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| {{SI}}
| | #Redirect [[Coronary collaterals]] |
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| {{CMG}}
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| __NOTOC__
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| '''Associate Editor-In-Chief:''' {{CZ}}
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| ==Overview==
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| During contraction of the ventricular [[myocardium]] ([[systole]]), the subendocardial coronary vessels (the vessels that enter the [[myocardium]]) are compressed due to the high intraventricular pressures. However the epicardial coronary vessels (the vessels that run along the outer surface of the heart) remain patent. Because of this, blood flow in the subendocardium is greatly reduced. As a result most [[myocardial perfusion]] to the left anterior descending and the left circumflex occurs during heart relaxation ([[diastole]]) when the subendocardial coronary vessels are patent and under low pressure. The right coronary artery, which terminates in the thin walled right ventricle, has greater filling during systole. Failure of [[oxygen]] delivery to rise as a result of increases in blood flow to meet the increased [[oxygen]] demand of the heart results in tissue [[ischemia]], a condition of [[oxygen]] debt.<ref>Fuchs S. Lack of correlation between angiographic grading of collateral and myocardial perfusion and function. Coron Ar Disease 2001; 12: 173-78.</ref> <ref>Abbott JD, Choi EJ, Selzer F, Srinivas VS, Williams DO Impact of Coronary Collaterals on Outcome Following PCI [from the NHLBI Dynamic Registry]. Am J Cardiol. 2005; 96: 676–680.</ref> <ref>Koerselman J, van der Graaf Y, de Jaegere PP, Grobbee DE. Coronary Collaterals an Important and Underexposed Aspect of Coronary Artery Disease. Circulation. 2003; 107: 2507-2511.</ref>
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| Brief [[ischemia]] is associated with [[chest pain]], a condition known as [[angina]]. Severe [[ischemia]] can cause the heart muscle to die of [[oxygen]] starvation, a condition termed [[myocardial infarction]]. Chronic moderate [[ischemia]] can result in weakening of myocardial contractility, a condition known as [[myocardial hibernation]].
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| The [[coronary circulation]] possesses unique pharmacologic characteristics. Prominent among these is its reactivity to adrenergic stimulation. The majority of vasculature in the body constricts to [[norepinephrine]], a sympathetic neurotransmitter the body uses to increase [[blood pressure]]. In the [[coronary circulation]], [[norepinephrine]] elicits vasodilation, due to the predominance of beta-adrenergic receptors in the [[coronary circulation]].
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| Agonists of alpha-receptors, such as [[phenylephrine]], elicit very little constriction in the [[coronary circulation]].
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| ==See Also==
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| *[[Coronary circulation]]
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| *[[Collateral circulation grading]]
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| *[[Rentrop and Cohen’s Collateral Classification]]
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| ==References==
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| {{Reflist}}
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| ==Additional Resources==
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| *[http://www.ajronline.org/cgi/reprint/119/3/463 Coronary Collateral Circulation by Levin, Kauff and Baltaxe]
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| {{Circulatory system pathology}}
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| [[Category:Cardiology]]
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