Improved long-term durability of allogeneic heart valves in the orthotopic sheep model.

OBJECTIVES: Frozen cryopreservation (FC) with the vapour phase of liquid nitrogen storage (-135°C) is a standard biobank technique to preserve allogeneic heart valves to enable a preferable allograft valve replacement in clinical settings. However, their long-term function is limited by immune responses, inflammation and structural degeneration. Ice-free cryopreserved (IFC) valves with warmer storage possibilities at -80°C showed better matrix preservation and decreased immunological response in preliminary short-term in vivo studies. Our study aimed to assess the prolonged performance of IFC allografts in an orthotopic pulmonary sheep model. METHODS: FC (n = 6) and IFC (n = 6) allografts were transplanted into juvenile Merino sheep. After 12 months of implantation, functionality testing via 2-dimensional echocardiography and histological analyses was performed. In addition, multiphoton autofluorescence imaging and Raman microspectroscopy analysis were applied to qualitatively and quantitatively assess the matrix integrity of the leaflets. RESULTS: Six animals from the FC group and 5 animals from the IFC group were included in the analysis. Histological explant analysis showed early inflammation in the FC valves, whereas sustainable, fully functional, devitalized acellular IFC grafts were obtained. IFC valves showed excellent haemodynamic data with fewer gradients, no pulmonary regurgitation, no calcification and acellularity. Structural remodelling of the leaflet matrix structure was only detected in FC-treated tissue, whereas IFC valves maintained matrix integrity comparable to that of native controls. The collagen crimp period and amplitude and elastin structure were significantly different in the FC valve cusps compared to IFC and native cusps. Collagen fibres in the FC valves were less aligned and straightened. CONCLUSIONS: IFC heart valves with good haemodynamic function, reduced immunogenicity and preserved matrix structures have the potential to overcome the known limitations of the clinically applied FC valve.

Allograft Heart Valves: Current Aspects and Future Applications.

Human heart valve allografts continue to represent almost perfect substitutes for heart valves. They have optimal hemodynamic characteristics and are highly resistant to infections. The first clinical use of allograft heart valves was as homovitals being transplanted after antibiotic incubation without any preservation. Since 1968, relatively standardized frozen cryopreservation (SFC) has been employed, including storage in vapor-phase liquid nitrogen. Disadvantages, particularly in pediatric patients, are limited availability due to organ scarcity, inability to grow, degeneration, immune response, and long-term failure. However, in contrast to alternative prosthetic or bioprosthetic heart valve replacements, they represent the best pediatric and juvenile replacement options for the pulmonary valve. Application of multiphoton imaging analysis for three-dimensional visualization of elastin and collagen by induction of autofluorescence without chemical fixation, embedding, and staining has revealed partial destruction of elastic and collagenous matrix in SFC valves. As the overall amount of collagen and elastin remains unchanged, the observed destruction is attributed to freezing-induced extracellular matrix damages due to ice crystal formation during SFC. The objective of this review is an assessment of current allograft preservation methods and the potential of novel preservation techniques to avoid ice formation with accompanied better long-term function.

Mitral valve surgery in 6 patients after failed MitraClip therapy.

The MitraClip percutaneous mitral valve repair system, developed as an option for percutaneous mitral repair, was clinically introduced in 2007. From 2010 through 2012, 6 of our patients underwent mitral valve surgery after MitraClip failure. Their mean age was 75 ± 7.7 years (range, 62-87 yr). Three had undergone cardiac surgery previously. In 5 of the 6 patients, mitral regurgitation recurred after initially successful MitraClip deployment and was the indication for surgery. The mean interval between MitraClip implantation and surgery was 106 ± 86 days (range, 0-238 d). Mitral valve repair was feasible in 3 patients; the others underwent valve replacement. All the patients underwent additional cardiac procedures, because the MitraClip worsened existing conditions. Echocardiograms revealed sufficient valvular repairs. Two patients died during hospitalization, one of cerebral infarction and the other of bowel ischemia. Mitral valve repair after failed MitraClip therapy can be complex and a surgical challenge. Careful consideration should be given to appropriate patient selection for MitraClip therapy, because the MitraClip can cause existing pathologic valvular conditions to deteriorate substantially. The interval between MitraClip failure and corrective surgery should be as short as possible. The primary indication is an issue of ongoing discussion.

Bridge to recovery or permanent system implantation: an eight-year single-center experience in transvenous semipermanent pacing.

BACKGROUND: To compare the risks, implications, and outcomes of transvenous semipermanent pacing as a bridge to permanent system implantation or recovery. METHODS: We investigated semipermanent transvenous pacing systems consisting of one (n = 57%) or two (n = 3%) bipolar active-fixation pacing leads and an attached epicutaneous pulse generator implanted from 2000 to 2009. The study population comprised 60 patients aged 72.9 ± 10.5 years (44 [73.3%] male). Forty-two (70%) were enrolled for complete system explantation for cardiac-implanted electronic devices associated infection. Eighteen (30%) required temporary pacing in the context of a variety of mostly severe cardiac and noncardiac conditions. The semipermanent pacing systems were removed after implantation of permanent systems or recovery of a noncompromising heart rhythm, respectively. RESULTS: Transvenous semipermanent lead implantation was successful in 59 (98.3%) patients. Major and minor intraoperative complications occurred in one case (1.7%) each. The semipermanent systems were left in situ for a mean period of 14.6 ± 8.1 days). They served as a bridge to permanent system implantation in 68.3% (n = 41) and as a bridge to recovery of a noncompromising heart rhythm in 11.7% (n = 7). Four patients (8.3%) died with the semipermanent pacing system in situ, and seven (11.7%) were transferred to external hospitals with semipermanent pacing systems. CONCLUSIONS: Transvenous semipermanent pacing with bipolar active-fixation leads and epicutaneous pulse generators provide an important option for prolonged temporary pacing as a bridge to permanent system implantation or recovery.

Numerical simulation techniques to study the structural response of the human chest following median sternotomy.

BACKGROUND: The optimal closure technique of median sternotomy remains controversial. The objective of this study was to analyze the structural response of the separated sternum using computer-based numerical discretization techniques, such as finite element methods. METHODS: Thoracic computer tomographic scans (2.5-mm slices) were segmented, analyzed by image processing techniques, and transferred into a three-dimensional finite element model. In a first approach a linear elastic material model was used; neglecting nonlinear and damage effects of the bones. The influence of muscles and tendons was disregarded. Nonlinear contact conditions were applied between the two sternal parts and between fixation wires and sternum. The structural response of this model was investigated under normal breathing and asymmetric leaning on one side of the chest. Displacement and stress response of the segmented sternum were compared regarding two different closure techniques (single loop, figure-of-eight). RESULTS: The obtained results revealed that for the normal breathing load case the single loop technique is capable of clamping the sternum sufficiently, assuming that the wires are prestressed. For asymmetric loading conditions, such as leaning on one side of the chest, the figure-of-eight loop can substantially reduce the relative longitudinal displacement between the two parts compared with the single loop. CONCLUSIONS: The application of numerical simulation techniques using complex computer models enabled the determination of structural behavior of the chest regarding the influence of different closure techniques. They allowed easy and fast modifications and therefore, in contrast to a real physical model, in-depth parameter studies.