Pathophysiology
The past 2
decades has greatly expanded our overall understanding of the
pathophysiology of myocardial ischemic syndromes. The primary
dysfunction in angina pectoris is decreased oxygen delivery to
myocardial muscle cells. The 2 predominant mechanisms by which delivery
is impaired appear to be coronary artery narrowing and endothelial
dysfunction. Any other mechanism that affects oxygen delivery can also
precipitate symptoms.
Extracardiac causes of angina include, but are by no means limited to, anemia, hypoxia, hypotension, bradycardia, carbon monoxide exposure, and inflammatory disorders.[3] The end result is a shift to anaerobic metabolism in the myocardial cells. This is followed by a stimulation of pain receptors that innervate the heart. These pain receptors ultimately are referred to afferent pathways, which are carried in multiple nerve roots from C7 through T4. The referred/radiating pain of angina pectoris is believed to occur because these afferent pathways also carry pain fibers from other regions (eg, the arm, neck, and shoulders).
The epicardial vessel, where atherosclerosis often takes place, has the capacity to dilate via autoregulatory mechanisms to respond to increased demand. Angina occurs as this compensatory mechanism is overwhelmed either by large plaques (typically considered 70% or greater obstruction) or by significantly increased myocardial demand.[4]
In the diseased coronary artery, NO production is reduced or absent. In this setting, the catecholamine drive can overwhelm the autoregulatory mechanisms. In addition, the endothelium of the plaque-laden artery may, in itself, be dysfunctional. This limits the ability of the intra-arterial endothelium to produce mediators, which, in a healthy artery, would protect against further vasoconstriction, assist dilatation, and provide protection from platelet aggregation. Small lesions in these vessels may produce incompletely obstructing aggregates of platelets. This would further impede flow through the affected vessel.[4]
In the diseased heart, these 2 factors, coronary artery narrowing and endothelial dysfunction, synergistically result in reduced oxygen delivery to the myocardium. The net result is angina pectoris.
Other extrinsic factors that affect hemoglobin formation, such as lead poisoning or iron-deficiency states, also lead to a similar decrease in oxygen-carrying capacity. Any mechanism that impedes oxygen delivery to the red blood cells has a similar effect. Therefore, any number of pulmonary causes, such as pulmonary embolism, pulmonary fibrosis or scarring, pneumonia, or congestive heart failure, can exacerbate angina. A decreased oxygen environment, such as travel to a higher elevation, has similar consequences due to the decrease in concentration of atmospheric oxygen.
The etiology of variant angina is
currently not well understood. Research suggests that inflammatory
mediators may result in focal coronary artery vasospasm. Another
possibility is that perfusion is decreased through microvascular
circulation. Spasm or intermittent narrowing of this microscopic lumen
may result in transient areas of hypoperfusion and oxygen deprivation.[6]
Each year, 400,000 new cases of angina pectoris develop.
Conservative 2006 data show 733,000 acute coronary syndrome (ACS) discharges from hospitals.[7]
Coronary heart disease is the single greatest killer of American men and women.[7]
The estimated direct and indirect cost for Americans with coronary heart disease in 2006 was $142.5 billion.
Extracardiac causes of angina include, but are by no means limited to, anemia, hypoxia, hypotension, bradycardia, carbon monoxide exposure, and inflammatory disorders.[3] The end result is a shift to anaerobic metabolism in the myocardial cells. This is followed by a stimulation of pain receptors that innervate the heart. These pain receptors ultimately are referred to afferent pathways, which are carried in multiple nerve roots from C7 through T4. The referred/radiating pain of angina pectoris is believed to occur because these afferent pathways also carry pain fibers from other regions (eg, the arm, neck, and shoulders).
Coronary artery narrowing
Coronary artery narrowing appears to be the etiology of cardiac ischemia in the preponderance of cases. This has clinical significance when atherosclerotic disease diminishes or halts blood flow through the coronary arterial circulation, interfering with normal laminar blood flow. The significance of even a small change in the diameter of a blood vessel can be profound. The Poiseuille law predicts this outcome—the rate of flow is decreased exponentially by any change in the radius of the lumen. As with a smaller pediatric airway, even relatively minute changes in diameter have dramatic consequences in flow rates. Thus, when a lumen is narrowed by one fifth, the flow rate is decreased by about one half. This predicts that even a small change in a coronary artery plaque size can affect the oxygenation through that vessel's territory.
