan's syndrome.

A 23-year-old man with Marfan's syndrome was admitted for repair of annulo-aortic ectasia and severe pectus excavatum. A submammary skin incision approach followed by bilateral subperichondrial resection of abnormal costal cartilages was performed. The left intercostal muscles and perichondrial sheaths were divided 2 inches lateral to the sternum in a parasternal fashion to place the retractor. The aortic root was replaced with a 23-mm St. Jude's composite graft (St. Jude Medical, Inc, St. Paul, MN). Chest wall reconstruction was completed with a high sternal osteotomy and support of the sternum was made with Gortex strips (W.L. Gore & Associates, Inc, Flagstaff, AZ). The patient made an uneventful recovery.

In-vitro assessment of the functional performance of the decellularized intact porcine aortic root.

BACKGROUND AND AIMS OF THE STUDY: Tissue-engineered heart valves offer the potential to deliver a heart valve replacement that will develop with the young patient. The present authors' approach is to use decellularized aortic heart valves reseeded in vitro or in vivo with the patient's own cells. It has been reported that treatment of porcine aortic valve leaflets with 0.1% (w/v) sodium dodecyl sulfate (SDS) in hypotonic buffer produced complete leaflet acellularity without affecting tissue strength. The present study aim was to investigate the effect of an additional treatment incorporating 1.25% (w/v) trypsin and 0.1% (w/v) SDS on the biomechanics and hydrodynamics of the aortic root. This treatment has been shown to produce decellularization of both the aorta and valve leaflets. METHODS: Fresh porcine aortic roots were treated to reduce the thickness of their aortic wall, and incubated in hypotonic buffer for 24 h. The leaflets were masked with agarose gel, and the aorta was treated with 1.25% (w/v) trypsin for 4 h at 37 degrees C. The trypsin and agarose were removed and the roots incubated with 0.1% (w/v) SDS in hypotonic buffer for 24 h. Fresh and treated circumferential and axial aortic specimens were subjected to uniaxial tensile testing, while intact porcine aortic roots were subjected to dilation and pulsatile flow testing. RESULTS: Decellularized aortic wall specimens demonstrated significantly decreased elastin phase slope and increased transition strain compared to the fresh control. However, the treatment did not impair tissue strength. Decellularized intact roots presented complete leaflet competence under systemic pressures, increased dilation and effective orifice areas, reduced pressure gradients, physiological leaflet kinematics and reduced leaflet deformation. CONCLUSION: The excellent leaflet kinematics and hydrodynamic performance of the decellularized roots, coupled with the excellent biomechanical characteristics of their aortic wall, form a promising platform for the creation of an acellular valve scaffold with adequate mechanical strength and functionality to accommodate dynamic cell repopulation in vitro or in vivo. This approach can be used for both allogeneic and xenogeneic tissue matrices.

Biocompatibility and recellularization potential of an acellular porcine heart valve matrix.

BACKGROUND AND AIM OF THE STUDY: Tissue-engineered heart valves have the potential to overcome the limitations of present heart valve replacements. The study aim was to investigate the biocompatibility and recellularization potential of an acellular porcine valve matrix. METHODS: Acellular porcine valve matrix contact and extract cytotoxicity was tested against porcine fibroblasts and smooth muscle cells (SMC). Porcine cells were incubated with decellularized aortic valve leaflets and aortic wall, and then assessed for changes in morphology and contact inhibition of growth. Soluble tissue extracts were prepared from decellularized leaflets and aortic wall, and assessed for their effect on the viability of cultured porcine cells. Acellular leaflets were seeded with either fibroblasts or SMC at 1 x 10(3) to 1 x 10(6) cells/cm2 for 24 h, or 5 x 10(4) cells/cm2 for 1-4 weeks. Cell attachment onto, and migration into, the acellular matrix was assessed by scanning electron microscopy and histology. RESULTS: No contact inhibition of growth, or changes in fibroblast or SMC morphology, were observed following contact with the acellular valve matrix. No soluble extract cytotoxicity was found. Intermediate cell-seeding densities (2.5 x 10(4) to 7.5 x 10(4) cells/cm2) of both cell types produced confluent cell attachment; at the lowest concentration (1 x 10(3) cells/cm2) cell attachment was sparse, and at the highest (1 x 10(6) cells/cm2) it was multilayered. The SMC migrated throughout the leaflet matrix over four weeks, but there was no fibroblast migration into the matrix. CONCLUSION: The absence of contact and extract cytotoxicity indicated that the acellular valve matrix was biocompatible in vitro. The failure of porcine fibroblasts to grow on, or infiltrate into, the matrix suggested that the SMC may be the preferred cell type for future leaflet recellularization studies in the development of a tissue-engineered heart valve replacement.

