In coronary angiography, a clinically significant blockage in a major coronary artery is considered to be an obstruction of at least?

Atherosclerosis:

The Atherosclerosis, is the disorder in which the narrowing of the arteries occurs and which is mainly due to the damage to the endothelium layer of the arteries. Which is caused by the deposition of the fat and cholesterol materials in the blood vessels, causing the blockage in the system.

LDL:

Low density Lipo-protein are called as "the bad cholestrol". As the lipo-protein serves as the function for the transportation of the fat molecules in the body through the extracellular water medium.

Explanation:

Coronary Angiography:

The medical procedure to analyze or measure the amount of blood flow inside the heart or mainly in the coronary arteries of the heart (arteries), by using the special contrast medium and x-rays is called as coronary angiography.

The main function of the coronary arteries in the blood circulation system is to supply oxygenated blood to the heart muscles. As they provide the energy to the heart pumping mechanism. Obstruction of Coronary artery:

The obstruction of the coronary artery can cause very chronic and life threatening disorders and can increase the risk of having the heart attack (which means the heart is no more supplied by oxygenated blood) so, the heart is no more able to performs its work properly its unable to perform its function in a proper manner.

Some of the causes are due to the deposition of the cholesterol, fat, in the arteries, which causes the narrowing of the arteries inside the blood circulation system. The deposition of the cholesterol is termed as Atherosclerosis.

Myocardial infarction:

Causes of the Atherosclerosis leads to many disorders but the main cause of the disorder is the Heart attack or in the medical term is called as myocardial infraction.