This condition of the heart may be associated with long-continued fatty infiltration, or it may follow an attack of inflammation (Myocarditis), or arise in the course of some wasting disease, or as a result of one or another of the acute specific fevers. It is mostly found to exist in old animals, and the progress of the malady is considerably favoured by a sedentary life; in fact it may occur in an exaggerated form in animals which are not plethoric, although it appears that want of sufficient exercise conduces very much to the progress of the malady. The anatomical changes resulting from the disease are extremely marked, and very easily recognized by the use of the microscope. The muscular walls are, as in the case of fatty infiltration, commonly paler in colour than the normal structure, and often present a faded yellow or pale-brown tint; the muscle is easily torn or broken down, and has been compared in texture to wet brown paper. Under the microscope the muscular fibres, instead of being well defined with perfectly distinct transverse markings, present a granular appearance owing to the presence of minute granules of fat in their structure, and in some advanced cases every trace of the fibrillated appearance of the normal fibre has become obscured, and only a mass of fat granules can be recog-nized.
Fig. 194. - Fatty Infiltration of Muscle. 1 Muscle Fibres (healthy). 2 Fat Corpuscles.
It is well known to pathologists that fatty degeneration may advance to a considerable extent without any symptoms becoming apparent. An animal may die suddenly from the disease the existence of which has not been suspected during its life. This will be quite intelligible to the veterinarian, as the occasional unpleasant sensations which are recognized by the human patient over the cardiac regions would find no expression in the horse. Occasional attacks of what in the human subject is described as " angina pectoris " may occur in the horse, but would either be, as is usually the case, unnoticed, or, if observed, would be referred to an attack of colic or probably a spasm of the diaphragm.
Williams, in his book on The Practice of Veterinary Medicine, records one case which came under his notice, which he considered to be an instance of angina pectoris in a well-defined form. The animal was an aged cart-horse, which for twelve months had clone very little work, owing to the fact that when he was excited by work or exertion, he suffered extreme pain in the left fore-limb, the muscles of which, with the muscles of the chest (pectorals), became violently convulsed. The paroxysm seldom occurred when the animal was at rest, but there was a continual twitching of the muscles, and the animal appeared to dread being approached. On examination by auscultation, a loud cooing or blowing sound was heard over the region of the heart, and there was a strong impulse indicative of hypertrophy. There was also observable a distinct regurgitation of the blood in the jugular vein or jugular pulse. No opportunity in this case was afforded for a post-mortem examination.
Fig. 195. - Fatty Degeneration of Muscle.
1 Muscle Fibre (healthy). 2 2 Muscle Fibres infiltrated with fatty granules.
In some cases of this disease the pulse is remarkably slow, the beats of the heart are generally feeble, irregular, and intermittent, and while exertion increases the frequency of the pulse, it also renders it more irregular, any severe effort soon brings about exhaustion, sighing, and giddiness.
Examination of the heart during life reveals certain signs which are said to be characteristic: the impulse is feeble, but is at the same time well defined; the sounds are weak, in the case of the first sound almost inaudible, and in very advanced cases the sounds may be altogether absent; and it is noticed in regard to the feeble pulse that there is sometimes only one pulsation to two beats of the heart.