Pacing activity, patient and lead survival over 20 years of permanent epicardial pacing in children.

BACKGROUND: We report on pediatric epicardial pacing activity, patient and lead survival for more than two decades in a single center. METHODS: The data cover 96 pacing leads implanted in 59 patients. Median age at implantation was 1.9 years (1 day to 18.2 years). Forty-four percent had structural cardiac disease. Most frequent indications for pacing were postoperative (42%) and congenital complete heart block (42%). RESULTS: Median activity was 3 pacing leads per year; 326 patient pacing years were observed (median 11.9 years; range, 1.1 to 22 years). Death due to pacemaker failure occurred in a single patient. Lead failure occurred in 33 of 96 leads (median of 28 months postimplantation) with lead fracture the commonest cause (47%). Risk factors for lead failure were decade of implant and nonsteroid eluting leads. Acute implant energy thresholds were significantly lower for steroid than nonsteroid eluting leads but did not predict subsequent lead failure. CONCLUSIONS: The epicardial approach has offered an effective solution to pacing problems in the pediatric age range. Lead survival has improved with more than 75% of modern steroid eluting leads surviving to 5 years.

Quantification of pulmonary autograft characteristics using magnetic resonance imaging.

BACKGROUND AND AIM OF THE STUDY: The diameters and distensibility of the native pulmonary root and their effect on pulmonary autograft performance were examined pre- and postoperatively using cardiac ultrasound and magnetic resonance imaging (MRI). METHODS: Eight patients undergoing the Ross procedure were prospectively involved. The diameters of the native aortic, native pulmonary and autograft roots were measured at the level of the annulus, sinus, sinotubular junction and in the main root using MRI through the cardiac cycle. Ultrasound was also used to estimate the degree of regurgitation, both pre- and postoperatively. RESULTS: The pulmonary root implanted into the systemic circulation increased in size but decreased in distensibility significantly at the sinus, sinotubular junction and main root, but not at the annulus. Postoperatively, the pulmonary autograft annulus showed a similar size and distensibility to that of the native aortic annulus. A wide range of aortic annular sizes (22-30 mm) produced clinically competent valves postoperatively. All undersized pulmonary valves showed only trivial regurgitation postoperatively. Although there was no clear correlation between root shape and valve insufficiency, two patients with mild and moderate autograft regurgitation both had divergent pulmonary roots (diameter at sinotubular junction > annulus diameter) preoperatively. CONCLUSION: The pulmonary autograft using the root replacement technique functioned well in all but one case. The shape of the native pulmonary root may be a determinant of early autograft regurgitation, as well as the diameter and the size mismatch between the great arteries.

Effect of two different bypass techniques on the serum troponin-T levels in newborns and children: does pH-Stat provide better protection?

