Heart Valve Disease & Therapy – The Value of Translational Animal Models

Valvular disease and successful therapy is dependent on a complex interplay of metabolic, hemodynamic / fluid dynamic, neuro‐hormonal and immunologic processes. In order to grasp the mechanism of a disease or evaluate novel therapies, biological systems are needed that are capable of mimicking this fascinating complexity. Due to the closely resembling anatomical landmarks of the valvular apparatus and ventricular cavities as well as intra‐ventricular and intra‐aortic fluid dynamic behavior of blood flow, farm pigs should be considered when there is a need for translational large animal model in the field of heart valve research. The use of 90‐100 kg pigs enables deployment of human grade devices as cardiac dimensions in this weight‐class of animals closely resembles one of adult patients. Further, clinical‐grade echocardiography imaging equipment with minimal adaptations of the application technique can be routinely used for TEE guidance of valvular procedures in experimental projects using this animal species. For navigationally challenging procedures, such as transseptal interventions on the mitral valve, porcine animal model could be humanized by relatively simple surgical intervention. Besides proving researchers with robust, human‐like platform for valvular implant testing and development, porcine models provide exceptional value in investigations of diseases where clinical studies are either impractical, time consuming or unethical. Such being studies of cardiac injury in poly‐trauma or precise hemodynamic effects of valvular regurgitation. In such studies, clinical grade medical equipment (such as standard CT and MRI machines and anesthesia equipment) can routinely be used and novel protocols developed and tested, which can then rapidly be adapted for human use, further closing the translation gap. Finally, experience gathered during preclinical testing and learning curve achieved with translational animal models could and should be used to provide practitioners with a solid starting point when novel valve therapies finally find their way to clinical use. Yet, a certain translational gap still remains

Housing of female mice in a new environment and its influence on post-surgical behaviour and recovery

The transportation of mice into a new clean cage after surgery is a standard procedure but might have detrimental effects during the critical post-surgical recovery phase. To analyse the effect of post-surgical housing, female C57BL/6J mice housed in their familiar home cage or in a new environment after minor surgery ± analgesia, anaesthesia only or no treatment were monitored using non-invasive methods during the immediate postsurgical period to assess pain and general impairment. Behavioural investigations and burrowing test revealed no significant differences between housing conditions in untreated mice. While no appearance or posture abnormalities were observed post-experiment, home cage behaviours were affected distinctly. Behavioural rhythmicity was disrupted, and behaviours related to well-being, such as burrowing performance, were less compared to untreated mice. Burrowing latency ranged from an intermediate level following anaesthesia only and surgery with analgesia, to pronounced prolongation after surgery without analgesia in animals housed in their home cage, while after all experimental treatments burrowing latency in animals in new cages was prolonged dramatically. General activity and climbing behaviour in treatment groups housed in new cages tend to be higher compared to animals in familiar cages, leading to significant interactions between housing and treatment conditions (p = 0.006; p = 0.014). These behavioural differences in animals housed in a new environment compared to animals housed in their familiar environment might be interpreted as signs of reduced well-being, agitation and restlessness in the new cages and may hint that animals cope better with surgical stress when housed in their familiar environment. The post-surgical transport to a new and clean cage might therefore be an additional stressor after an exhausting event and may affect recovery

Implantation of Radiotelemetry Transmitters Yielding Data on ECG, Heart Rate, Core Body Temperature and Activity in Free-moving Laboratory Mice

The laboratory mouse is the animal species of choice for most biomedical research, in both the academic sphere and the pharmaceutical industry. Mice are a manageable size and relatively easy to house. These factors, together with the availability of a wealth of spontaneous and experimentally induced mutants, make laboratory mice ideally suited to a wide variety of research areas

The sheep as a pre-clinical model for testing intra-aortic percutaneous mechanical circulatory support devices

The save deployment of intra-aortic percutaneous mechanical circulatory support devices is highly dependent on the inner aortic diameter. Finding the anatomically and ethically most suitable animal model for performance testing of new pMCS devices remains challenging. For this study, an ovine model using adult ewes of a large framed breed (Swiss White Alpine Sheep) was developed to test safety, reliability, and biocompatibility of catheter-mounted mechanical support devices placed in the descending thoracic aorta. Following the drawback of fluctuating aortic diameter and device malfunction in the first four animals, the model was improved by stenting the following animals with an aortic stent. Stenting the animals with an intra-aortic over the balloon stent was found to standardize the experimental set-up and to avoid early termination of the experiment due to non-device related issues. Keywords: 3R; Mechanical circulatory support; animal model; preclinical study; sheep; thoracic aort

