BLOOD SUPPLY TO THE HEART 



'57' 



flow or reduces the size of infarcts produced by subse- 

 quent coronary artery ligation (380, 404). The alleged 

 favorable effect on survival of the use of drugs such as 

 papaverine or quinidine is better explained by their 

 known action in raising the fibrillation threshold and 

 in reducing myocardial excitability (384). 



The capable experimental coronary surgeon has 

 been able to improve considerably on the state of 

 such hearts. Much of the advancement in the surgical 

 and physiological fields has arisen from the pioneer 

 investigations and stimulus of Beck (19, 50, 255). 

 The procedures used include section of the cardiac 

 sympathetic nerves (178), induction of myocardial 

 hypoxia by various manipulations of the coronary 

 venous system or by a coronary fistula (19, 79, 95, 

 158), production of mechanical and chemical 

 pericarditis between the epicardium and pericardium 

 to use the extracardiac anastomoses (19, 178), 

 application of extracardiac tissue to the heart (271, 

 324, 372, 373), internal mammary artery ligation 

 (99), sham operations (1, 19, 85), coronary endarterec- 

 tomy (241, 326), and coronary artery bypass (171 ). 



Many of these procedures in the experimental 

 animal are of positive benefit to the heart and give 

 immediate or sustained protection against subsequent 

 ligation of a major coronary artery ramus. Ligation 

 of a major ramus of the left coronary artery causes 

 about a 70 to 90 per cent mortality within the first 

 1 to 2 hours, and chronically there is considerable 

 infarction (95). When partial or complete occlusion of 

 the coronary sinus precedes coronary artery ligation, 

 or when a portion of the coronary bed is perfused in 

 retrograde fashion by connecting the coronary sinus 

 to an artery, the immediate mortality is reduced con- 

 siderably. With the exception of section of cardiac 

 sympathetic fibers and internal mammary artery 

 ligation, most other procedures — chronic coronary 

 venous maneuvers, application of various chemical 

 and mechanical irritants, separately or in combina- 

 tion, and application of extracardiac tissue to the 

 heart, generally lead to a significant reduction in 

 mortality and infarction (there are, however, 

 exceptions) (124). There is an increase in the in- 

 jectable and functional collaterals with the chronic 

 coronary venous maneuvers and with the application 

 of mechanical and chemical irritants to the heart. 

 The level of collateral flow, 5 to 12 ml in most in- 

 stances, considerably exceeds the control retrograde 

 flow of 3 ml with acute artery ligation alone. Accord- 

 ingly, it is deduced that these surgical maneuvers 

 give sustained, and in the case of the coronary venous 

 maneuvers, immediate protection against ligation of a 



major coronary artery branch. The retrograde flow in 

 the chronic experiments equals or exceeds that 

 estimated to be necessary to maintain viability. 



Cardiac benefit from these procedures could arise 

 from retrograde flow of blood from the superficial 

 veins through the capillary bed, from development of 

 intra- and extracardiac collaterals, or from elevation 

 of the ventricular fibrillation threshold, thus giving 

 nature time to develop additional collaterals to 

 sustain the heart. There are no critical experiments 

 to prove that with the acute coronary venous maneu- 

 vers, protection against fibrillation and death is 

 supplied by blood flowing in a retrograde direction 

 from coronary vein to capillary to ventricular cavity. 

 Acute perfusion of the coronary sinus with arterial 

 blood at or near aortic blood pressure, or acute 

 ligation of the coronary sinus, results in venous con- 

 gestion of the left heart with an increased coronary 

 venous pressure, at times equal to the aortic pressure, 

 a diffuse myocardial hemorrhage (with the exception 

 of the septum which remains pink in color), and a 

 sizeable reduction in left coronary inflow and cardiac 

 output. When the peripheral portion of the occluded 

 coronary artery is permitted to bleed externally, the 

 measured backflow is of highly reduced blood and the 

 volume is increased greatly (to 15 ml or more) over 

 that which occurs with acute coronary artery ligation 

 alone (153). It is very important to know that this 

 blood can be shown to have traversed the capillary 

 bed of the occluded coronary artery in a reverse 

 direction. However, proof is lacking that, when the 

 ligated coronary artery is not permitted to bleed 

 externally, flow from the superficial coronary veins is 

 diverted through the capillary bed of the left myo- 

 cardium and then into the left ventricular cavity. 

 Actually, the development of extreme myocardial 

 embarrassment, together with the fact that most of 

 left coronary artery inflow and the blood entering the 

 coronary sinus from the shunt can now be recovered 

 in the anterior cardiac veins of the right ventricle 

 (153), offers not quite certain evidence that the deep 

 ventricular drainage channels are not used. However, 

 the high values for venous pressure in the coronary 

 sinus and the augmentation of peripheral vascular 

 pressure and retrograde flow which appear in the 

 left coronary artery immediately after left coronary 

 venous ligation decrease after a time interval (up to 

 30 days) to values only slightly above normal (153). 



The observation that these procedures can elevate 

 the ventricular fibrillation threshold suggests but 

 does not prove that this is a major mechanism of 

 protection. In hearts with chronic application of these 



