When is myocardium supplied with blood

The left circumflex artery runs under the left atrial appendage on its way to the lateral wall of the left ventricle. Along the way, it spawns a number of branches that supply the left atrial and left ventricular walls. In some cases, a branch will course behind the aorta to the superior vena cava such that it can supply the sinus node.

The left anterior descending artery supplies a major portion of the ventricular septum, including the right and left bundle branches of the myocardial conduction system, and the anterior and apical portions of the left ventricle. Figure 7. Drawing of the coronary arterial circulation in the human heart. The normal human hears does not typically elicit collateralization; each area of myocardium is usually supplied by a single coronary artery.

Coronary arteries are so vital to the function of heart; whenever disease states are associated with flow restriction through the coronary arteries, and subsequently the remainder of the coronary circulations capillaries and veins , the effects on cardiac performance are quite dramatic and often fatal. Coronary artery disease CAD is generally defined as the gradual narrowing of the lumen of the coronary arteries due to coronary atherosclerosis. Atherosclerosis is a condition that involves thickening of the arterial walls from cholesterol and fat deposits that build up along the endoluminal surface of the arteries.

With severe disease, these plaques may become calcified and so large that they produce stenoses within the vessels, and thus permanently increase the vascular resistance which is normally low. When the walls of the coronary arteries thicken, the cross-sectional area of the arterial lumen decreases; resulting in higher resistance to blood flow through the coronary arteries.

This steady decrease in cross-sectional area can eventually lead to complete blockage of the artery. As a result, oxygen and nutrient supply to the myocardium drops below the demand of the myocardium. As the disease progresses, the myocardium downstream from the occluded artery becomes ischemic.

Eventually, myocardial infarction or known as a MI may occur if the coronary artery disease is not detected and treated in a timely manner. This is termed "functional sympatholysis. Parasympathetic stimulation of the heart i. However, if parasympathetic activation of the heart results in a significant decrease in myocardial oxygen demand due to a reduction in heart rate, then intrinsic metabolic mechanisms will increase coronary vascular resistance by constricting the vessels.

Progressive ischemic coronary artery disease results in the growth of new vessels termed angiogenesis and collateralization within the myocardium. Collateralization increases myocardial blood supply by increasing the number of parallel vessels, thereby reducing vascular resistance within the myocardium. Extravascular compression shown to the right during systole markedly affects coronary flow; therefore, most of the coronary flow occurs during diastole.

Because of extravascular compression, the endocardium is more susceptible to ischemia especially at lower perfusion pressures. Furthermore, with tachycardia there is relatively less time available for coronary flow during diastole to occur — this is particularly significant in patients with coronary artery disease where coronary flow reserve maximal flow capacity is reduced. In the presence of coronary artery disease , coronary blood flow may be reduced. This will increase oxygen extraction from the coronary blood and decrease the venous oxygen content.

This leads to tissue hypoxia and angina. If the lack of blood flow is due to a fixed stenotic lesion in the coronary artery because of atherosclerosis , blood flow can be improved within that vessel by 1 placing a stent within the vessel to expand the lumen, 2 using an intracoronary angioplasty balloon to stretch the vessel open, or 3 bypassing the diseased vessel with a vascular graft.

If the insufficient blood flow is caused by a blood clot thrombosis , a thrombolytic drug that dissolves clots may be administered.

Also, oxygen-depleted blood must be carried away. The coronary arteries wrap around the outside of the heart. Small branches dive into the heart muscle to bring it blood. Left main coronary artery LMCA. The left main coronary artery supplies blood to the left side of the heart muscle the left ventricle and left atrium.

The left main coronary divides into branches:. The left anterior descending artery branches off the left coronary artery and supplies blood to the front of the left side of the heart.

The circumflex artery branches off the left coronary artery and encircles the heart muscle.