Large Animal Translational Validation of 3 Mitral Valve Repair Operations for Mitral Regurgitation Using a Mitral Valve Prolapse Model: A Comprehensive In Vivo Biomechanical Engineering Analysis

BACKGROUND

Various mitral repair techniques have been described. Though these repair techniques can be highly effective when performed correctly in suitable patients, limited quantitative biomechanical data are available. Validation and thorough biomechanical evaluation of these repair techniques from translational large animal in vivo studies in a standardized, translatable fashion are lacking. We sought to evaluate and validate biomechanical differences among different mitral repair techniques and further optimize repair operations using a large animal mitral valve prolapse model.

METHODS

Male Dorset sheep (n=20) had P2 chordae severed to create the mitral valve prolapse model. Fiber Bragg grating force sensors were implanted to measure chordal forces. Ten sheep underwent 3 randomized, paired mitral valve repair operations: neochord repair, nonresectional leaflet remodeling, and triangular resection. The other 10 sheep underwent neochord repair with 2, 4, and 6 neochordae. Data were collected at baseline, mitral valve prolapse, and after each repair.

RESULTS

All mitral repair techniques successfully eliminated regurgitation. Compared with mitral valve prolapse (0.54±0.18 N), repair using neochord (0.37±0.20 N; P=0.02) and remodeling techniques (0.30±0.15 N; P=0.001) reduced secondary chordae peak force. Neochord repair further decreased primary chordae peak force (0.21±0.14 N) to baseline levels (0.20±0.17 N; P=0.83), and was associated with lower primary chordae peak force compared with the remodeling (0.34±0.18 N; P=0.02) and triangular resectional techniques (0.36±0.27 N; P=0.03). Specifically, repair using 2 neochordae resulted in higher peak primary chordal forces (0.28±0.21 N) compared with those using 4 (0.22±0.16 N; P=0.02) or 6 neochordae (0.19±0.16 N; P=0.002). No difference in peak primary chordal forces was observed between 4 and 6 neochordae (P=0.05). Peak forces on the neochordae were the lowest using 6 neochordae (0.09±0.11 N) compared with those of 4 neochordae (0.15±0.14 N; P=0.01) and 2 neochordae (0.29±0.18 N; P=0.001).

CONCLUSIONS

Significant biomechanical differences were observed underlying different mitral repair techniques in a translational large animal model. Neochord repair was associated with the lowest primary chordae peak force compared to the remodeling and triangular resectional techniques. Additionally, neochord repair using at least 4 neochordae was associated with lower chordal forces on the primary chordae and the neochordae. This study provided key insights about mitral valve repair optimization and may further improve repair durability.

Biomechanics and clinical outcomes of various conduit configurations in valve sparing aortic root replacement

Background

Several conduit configurations, such as straight graft (SG), Valsalva graft (VG), anticommissural plication (ACP), and the Stanford modification (SMOD) technique, have been described for the valve-sparing aortic root replacement (VSARR) procedure. Prior ex vivo studies have evaluated the impact of conduit configurations on root biomechanics, but the mock coronary artery circuits used could not replicate the physical properties of native coronary arteries. Moreover, the individual leaflet's biomechanics, including the fluttering phenomenon, were unclear.

Methods

Porcine aortic roots with coronary arteries were explanted (n=5) and underwent VSARR using SG, VG, ACP, and SMOD for evaluation in an ex vivo left heart flow loop simulator. Additionally, 762 patients who underwent VSARR from 1993 through 2022 at our center were retrospectively reviewed. Analysis of variance was performed to evaluate differences between different conduit configurations, with post hoc Tukey's correction for pairwise testing.

Results

SG demonstrated lower rapid leaflet opening velocity compared with VG (P=0.001) and SMOD (P=0.045) in the left coronary cusp (LCC), lower rapid leaflet closing velocity compared with VG (P=0.04) in the right coronary cusp (RCC), and lower relative opening force compared with ACP (P=0.04) in the RCC. The flutter frequency was lower in baseline compared with VG (P=0.02) and in VG compared with ACP (P=0.03) in the LCC. Left coronary artery mean flow was higher in SG compared with SMOD (P=0.02) and ACP (P=0.05). Clinically, operations using SG compared with sinus-containing graft was associated with shorter aortic cross-clamp and cardiopulmonary bypass time (P<0.001, <0.001).

Conclusions

SG demonstrated hemodynamics and biomechanics most closely recapitulating those from the native root with significantly shorter intraoperative times compared with repair using sinus-containing graft. Future in vivo validation studies as well as correlation with comprehensive, comparative clinical study outcomes may provide additional invaluable insights regarding strategies to further enhance repair durability.

