Chapter 8 



DAMAGE OF THE HEART MUSCLE CELL 



DUE TO ANOXIA 



METABOLISM OF NORMAL CARDIAC MUSCLE 



T, 



hree stages are recognisable in the metabolism of normal 

 cardiac muscle. During the first of these the heart muscle abstracts 

 fuel from the blood and metabolises it. The energy so liberated is 

 largely saved from dissipation and diverted by special channels to 

 the contractile mechanism where it is utilised in a series of complex 

 reactions (Bing, 1956; Olson and Patnek, 1959) . 



Energy Liberation 



Cardiac fuel consists largely of free fatty acids, glucose, lactate 

 and pyruvate which are extracted from the capillaries of the myo- 

 cardium and so changed that their energy is set free. Acetate, ketone 

 bodies and amino acids are also used, but to a much lesser extent. 

 Indeed, the heart can obtain energy from every form of fuel avail- 

 able to it in the blood. Pyruvate seems to be its favourite but the 

 muscle cells can shift from one preference to another. After a meal 

 or during the infusion of sugar, glucose, lactate and pyruvate be- 

 come the chief sources of energy, and consequently the cardiac 

 respiratory quotient is nearly 1.0. Following overnight fasting, 

 fatty acids are mainly utilised and the respiratory quotient drops 

 to about 0.82. With prolonged fasting and in diabetes mellitus 

 carbohydrates are even less utilised by the heart and its R.Q. falls 

 as low as 0.70 showing that now it depends almost wholly on fatty 

 acids for energy. When much food is available, therefore, carbohy- 

 drate provides most of the heart's energy but when fasting the 

 organ depends largely upon fats. 



The heart is well adapted for continuous aerobic work since it 

 is three to four times as vascular as skeletal muscle and its blood 

 flow is 10 to 20 times as great per unit weight of tissue. (Olson 

 and Schwartz, 1951) . Moreover, the heart muscle cells are very 

 good at extracting oxygen from the blood, and nowhere else in 



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