Serguei Melnitchouk

Human umbilical cord cells: a new cell source for cardiovascular tissue engineering

BACKGROUND Tissue engineering of viable, autologous cardiovascular constructs with the potential to grow, repair, and remodel represents a promising new concept for cardiac surgery, especially for pediatric patients. Currently, vascular myofibroblast cells (VC) represent an established cell source for cardiovascular tissue engineering. Cell isolation requires the invasive harvesting of venous or arterial vessel segments before scaffold seeding, a technique that may not be preferable, particularly in pediatric patients. In this study, we investigated the feasibility of using umbilical cord cells (UCC) as an alternative autologous cell source for cardiovascular tissue engineering. METHODS Human UCC were isolated from umbilical cord segments and expanded in culture. The cells were sequentially seeded on bioabsorbable copolymer patches (n = 5) and grown in vitro in laminar flow for 14 days. The UCC were characterized by flow cytometry (FACS), histology, immunohistochemistry, and proliferation assays and were compared to saphenous vein-derived VC. Morphologic analysis of the UCC-seeded copolymer patches included histology and both transmission and scanning electron microscopy. Characterization of the extracellular matrix was performed by immunohistochemistry and quantitative extracellular matrix protein assays. The tissue-engineered UCC patches were biomechanically evaluated using uniaxial stress testing and were compared to native tissue. RESULTS We found that isolated UCC show a fibroblast-like morphology and superior cell growth compared to VC. Phenotype analysis revealed positive signals for alpha-smooth muscle actin (ASMA), desmin, and vimentin. Histology and immunohistochemistry of seeded polymers showed layered tissue formation containing collagen I, III, and glycoaminoglycans. Transmission electron microscopy showed viable myofibroblasts and the deposition of collagen fibrils. A confluent tissue surface was observed during scanning electron microscopy. Glycoaminoglycan content did not reach values of native tissue, whereas cell content was increased. The biomechanical properties of the tissue-engineered constructs approached native tissue values. CONCLUSIONS Tissue engineering of cardiovascular constructs using UCC is feasible in an in vitro environment. The UCC demonstrated excellent growth properties and tissue formation with mechanical properties approaching native tissue. It appears that UCC represent a promising alternative autologous cell source for cardiovascular tissue engineering, offering the additional benefits of using juvenile cells and avoiding the invasive harvesting of intact vascular structures.

A new source for cardiovascular tissue engineering: human bone marrow stromal cells

OBJECTIVE Vascular-derived cells represent an established cell source for tissue engineering of cardiovascular constructs. Previously, cell isolation was performed by harvesting of vascular structures prior to scaffold seeding. Marrow stromal cells (MSC) demonstrate the ability to differentiate into multiple mesenchymal cell lineages and would offer an alternative cell source for tissue engineering involving a less invasive harvesting technique. We studied the feasibility of using MSC as an alternative cell source for cardiovascular tissue engineering. METHODS Human MSC were isolated from bone marrow and expanded in culture. Subsequently MSC were seeded on bioabsorbable polymers and grown in vitro. Cultivated cells and seeded polymers were studied for cell characterization and tissue formation including extracellular matrix production. Applied methods comprised flow cytometry, histology, immunohistochemistry, transmission (TEM) and scanning electron microscopy (SEM), and biochemical assays. RESULTS Isolated MSC demonstrated fibroblast-like morphology. Phenotype analysis revealed positive signals for alpha-smooth muscle actin and vimentin. Histology and SEM of seeded polymers showed layered tissue formation. TEM demonstrated formation of extracellular matrix with deposition of collagen fibrils. Matrix protein analysis showed production of collagen I and III. In comparison to vascular-derived cell constructs quantitative analysis demonstrated comparable amounts of extracellular matrix proteins in the tissue engineered constructs. CONCLUSIONS Isolated MSC demonstrated myofibroblast-like characteristics. Tissue formation on bioabsorbable scaffolds was feasible with extracellular matrix production comparable to vascular-cell derived tissue engineered constructs. It appears that MSC represent a promising cell source for cardiovascular tissue engineering.

A new approach to completely autologous cardiovascular tissue in humans.

In cardiovascular tissue engineering, synthetic or biologic scaffolds serve as templates for tissue development. Currently used scaffolds showing toxic degradation and immunogenic reactions are still far from ideal. We present a new alternative method to develop completely autologous human tissue without using any scaffold materials. Human vascular cells of arterial and venous origin were cultured to form cell sheets over a 4 week period under standard conditions. Thereafter, cell sheets of each origin were folded and cultured in a newly developed frame device for an additional 4 weeks. Controls remained under standard culture conditions. Tissue development was evaluated by morphology and biochemical assays. The formation of multilayered cell sheets and production of extracellular matrix were observed in all groups. Folded and framed neo-tissue showed a solid structure, with increased matrix formation and tissue organization when compared with the control groups. DNA content indicated significantly lower cell proliferation, and hydroxyproline assay indicated significantly higher collagen content in the framed cell sheets. We present a new approach to the engineering of cardiovascular tissue without the use of biodegradable scaffold material. Three-dimensional, completely autologous human tissue may be developed on the basis of this structure, thus avoiding scaffold induced toxic degradation or inflammatory reaction.

