Electrocardiography of the normal domestic pet rabbit

Preclinical Evaluation of a Novel Once-a-Day Brimonidine Ophthalmic Nanosuspension

Purpose: This article aims to describe a preclinical proof of concept for a novel once-a-day (OD) brimonidine ophthalmic nanosuspension. Methods: The preclinical proof of concept was established using New Zealand white rabbits as animal models. Dose-finding, multiple-dose efficacy, ocular pharmacokinetic, and hemodynamic studies were performed in normotensive rabbits. Steroid-induced ocular hypertension model in rabbits was used to study efficacy in glaucomatous pathophysiology. The test (0.35% OD suspension) and reference (0.15% three times a day [TID] solution) were compared. Results: The intraocular pressure (IOP) reduction was sustained for 0.35% and 0.5% strengths but not for other lower strengths tested or reference strengths. A 0.35% OD suspension reduced IOP >2 mmHg after 24 h of dosing, which was not seen with the reference. After multiple dosing, 0.35% OD suspension reduced IOP by 4-6 mmHg after 24 h, which was comparable to the 0.15% TID reference solution. An ocular pharmacokinetic study showed that the brimonidine was rapidly absorbed and distributed throughout the eye after topical administration. Concentration was higher in tissues with high α2 receptors, such as cornea-conjunctiva, iris/ciliary body, and choroid/retina. The steady-state concentrations in these organs were also significant after 24 h of the last dose. There was an indication of increased plasma levels, so a hemodynamic study was performed to assess any adverse effects. All hemodynamic parameters were normal and no new unusual safety findings were observed. Conclusions: The study demonstrated that the novel brimonidine 0.35% ophthalmic nanosuspension is both safe and effective when administered OD and is comparable to the marketed reference formulation administered TID.

Gender Difference in Lithium-Induced Sodium Current Dysregulation and Ventricular Arrhythmogenesis in Right Ventricular Outflow Tract Cardiomyocytes

Lithium intoxication induces Brugada-pattern ECG, ventricular arrhythmia, and sudden death with the predominant preference for the male over the female gender. This study investigated the mechanisms of gender difference in lithium-induced arrhythmogenesis. The ECG parameters were recorded in male and female rabbits before and after the intravenous administration of lithium chloride (LiCl) (1, 3, 10 mmol/kg). Patch clamps were used to study the sodium current (INa) and late sodium current (INa-late) in the isolated single male and female right ventricular outflow tract (RVOT) cardiomyocytes before and after LiCl. Male rabbits (n = 9) were more prone to developing lithium-induced Brugada-pattern ECG changes (incomplete right bundle branch block, ST elevation and QRS widening) with fatal arrhythmia (66.7% vs. 0%, p = 0.002) than in female (n = 7) rabbits at 10 mmol/kg (but not 1 or 3 mmol/kg). Compared to those in the female RVOT cardiomyocytes, LiCl (100 μM) reduced INa to a greater extent and increased INa-late in the male RVOT cardiomyocytes. Moreover, in the presence of ranolazine (the INa-late inhibitor, 3.6 mg/kg iv loading, followed by a second iv bolus 6.0 mg/kg administered 30 min later, n = 5), LiCl (10 mmol/kg) did not induce Brugada-pattern ECG changes (p < 0.005). The male gender is much predisposed to lithium-induced Brugada-pattern ECG changes with a greater impact on INa and INa-late in RVOT cardiomyocytes. Targeting INa-late may be a potential therapeutic strategy for Brugada syndrome-related ventricular tachyarrhythmia.

A computational model of rabbit geometry and ECG: Optimizing ventricular activation sequence and APD distribution

Computational modeling of electrophysiological properties of the rabbit heart is a commonly used way to enhance and/or complement findings from classic lab work on single cell or tissue levels. Yet, thus far, there was no possibility to extend the scope to include the resulting body surface potentials as a way of validation or to investigate the effect of certain pathologies. Based on CT imaging, we developed the first openly available computational geometrical model not only of the whole heart but also the complete torso of the rabbit. Additionally, we fabricated a 32-lead ECG-vest to record body surface potential signals of the aforementioned rabbit. Based on the developed geometrical model and the measured signals, we then optimized the activation sequence of the ventricles, recreating the functionality of the Purkinje network, and we investigated different apico-basal and transmural gradients in action potential duration. Optimization of the activation sequence resulted in an average root mean square error between measured and simulated signal of 0.074 mV/ms for all leads. The best-fit T-Wave, compared to measured data (0.038 mV/ms), resulted from incorporating an action potential duration gradient from base to apex with a respective shortening of 20 ms and a transmural gradient with a shortening of 15 ms from endocardium to epicardium. By making our model and measured data openly available, we hope to give other researchers the opportunity to verify their research, as well as to create the possibility to investigate the impact of electrophysiological alterations on body surface signals for translational research.

