VARIETIES.—Two forms may be recognized—simple hypertrophy, in which the cavity or cavities remain of the normal size; and eccentric hypertrophy, in which with increased thickness of the walls there is enlargement of the cavities. Dilated hypertrophy and hypertrophy with dilatation are terms by which the latter form is most frequently described.
By many writers a third variety, concentric hypertrophy, is recognized, in which there is diminution in the size of the cavity with thickening of the walls; but in these cases we have to deal with a post-mortem change—rigor mortis; and if the organ is kept for twenty-four hours or soaked in water, the so-called concentric hypertrophy will usually disappear.
The increased size may affect the entire organ, general hypertrophy; or only one side or one cavity, partial hypertrophy. The latter is the most common. Of the single chambers the left ventricle is most frequently involved, then the right. The auricles are rarely affected alone, but the left is more often than the right.
ETIOLOGY.—Disturbed innervation and increased work are the two principal causes of cardiac hypertrophy. We see hypertrophy from deranged innervation (1) in Basedow's disease (exophthalmic goitre); (2) in long-continued nervous palpitation from any cause, particularly sexual excesses; (3) certain poisons and articles of diet appear to act in this way, as tea, coffee, alcohol, and tobacco.
In all these cases there is simple over-action or increased functional activity, which, if prolonged, certainly produces some degree of hypertrophy. How this condition is brought about is not very clear. We may suppose the increased frequency of contraction to result from stimulation of the accelerator nerves, as seems probably the case in exophthalmic goitre; from irritability of the cardiac ganglia themselves, owing to the influence of such toxic agents as tea, tobacco, etc.; or from defective vagus control. Long-continued neurotic palpitation in reality causes hypertrophy by increasing the work of the heart, for under perverted stimuli the ventricular contractions are doubled in frequency—sometimes in force as well—while maintaining the circulation in normal vessels offering no increased resistance to the blood-flow.
There can be no doubt of the occurrence of actual hypertrophy as a sequence of the irritable heart induced by sexual excesses and tobacco. I had under observation on and off for several years a very emotional and hypochondriacal young man addicted to venery, whose left ventricle became strongly developed and beat outside the nipple-line. His entire thoughts became centred in his heart trouble, and he travelled from one authority to another in this country and Europe seeking advice.41 The smoker's heart rarely leads to much hypertrophy, but in young lads it may do so, and even induce more serious disease, as indicated by the presence of murmurs and signs of cardiac failure. The abuse of spirits as a cause of hypertrophy is not very clearly established. Alcoholism appears to be a factor in the production of atheroma. I have been struck by the fact that in four typical instances of so-called idiopathic hypertrophy occurring in powerfully-built workers there was a history of intemperance; and it is quite possible that this may have combined with the muscular efforts in inducing the heart disease; at any rate, it would prove an important element in hastening the final breakdown when from any cause hypertrophy had arisen.
41 After three or four years of most unnecessary worry in the expectation of death from heart disease, this patient has quieted into the belief that there is not anything seriously wrong with his heart, and has now rarely any indications of trouble.
The majority of cases of hypertrophy of the heart are due to mechanical causes leading to increased resistance and increased work on the part of the organ. Under these circumstances, as in other hollow viscera, the muscle develops, gets thicker and firmer, and capable of accomplishing the extra labor thrown upon it. Defects in the valvular mechanism, obstruction, or incompetency, and increased resistance to the blood-flow in the arteries, are the most important causes of hypertrophy. The ultimate factor in all is heightened pressure within the cardiac cavities due to one of two things—increased volume of blood to be moved or difficulty in propelling the normal volume, caused by obstruction to the flow either central or peripheral.
Pericardial adhesions may impede the action of the heart, and either directly cause hypertrophy or induce dilatation and a consequent hypertrophy.
The details regarding the etiology are best considered in a study of hypertrophy as it affects the individual chambers.