The epicardial vessel, where atherosclerosis often takes place, has the capacity to dilate via autoregulatory mechanisms to respond to increased demand. Angina occurs as this compensatory mechanism is overwhelmed either by large plaques (typically considered 70% or greater obstruction) or by significantly increased myocardial demand.[4]
Endothelial factors
Endothelial factors also play an important role in angina pectoris. During sympathetic stimulation, the endothelium is subjected to mediators of both vasoconstriction and vasodilatation. Alpha-agonists (catecholamines) directly cause vasoconstriction, while endothelial nitrous oxide synthase creates nitrous oxide (NO), which counteracts this constricting force via vasodilatation.In the diseased coronary artery, NO production is reduced or absent. In this setting, the catecholamine drive can overwhelm the autoregulatory mechanisms. In addition, the endothelium of the plaque-laden artery may, in itself, be dysfunctional. This limits the ability of the intra-arterial endothelium to produce mediators, which, in a healthy artery, would protect against further vasoconstriction, assist dilatation, and provide protection from platelet aggregation. Small lesions in these vessels may produce incompletely obstructing aggregates of platelets. This would further impede flow through the affected vessel.[4]
In the diseased heart, these 2 factors, coronary artery narrowing and endothelial dysfunction, synergistically result in reduced oxygen delivery to the myocardium. The net result is angina pectoris.
Extrinsic factors
Extrinsic factors can also play a role in specific circumstances. The oxygen-carrying capacity of blood is based on a number of factors. The most important of which is the amount of hemoglobin. Any alteration in the ability of blood to carry oxygen can precipitate angina. Anemia of any degree can result in anginal symptoms. Given a scenario where demand is increased, such as climbing a flight of stairs, increased stress, or even sexual intercourse, the anginal symptoms may appear.[5] Abnormal hemoglobin, such as methemoglobin, carboxyhemoglobin, or any of a number of hemoglobinopathies, creates an environment at greater risk for precipitating angina.Other extrinsic factors that affect hemoglobin formation, such as lead poisoning or iron-deficiency states, also lead to a similar decrease in oxygen-carrying capacity. Any mechanism that impedes oxygen delivery to the red blood cells has a similar effect. Therefore, any number of pulmonary causes, such as pulmonary embolism, pulmonary fibrosis or scarring, pneumonia, or congestive heart failure, can exacerbate angina. A decreased oxygen environment, such as travel to a higher elevation, has similar consequences due to the decrease in concentration of atmospheric oxygen.
Variant angina
The etiology of variant angina is
currently not well understood. Research suggests that inflammatory
mediators may result in focal coronary artery vasospasm. Another
possibility is that perfusion is decreased through microvascular
circulation. Spasm or intermittent narrowing of this microscopic lumen
may result in transient areas of hypoperfusion and oxygen deprivation.[6] Syndrome X
Syndrome X is the triad of angina pectoris, a positive ECG stress test result, and a normal coronary angiogram. The pathophysiology of this disease is not well understood. Many theories exist as to the underlying pathology. Decreased oxygenation of the underlying myocardium may be the result of impaired vasodilatation, dysfunctional smooth muscle cells, poor or deficient microvascular circulation, or even structural problems on a cellular level (eg, an inappropriately functioning sodium ion channel).[6]Frequency
United States
An estimated 6,500,000 people in the United States experience angina pectoris.Each year, 400,000 new cases of angina pectoris develop.
Conservative 2006 data show 733,000 acute coronary syndrome (ACS) discharges from hospitals.[7]
Mortality/Morbidity\
In 2005, 1 in 5 deaths is from coronary heart disease (both angina and myocardial infarction).
Coronary heart disease is the single greatest killer of American men and women.[7]
The estimated direct and indirect cost for Americans with coronary heart disease in 2006 was $142.5 billion.
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