90 



Collateral circulation obviously plays an important part; it 

 is now well known that the coronary branches are not end 

 arteries, as was at one time believed, but have numerous 

 anastomotic connexions. Further, as described by Gross,^* 

 the blood vessels (arteriae telae adiposae) of the subepi- 

 cardial fat, which increases in amount as life advances, can 

 in some measure exercise a compensating influence, supply- 

 ing a considerable amount of blood to the subjacent muscle. 

 Belonging to this system are delicate parallel vessels accom- 

 panying (at some distance) the main coronary branches, as 

 well as a feltwork of vessels in the fat of the auriculo- 

 ventricular groove. Gross emphasizes the importance of a 

 relative anaemia of the muscular walls of the right heart in 

 old age, as bearing on failure in pneumonia, etc. ; he 

 suggests a variation of the adage that a man is "as old as 

 his arteries " to "as old as his right coronary artery." 



It is noteworthy that when the main trunks and large 

 branches of the coronaries are the seat of pronounced 

 sclerotic changes the intramuscular twigs and finer ramifica- 

 tions may remain practically unaffected. The extent and 

 efl&ciency of the capillary system are obviously of prime 

 importance. 

 Syncope from Ventricular Standstill due to Seart-hlocJc. 



In cases of heart-block, Adams-Stokes syndrome, etc., 

 Avhere death occurs suddenly, it is uncertain whether simple 

 stoppage of the ventricular beat in the state of diastolic 

 relaxation alwaj's lasts long enough to kill by paralysis of 

 the nerve centres, following the phases of unconsciousness 

 and convulsive phenomena. The time needed in man for 

 irretrievable damage of these centres by acute anaemia is 

 not known ; in the ordinary experimental animals it is rela- 

 tively long — a number of minutes. Of course, there may 

 sometimes be morbid conditions present in man which would 

 shorten the time that circulatory arrest can be survived. 

 But in view of the associated structural damage present 

 in the Adams-Stokes syndrome, the possibility of the ven- 

 tricular standstill terminating in fibrillation in some 

 instances must not be overlooked, though there seems to be 

 at present no actual evidence of this happening in man. On 

 the other hand, it is true that a fall of blood pressure, such 

 as accompanies ventricular standstill, exercises a restrain- 

 ing influence on the development of fibrillation under cer- 

 tain conditions; but this does not always hold good under 

 other conditions — for example, fibrillation sometimes develops 

 in the gravely depressed or dying heart, notwithstanding the 

 fact of excessively low blood pressure. In any case it must 

 be concluded that only a fraction of cases of sudden death 

 can possibly be attributed to ventricular standstill depending 

 on the relatively rare condition of heart-block. 



Syncope during Tachycardia. 

 There is strong reason to believe that the fibrillation 

 mechanism is operative in many cases of sudden death 



