Etiology.—Increase in the cavities of the heart must be due either to abnormal weakness of their walls or excessive labor in the propulsion of the blood-current. Among obstacles to the circulation should be enumerated valvular disease, arteriosclerosis, chronic interstitial ne phritis, atheroma, and congenital nar rowness of the aorta. Contrary to what might be presupposed, thoracic aneu rism does not cause change in the heart walls, unless associated with aortic re gurgitations. Pericardial adhesions may cause dilatation of the heart, more es pecially when the outer surface of the pericardium is fastened to the chest-wall or diaphragm.
Exophthalmic goitre and tachycardia cause cardiac dilatation, as may also ex cesses in tobacco and venery, great anxi ety and despondency, leukmmia, and chlorosis.
Causes in 360 cases: Arteriosclerosis in 59 per cent.; chronic nephritis in 13.4 per cent.; valvular lesions in 12.4 per cent.; adhesions in the pericardium in 7.6 per cent.; excessive muscular work in 3.3 per cent.; tumors in 1.9 per cent.; aneurisms in 0.95 per cent. Lafleur (Montreal Med. Jour., May, '95).
Principal causes, other than disease of the valves, niyocardium, and pericar dium: 1. Organic changes in arterial system. 2. Overfilling of circulation. 3. Foreign substances in the blood. 4. Causes that act on general cardiac nerv ous system. Arteriosclerosis the most important factor. J. Stewart (Montreal Med. Jour., Apr., '95).
Acute dilatation of the heart can occur in acute rheumatism. Four cases in which no valvular lesion could be found. The lack of resistance of the myocardium doubtless permitted the dilatation to occur. Dilatation is di visible into two classes: one due to pri mary atony of the myocardium, to be treated by digitalis; the other due to secondary atony of the myocardium, following vasoconstriction and arterial tension. Huchard (Jour. des Praticiens, Apr. 27, 1901).
Habitual severe and sustained physical exertion may cause cardiac dilatation, as seen in both athletes and in men follow ing laborious occupations. Sudden dila tation may, indeed, ensue upon a single violent or prolonged muscular effort. In many cases of this sort it is presumable that the myocardium was previously in a vulnerable condition; but yet dilata tion may occur in young and apparently healthy men after mountain-climbing, and, after a period of due rest, be com pletely recovered from. In other cases, however, especially in persons with less elasticity of constitution, the lesion is a permanent one and progresses to a fatal termination.
In ten runners, who had just reached the goal, apex seemed to have deviated to the left from two to three centime tres. In one, affected with aortic in sufficiency, apex lowered and notable in crease of prxcordial dullness, evidently connected with dilatation of right cavi ties. Among all the men arterial press
ure lowered. Mechanism seems to relate to overtaxing, general fatigue, and to se creted toxic products. Teissier (Le Bull. Ated., Dec. 19, '94).
Excessive work thrown upon normal right ventricle presents fairly-distinctive symptom.—namely, pain, localized in the region of the second and third left costal cartilages; usually dull, but may be acute; sense of tightness in prrecordia. In the adolescent type of dilatation in crease of size upward and to the left, giving increased area of relative cardiac dullness in third, second, and sometimes first left interspaces. F. Stacey Wilson (Birmingham Med. Rev., Sept., '94).
Cycling tells primarily and distinct ively on the heart and circulation. Ben jamin Ward Richardson (Asclepiad, Third Quarter, '94-'95).
Several subjects in which death had occurred from heart-strain. Marked dila tation of coronary veins and their sub epicardial branches. Microscopically, dilatation seen to extend to capillaries between individual muscle-bundles. In termuscular connective tissue granular and cloudy. Muscle-cells showed vacuo Jar degeneration. Venous congestion and cedema of muscular bundles and con nective tissue. Banti (Centralb. f. allg. Path. u. path. Anat., B. 6, Nos. 14, 15, '95).
Segmentary dissociation of the myo cardium in a fatal case of strained heart. Fibre seemed to have its continuity broken at the level of the intercellular cement. FOlex Ramond (Le Bull. Med., Dec. S, '95).
Pulse after violent use of bicycle in some cases reached 250; aften ten hours' rest, heart still accelerated: a sign of beginning insufficiency. Mendelssohn (Med. Press and Circular, Jan. 35, '96).
Study of the lesser degrees of cardiac weakness and dilatation. After fatigue the Least is in a temporarily-relaxed condition, similar to that of the skeletal muscles after severe exertion. After wrestling the heart may be temporarily dilated, and, as the pulse indicates, may contract with much diminished force. The temporary and physiological relaxed condition of the organ merges by inter niediate degrees into one of actual dila tation. Clinical observations indicating three phases of pathological relaxation of the heart:— 1. A premonitory stage characterized by palpitation, excitability of the heart's action, feeling of fatigue, and slight anxiety. Cases of this kind should not be regarded as merely nervous. As etio logical factors the following are men tioned: Rapid growth at puberty, sex ual excesses and masturbation, physical and mental overwork, mental troubles, antnia, alcohol and nicotine, fatty in filtration, previous illnesses, and prema ture old age.