Clinicopathological findings in and prognostic factors for domestic rabbits with liver lobe torsion: 82 cases (2010–2020)

OBJECTIVE

To document clinicopathologic findings in domestic rabbits with liver lobe torsion and identify prognostic factors.

ANIMALS

82 rabbits.

PROCEDURE

Medical records of 4 institutions were reviewed to identify rabbits with an antemortem diagnosis of liver lobe torsion that were examined between 2010 and 2020.

RESULTS

The prevalence of liver lobe torsion was 0.7% (82/11,402). In all 82 rabbits, the diagnosis was made by means of abdominal ultrasonography. Fifty (60.1%) rabbits underwent liver lobectomy, 23 (28%) received medical treatment alone, and 9 (10.9%) were euthanized or died on presentation. Overall, 32 (39%) rabbits died within 7 days of initial presentation and 50 (61%) survived. Seven-day survival rate did not differ significantly between medical treatment alone and surgical treatment. However, median survival time following medical treatment (530 days) was shorter than that following surgical treatment (1,452 days). Six of 14 rabbits had evidence of systemic inflammatory disease on necropsy. Rabbits with right liver lobe torsion were less likely to survive for 7 days than were those with caudate torsions (P = 0.046; OR, 3.27; 95% CI, 1.04 to 11.3). Rabbits with moderate to severe anemia were less likely to survive for 7 days than were rabbits that were not anemic or had mild anemia (P = 0.006; OR, 4.41; 95% CI, 1.55 to 12.51). Other factors associated with a decreased 7-day survival rate were high heart rate at admission (P = 0.013) and additional days without defecation after admission (P < 0.001). Use of tramadol was associated with an increased survival rate (P = 0.018).

CLINICAL RELEVANCE

The prognosis for rabbits with liver lobe torsions was more guarded than previously described. Rabbits that underwent liver lobectomy had a longer median survival time than did rabbits that only received medical treatment.

Protective Effectiveness of an Immunization Protocol Against the Toxic Effects of Loxosceles intermedia Venom in Rabbits

Loxosceles spp. (brown spiders) bites are responsible for the development of a syndrome consisting mainly of dermonecrotic lesions, and also systemic effects. Rabbits are one of the main experimental models used for better understanding the systemic and local effects of Loxosceles venom. The aim of this study is to evaluate the toxic and protective effects of rabbits immunized with Loxosceles spp. venom. Male New Zealand rabbits were allocated as a control group (CG; n = 5) that received adjuvant (Montanide) and phosphate-buffer saline (PBS), or as venom group (VG; n = 5) that received 21 μg of Loxosceles venom using Montanide as adjuvant. After five immunization cycles, a trial with 7 μg of Loxosceles intermedia (L. intermedia) venom was performed, and dermonecrotic lesions were measured. The rabbits were then euthanized, and their organs were collected for histopathology analysis. Rabbits that had undergone Loxosceles venom immunization protocol showed minor clinical disturbances during the experimental period. The used immunization protocol protected the rabbits against the toxic effect of the Loxosceles venom because they showed minor clinical disturbances during the experimental period.

Cardiology in Rodents, Rabbits, and Small Exotic Mammals-Diagnostic Workup

The incidence of cardiac diseases in pet rabbits and rodents increased over the past decade as these species live longer and diagnostics methods are more precise to diagnose heart diseases even in small-sized animals. The article summarizes diagnostics of cardiac diseases in selected exotic companion mammals, particularly in rabbits, guinea pigs, chinchillas, and rats. The emphasis of the paper is given on clinical examination, thoracic radiography, electrocardiography, and echocardiography.

