Variations in the Coronary Arteries/ Coronary Dominance

The origin, course, and distribution of the posterior interventricular artery are variable.

In right coronary dominance, the posterior interventricular artery is a branch of the right coronary artery. It’s seen in 90% of the individuals.

In left coronary dominance, the posterior interventricular artery originates from circumflex branch of the left coronary artery. It’s seen in 10% of the individuals.

Anastomoses Of The Coronary Arteries

Anastomoses exist between the terminal branches of the coronary arteries at the arteriolar level (collateral circulation). The time factor in occlusion of an artery is very significant. If occlusion takes place slowly, there’s a time for the healthy arterioles to open up and collateral circulation is established, i.e., the anastomoses become functional. But if sudden occlusion of one of the large branches (coronary artery) takes place, the arterioles don’t get time to open up to provide collateral circulation.

Clinical Significance

Angina Pectoris

If the coronary arteries are narrowed, the blood supply to the cardiac muscles is reduced. Consequently, on exertion, the patient feels moderately severe pain in the region of left precordium that may last as long as 20 minutes. The pain is frequently referred to the left shoulder and medial side of the arm and forearm.

In angina pectoris pain takes place on exertion and relieved by rest. This is since the coronary arteries are so narrowed the ischemia of cardiac muscle takes place only on exertion.

Myocardial Infarction (Mi)

A sudden block of one of the larger branches of either coronary artery generally leads to myocardial ischemia followed by the myocardial necrosis (myocardial infarction). The part of the heart suffering from MI stops functioning and frequently causes death. This condition is named heart attack or coronary attack.

The clinical features of MI are as follows:

A. A sensation of pressure/sinking and pain in the chest that lasts longer than 30 minutes.

B. Nausea or vomiting, sweating, shortness of breath, and tachycardia.

C. Pain radiates to the medial side of the arm, forearm, and hand. Sometimes, it might be referred to jaw or neck.

Sites Of Coronary Artery Occlusion

The 3 most common sites of the coronary artery occlusion are as under:

A. Anterior interventricular artery/left anterior descending (LAD) artery = 40-50 %.

B. Right coronary artery = 30-40%.

C. Circumflex branch of the left coronary artery = 15-20 %.

Note:

A. The MI mostly takes place at rest on the other hand angina takes place on exertion.

B. Anterior interventricular artery/left anterior descending (LAD) artery is most commonly blocked.

Coronary Angiography

The coronary angiography is a radiological procedure to visualize the coronary arteries after injecting contrast medium in their own lumen. The coronary angiography is useful in localizing the sites of the blocks in the coronary arteries.

Coronary Bypass Surgery

The coronary bypass surgery has become common in recent times in patients with unstable/severe angina as a result of obstruction of the coronary artery. A segment of a vein or an artery is connected to the ascending aorta (or to the proximal part of the coronary artery) and after that to coronary artery distal to the obstruction. A coronary bypass graft shunts blood from the aorta to coronary artery distal to the blockage to increase the circulation.

Points to be noted:

A. The great saphenous vein is commonly utilized for grafting because (a) it is easily dissected, (b) it’s diameter is equal to or greater than that of coronary artery, and (c) it gives lengthy portions using a minimum occurrence of valves or branching.

B. The use of left internal mammary artery graft (LIMA graft) and radial artery graft (RA graft) have also become increasingly common.

Coronary Angioplasty

In this process the cardiologists pass a small catheter with a small inflatable balloon connected to its tip into the obstructed coronary artery. As the catheter reaches the obstruction, the balloon in inflated. As a result atherosclerotic plaque is flattened against the vessel wall and the vessel is stretched to increase the lumen. Consequently the blood flow is increased. Sometimes transluminal instruments with rotating blades and lasers are utilized to cut the clot. Following the artery is dilated, an intravascular stentis introduced to maintain the dilatation.