Collaterals in the coronary circulation
Atherosclerosis or cholesterol blocks in the arteries is the single most cause of death in the world. Heart attacks or myocardial infarction is now not an alien term. Many factors determine survival after an heart attack. The apparent discordance in the outcomes of some people who survive a heart attack as compared to those who succumb has been explained on the basis of various reasons. People who have well developed collaterals tend to have survival advantage. What are these collaterals? Can we develop them.
Coronary collaterals or natural bypasses, are channels that connect from one coronary territory to another without having to go through the capillaries. Classically, arteries that supply the heart, the coronaries, are called end arteries. This means that there is no overlap between them. Any thing that stops blood supply in an artery leads to that death of the tissues supplied by the vessel. Collateral circulation is a potential source of blood supply in such situation. About one third of normal individuals have some amount of primitive collateral circulation. Generally they are insufficient in keeping the heart muscle alive by themselves. These channels have the potential of growth, expansion and remodeling. The strongest stimulus for this is chronically reduced blood supply. Ischemia is known to promote release of various angiogenic growth factors that promote development of collaterals. Various synthetically developed Angiogenic growth factors have being evaluated in peripheral arterial disease. But none has been so far found to have clinical utility.
When well developed,collaterals not only prevent injury to the muscle but may abolish symptoms completely.
Figure 1 Presence of collaterals( on the left) leads to much smaller area of injury in comparison to absence of collateral circulation(on the right) in the event of heart attack
Assessment of Collateral circulation
Walk through angina is a phenomenon that is well described where in a person starts having angina on walking certain distance, but the angina disappears as he continues to walk. Various explanations are available for this phenomenon, one of which is collateral recruitment.
Other than this collaterals are well visualized on catheter angiography. Potential collaterals can be demonstrated by assesing angina or ST elevation during balloon occlusion of a coronary artery. Finally there are sophisticated means like pressure wire and flow wire to assess coronary circulation.
Ways to improve Collateral circulation
1 Exercise 150 min/week of moderate intensity aerobic exercise has been observed to reduce cardiac events
2 External Counter Pulsation: is a technique wherein, sequential squeezing o calf muscles using BP cuffs in sync with the cardiac cycle is used to improve sym[ptoms of angina that does not resolve with medicines.
3 Growth Factors: Various angiogenic(new blood vessel generating) growth factors have been studied. They have been tried as injections, subcutaneous or locally inside the coronary arteries
None of the above mentioned ways have been found to have been conclusively proven to have a beneficial effect on collateral circulation
Impact of Yoga
Although, yoga has not been studied to assess impacton coronary collaterals, in a study on 42 men with coronary artery disease, it was found that a user friendly yoga with dietary modification and moderate exercise was far superior to conventional management*
References
*Manchanda S.C. et al. (2003) Reversal of Coronary Atherosclerosis by Yoga Lifestyle Intervention. In: Dhalla N.S., Chockalingam A., Berkowitz H.I., Singal P.K. (eds) Frontiers in Cardiovascular Health. Progress in Experimental Cardiology, vol 9. Springer, Boston, MA.