Congestive
heart failure in rabbits
Esther van Praag, Ph.D.
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The
heart is located in the thoracic cavity, its apex (tip of the heart) is
directed backwards and slightly to the left; the base is directed forwards.
Like other small animals, the rabbit heart is formed by 4 chambers, 2 atria
and 2 ventricles separated by inter-auricular and inter-ventricular septa,
but it also possesses some anatomical and physiological particularities.
Atria
are thin walled chambers that receive blood, while the ventricles are thick
walled muscular structures that pump the blood out of the atrium, back into
the blood system.
When
the left ventricle is not able to pump the blood out of the left
atrium, or when the mitral valve is not working properly, the blood will
accumulate in the lungs (left sided-heart failure). These become congested,
leading to pulmonary edema (accumulation of fluids). As a consequence, the
oxygen uptake and its movement from the lungs to the heart will be impaired,
causing tiredness. It is often accompanied by labored breathing (dyspnea).
When
the right ventricle is not able to function properly, or the tricuspid
valve is defective, the blood pressure will rise,
leading to fluid accumulation in body tissues, mainly the abdomen and the
lower body parts.
Causes
The main
cause for congestive heart failure is a malfunctioning of the left ventricle.
Regularly it also is caused by a lack of movement or a diet deficiency
(vitamin and mineral deficiencies) in rabbits. Further causes leading to this
disorder include:
·
Arrhythmia
(abnormal heart beat);
·
Bicuspid
or mitral valve defect, either of congenital origin, or caused by an
infection (viral or bacterial), or other diseases;
·
Coronary
disease;
·
Myocardia
related disorders, inflammation or cardiomyopathy;
·
Anemia
or low red blood cell count;
·
Lung diseases, e.g., pneumonia.
Clinical
signs
Signs
of congestive heart failure include tiredness, weakness, loss
of appetite, intolerance to exercice, persistent
coughing or wheezing, dyspnea.
Various
clinical tests (see: Cardiology
and techniques to detect cardiac diseases in rabbits) will often reveal an enlarged heart, increased
heart rate, arrhythmia, and the presence of (lung) edema.
Michel Gruaz The presence of foam in the nasal cavity
(arrow) in this Belgian bearded rabbit that died suddenly is the sign of a
mixed pulmonary and cardiac distress. . Michel Gruaz During the autopsy, heart of the same Belgian bearded rabbit,
with dark heart auricles (arrows), after a heart attack and sudden death.
Treatment
The
treatment of congestive heart failure will not heal the problem, but helps
keeping it under control. It includes the treatment of the underlying disease
(e.g., pneumonia, treated with appropriate antibiotics), and the inset of
medication that will prevent further deterioration of the heart function.
Acute
treatment of congestive heart failure consists of oxygen administration and
rest in a quiet place. The use of diuretics will help relieve the sodium and
fluid retention. Nitrate-based drugs (e.g., nitroglycerin) will help reduce
the strain on the heart. Sometimes, therapeutic pleurocentesis
is needed in a rabbit suffering from pleural effusion
and
severe dyspnea. The cause(s) should be investigated, by means of
echocardiography (ultrasound) for instance.
In
rabbits, long-term management of congestive heart failure includes the use
of:
·
Angiotensin
converting enzyme (ACE) inhibitors (e.g., enalapril)
smoothen the blood vessels so that blood can flow more easily through them or
give rest to the heart, in the hope that it will decrease in size and
respiration will become easier. Enalapril has a
slight little advantage over the other available drugs.
·
Diuretics (e.g., furosemide) help reduce fluid buildup in
the body. Increased excretion of water and sodium will reduce the symptoms of
heart failure. Their dosage is based on the body weight. Indeed, to much will lead to dehydration
and potential kidney failure, while to little will
not bring the expected relief or improvement of the symptoms. The side
effects of diuretics may be a low potassium blood level.
·
Inotropic
agents (e.g., digoxin) are used to stimulate a stronger
heart beating and slightly increase the amount of blood pumped out of the
left ventricle at each contraction. In rabbits, they are used to control
sub-acute and chronic disorders of the myocardium, supraventricular
arrhythmia, or valve regurgitation (leakage of blood from the ventricle back
into the atrium during systole). These drugs should only be used if a regular
monitoring of the hydration state, body weight, appetite, and serum levels of
electrolytes, BUN, and creatinine is possible.
Acknowledgement
Many thanks to Tom Chlebecek, DVM, (Makai Animal Clinic, Kailua, HI), to Frossie Economou and to Michel
Gruaz (Switzerland), for giving the permission to use their
pictures for this page in MediRabbit.
Further
information
M.V. Bray MV, WE. C. Weir EC, D.
G. Brownstein, M. L. Delano, (1992) Endometrial venous aneurysms in three New
Zealand white rabbits. Lab Anim Sci.; 42(4):360-2. Farkas, A. J. Batey, S. J. Coker (2004) How to measure
electrocardiographic QT interval in the anaesthetized rabbit. J Pharmacol Toxicol Methods.; 50:175-85. L.C. St John, F. P. Bell (1990)
Arterial fatty acid-binding protein activity associated with dietarily-induced and spontaneously occurring
atherosclerosis in the rabbit (Oryctolagus cuniculus). Comp Biochem Physiol B.;
97(1):123-7. C. Kozma,
W. Macklin, L. M. Cummins, R. Mauer (1974) The
anatomy, physiology and biochemistry of the rabbit, in The Biology of the
Laboratory Rabbit (Weisbroth et al., eds), pp 50-69. L. I. Kupferwasser,
M. R. Yeaman, S. M. Shapiro, C. C. Nast, A. S.
Bayer (2002) In vitro susceptibility to thrombin-induced platelet microbicidal protein is associated with reduced disease
progression and complication rates in experimental Staphylococcus aureus
endocarditis: microbiological, histopathologic, and echocardiographic analyses.
Circulation;105:746-52. C. J. Orcutt (2000) Cardiac and respiratory
disease in rabbits. Proceedings of the British veterinary Zooligical
Society (Autumn meeting). K. E. Quesenberry, J. W. Carpenter, P. Quesenberry (2004) Ferrets, Rabbits and Rodents: Clinical
Medicine and Surgery Includes Sugar Gliders and Hedgehogs, Elsevier Health,
pp 211-216. R. S. Simons (1996) Lung
morphology of cursorial and non-cursorial mammals: lagomorphs as a case study
for a pneumatic stabilization hypothesis. J Morphol.
1996; 230(3):299-316. F.
Harcourt-Brown Textbook of Rabbit Medicine, Oxford, UK:
Butterworth-Heinemann, 2001. |
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