Coronary steal (with its symptoms termed cardiac steal syndrome) is a phenomenon where an alteration of circulation patterns lead to a reduction in the blood directed to the coronary circulation. It is caused when there is narrowing of the coronary arteries and a coronary vasodilator is used - "stealing" blood away from those parts of the heart. This happens as a result of the narrowed coronary arteries being always maximally dilated to compensate for the decreased upstream blood supply. Thus, dilating the resistance vessels in the coronary circulation causes blood to be shunted away from the coronary vessels supplying the ischemic zones, creating more ischemia.
Coronary steal is also the mechanism in most drug-based cardiac stress tests; When a patient is incapable of doing physical activity they are given a vasodilator that produces a "cardiac steal syndrome" as a diagnostic procedure. The test result is positive if the patient's symptoms reappear or if ECG alterations are seen.
It is also associated with the administration of Isoflurane, which is an inhaled anesthetic. Hydralazine can potentially cause this condition as well, as it is a direct arteriolar vasodilator.
Coronary arteriovenous fistula between coronary artery and another cardiac chamber, like, the coronary sinus, right atrium, or right ventricle ; may cause steal syndrome under conditions like myocardial infarction and possible angina or ventricular arrhythmias, if the shunt is large in magnitude.
It can also be associated with new patterns of blood vessel growth.
It is sometimes treated by surgery.
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