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Fractional Flow Reserve, Myocardial: The ratio of maximum blood flow to the MYOCARDIUM with CORONARY STENOSIS present, to the maximum equivalent blood flow without stenosis. The measurement is commonly used to verify borderline stenosis of CORONARY ARTERIES.Coronary Stenosis: Narrowing or constriction of a coronary artery.Coronary Circulation: The circulation of blood through the CORONARY VESSELS of the HEART.Coronary Angiography: Radiography of the vascular system of the heart muscle after injection of a contrast medium.Hyperemia: The presence of an increased amount of blood in a body part or an organ leading to congestion or engorgement of blood vessels. Hyperemia can be due to increase of blood flow into the area (active or arterial), or due to obstruction of outflow of blood from the area (passive or venous).Adenosine: A nucleoside that is composed of ADENINE and D-RIBOSE. Adenosine or adenosine derivatives play many important biological roles in addition to being components of DNA and RNA. Adenosine itself is a neurotransmitter.Blood Flow Velocity: A value equal to the total volume flow divided by the cross-sectional area of the vascular bed.Coronary Vessels: The veins and arteries of the HEART.Cardiac Catheterization: Procedures in which placement of CARDIAC CATHETERS is performed for therapeutic or diagnostic procedures.Myocardial Perfusion Imaging: The creation and display of functional images showing where the blood is flowing into the MYOCARDIUM by following over time the distribution of tracers injected into the blood stream.Ultrasonography, Interventional: The use of ultrasound to guide minimally invasive surgical procedures such as needle ASPIRATION BIOPSY; DRAINAGE; etc. Its widest application is intravascular ultrasound imaging but it is useful also in urology and intra-abdominal conditions.Myocardial Bridging: A malformation that is characterized by a muscle bridge over a segment of the CORONARY ARTERIES. Systolic contractions of the muscle bridge can lead to narrowing of coronary artery; coronary compression; MYOCARDIAL ISCHEMIA; MYOCARDIAL INFARCTION; and SUDDEN CARDIAC DEATH.Vasodilator Agents: Drugs used to cause dilation of the blood vessels.Severity of Illness Index: Levels within a diagnostic group which are established by various measurement criteria applied to the seriousness of a patient's disorder.Cardiac Catheters: Catheters inserted into various locations within the heart for diagnostic or therapeutic purposes.Atrial Pressure: The pressure within the CARDIAC ATRIUM. It can be measured directly by using a pressure catheter (see HEART CATHETERIZATION). It can be also estimated using various imaging techniques or other pressure readings such as PULMONARY CAPILLARY WEDGE PRESSURE (an estimate of left atrial pressure) and CENTRAL VENOUS PRESSURE (an estimate of right atrial pressure).Coronary Artery Disease: Pathological processes of CORONARY ARTERIES that may derive from a congenital abnormality, atherosclerotic, or non-atherosclerotic cause.Predictive Value of Tests: In screening and diagnostic tests, the probability that a person with a positive test is a true positive (i.e., has the disease), is referred to as the predictive value of a positive test; whereas, the predictive value of a negative test is the probability that the person with a negative test does not have the disease. Predictive value is related to the sensitivity and specificity of the test.Angioplasty, Balloon, Coronary: Dilation of an occluded coronary artery (or arteries) by means of a balloon catheter to restore myocardial blood supply.Models, Cardiovascular: Theoretical representations that simulate the behavior or activity of the cardiovascular system, processes, or phenomena; includes the use of mathematical equations, computers and other electronic equipment.Microcirculation: The circulation of the BLOOD through the MICROVASCULAR NETWORK.Percutaneous Coronary Intervention: A family of percutaneous techniques that are used to manage CORONARY OCCLUSION, including standard balloon angioplasty (PERCUTANEOUS TRANSLUMINAL CORONARY ANGIOPLASTY), the placement of intracoronary STENTS, and atheroablative technologies (e.g., ATHERECTOMY; ENDARTERECTOMY; THROMBECTOMY; PERCUTANEOUS TRANSLUMINAL LASER ANGIOPLASTY). PTCA was the dominant form of PCI, before the widespread use of stenting.Hemodynamics: The movement and the forces involved in the movement of the blood through the CARDIOVASCULAR SYSTEM.Collateral Circulation: Maintenance of blood flow to an organ despite obstruction of a principal vessel. Blood flow is maintained through small vessels.Multidetector Computed Tomography: Types of spiral computed tomography technology in which multiple slices of data are acquired simultaneously improving the resolution over single slice acquisition technology.Regional Blood Flow: The flow of BLOOD through or around an organ or region of the body.Coronary Disease: An imbalance between myocardial functional requirements and the capacity of the CORONARY VESSELS to supply sufficient blood flow. It is a form of MYOCARDIAL ISCHEMIA (insufficient blood supply to the heart muscle) caused by a decreased capacity of the coronary vessels.Vascular Resistance: The force that opposes the flow of BLOOD through a vascular bed. It is equal to the difference in BLOOD PRESSURE across the vascular bed divided by the CARDIAC OUTPUT.ROC Curve: A graphic means for assessing the ability of a screening test to discriminate between healthy and diseased persons; may also be used in other studies, e.g., distinguishing stimuli responses as to a faint stimuli or nonstimuli.Myocardial Revascularization: The restoration of blood supply to the myocardium. (From Dorland, 28th ed)Stents: Devices that provide support for tubular structures that are being anastomosed or for body cavities during skin grafting.Sensitivity and Specificity: Binary classification measures to assess test results. Sensitivity or recall rate is the proportion of true positives. Specificity is the probability of correctly determining the absence of a condition. (From Last, Dictionary of Epidemiology, 2d ed)Blood Pressure: PRESSURE of the BLOOD on the ARTERIES and other BLOOD VESSELS.Myocardial Ischemia: A disorder of cardiac function caused by insufficient blood flow to the muscle tissue of the heart. The decreased blood flow may be due to narrowing of the coronary arteries (CORONARY ARTERY DISEASE), to obstruction by a thrombus (CORONARY