Coronary Artery Disease Patophysio

1. Diagnosis: Coronary Artery Disease
Coronary artery disease (CAD) also known as atherosclerotic heart disease, coronary heart
disease, or ischemic heart disease (IHD),is the most common type of heart disease and cause of heart
attacks.The disease is caused by plaque building up along the inner walls of thearteries of the heart, which
narrows the arteries and reduces blood flow to the heart.
Atherogenesis in humans typically occurs over a period of many years, usually many decades.
Growth of atherosclerotic plaques probably does not occur in a smooth, linear fashion but discontinuously,
with periods of relative quiescence punctuated by periods of rapid evolution. It undergoes different steps;
Initiation, Leukocyte recruitment and Foam Cell formation.
Initiation
Studies of human atherosclerosis suggests that the "fatty streak" represents the initial lesion of
atherosclerosis. These early lesions most often seem to arise from focal increases in the content of
lipoproteins within regions of the intima. Our patient being a smoker without exercise and with a
susceptible age predisposes him to atherosclerotic plaque formation which is heralded by the Fatty streak
formation from lipoprotein accumulation. This accumulation of lipoprotein particles may not result simply
from increased permeability, or "leakiness," of the overlying endothelium. Rather, the lipoproteins may
collect in the intima of arteries because they bind to constituents of the extracellular matrix, increasing the
residence time of the lipid-rich particles within the arterial wall. Lipoproteins that accumulate in the
extracellular space of the intima of arteries often associate with glycosaminoglycans of the arterial
extracellular matrix, an interaction that may slow the egress of these lipid-rich particles from the intima.
Lipoprotein particles in the extracellular space of the intima, particularly those retained by binding to matrix
macromolecules, may undergo oxidative modifications. Considerable evidence supports a pathogenic role
for products of oxidized lipoproteins in atherogenesis. Lipoproteins sequestered from plasma antioxidants
in the extracellular space of the intima become particularly susceptible to oxidative modification, giving rise
to hydroperoxides, lysophospholipids, oxysterols, and aldehydic breakdown products of fatty acids and
phospholipids. Considerable evidence supports the presence of such oxidation products in atherosclerotic
lesions.
Leukocyte Recruitment
Accumulation of leukocytes characterizes the formation of early atherosclerotic lesions. Thus, from its very
inception, atherogenesis involves elements of inflammation, a process that now provides a unifying theme
in the pathogenesis of this disease. The inflammatory cell types typically found in the evolving atheroma
include monocyte-derived macrophages and lymphocytes. A number of adhesion molecules or receptors
for leukocytes expressed on the surface of the arterial endothelial cell probably participate in the
recruitment of leukocytes to the nascent atheroma. Constituents of oxidatively modified low-density
lipoprotein can augment the expression of leukocyte adhesion molecules. This example illustrates how the
accumulation of lipoproteins in the arterial intima may link mechanistically with leukocyte recruitment, a
key event in lesion formation.

2. Once captured on the surface of the arterial endothelial cell by adhesion receptors, the monocytes
and lymphocytes penetrate the endothelial layer and take up residence in the intima. In addition to
products of modified lipoproteins, cytokines (protein mediators of inflammation) can regulate the
expression of adhesion molecules involved in leukocyte recruitment. For example, interleukin 1 (IL-1) or
tumor necrosis factor (TNF-) induce or augment the expression of leukocyte adhesion molecules on
endothelial cells. Because products of lipoprotein oxidation can induce cytokine release from vascular wall
cells, this pathway may provide an additional link between arterial accumulation of lipoproteins and
leukocyte recruitment. Chemoattractant cytokines such as monocyte chemoattractant protein 1 appear to
direct the migration of leukocytes into the arterial wall.