Impact of inhalation anaesthesia, surgery and analgesic treatment on home cage behaviour in laboratory mice

Anaesthesia and analgesia are used frequently in laboratory routine to ensure animal welfare and good scientific outcomes in experiments that may elicit pain or require immobilisation of the animal. However, there is concern regarding the effect of these procedures on animal behaviour in subsequent experiments. Our study determined the impact of short inhalation anaesthesia (sevoflurane, 15 min, 4.9%) and minor surgery (one-sided sham embryo transfer in females, one-sided sham vasectomy in males) with or without pain treatment (carprofen, 5 mg/kg, bid) on spontaneous species-specific home cage behaviours in inbred mice. Analysis of 18-h continuous video recordings showed clear post-procedural changes in spontaneous home cage behaviours, with changes of a moderate level after anaesthesia being marked after surgery. Self-grooming, resting and locomotion were the most important behaviours for group separation. Analysis of the temporal distribution of behavioural changes revealed that resting behaviour was altered contradictory to its circadian rhythm as it was decreased in the light phase and increased in the dark phase. Also, locomotion was decreased in the dark phase at 12 to 18 h after surgery and anaesthesia. In contrast, self-grooming was increased independently of circadian rhythm, being increased for up to 18 h after surgery and anaesthesia. Following surgery, there was no significant difference in duration of behaviours between animals that were treated with carprofen or left without pain relief. In conclusion, it can be assumed that the changes observed in home cage behaviours hint at reduced animal well-being. However, pain or the efficacy of post-operative pain treatment could not be discriminated reliably from the impact of the surgical procedure including inhalation anaesthesia by observing animals’ home cage behaviour. However for the interpretation of behavioural research data, the distinct impact of anaesthesia, surgery, pain treatment and other experimental procedures has to be considered. Our results highlight the requirement for knowledge of species-specific circadian rhythms of behaviours as well as the importance of determining the appropriate time of day for behavioural and welfare assessment

Efficacy of catheter-based drug delivery in a hybrid in vitro model of cardiac microvascular obstruction with porcine microthrombi.

Microvascular obstruction (MVO) often occurs in ST-elevation myocardial infarction (STEMI) patients after percutaneous coronary intervention (PCI). Diagnosis and treatment of MVO lack appropriate and established procedures. This study focused on two major points by using an in vitro multiscale flow model, which comprised an aortic root model with physiological blood flow and a microfluidic model of the microcirculation with vessel diameters down to 50 μm. First, the influence of porcine microthrombi (MT), injected into the fluidic microchip, on perfusion was investigated. We found that only of all injected MT were fully occlusive. Second, it could also be shown that the maximal concentration of a dye (representing therapeutic agent) during intracoronary infusion could be increased on average by , when proximally occluding the coronary artery by a balloon during drug infusion. The obtained results and insights enhance the understanding of perfusion in MVO-affected microcirculation and could lead to improved treatment methods for MVO patients

Burrowing Behavior as an Indicator of Post-Laparotomy Pain in Mice

Detection of persistent pain of a mild-to-moderate degree in laboratory mice is difficult because mice do not show unambiguous symptoms of pain or suffering using standard methods of short-term observational or clinical monitoring. This study investigated the potential use of burrowing performance – a spontaneous and highly motivated behavior – as a measure of post-operative pain in laboratory mice. The influence of minor surgery on burrowing was investigated in adult C57BL/6J mice of both genders in a modified rodent burrowing test (displacement of food pellets from a pellet-filled tube) within the animal's home cage. Almost all (98%) healthy mice burrowed (mean latency 1.3 h, SEM 0.5 h). After surgery without pain treatment, latency of burrowing was significantly prolonged (mean Δ latency 10 h). Analgesic treatment using the anti-inflammatory drug carprofen (5 mg/kg bodyweight) decreased latency of burrowing after surgery (mean Δ latency 5.5 h) to the level found in mice that had been anesthetized (mean Δ latency 5.4 h) or had received anesthesia and analgesia (mean Δ latency 4.6 h). Analgesia during surgery was associated with a significantly earlier onset of burrowing compared to surgery without pain treatment. A distinct gradation in burrowing performance was found ranging from the undisturbed pre-operative status to the intermediate level following anesthesia/analgesia and surgery with analgesia, to the pronounced prolongation of latency to burrow after surgery without pain relief. In conclusion, post-surgical impairment of general condition, probably mainly attributable to pain, can be conveniently assessed in laboratory mice on the basis of the burrowing test