Are homografts superior to conventional prosthetic valves in the setting of infective endocarditis involving the aortic valve

BACKGROUND Surgical dogma suggests that homografts should be used preferentially, compared with conventional xenograft or mechanical prostheses, in the setting of infective endocarditis (IE), because they have greater resistance to infection. However, comparative data that support this notion are limited. METHODS From the prospective databases of 2 tertiary academic centers, we identified 304 consecutive adult patients (age ≥17 years) who underwent surgery for active IE involving the aortic valve (AV), in the period 2002 to 2014. Short- and long-term outcomes were evaluated using propensity scores and inverse-probability weighting to adjust for selection bias. RESULTS Homografts, and xenograft and mechanical prostheses, were used in 86 (28.3%), 139 (45.7%), and 79 (26.0%) patients, respectively. Homografts were more often used in the setting of prosthetic valve endocarditis (58.1% vs 28.8%, P = .002) and methicillin-resistant Staphylococcus (25.6% vs 12.1%, P = .002), compared with conventional prostheses. Early mortality occurred in 17 (19.8%) in the homograft group, and 20 (9.2%) in the conventional group (P = .019). During follow-up (median: 29.4 months; interquartile-range: 4.7-72.6 months), 60 (19.7%) patients died, and 23 (7.7%) experienced reinfection, with no significant differences in survival (P = .23) or freedom from reinfection rates (P = .65) according to the types of prostheses implanted. After adjustments for baseline characteristics, using propensity-score analyses, use of a homograft did not significantly affect early death (odds ratio 1.61; 95% confidence interval [CI], 0.73-3.40, P = .23), overall death (hazard ratio 1.10; 95% CI, 0.62-1.94, P = .75), or reinfection (hazard ratio 1.04; 95% CI, 0.49-2.18, P = .93). CONCLUSIONS No significant benefit to use of homografts was demonstrable with regard to resistance to reinfection in the setting of IE. The choice among prosthetic options should be based on technical and patient-specific factors. Lack of availability of homografts should not impede appropriate surgical intervention.

Impact of Left Ventricular to Mitral Valve Ring Mismatch on Recurrent Ischemic Mitral Regurgitation After Ring Annuloplasty.

Background: In ischemic mitral regurgitation (IMR), ring annuloplasty is associated with a significant rate of recurrent MR. Ring size is based on intertrigonal distance without consideration of left ventricular (LV) size. However, LV size is an important determinant of mitral valve (MV) leaflet tethering before and after repair. We aimed to determine whether LV-MV ring mismatch (mismatch of LV size relative to ring size) is associated with recurrent MR in patients with IMR after restrictive ring annuloplasty. Methods: Patients with moderate or severe IMR from the 2 Cardiothoracic Surgical Trials Network IMR trials who received MV repair were examined at 1 year after surgery. Baseline LV size was assessed by LV end-diastolic dimension and LV end-systolic dimension (LVESd). LV-MV ring mismatch was calculated as the ratio of LV to ring size (LV end-diastolic dimension/ring size and LVESd/ring size). Results: At 1 year after ring annuloplasty, 45 of 214 patients with MV repair (21%) had moderate or greater MR. In univariable logistic regression analysis, larger LVESd (P=0.02) and LVESd/ring size (P=0.007) were associated with recurrent MR. In multivariable models adjusted for age, sex, baseline LV ejection fraction, and severe IMR, only LVESd/ring size (odd ratio per 0.5 increase, 2.20; 95% confidence interval, 1.05–4.62; P=0.038) remained significantly associated with 1-year MR recurrence. Conclusions: LV-MV ring size mismatch is associated with increased risk of MR recurrence. This finding may be helpful in guiding choice of ring size to prevent recurrent MR in patients undergoing MV repair and in identifying patients who may benefit from MV repair with additional subvalvular intervention or MV replacement rather than repair alone. Clinical Trial Registration: URL:http://clinicaltrials.gov. Unique identifiers: NCT00806988 and NCT00807040.