BACKGROUND: Cardiac troponin-T is a sensitive marker of myocardial damage. In a prospective study, the effect of 2 different pH strategies during cardiopulmonary bypass on ischemic myocardial injury and clinical outcome was measured in a pediatric population. METHODS AND RESULTS: One hundred one patients (31 neonates 13.2+/-8.3 days and 70 children 34.5+/-44.1 months of age) undergoing open-heart surgery were selected to either alpha-stat (n=51) or pH-stat (n=50) acid-based management protocol. Serum troponin-T levels were measured before and 30 minutes after bypass and then 4 and 24 hours postoperatively. Surgical procedure, bypass details, inotropic support requirement, and postoperative recovery were recorded. Baseline troponin-T level was higher in neonates than in children (0.18+/-0.22 versus 0.04+/-0.05 microg/L, P=0.02). Also, a higher baseline level was found in patients with pulmonary hypertension (0.13+/-0.21 versus 0.04+/-0.05 microg/L, P=0.04). Cyanotic children showed a higher peak troponin-T level (3.76+/-3.11 versus 1.67+/-1.33 microg/L, P=0.04). Peak troponin levels showed a correlation with the length of circulatory arrest and aortic cross-clamp time. Postoperative levels remained high at 24 hours in patients requiring inotropic support. Peak troponin-T levels were significantly lower in the pH-stat group in patients with pulmonary hypertension (P=0.03) and in cases where circulatory arrest (P=0.01) or inotropic support (P=0.01) was necessary during operation than in those with alpha-stat technique. Postoperative ventilation time and length of intensive care unit stay were also significantly longer with alpha-stat than with pH-stat technique (P=0.005 and P=0.006, respectively). CONCLUSIONS: Cardiac troponin-T sensitively reflects myocardial damage in children. Our results suggest that pH-stat acid-based management protocol may provide better protection against ischemic myocardial damage than alpha-stat technique.

The pulmonary bioprosthetic heart valve: its unsuitability for use as an aortic valve replacement.

BACKGROUND AND AIM OF THE STUDY: The porcine pulmonary bioprosthetic heart valve represents an alternative means of aortic valve replacement (AVR), though knowledge of its biomechanical function and characteristics is limited. The valve has potential advantages over the aortic bioprosthesis; notably, it lacks the muscular shelf of the right coronary cusp of the latter bioprosthesis. The study aim was to investigate the suitability of the porcine pulmonary bioprosthetic valve for AVR. METHODS: Porcine pulmonary and aortic roots were zero pressure-fixed with 0.5% buffered glutaraldehyde, characterized, and compared with fresh porcine pulmonary and aortic roots. The in-vitro analysis included assessment of mechanical properties, hydrodynamic function, geometry of the pulmonary root, and durability. RESULTS: The fixed pulmonary roots and fresh aortic roots were similar in certain aspects of mechanical response, notably leaflets in the radial direction and the root wall. The fixed pulmonary root was slightly more compliant than the fixed aortic root, and this led to an improvement in forward flow hydrodynamic function. The reverse flow hydrodynamic function of the pulmonary roots was poor; fresh pulmonary roots exhibited a trivial closed valve regurgitant volume. On fixation, this characteristic was aggravated, leading to a gross closed valve regurgitant volume in 50% of all fixed pulmonary roots. The cause of leakage was identified as a prolapsed anterior leaflet. Durability of the fixed pulmonary root was also inferior to that of the fixed aortic root; three fixed pulmonary roots subjected to accelerated fatigue testing showed signs of leaflet macroscopic damage. CONCLUSION: Overall, the performance of the porcine pulmonary bioprosthesis was far inferior to that of the currently used porcine aortic bioprosthesis. Hence, the porcine pulmonary bioprosthetic valve was deemed unsuitable for AVR.

Tissue engineering of cardiac valve prostheses I: development and histological characterization of an acellular porcine scaffold.

