Heart Diseases

By | 2010-08-29

As in man, heart troubles are very much more common in old age. However, even young animals may suffer from faulty heart action due to congenital defects.

Signs

Irregularity in the heartbeat, some difficulty in breathing without obvious changes in the lungs or pleura, breathlessness when the animals are compelled to exert themselves, a tendency to swelling of the dependent parts of the body (e.g. along the lower line of the chest and abdomen and ‘filling’ of the limbs), are among the signs. A cough is sometimes a symptom of valvular disease.

Congestive heart failure

Disease of the right side of the heart often gives rise to ascites, sometimes to swelling of one or more limbs due to oedema. Engorgement of the veins often occurs, with enlargement of the liver. The animal becomes easily tired and may lose weight. Ultimately congestive heart failure is likely to occur. This may also result from left-sided failure due to myocarditis or mitral valve incompetence. In small animals, treatment consists in reducing exercise and giving diuretics.

A common cause of heart failure in dogs is degeneration of a MITRAL VALVE.

Pericarditis

Pericarditis is an inflammation of the membrane covering the exterior of the heart. It may be ‘idiopathic’, when its cause is not known; it may be ‘traumatic’, when it is due to a wound; or it may follow a general infection (e.g. ‘heart-water’) or a local infection (e.g. pleurisy) or an abscess in a remote part of the body. Pericarditis may be ‘dry’, in which case the 2 opposing surfaces of the membrane are covered by a layer of fibrin; or oedema may accompany this condition, in which case fluid fills up the pericardial sac and, when no more distension of the sac can occur, presses upon the outside of the heart itself. Pericarditis has been reported in very young pigs at grass. The piglet, often in good condition and not anaemic, dies suddenly at about 2 to 3 weeks of age. (See also ‘MULBERRY HEART’.)

Tamponade

A rapid accumulation of blood in the pericardium, suddenly arresting heart function.

Acute or chronic tamponade was the presenting sign in 42 cases of pericardial effusion in a series of large dogs with an average age of 9 years. Twenty-four of the cases were associated with neoplasia, 8 with benign idiopathic effusions, 6 with primary heart disease, and 2 with trauma.

Echocardiography was found to be the best way of detecting pericardial effusion; and the idiopathic effusions responded well to pericardiectomy.

Congenital heart disease in dogs and cats

Congenital heart disease in dogs and cats is usually indicated by a cardiac murmur, the site and nature of which shows whether a valve or a shunt is involved.

Shunts include ‘holes’ in the heart, and patent ductus arteriosus.

Radiography and Doppler ultrasound are helpful in diagnosis.

Surveys of a total of 580 dogs with congenital heart disease showed that 28 per cent had patent ductus arteriosus; 16 per cent had pulmonary stenosis; 9 per cent had persistent right aortic arch; over 7 per cent had a ventricular septal defect; and over 7 per cent had stenosis of the aorta. (See also HEARTWORMS.)

Deficiency of vitamin E

Deficiency of vitamin E is one cause of sudden cardiac arrest in cattle.

Signs

These are not always characteristic, but they include breathlessness, pain on pressure of the left side of the chest, a jugular pulse (seen along the jugular furrow with each heartbeat), and oedema. On listening to the heart a variation in the normal sounds may be heard, or they may be altogether masked by the presence of the fluid. A tinkle is sometimes audible over the region of the heart; friction sounds indicate the presence of dry pericarditis; and irregularity or even palpitation may be noticed.

Traumatic pericarditis of cattle

Sometimes when the animal is thought to be suffering from simple digestive disturbance, it is found that a nail or piece of wire has been swallowed and arrives in the reticulum.

A distance of about only 5 cm separates the heart from the reticulum, so that the foreign body is liable to penetrate the pericardium.

Attacks of pain may occur, the appetite is irregular, but after a time the animal regains its normal health, since an adhesion has occurred around the hole in the reticulum wall, and the inflammation subsides. A cow may die suddenly before symptoms of pericarditis appear, or soon afterwards.

Treatment

Treatment is sometimes feasible by surgically opening the rumen and removing the piece of metal.

Prevention

In Switzerland the percentage of cows slaughtered on account of traumatic pericarditis was reduced following the use of magnets for the treatment of traumatic reticulitis. Magnets weighing 114 g, 90 mm long and 15 mm in diameter were used orally 10 minutes after a subcutaneous injection of atropine sulphate. Without this it was found that only 53 per cent of the magnets dropped at once into the reticulum. The correct siting of the magnets was checked with a compass.

Myocarditis

Myocarditis is inflammation of the heart muscle. In the pig it is seen in HERZTOD disease, for example; in cattle, in MUSCULAR DYSTROPHY. (See also CANINE PARVOVTRUS; MYOCARDIUM.)

Endocarditis

Endocarditis is an inflammation of the membrane lining the heart. It frequently leads to the development of nodules on the valves.

The nodules result in an incomplete closing of the valves, and since the fibrin deposited upon them tends to become converted into fibrous tissue (‘organised’), the growths slowly increase in size. They are seen in chronic erysipelas of pigs. (See SWINE ERYSIPELAS.)

