HYPERTROPHY. 



319 



HYPERTROPHY. 



Three varieties of cardiac hypertrophy are usually described, 

 according to the size of the cavities associated with the 

 increased thickness in the muscle-walls; simple, in which the 

 cavities are of normal size ; concentric, in which they are 

 smaller than normal ; and eccentric, in which they are dilated. 

 In x'nnple dilatation also the heart is enlarged, but not hyper- 

 trophied. 



Causes : The hypertrophy is the result of increased demands 

 made upon the heart-muscle. Stenotic and incompetent valves 

 are a very frequent cause. General arterio-sclerosis, often 



--LV 



Hypertrophy of left ventricle (front view). Heart is elongated. Septum occupies 

 middle of anterior surface. (From a case of granular kidney from a specimen 

 in Charing Cross Hospital Museum (Green).) 



associated with interstitial nephritis, greatly increases the work 

 of the left ventricle and leads to its hypertrophy (Figs. 138 

 and 139). Obstruction to the pulmonary circulation, as, for 

 instance, in fibroid phthisis and emphysema, leads to hyper- 

 trophy of the right ventricle (Figs. 140 and 141). Simple 

 functional overactivity, as in hysteria and exophthalmic goitre, 

 may lead to a uniform hypertrophy of the whole heart. 



Dilatation occurs where the heart-muscle is exhausted and 

 unable to overcome the impediment. 



Microscopically is noted an increase in the size of the 

 muscle-fibres ; there is also probably an increase in their 