Outcomes of Heart Transplantation Using a Temperature-controlled Hypothermic Storage System

BACKGROUND

The SherpaPak Cardiac Transport System is a novel technology that provides stable, optimal hypothermic control during organ transport. The objectives of this study were to describe our experience using the SherpaPak system and to compare outcomes after heart transplantation after using SherpaPak versus the conventional static cold storage method (non-SherpaPak).

METHODS

From 2018 to June 2021, 62 SherpaPak and 186 non-SherpaPak patients underwent primary heart transplantation at Stanford University with follow-up through May 2022. The primary end point was all-cause mortality, and secondary end points were postoperative complications. Optimal variable ratio matching, cox proportional hazards regression model, and Kaplan-Meier survival analyses were performed.

RESULTS

Before matching, the SherpaPak versus non-SherpaPak patients were older and received organs with significantly longer total allograft ischemic time. After matching, SherpaPak patients required fewer units of blood product for perioperative transfusion compared with non-SherpaPak patients but otherwise had similar postoperative outcomes such as hospital length of stay, primary graft dysfunction, inotrope score, mechanical circulatory support use, cerebral vascular accident, myocardial infarction, respiratory failure, new renal failure requiring dialysis, postoperative bleeding or tamponade requiring reoperation, infection, and survival.

CONCLUSIONS

In conclusion, this is one of the first retrospective comparison studies that evaluated the outcomes of heart transplantation using organs preserved and transported via the SherpaPak system. Given the excellent outcomes, despite prolonged total allograft ischemic time, it may be reasonable to adopt the SherpaPak system to accept organs from a remote location to further expand the donor pool.

Three-Dimensional Bioprinting with Alginate by Freeform Reversible Embedding of Suspended Hydrogels with Tunable Physical Properties and Cell Proliferation

Extrusion-based three-dimensional (3D) bioprinting is an emerging technology that allows for rapid bio-fabrication of scaffolds with live cells. Alginate is a soft biomaterial that has been studied extensively as a bio-ink to support cell growth in 3D constructs. However, native alginate is a bio-inert material that requires modifications to allow for cell adhesion and cell growth. Cells grown in modified alginates with the RGD (arginine-glycine-aspartate) motif, a naturally existing tripeptide sequence that is crucial to cell adhesion and proliferation, demonstrate enhanced cell adhesion, spreading, and differentiation. Recently, the bioprinting technique using freeform reversible embedding of suspended hydrogels (FRESH) has revolutionized 3D bioprinting, enabling the use of soft bio-inks that would otherwise collapse in air. However, the printability of RGD-modified alginates using the FRESH technique has not been evaluated. The associated physical properties and bioactivity of 3D bio-printed alginates after RGD modification remains unclear. In this study, we characterized the physical properties, printability, and cellular proliferation of native and RGD-modified alginate after extrusion-based 3D bioprinting in FRESH. We demonstrated tunable physical properties of native and RGD-modified alginates after FRESH 3D bioprinting. Sodium alginate with RGD modification, especially at a high concentration, was associated with greatly improved cell viability and integrin clustering, which further enhanced cell proliferation.

A novel photosynthetic biologic topical gel for enhanced localized hyperoxygenation augments wound healing in peripheral artery disease

Peripheral artery disease and the associated ischemic wounds are substantial causes of global morbidity and mortality, affecting over 200 million people worldwide. Although advancements have been made in preventive, pharmacologic, and surgical strategies to treat this disease, ischemic wounds, a consequence of end-stage peripheral artery disease, remain a significant clinical and economic challenge. Synechococcus elongatus is a cyanobacterium that grows photoautotrophically and converts carbon dioxide and water into oxygen. We present a novel topical biologic gel containing S. elongatus that provides oxygen via photosynthesis to augment wound healing by rescuing ischemic tissues caused by peripheral artery disease. By using light rather than blood as a source of energy, our novel topical therapy significantly accelerated wound healing in two rodent ischemic wound models. This novel topical gel can be directly translated to clinical practice by using a localized, portable light source without interfering with patients' daily activities, demonstrating potential to generate a paradigm shift in treating ischemic wounds from peripheral artery disease. Its novelty, low production cost, and ease of clinical translatability can potentially impact the clinical care for millions of patients suffering from peripheral arterial disease.