3. Foam-Cell Formation
Once resident within the intima, the mononuclear phagocytes mature into macrophages and
become lipid-laden foam cells, a conversion that requires the uptake of lipoprotein particles by receptor-
mediated endocytosis. One might suppose that the well-recognized "classic" receptor for LDL mediates this
lipid uptake; however, humans or animals lacking effective LDL receptors due to genetic alterations (e.g.,
familial hypercholesterolemia) have abundant arterial lesions and extraarterial xanthomata rich in
macrophage-derived foam cells. In addition, the exogenous cholesterol suppresses expression of the LDL
receptor; thus, the level of this cell-surface receptor for LDL decreases under conditions of cholesterol
excess. Candidates for alternative receptors that can mediate lipid loading of foam cells include a growing
number of macrophage "scavenger" receptors, which preferentially endocytose modified lipoproteins, and
other receptors for oxidized LDL or very low-density lipoprotein (VLDL). Monocyte attachment to the
endothelium, migration into the intima, and maturation to form lipid-laden macrophages thus represent
key steps in the formation of the fatty streak, the precursor of fully formed atherosclerotic plaques.
Arterial remodeling during atherogenesis. During the initial part of the life history of an atheroma,
growth is often outward, preserving the caliber of the lumen. This phenomenon of "compensatory
enlargement" accounts in part for the tendency of coronary arteriography to underestimate the degree of
atherosclerosis. Rupture of the plaque's fibrous cap causes thrombosis. Physical disruption of the
atherosclerotic plaque commonly causes arterial thrombosis by allowing blood coagulant factors to contact
thrombogenic collagen found in the arterial extracellular matrix and tissue factor produced by macrophage-
derived foam cells in the lipid core of lesions. In this manner, sites of plaque rupture form the nidus for
thrombi. The normal artery wall has several fibrinolytic or antithrombotic mechanisms that tend to resist
thrombosis and lyse clots that begin to form in situ. Such antithrombotic or thrombolytic molecules include
thrombomodulin, tissue- and urokinase-type plasminogen activators, heparan sulfate proteoglycans,
prostacyclin, and nitric oxide. When the clot overwhelms the endogenous fibrinolytic mechanisms, it may
propagate and lead to arterial occlusion. The consequences of this occlusion depend on the degree of
existing collateral vessels. In a patient with chronic multivessel occlusive coronary artery disease (CAD),
collateral channels have often formed. In such circumstances, even a total arterial occlusion may not lead
to myocardial infarction (MI), or it may produce an unexpectedly modest or a non-ST-segment elevation
infarct because of collateral flow. In a patient with less advanced disease and without substantial stenotic
lesions to provide a stimulus for collateral vessel formation, sudden plaque rupture and arterial occlusion
commonly produces an ST-segment elevation infarction. These are the types of patients who may present
with MI or sudden death as a first manifestation of coronary atherosclerosis. In some cases, the thrombus
may lyse or organize into a mural thrombus without occluding the vessel. Such instances may be clinically
silent. The subsequent thrombin-induced fibrosis and healing causes a fibroproliferative response that can
lead to a more fibrous lesion that can produce an eccentric plaque that causes a hemodynamically
significant stenosis. In this way, a nonocclusive mural thrombus, even if clinically silent or causing unstable
angina rather than infarction, can provoke a healing response that can promote lesion fibrosis and luminal
encroachment. Such a sequence of events may convert a "vulnerable" atheroma with a thin fibrous cap
that is prone to rupture into a more "stable" fibrous plaque with a reinforced cap. Angioplasty of unstable
coronary lesions may "stabilize" the lesions by a similar mechanism, producing a wound followed by
healing.

4. Myocardial Ischemia as cause of patients chest pain
Central to an understanding of the pathophysiology of myocardial ischemia is the concept of
myocardial supply and demand. In normal conditions, for any given level of a demand for oxygen, the
myocardium will control the supply of oxygen-rich blood to prevent underperfusion of myocytes and the
subsequent development of ischemia and infarction. The major determinants of myocardial oxygen
demand are heart rate, myocardial contractility, and myocardial wall tension (stress).The normal coronary
circulation is dominated and controlled by the heart's requirements for oxygen. This need is met by the
ability of the coronary vascular bed to vary its resistance (and, therefore, blood flow) considerably while
the myocardium extracts a high and relatively fixed percentage of oxygen. By reducing the lumen of the
coronary arteries, atherosclerosis limits appropriate increases in perfusion when the demand for flow is
augmented, as occurs during exertion or excitement.
During episodes of inadequate perfusion caused by coronary atherosclerosis, myocardial tissue
oxygen tension falls and may cause transient disturbances of the mechanical, biochemical, and electrical
functions of the myocardium. Coronary atherosclerosis is a focal process that usually causes nonuniform
ischemia. During ischemia, regional disturbances of ventricular contractility cause segmental hypokinesia,
akinesia, or, in severe cases, bulging (dyskinesia), which can reduce myocardial pump function.