Intrinsically stretchable electronics with ultrahigh deformability to monitor dynamically moving organs

Intrinsically stretchable electronics represent an attractive platform for next-generation implantable devices by reducing the mechanical mismatch and the immune responses with biological tissues. Despite extensive efforts, soft implantable electronic devices often exhibit an obvious trade-off between electronic performances and mechanical deformability because of limitations of commonly used compliant electronic materials. Here, we introduce a scalable approach to create intrinsically stretchable and implantable electronic devices featuring the deployment of liquid metal components for ultrahigh stretchability up to 400% tensile strain and excellent durability against repetitive deformations. The device architecture further shows long-term stability under physiological conditions, conformal attachments to internal organs, and low interfacial impedance. Successful electrophysiological mapping on rapidly beating hearts demonstrates the potential of intrinsically stretchable electronics for widespread applications in health monitoring, disease diagnosis, and medical therapies.

Pharmacokinetics of pimobendan following oral administration to New Zealand White rabbits (Oryctolagus cuniculus)

OBJECTIVE

To determine the pharmacokinetics and potential adverse effects of pimobendan after oral administration in New Zealand White rabbits (Ocytolagus cuniculi).

ANIMALS

10 adult sexually intact (5 males and 5 females) rabbits.

PROCEDURES

2 pilot studies were performed with a pimobendan suspension or oral tablets. Eight rabbits received 7.5 mg of pimobendan (mean 2.08 mg/kg) suspended in a critical care feeding formula. Plasma concentrations of pimobendan and O-demethylpimobendan (ODMP) were measured, and pharmacokinetic parameters were calculated for pimobendan by noncompartmental analysis. Body weight, food and water consumption, mentation, urine, and fecal output were monitored.

RESULTS

Mean ± SD maximum concentration following pimobendan administration was 15.7 ± 7.54 ng/mL and was detected at 2.79 ± 1.25 hours. The half-life was 3.54 ± 1.32 hours. Plasma concentrations of pimobendan were detectable for up to 24 hours. The active metabolite, ODMP, was detected in rabbits for 24 to 36 hours. An adverse event occurred following administration of pimobendan in tablet form in 1 pilot study, resulting in death secondary to aspiration. No other adverse events occurred.

CLINICAL RELEVANCE

Plasma concentrations of pimobendan were lower than previously reported for dogs and cats, despite administration of higher doses, and had longer time to maximum concentration and half-life. Based on this study, 2 mg/kg of pimobendan in a critical care feeding formulation should maintain above a target plasma concentration for 12 to 24 hours. However, further studies evaluating multiple-dose administration as well as pharmacodynamic studies and clinical trials in rabbits with congestive heart failure are needed to determine accurate dose and frequency recommendations.

Clinical and pathological findings in rabbits with cardiovascular disease: 59 cases (2001-2018)

OBJECTIVE

To determine epidemiological features of cardiovascular disease in rabbits examined at a veterinary teaching hospital and characterize clinical and pathological findings.

ANIMALS

59 rabbits.

PROCEDURES

Medical records from 2001 to 2018 were reviewed, and data were collected. Echocardiographic images and histologic diagnoses were reviewed.

RESULTS

The prevalence of cardiovascular disease was 2.6% (59/2,249). Clinical signs related to cardiac disease included heart murmur (n = 25 rabbits), arrhythmia (22), tachypnea or dyspnea (13), hyporexia or anorexia (13), and muscle wasting (9). Radiographic (n = 39) abnormalities included cardiomegaly (19) and peritoneal (12) and pleural (11) effusion. Common echocardiographic (n = 37) diagnoses included degenerative valve disease (15), dilated cardiomyopathy (7), unclassified cardiomyopathy (4), restrictive cardiomyopathy (3), and hypertrophic cardiomyopathy (2). On ECG (n = 19), supraventricular arrhythmias (16) were more common than ventricular arrhythmias (12). Thirty-five necropsy reports were available, and diagnoses included cardiomyopathy (n = 14), myocarditis (10), and arteriosclerosis (9). Medical management (n = 20) included a wide range of drugs and dosages with few adverse effects. Survival times (n = 36 rabbits) ranged from 1 to 2,353 days with a median cardiac disease-specific survival time of 306 days.

CONCLUSIONS AND CLINICAL RELEVANCE

The findings provided information on the prevalence of cardiovascular disease in rabbits and survival times for affected rabbits. Right-sided, left-sided, and biventricular congestive heart failure occurred equally. Median survival time was lower than that reported for other species. Further research on the diagnosis and treatment of cardiovascular disease in rabbits is needed.