Contribution of PARP to endothelial dysfunction and hypertension in a rat model of pre-eclampsia

BACKGROUND AND PURPOSE

Under conditions of increased oxidative stress, such as pre-eclampsia and diabetes, overstimulation of PARP leads to endothelial dysfunction. Inhibition of PARP has been demonstrated to reverse the vascular dysfunction associated with diabetes in vivo. The present study was carried out to investigate the role of PARP in mediating the endothelial dysfunction associated with pre-eclampsia.

EXPERIMENTAL APPROACH

Uteroplacental perfusion was surgically reduced in pregnant rats to produce the reduced uterine perfusion pressure (RUPP) rat model of pre-eclampsia and the PARP inhibitor, PJ34, was administered either before or after surgery. Mean arterial BP and vascular function were measured in normal pregnant (NP) and both control and PJ34-treated RUPP rats. Mesenteric vessels from NP rats were incubated with either 3% RUPP or NP plasma alone or in combination with PJ34. Finally, immunohistochemical staining was carried out to measure nitrotyrosine (byproduct of peroxynitrite) immunoreactivity.

KEY RESULTS

RUPP rats were characterized by hypertension, fetal growth restriction and endothelial dysfunction when compared with NP rats. PJ34 administered in vivo before, but not after, surgery prevented the development of both endothelial dysfunction and hypertension. RUPP plasma-induced impaired vasorelaxation was prevented following co-incubation with PJ34 in vitro. Furthermore, the protective effect of PARP inhibition in vivo was accompanied by a reduction in nitrotyrosine immunoreactivity.

CONCLUSIONS AND IMPLICATIONS

PJ34 prevented the development of both endothelial dysfunction and hypertension and reduced vascular nitrotyrosine immunoreactivity, thus suggesting a role for oxidative-nitrosative stress/PARP activation in the aberration in both vascular and haemodynamic function in this rat model of pre-eclampsia.

Mast cells, peptides and cardioprotection - an unlikely marriage?

1 Mast cells have classically been regarded as the 'bad guys' in the setting of acute myocardial ischaemia, where their released contents are believed to contribute both to tissue injury and electrical disturbances resulting from ischaemia. Recent evidence suggests, however, that if mast cell degranulation occurs in advance of ischaemia onset, this may be cardioprotective by virtue of the depletion of mast cell contents that can no longer act as instruments of injury when the tissue becomes ischaemic. 2 Many peptides, such as ET-1, adrenomedullin, relaxin and atrial natriuretic peptide, have been demonstrated to be cardioprotective when given prior to the onset of myocardial ischaemia, although their physiological functions are varied and the mechanisms of their cardioprotective actions appear to be diverse and often ill defined. However, one common denominator that is emerging is the ability of these peptides to modulate mast cell degranulation, raising the possibility that peptide-induced mast cell degranulation or stabilization may hold the key to a common mechanism of their cardioprotection. 3 The aim of this review was to consolidate the evidence implying that mast cell degranulation could play both a detrimental and protective role in myocardial ischaemia, depending upon when it occurs, and that this may underlie the cardioprotective effects of a range of diverse peptides that exerts physiological effects within the cardiovascular system.

Mast cell degranulation--a mechanism for the anti-arrhythmic effect of endothelin-1?

BACKGROUND AND PURPOSE

The aim of this study was to investigate whether the previously reported anti-arrhythmic effect of endothelin-1 (ET-1) is mediated by degranulation of cardiac mast cells prior to myocardial ischaemia.

EXPERIMENTAL APPROACH

Male Sprague-Dawley rats received either ET-1 (1.6 nmolxkg(-1)) in the presence or absence of disodium cromoglycate (DSCG; 20 mgxkg(-1)xh(-1)) prior to coronary artery occlusion (CAO). In separate experiments rats were given compound 48/80 (50 microgxkg(-1)) to compare the effects of ET-1 with those of a known mast cell degranulator. Ischaemia-induced ventricular arrhythmias were detected through continuous monitoring of a lead I electrocardiogram. After 30 min of CAO, the hearts were removed and mast cell degranulation determined by histological analysis. A parallel series of sham groups were performed to determine the direct effects of ET-1 and compound 48/80 on mast cell degranulation in the absence of ischaemia.

KEY RESULTS

ET-1 and compound 48/80 both exerted profound anti-arrhythmic effects, significantly reducing the total number of ventricular ectopic beats (P < 0.001) and the incidence of ventricular fibrillation (P < 0.05). These anti-arrhythmic effects were abolished by concomitant DSCG infusion prior to CAO. In sham animals ET-1 and compound 48/80 both induced mast cell degranulation (P < 0.001), an effect which was abolished by DSCG, confirming their ability to induce degranulation of mast cells.