THROMBOSIS), or less commonly, to diffuse narrowing of arterioles and other small vessels within the heart. Severe interruption of the blood supply to the myocardial tissue may result in necrosis of cardiac muscle (MYOCARDIAL INFARCTION).Angina Pectoris: The symptom of paroxysmal pain consequent to MYOCARDIAL ISCHEMIA usually of distinctive character, location and radiation. It is thought to be provoked by a transient stressful situation during which the oxygen requirements of the MYOCARDIUM exceed that supplied by the CORONARY CIRCULATION.Coronary Restenosis: Recurrent narrowing or constriction of a coronary artery following surgical procedures performed to alleviate a prior obstruction.Thermodilution: Measurement of blood flow based on induction at one point of the circulation of a known change in the intravascular heat content of flowing blood and detection of the resultant change in temperature at a point downstream.Dipyridamole: A phosphodiesterase inhibitor that blocks uptake and metabolism of adenosine by erythrocytes and vascular endothelial cells. Dipyridamole also potentiates the antiaggregating action of prostacyclin. (From AMA Drug Evaluations Annual, 1994, p752)Prospective Studies: Observation of a population for a sufficient number of persons over a sufficient number of years to generate incidence or mortality rates subsequent to the selection of the study group.Tomography, Emission-Computed, Single-Photon: A method of computed tomography that uses radionuclides which emit a single photon of a given energy. The camera is rotated 180 or 360 degrees around the patient to capture images at multiple positions along the arc. The computer is then used to reconstruct the transaxial, sagittal, and coronal images from the 3-dimensional distribution of radionuclides in the organ. The advantages of SPECT are that it can be used to observe biochemical and physiological processes as well as size and volume of the organ. The disadvantage is that, unlike positron-emission tomography where the positron-electron annihilation results in the emission of 2 photons at 180 degrees from each other, SPECT requires physical collimation to line up the photons, which results in the loss of many available photons and hence degrades the image.Papaverine: An alkaloid found in opium but not closely related to the other opium alkaloids in its structure or pharmacological actions. It is a direct-acting smooth muscle relaxant used in the treatment of impotence and as a vasodilator, especially for cerebral vasodilation. The mechanism of its pharmacological actions is not clear, but it apparently can inhibit phosphodiesterases and it may have direct actions on calcium channels.Drug-Eluting Stents: Stents that are covered with materials that are embedded with chemicals that are gradually released into the surrounding milieu.Reproducibility of Results: The statistical reproducibility of measurements (often in a clinical context), including the testing of instrumentation or techniques to obtain reproducible results. The concept includes reproducibility of physiological measurements, which may be used to develop rules to assess probability or prognosis, or response to a stimulus; reproducibility of occurrence of a condition; and reproducibility of experimental results.Treatment Outcome: Evaluation undertaken to assess the results or consequences of management and procedures used in combating disease in order to determine the efficacy, effectiveness, safety, and practicability of these interventions in individual cases or series.Cognitive Reserve: Capacity that enables an individual to cope with and/or recover from the impact of a neural injury or a psychotic episode.Nitrogen Radioisotopes: Unstable isotopes of nitrogen that decay or disintegrate emitting radiation. N atoms with atomic weights 12, 13, 16, 17, and 18 are radioactive nitrogen isotopes.Myocardial Infarction: NECROSIS of the MYOCARDIUM caused by an obstruction of the blood supply to the heart (CORONARY CIRCULATION).Pressure: A type of stress exerted uniformly in all directions. Its measure is the force exerted per unit area. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Radiographic Image Interpretation, Computer-Assisted: Computer systems or networks designed to provide radiographic interpretive information.Follow-Up Studies: Studies in which individuals or populations are followed to assess the outcome of exposures, procedures, or effects of a characteristic, e.g., occurrence of disease.Linear Models: Statistical models in which the value of a parameter for a given value of a factor is assumed to be equal to a + bx, where a and b are constants. The models predict a linear regression.Chi-Square Distribution: A distribution in which a variable is distributed like the sum of the squares of any given independent random variable, each of which has a normal distribution with mean of zero and variance of one. The chi-square test is a statistical test based on comparison of a test statistic to a chi-square distribution. The oldest of these tests are used to detect whether two or more population distributions differ from one another.Infusions, Intravenous: The long-term (minutes to hours) administration of a fluid into the vein through venipuncture, either by letting the fluid flow by gravity or by pumping it.Microvascular Angina: ANGINA PECTORIS or angina-like chest pain with a normal coronary arteriogram and positive EXERCISE TEST. The cause of the syndrome is unknown. While its recognition is of clinical importance, its prognosis is excellent. (Braunwald, Heart Disease, 4th ed, p1346; Jablonski Dictionary of Syndromes & Eponymic Diseases, 2d ed). It is different from METABOLIC SYNDROME X, a syndrome characterized by INSULIN RESISTANCE and HYPERINSULINEMIA, that has increased risk for cardiovascular disease.Tomography, X-Ray Computed: Tomography using x-ray transmission and a computer algorithm to reconstruct the image.Patient Selection: Criteria and standards used for the determination of the appropriateness of the inclusion of patients with specific conditions in proposed treatment plans and the criteria used for the inclusion of subjects in various clinical trials and other research protocols.Time Factors: Elements of limited time intervals, contributing to particular results or situations.Rubidium Radioisotopes: Unstable isotopes of rubidium that decay or disintegrate emitting radiation. Rb atoms with atomic weights 79-84, and 86-95 are radioactive rubidium isotopes.