Total coronary artery occlusion is a common finding in CAD especially in chronic stable angina. Normal coronary blood flow is 5 % of cardiac output that amounts to 250-300ml/mt.At an average heart rate of 70/mt , each beat injects about 5cc blood into the coronary circulation.This is shared between two coronary arteries. This means , only few CC (2-3cc) of blood enters each coronary artery with each cardiac cycle .
When one of coronary artery is totally occluded what happens to the coronary
blood flow ?
A.Total coronary blood flow is thought to be maintained at 5% of cardiac output or only slightly reduced .
B. It is believed , the unobstructed coronary artery could receive the blood meant for the contralateral coronary artery. This possibly explains the increased coronary artery diameter in the non obstructed artery.
C. It’s nature’s wish , that the normal coronary artery tries to shunt 50% of the blood through collaterals if available.
D.If collaterals are not formed it , the unonstructed coronary artery may be over perfused with double the amount of blood flow.
E. Some times , the collaterals steal much more than what the obstructed coronary artery deserves and make the feeding coronary artery ischemic. This is many times observed in total RCA occlusion with well formed collaterals from LAD/ LCX.
F.The collateral flow in CTO also depend on whether flow is directed from LAD system to RCA or from RCA -LAD system. The LAD is better placed to assist RCA than vice versa.This is for two reasons.1.LAD blood flow is higher than RCA so it can share it.2.The driving pressure is more from LAD -RCA , as RCA can receive blood flow even during diastole .
F.During exertion , the coronary hemodynamics become further complex.The collateral’s are traditionally thought to be less than adequate during times of exercise.But it is more of a perception than solid scientific data.This rule may be applicable in only certain group of patients. We know CTO patients with very good exercise tolerance who have documented collateral’s.
G. Collaterals can be either visible or invisible by CAG. The strength of collateral circulation is not in it’s visibility but it’s capacity to dilate and respond to neurohumoral mediators at times of demand. Currently , there is lot to be desired regarding our knowledge about the physiology of visible collaterals, no need to mention about invisible collaterals!
The above statements are based on logics and observations .
Is it not a irony in cardiac literature , where thousands of articles are coming out every month to tackle totally occluded coronary artery( CTOs ) , there is very little data regarding the coronary hemodynamics in chronic total occlusion . How does a patient with CTO can manage a active life with only one functioning coronary artery ?