CONCLUSIONS AND IMPLICATIONS

These results demonstrate for the first time that when given prior to ischaemia ET-1 mediates its anti-arrhythmic effects, at least in part, via cardiac mast cell degranulation.

High yield and rapid growth of Neoparamoeba pemaquidensis in co-culture with a rainbow trout gill-derived cell line RTgill-W1

Neoparamoeba pemaquidensis is an ubiquitous amphizoic marine protozoan and has been implicated as the causative agent for several diseases in marine organisms, most notably amoebic gill disease (AGD) in Atlantic salmon. Despite several reports on the pathology of AGD, relatively little is known about the protozoan and its relationship to host cells. In this study, an in vitro approach using monolayers of a rainbow trout gill cell line (RTgill-W1, ATCC CRL-2523) was used to rapidly grow large numbers of N. pemaquidensis (ATCC 50172) and investigate cell-pathogen interactions. Established cell lines derived from other tissues of rainbow trout and other fish species were also evaluated for amoeba growth support. The amoebae showed preference and highest yield when grown with RTgill-W1 over nine other tested fish cell lines. Amoeba yields could reach as high as 5 x 10(5) cells mL(-1) within 3 days of growth on the gill cell monolayers. The amoebae caused visible focal lesions in RTgill-W1 monolayers within 24 h of exposure and rapidly proliferated and spread with cytopathic effects destroying the neighbouring pavement-like cells within 48-72 h after initial exposure in media above 700 mOsm kg(-1). Disruption of the integrity of the gill cell monolayers could be noted within 30 min of exposure to the amoeba suspensions by changes in transepithelial resistance (TER) compared with control cell monolayers maintained in the exposure media. This was significantly different by 2 h (P < 0.05) compared with control cells and remained significantly different (P < 0.01) for the remaining 72 h that the TER was monitored. The RTgill-W1 cell line is thus a convenient model for growing N. pemaquidensis and for studying host-pathogen interactions in AGD.

DEVELOPMENT OF A CONTINUOUS CELL LINE, PBLE, FROM AN AMERICAN EEL PERIPHERAL BLOOD LEUKOCYTE PREPARATION

A continuous cell line, PBLE, was developed from the adherent cells in a culture of peripheral blood leukocytes from the American eel, Anguilla rostrata. The cells were grown in Leibovitz's L-15 basal medium supplemented with 20% fetal bovine serum (FBS). Under normal culture conditions at 18 degrees C, the morphology of PBLE was fibroblast-like. The cultures have been subcultured over 80 times and have been cryopreserved successfully. These cells have a diploid karyotype of 38 chromosomes, survived temperatures from 5 to 36 degrees C, and proliferated at temperatures from 5 degrees C to at least 30 degrees C. PBLE underwent apoptosis in response to gliotoxin, but did not show a respiratory burst. Results suggest that PBLE may have arisen from a circulating mesenchymal stem cell. PBLE was susceptible to Chum salmon reovirus (CSV) and supported CSV replication. Therefore this cell line should be useful in studying eel specific virus-host interactions.

Split-night studies for the diagnosis and treatment of sleep-disordered breathing

We examined the effect of split-night polysomnography on compliance with positive pressure via a mask for the treatment of obstructive sleep-disordered breathing. A comparison of objective compliance (hours/day) at the first meter read from the positive-pressure device (4-6 weeks after set-up) in patients who had a successful split-night positive-pressure titration vs. patients who had traditional full-night positive-pressure titration was performed. Patients were matched for age, sex, and severity of the obstructive sleep-disordered breathing. Twelve patients were matched with controls who underwent full-night polysomnography. There were no significant differences between the split-night patients and the full-night patients with regard to age, sex, body mass index, and pretreatment Epworth Sleepiness Score. In addition, there was no significant difference between apnea-hypopnea index and the desaturation-event frequency for both groups pre- and post-treatment. The average daily use of continuous positive airway pressure (CPAP) at the time of the first meter reading in the group that underwent full-night positive-pressure titrations as opposed to split-night titrations was 5.2 hours/day +/- 2.2 vs. 3.8 hours/day +/- 2.9, respectively (p = 0.29). The Epworth Sleepiness Scale on the initial clinic visit (as an index of patient-perceived impairment) did not predict compliance at 4-6 weeks. The time at the final positive pressure did not correlate with compliance. Acceptance of positive pressure in the split-night patients ranged from 62 to 67%.