BACKGROUND AND AIMS OF THE STUDY: Several deficiencies in current heart valve prostheses make them problematic for use in younger patients. Tissue valve substitutes are non-viable with a life expectancy of only 10-15 years, while mechanical valves require long-term anti-coagulation therapy. A solution to these problems would be to develop a tissue-engineered heart valve containing autologous cells, enabling the valve to maintain its biochemical and mechanical properties, yet grow with the patient. The study aim was to optimize a protocol to produce a porcine acellular matrix scaffold for use in developing a tissue-engineered heart valve. METHODS: Fresh porcine aortic valve leaflets were treated with Triton X-100, sodium dodecyl sulfate (SDS), sodium deoxycholate, MEGA 10, TnBP, CHAPS, and Tween 20, over a range of concentrations, in the presence of protease inhibitors for up to 72 h. Histological analysis was used to detect the major structural proteins of the heart valve, collagen I, elastin and glycosaminoglycans. RESULTS: After 72 h, most protocols resulted in the retention of large numbers of whole cells and cell fragments. Only SDS (0.03-1%) or sodium deoxycholate (0.5-2%) resulted in total decellularization at 24 h. Histological analysis of acellular matrices showed that the major structural proteins had been retained and appeared to be intact. CONCLUSION: Protocols utilizing SDS or sodium deoxycholate were successful for leaflet decellularization, and histological analysis showed that the major structural components of the valve matrix had been maintained. These methods are being developed further with a view to reseeding with autologous cells to produce tissue-engineered solutions for clinical implantation.

Tissue engineering of cardiac valve prostheses II: biomechanical characterization of decellularized porcine aortic heart valves.

BACKGROUND AND AIMS OF THE STUDY: For both young patients with congenital heart disease and young, growing adults there is a need for replacement heart valves that will develop with the patient. Tissue-engineered heart valves coupled with in-vitro recellularization have this potential. One approach is to use acellular tissue matrices, but the decellularization treatment must not affect the biomechanical integrity of the valvular matrix. This study investigated the effect of 0.03% (w/v) and 0.1% (w/v) sodium dodecyl sulfate (SDS) on the mechanical integrity of porcine aortic valve leaflets. METHODS: Left coronary porcine leaflets were treated with SDS (0.03% or 0.1%, w/v) in hypotonic or isotonic buffer and buffer alone. SDS in hypotonic buffer produced accellularity. Circumferential and radial specimens of treated leaflets were subjected to uniaxial tensile testing, and the effect of the buffer on leaflet morphology was assessed. Whole porcine aortic roots were also treated with 0.1% (w/v) SDS and subjected to function testing. RESULTS: SDS treatment significantly increased extensibility of the leaflet specimens, which was greater in the circumferential than radial direction. This was seen as a significantly decreased slope of both the elastic and collagen phases of the stress-strain behavior. The ultimate tensile strength and transition stress were not affected significantly; nor was there any significant difference between hypotonic buffer and hypotonic buffer + SDS treatments. Study of the leaflet morphology suggested that the increased extensibility was due to shrinkage as well as to increased hydration of the treated leaflets caused by the hypotonic buffer. CONCLUSION: SDS treatment produced a more extensible tissue with equal strength compared with the fresh aortic valve. Functionality experiments with SDS-treated whole aortic roots showed complete valve leaflet competence under physiological pressures (120 mmHg) as well as physiological leaflet kinematics.

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.

The quantification of pulmonary valve haemodynamics using MRI.

The optimum slice location within the pulmonary root to quantify pulmonary valve haemodynamics was examined using magnetic resonance (MR) phase velocity mapping. MRI was carried out on 15 patients with congenital aortic valve disease. Although the patients had aortic valve disease, all measurements were made on the pulmonary valve. Systolic (Q(SYS)) and diastolic (Q(DIAS)) blood flow volume and cardiac index (CI) were determined at four pulmonary artery locations. The change in diastolic flow volume relative to slice 1, closest to the pulmonary valve, was also calculated. For a change in axial position of 1.5 cm, i.e. from 0.5 to 2 cm from the annulus, there was a change in diastolic flow volume of 4.4 ml. There was a significant increase in the mean diastolic flow from 3.4 to 7.7 ml (p = 0.01 between slice positions 0.5 and 2 cm. However, there was no significant change in CI, 3.4-3.7 l/min/m2 (p = 0.14) over the same distance. We believe that two factors are responsible for these results. The first is that of compliance, whose effects can be minimized by placing the MR slice close to the valve, however, this will not account for the second factor, being that of valve motion, and hence diastolic pulmonary valve flow or regurgitant volume will be underestimated. The degree of underestimation may only be important at mild and moderate levels of regurgitation or if changes in regurgitation are to be temporally measured.