Barlow’s mitral valve disease: results of conventional and minimally invasive repair approaches

Barlows valve is a clinically important form of degenerative mitral valve (MV) disease that is characterized by unique clinical, echocardiographic and pathological features. Successful and durable repair of Barlows MV represents a clinical challenge for most cardiac surgeons. An armamentarium of different MV repair techniques may be required, resectional, neochordal or plicational techniques. Although conventional sternotomy remains the mainstay approach for MV surgery in the majority of cardiac surgery centers, minimally invasive surgery (MIS) is becoming increasingly accepted amongst patients, referring physicians and practicing cardiac surgeons. As surgical approaches, instrumentation and operative experience develop, select centers are now performing MIS MV surgery for nearly all MV patients. Although successful Barlows MV repair is more complex than that for most degenerative pathologies, several centers have published relatively large series of MIS MV repair for Barlows disease. In this review article, we highlight and compare the early and long-term results of conventional and minimally invasive approaches to Barlows and bileaflet mitral prolapse disease. Recent studies from various large volume centers around the world have demonstrated equivalent safety and efficacy outcomes of the MIS approach compared to conventional sternotomy surgery. In addition, MIS MV surgery may allow patients to benefit from a cosmetically appealing incision, a faster recovery and a quicker return to normal activities. However, a definite learning curve has been demonstrated for MIS MV surgery. If a patient with Barlows disease or other complex MV pathology desires to undergo MIS MV surgery, referral to a center and/or surgeon with extensive experience in MIS MV surgery is recommended.

Advances in Perfusion Techniques Minimally Invasive Procedures

There is a growing demand from patients and referring physicians for minimally invasive cardiac surgery. Minimally invasive cardiac procedures are technically unique from conventional cardiac procedures and require a thorough understanding of the surgical, anesthetic, and perfusion strategies. Strategies include routine use of augmented venous drainage, alternative arterial and venous cannulation sites, and special cannulas designed for minimally invasive procedures. The following review describes the strategies and safety systems that should be considered when performing minimally invasive cardiac surgery.

Continued expansion of the Heart Team concept

The concept of a multidisciplinary Heart Team approach to treating cardiovascular disease has garnered increasing interest in recent years. This team-based approach has been a cornerstone of practice in other medical fields, such as oncology and solid organ transplantation. Advances in technology and new therapeutic strategies now offer multiple treatment options to patients with complex coronary artery or valvular heart disease, making therapeutic decision-making more challenging. There is a growing literature that use of a Heart Team for management of these complex cardiovascular diseases has demonstrated great merit. While the composition and implementation of Heart Team will vary, this multidisciplinary team-based approach will become the standard of care in cardiovascular medicine in the future.

Aortic valve replacement associated with survival in severe regurgitation and low ejection fraction

Objectives Although guidelines support aortic valve replacement (AVR) in patients with severe aortic regurgitation (AR) and left ventricular ejection fraction (LVEF) <50%, severe left ventricular dysfunction (LVEF <35%) is thought to confer high surgical risk. We sought to determine if a survival benefit exists with AVR compared with medical management in this high-risk, relatively rare population. Methods A large institutional echocardiography database was queried to identify patients with severe AR and LVEF <35%. Manual chart review was performed. Due to small sample size and population heterogeneity, corrected group prognosis method was applied, which calculates the adjusted survival curve for each individual using fitted Cox proportional hazard model. Average survival adjusted for comorbidities and age was then calculated using the weighted average of the individual survival curves. Results Initially, 2 54 614 echocardiograms were considered, representing 1 45 785 unique patients, of which 40 patients met inclusion criteria. Of those, 18 (45.0%) underwent AVR and 22 (55.0%) were managed medically. Absolute mortality was 27.8% in the AVR group and 91.2% in the medical management group. After multivariate adjustment, end-stage renal disease (HR=17.633, p=0.0335) and peripheral arterial disease (HR=6.050, p=0.0180) were associated with higher mortality. AVR was associated with lower mortality (HR=0.143, p=0.0490). Mean follow-up time of the study cohort was 6.58 years, and mean survival for patients undergoing AVR was 6.31 years. Conclusions Even after adjustment for clinical characteristics and patient age, AVR is associated with higher survival for patients with low LVEF and severe AR. Although treatment selection bias cannot be completely eliminated by this analysis, these results provide some evidence that surgery may be associated with prolonged survival in this high-risk patient group.

Minimally Invasive Mitral Valve Surgery via Mini-Thoracotomy: Current Update

Opinion statementIn recent years, minimally invasive mitral valve surgery (MIMVS) has established itself as an alternative and increasingly used option for patients with mitral valve (MV) pathology. MIMVS is associated with a very low perioperative morbidity and mortality rate in appropriately selected patients, comparable to a full sternotomy approach. Besides superior cosmetic results, patients after MIMVS enjoy shorter recovery times and earlier returns to full activity. A number of approaches are branded as minimally invasive, but the most widely used one entails peripheral cardiopulmonary bypass and a small right anterolateral mini-thoracotomy. The operative technique and outcomes of this approach are summarized in the current update.