Pathology and advanced imaging – characterization of a congenital cardiac defect and complex hemodynamics in a pig: A case report

Domestic pigs are widely used in cardiovascular research as the porcine circulatory system bears a remarkable resemblance to that of humans. In order to reduce variability, only clinically healthy animals enter the study as their health status is assessed in entry examination. Like humans, pigs can also suffer from congenital heart disease, such as an atrial septal defect (ASD), which often remains undetected. Due to the malformation of the endocardial cushion during organ development, mitral valve defects (e.g., mitral clefts) are sometimes associated with ASDs, further contributing to hemodynamic instability. In this work, we report an incidental finding of a hemodynamically highly relevant ASD in the presence of incompetent mitral and tricuspid valves, in an asymptomatic, otherwise healthy juvenile pig. In-depth characterization of the cardiac blood flow by four-dimensional (4D) flow magnetic resonance imaging (MRI) revealed a prominent diastolic left-to-right and discrete systolic right-to-left shunt, resulting in a pulmonary-to-systemic flow ratio of 1.8. Severe mitral (15 mL/stroke) and tricuspid (22 mL/stroke) regurgitation further reduced cardiac output. Pathological examination confirmed the presence of an ostium primum ASD and found a serous cyst of lymphatic origin that was filled with clear fluid partially occluding the ASD. A large mitral cleft was identified as the most likely cause of severe regurgitation, and histology showed mild to moderate endocardiosis in the coaptation area of both atrio-ventricular valves. In summary, although not common, congenital heart defects could play a role as a cause of experimental variability or even intra-experimental mortality when working with apparently heathy, juvenile pigs

Computed tomography for planning and postoperative imaging of transvenous mitral annuloplasty: first experience in an animal model

To investigate the use of computed tomography (CT) to measure the mitral valve annulus size before implantation of a percutaneous mitral valve annuloplasty device in an animal trial. Seven domestic pigs underwent CT before and after implantation of a Cardioband™ (a percutaneously implantable mitral valve annuloplasty device) with a second-generation 128-section dual-source CT machine. Implantation of the Cardioband™ was performed in a standard fashion according to a protocol. Animals were sacrificed afterwards and the hearts explanted. The Cardioband™ was found to be adequately implanted in all animals, with no anchor dehiscence and no damage of the circumflex artery (CX) or the coronary sinus (CS). The correct length of the band as chosen according to the length of the posterior mitral annulus measured in CT before implantation was confirmed in gross examination in all animals. The device did not result in a metal artifact-related degradation of image quality. The closest distance from the closest anchor to the CX was 2.1 ± 0.7 mm in diastole and 1.6 ± 0.5 mm systole. Mitral annulus distance to the CS was 6.4 ± 1.3 mm in diastole and 7.7 ± 1.1 mm in systole. CT visualization and measurement of the mitral valve annulus dimensions is feasible and can become the imaging method of choice for procedure planning of Cardioband™ implantations or other transcatheter mitral annuloplasty devices

Continuous Monitoring of Blood Pressure and Vascular Hemodynamic Properties With Miniature Extravascular Hall-Based Magnetic Sensor

Continuous measurement of vascular and hemodynamic parameters could improve monitoring of disease progression and enable timely clinical decision making and therapy surveillance in patients suffering from cardiovascular diseases. However, no reliable extravascular implantable sensor technology is currently available. Here, we report the design, characterization, and validation of an extravascular, magnetic flux sensing device capable of capturing the waveforms of the arterial wall diameter, arterial circumferential strain, and arterial pressure without restricting the arterial wall. The implantable sensing device, comprising a magnet and a magnetic flux sensing assembly, both encapsulated in biocompatible structures, has shown to be robust, with temperature and cyclic-loading stability. Continuous and accurate monitoring of arterial blood pressure and vascular properties was demonstrated with the proposed sensor in vitro with a silicone artery model and validated in vivo in a porcine model mimicking physiologic and pathologic hemodynamic conditions. The captured waveforms were further used to deduce the respiration frequency, the duration of the cardiac systolic phase, and the pulse wave velocity. The findings of this study not only suggest that the proposed sensing technology is a promising platform for accurate monitoring of arterial blood pressure and vascular properties, but also highlight the necessary changes in the technology and the implantation procedure to allow the translation of the sensing device in the clinical setting