Narrowing of the Mitral orifice. In addition to the same general symptoms as the last named lesions, there is a sighing, blowing, purring or rasping sound, according to the degree of narrowing, heard before the first sound of the heart. It is the noise of the blood rushing through the narrowed orifice between auricle and ventricle. It is usually loudest behind the middle of the shoulder on the left side. Feeble pulse, frequent imminence of suffocation and filling of the limbs, etc., are nearly constant.
Narrowing of the Tricuspid orifice. Symptoms nearly identical with the last. Venous pulse more constant. Blowing murmur sometimes loudest on the right side of the chest.
Induration or insufficiency of the aortic valves. Blowing murmur with the second sound of the heart. Double rushing sound in the carotid with each heart’s beat. There is an appreciable interval between the beat of the heart and corresponding pulsation at the jaw.
Induration or insufficiency of the pulmonary valves. Blowing murmur with the second heart sound, but no corresponding double sound in the carotid, nor any marked retarding of the pulse.
Loose coagula in the heart or adherent ones (polypi) produce one or other of the above class of symptoms, according to the particular orifice they tend to block or the valves whose function they impair.
Anæmia and leukæmia may have blowing murmurs with the first or second heart sound.
Embolism. Plugging of arteries. Another class of symptoms sometimes supervenes because of loose clots being washed on into the arteries, and blocking them when they reach those that are too small to transmit them. These symptoms will be as varied as the organs whose arteries are plugged. If in the brain there may be dulness, stupor, vertigo, somnolence, delirium; if in the liver, biliary and digestive derangement; if in the lungs, cough with the other signs of pneumonia and abscess; and if in the limbs lameness and paralysis, (brought on or aggravated by exercise, and often removed by a few minutes’ rest), wasting of the muscles, etc. (See Embolism).
Causes. These are in the main the same as those of pericarditis. Weak health, exposure to extremes of weather, punctures with foreign bodies, but above all, the rheumatic constitution are common causes. Indeed rheumatism appears more prone to attack the serous membrane lining the heart cavities than that enveloping it externally. One reason for this is to be found in the great and incessantly recurring strain on the fibrous structure of the valves, and particularly in hard worked horses and hunting dogs in which the strain is often extreme. It has been argued that the increased blood pressure caused by digitalis is an appreciable cause. Its frequent connection with rheumatism is shown in the rheumatic lesions of joints and fibrous structures seen in carcasses dead of endocarditis.
Diseases in the muscular substance of the heart as cysts, abscess, etc., frequently extend to the endocardium.
Among other causes must be mentioned disease-changes in the blood. These may act on the valves directly as in the case of lactic acid injected by Dr. Richardson, into the peritoneum with the view of producing rheumatism and successfully as regards the lesions of the cardiac valves; or indirectly by determining coagulation and irritation of the lining membrane coming into contact with the clot. The very fibrinous and plastic state of the blood in extensive inflammations is a probable cause of the occurrence of clots in the heart, and the frequency of such clots in the dog has been ascribed to the plasticity of his blood (Leblanc). The injection of pus into the blood or the absorption of microbes from diseased surfaces will sometimes produce ulcerative disease of the valves. The same is true as regards the germs of omphalitis, pneumonia, arthritis and other infectious diseases.