Heart Disease

Medical definition108-121

  • Cardiovascular disease (CVD) or heart disease refers to a class of diseases that involve the heart muscle (myocardium) and/or the blood vessels (mainly arteries and veins).
  • Coronary heart disease (CHD) or coronary artery disease (CAD) is a cardiovascular disease characterized by an impedance or blockage in one or more arteries that supply oxygen and nutrient-rich blood to the heart muscle (myocardium).
  • Heart attack is a serious manifestation or expression of CHD. Heart attack occurs when blood flow to a part of the heart muscle is blocked for a certain period of time leading to heart muscle damage. A heart attack occurs when a blocked artery prevents oxygen-rich blood from reaching a section of the heart. If the blocked artery is not reopened quickly, the part of the heart normally nourished by that artery begins to die. The longer a person goes without treatment, the greater the damage.
  • The coronary arteries supply oxygen and nutrient-rich blood to the heart, and hence a blood clot in these arteries can cause heart attack.

Role of coronary arteries in heart disease

Like all other cells in the body, the cells that comprise the heart muscle also need oxygen & nutrient -rich blood for their survival & normal functioning. And on the other hand, oxygen-depleted blood from these cells must be carried away from them for oxygenation in the lungs. Since coronary arteries deliver blood to the heart muscle, any coronary artery disorder /disease can have serious implications by reducing the flow of oxygen and nutrients to the heart muscle. Blood is supplied to the heart by its own vascular system, called coronary circulation.

  • The aorta (the main blood supplier to the body) branches off into two main coronary blood vessels (also called coronary arteries). These coronary arteries branch off into smaller arteries, which supply oxygen-rich blood to the entire heart muscle.
  • The left and right coronary arteries originate at the base of the aorta from openings called the coronary ostia located behind the aortic valve leaflets.
  • The right coronary artery (RCA) supplies blood to the right atrium & right ventricle; and the Sinoatrial & Atrioventricular nodes (which regulate heart rhythm). The right coronary artery divides into smaller branches, including the right posterior descending artery and the acute marginal artery.
  • The left coronary artery, which branches into the left anterior descending artery and the circumflex artery, supplies blood to the left side of the heart. The left side of the heart is larger and more muscular because it pumps blood to the rest of the body.
  • The left main coronary artery (LMCA) supplies blood to the left side of the heart muscle (the left ventricle & left atrium). The left main coronary divides into branches:
    • The left anterior descending artery, which branches off the left coronary artery and supplies blood to the front of the left side of the heart.
    • The circumflex artery, which branches off the left coronary artery and encircles the heart muscle. This artery supplies blood to the outer side and back of the heart.
  • The cardiac veins return deoxygenated blood (containing metabolic waste products) from the heart muscle (myocardium) to the right atrium. This blood then flows back to the lungs for reoxygenation. The major venous vessels of the heart (that is, blood vessels carrying deoxygenated blood from the cardiac cells) are: coronary sinus, the anterior interventricular veins, left marginal veins, posterior veins of the left ventricle, and the posterior interventricular veins
  • The coronary system is comprised of arteries, arterioles, capillaries, venules and veins. From the innumerable cardiac capillaries, blood flows back to the cardiac chambers through venules, which in turn coalesce into the cardiac veins. Most cardiac veins collect and return blood to the right atrium through the coronary sinus.

Interaction between blood vessel (vascular) wall and blood circulation is crucial for heart disease

Understand your blood vessels… Blood vessel is a vehicle for blood transport in the body. It is a vessel in the body through which blood circulates. The vessels that carry oxygenated blood (or oxygen & nutrient-rich blood) away from the heart & towards the body cells are called arteries, and their very small branches are arterioles. Very small branches that collect the deoxygenated blood (or blood devoid of oxygen) from the various body cells towards the heart are called venules, and they unite to form veins, which return the blood to the heart. Capillaries are minute thin-walled vessels that connect the arterioles and venules; it is through the capillaries that nutrients and wastes are exchanged between the blood and body cells.

Blood vessel wall … The largest blood vessels are arteries and veins, which have a thick, tough wall of connective tissue and many layers of smooth muscle cells. The wall is lined by an exceedingly thin single sheet (monolayer) of endothelial cells, called the endothelium. Endothelium is separated from the surrounding outer layers by a basal lamina. The amount of connective tissue and smooth muscle in the vessel wall vary according to the vessel's diameter and function, but the endothelial lining is always present. Lumen is the inner space or central space of a blood vessel through which blood flows. Endothelium is the innermost lining of a blood vessel wall and it forms an interface between circulating blood or lymph in the lumen and the rest of the vessel wall.