A comparative review on heart ion channels, action potentials and electrocardiogram in rodents and human: extrapolation of experimental insights to clinic

Electrocardiogram (ECG) is a non-invasive valuable diagnostic tool that is used in clinics for investigation and monitoring of heart electrical rhythm/conduction, ischemia/injury of heart, electrolyte disturbances and agents/drugs induced cardiac toxicity. Nowadays using animal models to study heart diseases such as electrical and mechanical disturbance is common. In addition, given to ethical consideration and availability, the use of small rodents has been a top priority for cardiovascular researchers. However, extrapolation of experimental findings from the lab to the clinic needs sufficient basic knowledge of similarities and differences between heart action potential and ECG of rodents and humans in normal and disease conditions. This review compares types of human action potentials, the dominant ion currents during action potential phases, alteration in ion channels activities in channelopathies-induced arrhythmias and the ECG appearance of mouse, rat, guinea pig, rabbit and human. Also, it briefly discusses the responsiveness and alterations in ECG following some interventions such as cardiac injury and arrhythmia induction. Overall, it provides a roadmap for researchers in selecting the best animal model/species whose studies results can be translated into clinical practice. In addition, this study will also be useful to biologists, physiologists, pharmacologists, veterinarians and physicians working in the fields of comparative physiology, pharmacology, toxicology and diseases.

Self-Similar Synchronization of Calcium and Membrane Potential Transitions During Action Potential Cycles Predict Heart Rate Across Species

OBJECTIVES

The purpose of this study was to discover regulatory universal mechanisms of normal automaticity in sinoatrial nodal (SAN) pacemaker cells that are self-similar across species.

BACKGROUND

Translation of knowledge of SAN automaticity gleaned from animal studies to human dysrhythmias (e.g., "sick sinus" syndrome [SSS]) requiring electronic pacemaker insertion has been suboptimal, largely because heart rate varies widely across species.

METHODS

Subcellular Ca²⁺ releases, whole cell action potential (AP)-induced Ca²⁺ transients, and APs were recorded in isolated mouse, guinea pig, rabbit, and human SAN cells. Ca²⁺-Vm kinetic parameters during phases of AP cycles from their ignition to recovery were quantified.

RESULTS

Although both action potential cycle lengths (APCLs) and Ca²⁺-Vm kinetic parameters during AP cycles differed across species by 10-fold, trans-species scaling of these during AP cycles and scaling of these to APCL in cells in vitro, electrocardiogram RR intervals in vivo, and body mass (BM) were self-similar (obeyed power laws) across species. Thus, APCL in vitro, heart rate in vivo, and BM of any species can be predicted by Ca²⁺-Vm kinetics during AP cycles in SAN cells measured in any single species in vitro.

CONCLUSIONS

In designing optimal heart rate to match widely different BM and energy requirements from mice to humans, nature did not "reinvent pacemaker cell wheels," but differentially scaled kinetics of gears that regulate the rates at which the "wheels spin." This discovery will facilitate the development of novel pharmacological and biological pacemakers featuring a normal, wide-range rate regulation in animal models and the translation of these to humans to target recalcitrant human SSS.

Animal models of arrhythmia: classic electrophysiology to genetically modified large animals

Arrhythmias are common and contribute substantially to cardiovascular morbidity and mortality. The underlying pathophysiology of arrhythmias is complex and remains incompletely understood, which explains why mostly only symptomatic therapy is available. The evaluation of the complex interplay between various cell types in the heart, including cardiomyocytes from the conduction system and the working myocardium, fibroblasts and cardiac immune cells, remains a major challenge in arrhythmia research because it can be investigated only in vivo. Various animal species have been used, and several disease models have been developed to study arrhythmias. Although every species is useful and might be ideal to study a specific hypothesis, we suggest a practical trio of animal models for future use: mice for genetic investigations, mechanistic evaluations or early studies to identify potential drug targets; rabbits for studies on ion channel function, repolarization or re-entrant arrhythmias; and pigs for preclinical translational studies to validate previous findings. In this Review, we provide a comprehensive overview of different models and currently used species for arrhythmia research, discuss their advantages and disadvantages and provide guidance for researchers who are considering performing in vivo studies.

