Diseases of the cardiovascular system are rare in horses. Unlike man, horses do not have heart attacks from coronary artery disease. Signs of cardiovascular disease are; an erratic or irregular pulse (arrhythmia – variation from normal rhythm), pulse over 50 or under 25bpm, exercise intolerance & rapid laboured breathing (cardiovascular insufficiency), turbulence in blood flow (murmurs), exaggerated jugular pulse, grey/bluish gums (insufficient O2 – cyanosis), and unexplained fever. Valves keep the blood flowing in one direction – when diseased, blood can leak back, causing the heart muscle extra work.
The main causes of heart disease are; acquired valvular disease, myocarditis, pericarditis & congenital heart defects, all of which can produce heart failure.
Acquired valvular disease – the exact cause is unclear, possibly due to natural ageing and poor blood supply to the edges of the valves. Once damaged, the valves no longer function effectively, creating extra work for the heart, which begins to fail. Less commonly, valves can be damaged by bacterial endocarditis e.g. strangles; this can be treated by prompt action with antibiotics.
Myocarditis – inflammation of the heart muscle. The muscle is unable to contract, leading to left or right sided congestive heart failure. Caused by infectious/parasitic diseases e.g. equine flu, colic, kidney failure, nutritional deficiencies & drug intoxications. Signs occur rapidly, sudden death can occur with no warning. Treatment is directed at the underlying illness, chances of recovery are good if the damage is minimal.
Pericarditis – inflammation of the pericardial sac which surrounds the heart. Caused by pneumonia/pleuritis. Fluid build-up in the sac restricts the heart & interferes with filling. Fluid can be drawn off with a needle giving temporary improvement, although the long term outlook is poor.
Congenital heart disease (birth defects) – most common are septal defects (holes connecting one or more heart chambers), or malformation of the heart valves. Several defects can exist at once, and symptoms depend on type & location, mild defects don’t normally cause a problem. No treatment is available, open heart surgery has not yet been done successfully. Defects are genetic; it is unwise to use the sufferer for breeding.
Heart failure – heart failure can occur suddenly if heart disease is unsuspected, a diseased heart can compensate for many years unnoticed. When a diseased heart weakens, right or left sided congestive failure occurs. The treatment of heart disease aims to prevent & treat the symptoms of heart failure.
Treatment of heart failure- an accurate diagnosis of stage & type of heart disease using x-ray & ECG is required. Diuretics can treat fluid build up, other drugs can increase the force of contraction, and stabilise the heart rate & rhythm. Activity must be restricted.
- Be aware of the normal status, resting heart rate, rhythm & sounds etc.
- Invest in a stethoscope & practice!
- Become familiar with the symptoms of heart disease; exercise intolerance, laboured breathing, high or low pulse, unexplained fever, arrhythmias, murmurs etc.
- Early treatment of inflammation (myo/pericarditis) & bacterial infection (valvular disease) reduces damage.
- Mild birth defects can be tolerated, not recommended for breeding.
- Remember, heart disease is relatively rare in horses.
Giffin, J. M. & Gore, T., (1989) Horse Owner’s Veterinary Handbook. Howell Book House. USA
Marr, C., (1999) Cardiology of the horse. W. B. Saunders. London.