Importance of the endothelial layer in blood vessel wall

Although only a simple monolayer, the healthy endothelium is optimally placed and is able to respond to physical and chemical signals by production of a wide range of factors that regulate vascular tone, cellular adhesion, thromboresistance, smooth muscle cell proliferation, and vessel wall inflammation.

  • Endothelium in the normal/healthy state has vasoprotective (blood vessel protective) effects
    • It helps in blood pressure regulation by maintaining a balance between vasoconstriction (blood vessel constriction) & vasodialation (blood vessel dialation)
    • It suppresses smooth muscle cell proliferation
    • It inhibits inflammatory responses
  • Endothelium’s vasoprotective effects are mainly attributed to a component called Nitric Oxide (Endothelium Derived Relaxing Factor, EDRF) which relaxes the blood vessel wall & prevents its undue narrowing

What is Atherosclerosis? Does it have a role in heart disease?

  • Atherosclerosis, or hardening of the arteries, is a condition in which plaque builds up inside the arteries.
  • Plaque is made of cholesterol, fatty substances, cellular waste products, calcium and fibrin (a clotting material in the blood).
  • Plaque may partially or totally block the blood's flow through an artery in the heart, brain, pelvis, legs, arms or kidneys.
  • Two things that can happen where plaque occurs are:
    • A piece of the plaque may break off.
    • A blood clot (thrombus) may form on the plaque's surface.
    • If either of these occurs and blocks the artery, a heart attack or stroke may result.
  • Atherosclerosis can affect any artery in the body, including arteries in the heart, brain, arms, legs, pelvis, and kidneys. As a result, different diseases may develop based on which arteries are affected.
  • Some of the diseases that may develop as a result of atherosclerosis include
    • coronary heart disease & angina (chest pain),
    • carotid artery disease (occurs if plaque builds up in carotid arteries on each side of neck which supply oxygen-rich blood to the brain predisposing to a stroke),
    • peripheral artery disease (or PAD, occurs if plaque builds up in major arteries supplying oxygen-rich blood to legs, arms, & pelvis, blockage may result in numbness, pain, and, sometimes, dangerous infections)
    • chronic kidney disease (occurs if plaque builds up in the renal arteries that supply oxygen-rich blood to kidneys, causing a slow loss of kidney function)
Atherosclerosis in coronary arteries
  • Coronary heart disease (CHD), also called coronary artery disease, occurs when plaque builds up in the coronary arteries that supply oxygen-rich blood to the heart
  • Plaque narrows the coronary artery lumen and reduces blood flow to the heart muscle. Plaque buildup also makes it more likely that blood clots will form in arteries. Blood clots can partially or completely block blood flow.
  • If blood flow to the heart muscle is reduced or blocked, you may have angina (chest pain or discomfort) or a heart attack.
  • Plaque begins to form because the inner lining of the artery, called the endothelium, becomes damaged.
  • Because of the damage, fats, cholesterol, platelets, cellular debris and calcium accumulate over time in the artery wall.
  • These substances may stimulate the cells of the artery wall to produce other inflammatory substances, resulting in the accumulation of more cells in the innermost layer of the artery wall where the atherosclerotic lesions (injury) form.
  • These cells accumulate, and many divide. At the same time, fat builds up within and around these cells. They also form connective tissue.
  • The arterial wall becomes markedly thickened by these accumulating cells and surrounding material. The artery narrows and blood flow is reduced, thus decreasing the oxygen supply.
  • Often a blood clot forms and blocks the artery, stopping the flow of blood. If the oxygen supply to the heart muscle is reduced, a heart attack can occur. If the oxygen supply to the brain is cut off, a stroke can occur. And if the oxygen supply to the extremities is reduced, gangrene can result.
  • There are predominantly 3 major vascular events underlying a blood clot-induced blockage (thrombotic coronary occlusions) responsible for heart attack (MI), and these include-
    • plaque rupture
    • plaque erosion
    • calcific nodule

Most heart attacks are caused not by an artery narrowing due to the build-up of hard, large plaques detectable on an angiogram, but by a blood clot that forms after the rupture of a soft, inflamed, lipid-rich plaque, often quite small. Narrowing of coronary arteries causes angina pectoris or chest pain, whereas occlusion can cause myocardial infarction or death of the cardiac muscle. Heart disease gives advanced warning in the form of angina only one-third of the time. Most of the time, it manifests as a heart attack or sudden death without warning.