Ventricular septal defect with aortic valve insufficiency in a New Zealand White rabbit

Rabbit Pediatrics

Rabbits encompass roles spanning from companion animals, wildlife species to laboratory animal models. Pediatric care of these species therefore may extend to various disciplines of veterinary medicine. Rabbits are born altricial but have a unique perinatal relationship between kit and doe with infrequent nursing. Nursing is immunologically protective to the kit and close contact with the doe allows for colonization of their gastrointestinal tract with bacterial flora. The most common diseases that pediatric rabbits are faced with are gastrointestinal in nature with orphaned and hand-reared rabbits at higher risk due to the aforementioned effects on their immune system.

Cardiology in Rabbits and Rodents-Common Cardiac Diseases, Therapeutic Options, and Limitations

Information about heart diseases and their treatment is still sparce for rabbits and rodents. Dilated cardiomyopathy seems to occur more frequently in rabbits, whereas in guinea pigs pericardial effusion is often diagnosed. There are still no available therapeutic studies for heart diseases in rabbits and rodents, and treatment is often extrapolated from dogs and cats. Consideration should be given to the off-label use of drugs, mostly not licensed in the species mentioned in this article.

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.

International Harmonization of Nomenclature and Diagnostic Criteria (INHAND): Nonproliferative and Proliferative Lesions of the Rabbit

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions Project (www.toxpath.org/inhand.asp) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP) and North America (STP) to develop an internationally accepted nomenclature for proliferative and non-proliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying microscopic lesions observed in most tissues and organs from the laboratory rabbit used in nonclinical safety studies. Some of the lesions are illustrated by color photomicrographs. The standardized nomenclature presented in this document is also available electronically on the internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous lesions as well as lesions induced by exposure to test materials. Relevant infectious and parasitic lesions are included as well. A widely accepted and utilized international harmonization of nomenclature for lesions in laboratory animals will provide a common language among regulatory and scientific research organizations in different countries and increase and enrich international exchanges of information among toxicologists and pathologists.

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.

Right Atrioventricular Valvular Dysplasia in a New Zealand White Rabbit

A sixteen-week-old, male New Zealand White rabbit was euthanized following an acute onset of respiratory distress and cyanosis. On necropsy, the rabbit had marked right atrioventricular eccentric hypertrophy, absence or rudimentary presence of the septal leaflet of the right atrioventricular valve, focally extensive left ventricular infarction, diffuse hepatic chronic passive congestion, and diffuse pulmonary edema. To our knowledge, right atrioventricular valvular hypoplasia, dysplasia, or aplasia has not been previously described in rabbits.

Ostium secundum type of atrial septal defect in a rabbit

A 14-month-old, female mini rex was referred for a detailed examination because of exercise intolerance with associated dyspnea. The thoracic radiograph demonstrated severe cardiac enlargement and elevation of the trachea. The echocardiography revealed dilatations of the right-side heart and pulmonary artery, and the color flow Doppler echocardiography demonstrated an atrial septum defect with left to right shunt, resulting in a disturbed flow. The rabbit died 19 days after the initial presentation, and a necropsy was performed. At the necropsy, a defect, 5 mm in diameter, was detected in the atrial septum. Based on the location of the defect, an ostium secundum type atrial septal defect was diagnosed. This is the first clinical report of atrial septal defect in rabbits.

[Restrictive ventricular septal defect in a dwarf rabbit]

A 9-week-old intact female dwarf rabbit was presented for evaluation of a heart murmur. Physical examination revealed a grade IV/VI systolic heart murmur with the maximal intensity over the right heart base. Evidence for a left-sided cardiomegaly was present on lateral and dorsoventral radiographs. An electrocardiogram was recorded in right lateral recumbency, which revealed a sinus tachycardia with a heart rate of 360 beats/minute. Echocardiography showed normal dimensions for the atria and ventricles. Two-dimensional echocardiography confirmed the presence of a perimembranous ventricular septal defect (VSD) with a diameter of 0.8 mm. Identification of the VSD was possible from a right (long and short axes) and a left parasternal window. Peak flow velocity of the systolic left to right shunt was 5.2 m/s. Additionally, a relative pulmonic stenosis (peak flow in the pulmonary artery of 1.02 m/s, pulsed-wave Doppler) was present. According to these findings, the VSD was classified as restrictive. At this time point, medical treatment was unnecessary. The re-examination after 7 weeks revealed unchanged morphological and haemodynamic findings. The VSD in this dwarf rabbit displayed both in the physical and echocardiographic examinations typical features as seen in dogs and cats as well as in one New Zealand white rabbit.

Left ventricular radial colour and longitudinal pulsed-wave tissue Doppler echocardiography in 39 healthy domestic pet rabbits

This paper reports radial colour and longitudinal mitral annulus pulsed-wave tissue Doppler findings in a large cohort of healthy, adult pet rabbits. Thirty-nine rabbits (22 Dwarf Lops, 14 French Lops and three Alaskans) underwent conscious echocardiography. The median age of the rabbits was 22 months and the median weight was 2.8 kg (Dwarf Lop 2.4 kg/French Lop 6.0 kg). Adequate radial colour and longitudinal pulsed-wave tissue Doppler traces were obtained in 100% and 85% of cases, respectively. Most systolic tissue Doppler parameters were significantly higher in French Lops than in Dwarf Lops. Separation of mitral inflow diastolic waves was present in 40% of cases using conventional spectral Doppler and in >60% of cases using pulsed-wave tissue Doppler which could be beneficial when evaluating diastolic function in rabbits. This study can be used as a reference for normal echocardiographic tissue Doppler values for adult rabbits undergoing conscious echocardiography in clinical practice.