The valvular insufficiency can be diagnosed by auscultation. Congestive heart failure may be the outcome (sometimes embolism); but compensation takes place, and the animal may live a long time with faulty valves.

Bacterial endocarditis is a cause of death in cattle, especially in South Wales. (See HEARTWORMS for another cause of endocarditis in the dog.)

Valvular diseases

Valvular diseases form a most important and common group of heart disorders, and although the power of compensation already referred to may so neutralise the ill-effects of a narrowed valve, or one which leaks, severe strains or exertion — or even trying conditions such as parturition — may precipitate ill-effects. Very often when an animal ‘drops dead’, perhaps after running a race or while undergoing some departure from its normal mode of life, the actual cause is afterwards found to be a diseased heart valve. Fainting fits are not by any means rare in incompetence of the tricuspid valves. Congestion of the lungs may be brought about by incompetence of the auriculo-ventric-ular valve on the left side of the heart (mitral insufficiency); this same condition may lead to a chronic asthmatical cough in old dogs, which is occasionally mistaken for bronchitis.

Canine heart repair

Skeletal muscle transplants were used to replace or repair defects in the left ventricle of dogs, some of which were kept alive for over a year. At autopsy the transplants were found to be in good condition, according to a report in Circulation.

Hypertrophy

Hypertrophy, or enlargement of the heart, takes place as the result of some constant simple strain, such as occurs in racehorses, hunters, and sporting dogs; or as the result of backward pressure from a diseased valve, and which entails the heart muscle ‘compensating’ for the effects of valvular disease. Alternatively it may be due to resistance to the flow of blood in some diseased organ or tissue which results in high blood pressure. (See COMPENSATION.)

Hypertrophy of the left ventricle, leading to heart failure, may in the dog follow Leptospira canicola infection.

Dilatation of the heart may precede hypertrophy, i.e. when it occurs before the heart muscle has had an opportunity to increase to meet the extra demands upon it; and it very frequently follows hypertrophy, especially when there is some disease process at work which hinders the proper nutrition of the heart muscle.

Hypertrophy may be a beneficial condition in any animal, and, except when it is due to valvular trouble, need not cause any worry to the owner. It is sometimes excessive in horses; in some instances the heart may weigh as much as 11 kg (25 lb) instead of the 3 or 3.5 kg (7 or 8 lb) of the normal. Degenerative changes may follow hypertrophy when the animal becomes less active during later life.

Congenital defects

These include a patent ductus arteriosus. (See diagram of fetal circulation undtr CIRCULATION OF BLOOD; also LIGAMENTUM ARTERIOSUM; ECTOPIA CORDIS.) Tetralogy of Fallot consists of: (1) stenosis of the pulmonary valve; (2) a defect in the septum which separates the 2 ventricles; (3) the aorta over-riding both ventricles; (4) marked hypertrophy of the right ventricle.

The signs are often vague: in kittens, for example, these may be a failure to thrive, and inability to cope with exercise. More serious defects result in the death of newborn kittens.

Functional disorders

Palpitation is a condition in which the heart beats fast and strongly, due to fright, for example(see tachycardia, below).

Bradycardia is a condition of unusually slow action of the heart. Intermittency or irregularity is an exceedingly common condition among animals, and as a rule appears to cause them no inconvenience whatever. In some horses at rest in the stable the heart constantly misses every 3rd, 4th, or 5th beat, a long pause taking the place of the pulsation, but when at exercise or work the normal rhythm is restored.

Heart-block is a condition in which the conducting mechanism between atrium and ventricle (atrio-ventricular bundle of His) is damaged in whole or part, so that the two beat independently of each other.

Rapid heart action (tachycardia) may have a number of causes including exertion or excitement. It is normally harmless in such cases. It is also seen in diseases which affect the transmission of the heartbeat stimulus.

Cardiac flutter and fibrillation are conditions of great irregularity in the pulse, due to the atria emptying themselves, not by a series of regular waves, but by an irregular series of flutters or twitches instead, which fail to stimulate the ventricles properly.

Five cases of atrial fibrillation were described in horses after racing. In 4 of them, which had performed poorly during their races, the arrhythmias disappeared spontaneously within 24 hours; these cases were regarded as paroxysmal. In the 5th horse, which won its race, the arrhythmia persisted for at least 45 hours after the race and it was regarded as an example of persistent atrial fibrillation. Treatment with quinidine sulphate restored the sinus rhythm. Paroxysmal atrial fibrillation may cause a sudden decrease in racing performance.

Diagnosis of heart disease

Diagnosis of heart disease is based largely on the character of the pulse and heart sounds. Murmurs, for example, indicate valvular incompetence, cardiac dilatation, or congenital lesions. Muffled sounds may indicate fluid in the pericardium (or pleurisy).

Additionally radiography and cardiography are used in diagnosis. (See PACEMAKERS as a possible treatment of some canine patients.)

Heart Stimulants

Drugs used as cardiac stimulants include theophylline, adrenaline, isoprenaline and dobutamine.