Cardiac MRI > Pathology > Coronary Artery Disease > Detection of Coronary Artery Disease
Detection of Coronary Artery Disease
Coronary artery disease is the presence of atherosclerotic plaques in the coronary arteries. As a plaque enlarges, it limits the amount of blood flow to the myocardium. If the stenosis is severe enough, the myocardium experiences ischemia. Ischemia leads to myocardial dysfunction which appears as a regional wall motion abnormality on cine MRI. The extent of the myocardial dysfunction is dependent on the vascular distribution of the stenotic vessel.
Ischemia due to a stenosis may not be realized until the heart is stressed and there is an increased demand for oxygen. Typical cardiac imaging stress testing is performed by exercising the patient and then immediately imaging. However, this is not possible with MRI, so medications are used to stress the heart. Dobutamine is the agent of choice when evaluating for stress induced wall motion abnormalities. Dobutamine increases both the contractility of the heart and heart rate. Atropine can be added if the target heart rate is not obtained.
The above dobutamine stress test demonstrated stress induced ischemia of the left anterior descending coronary (LAD) artery territory. Normal myocardial function at 10 and 40 ug/kg/min is demonstrated by cavity obliteration. Ischemia was not uncovered until atropine was added and the target heart rate was achieved. Note the wall motion abnormality involving the apical septum.
Coronary artery disease can also be detected by evaluating myocardial perfusion. At rest, the coronary bed is often able to vasodilate distal to a subcritical stenosis to compensate for the stenosis and maintain adequate blood flow. Prior to perfusion imaging, adenosine is administered to maximally vasodilate the entire coronary bed to uncover regional differences in blood flow due to a stenosis. Ischemic areas are identified by decreased enhancement during first pass imaging after intravenous administration of gadolinium and adenosine.
Rest images are then acquired by repeating the technique in the absence of adenosine. If a perfusion defect persists on rest images, this may represent an infarction which can be confirmed with delayed enhanced images. It may also represent an artifact, in which case no delayed enhancement will be seen.
Perfusion imaging with adenosine reveals a perfusion defect in the distribution of the right coronary artery (RCA). The stress images show a focal defect in the inferoseptum which is not present on rest images indicative of a stenosis in the RCA.
Stunned myocardium is myocardium with normal perfusion, abnormal function, and absence of delayed enhancement; it represents transient myocardial dysfunction after a bout of acute ischemia with restoration of blood flow. Hibernating myocardium has poor function, low resting perfusion, and absence of delayed enhancement; it represents chronic ischemia and down regulated metabolic needs of the myocardium.
In young patients (25 years or younger) who have myocardial ischemia as diagnosed by ECG or other modality, it is more likely that insufficient blood flow secondary to an anomalous coronary artery is the cause rather than an atherosclerotic plaque.
The most serious coronary anomaly is when the left main (LM) coronary artery arises from the right coronary sinus and courses between the aorta and pulmonary artery, where it can be squeezed and result in myocardial ischemia due to reduced blood flow. The right coronary artery (RCA) can arise from the left coronary sinus and also pass between the aorta and pulmonary artery. The anomalous origin of the LM is always treated with bypass surgery, while the anomalous RCA is treated when symptoms warrant.
The above image shows the left main coronary artery (arrow) arising from the right coronary sinus and passing between the aorta and the pulmonary artery.
© Copyright Rector and Visitors of the University of Virginia 2013