Cardiovascular Disease

Cardiac disease is increasingly diagnosed in pet rabbits, presumably because of their lengthening life span and the increased sophistication of their veterinary care. However, relatively little is known about the origins of and therapy for cardiac disease in pet rabbits. Dyspnea, murmurs, and arrhythmias are common clinical signs in rabbits with cardiac disease. However, rabbits with congestive heart failure may hide signs of illness until the disease has become severe. Unique physiologic characteristics (e.g., obligate nasal breathing and limited collateral circulation to the myocardium) predispose rabbits to collapse from stress and oxygen deprivation; therefore, oxygen supplementation and stabilization are priorities for the rabbit presenting in cardiorespiratory distress. The diagnostic workup for cardiac disease in rabbits is very similar to that for traditional pets and involves radiography, electrocardiography, and echocardiography. Cardiomyopathy and valvular degeneration are relatively common forms of cardiac disease in rabbits, while congenital anomalies are rare. Use and dosing of therapeutic agents is extrapolated from dogs and cats. Spontaneous arteriosclerosis is prevalent in rabbits, with an historical incidence of up to 40% in large breeds.

PhysioZoo: A Novel Open Access Platform for Heart Rate Variability Analysis of Mammalian Electrocardiographic Data

Background: The time variation between consecutive heartbeats is commonly referred to as heart rate variability (HRV). Loss of complexity in HRV has been documented in several cardiovascular diseases and has been associated with an increase in morbidity and mortality. However, the mechanisms that control HRV are not well understood. Animal experiments are the key to investigating this question. However, to date, there are no standard open source tools for HRV analysis of mammalian electrocardiogram (ECG) data and no centralized public databases for researchers to access. Methods: We created an open source software solution specifically designed for HRV analysis from ECG data of multiple mammals, including humans. We also created a set of public databases of mammalian ECG signals (dog, rabbit and mouse) with manually corrected R-peaks (>170,000 annotations) and signal quality annotations. The platform (software and databases) is called PhysioZoo. Results: PhysioZoo makes it possible to load ECG data and perform very accurate R-peak detection (F 1 > 98%). It also allows the user to manually correct the R-peak locations and annotate low signal quality of the underlying ECG. PhysioZoo implements state of the art HRV measures adapted for different mammals (dogs, rabbits, and mice) and allows easy export of all computed measures together with standard data representation figures. PhysioZoo provides databases and standard ranges for all HRV measures computed on healthy, conscious humans, dogs, rabbits, and mice at rest. Study of these measures across different mammals can provide new insights into the complexity of heart rate dynamics across species. Conclusion: PhysioZoo enables the standardization and reproducibility of HRV analysis in mammalian models through its open source code, freely available software, and open access databases. PhysioZoo will support and enable new investigations in mammalian HRV research. The source code and software are available on www.physiozoo.com.

Electrocardiographic reference values for healthy Netherland Dwarf rabbits and the influence of body position, age and gender

<p>The aim of this study was to provide reference values for a single, popular breed of pet rabbit. Moreover, additional objectives were to determine whether sex, body position or age alter Netherland Dwarf rabbit electrocardiographic variables and whether the use of electrocardiographic filters affects those variables. Forty Netherland Dwarf rabbits were examined clinically and standard six-lead electrocardiograms (ECGs) were recorded in sternal and then dorsal recumbency. At first power-line and anti-drift filters were used and then they were disabled. The following variables were measured in lead II: heart rate; P wave duration and amplitude; P-R interval; QRS duration; R wave amplitude (with and without filters); Q-T interval; T wave duration and amplitude; S-T segment; J-T duration; and mean electrical axis (MEA) (with and without filters). MEA was determined by 3 different methods. After statistical processing of the data, our results showed that there were no significant differences between both recumbencies, with the exception of the J-T duration, which was higher in dorsal recumbency. The R wave amplitude using electrocardiographic filters showed significant differences between males (0.083 mV) and females (0.115 mV; P&lt;0.05); and between younger rabbits (0.108 mV) and older rabbits (0.097 mV; P&lt;0.05). These differences were not shown between R waves with filters disabled. Moreover, the strongest correlation was between 2 MEA methods without filters. MEA was more leftward in the pet rabbit than in other species (dog or cats). In conclusion, electrocardiography recording without electrocardiographic filters should be assessed when it is possible, and the specific ECGs characteristics for Netherland Dwarf rabbit should be taken into account.</p>