With the increasing application of coronary computed tomography angiography (CCTA) as the standard of care for patients with acute chest pain, health care providers will encounter both coronary artery anomalies and variants more frequently. The majority of coronary artery anomalies and variants do not have clinical significance; however, some can cause myocardial ischemia due to flow-limiting effects of the anomalous artery. It is important to distinguish those that are clinically important and may require intervention from incidental coronary artery variants that pose little to no risk to the patient.
Coronary artery anomalies occur because of a developmental abnormality of a coronary artery. These include abnormalities of a vessel’s:
The accepted definition of an anomaly is a developmental finding that occurs in less than 1% of the population, as opposed to an anatomic or normal variant, which occurs in greater than 1% of the general population. For this discussion, the term anomaly will be used interchangeably for both entities.
The frequency of coronary artery anomalies has been defined as 0.78% to 1.3% of the general population (as determined by invasive coronary angiography) but shows a higher incidence of 0.99% to 5.8% on CCTA studies due to the higher sensitivity of CCTA and its broader inclusion criteria compared to invasive angiography. For example, CCTA anomalies include an intramyocardial course (also known as a myocardial bridge); in this entity, instead of traveling on the surface of the heart within the fat-filled epicardial space, the coronary artery (usually the left anterior descending) at least partially travels a deeper course within the left ventricular myocardium. An intramyocardial course is common, usually of no clinical importance, and may not be apparent on invasive angiography. In rare instances, the intramyocardial course may produce compression of the artery due to the natural contraction of the left ventricular myocardium, leading to ischemia from prolonged compression or predisposing the patient to coronary artery dissection, plaque rupture or coronary spasm from the mechanical effects of contraction on the vessel.
Coronary artery anomalies are hemodynamically significant if they either transiently or permanently adversely alter the blood flow to the subtended myocardium. Origin of a coronary artery from the pulmonary circulation, such as anomalous left coronary artery from the pulmonary artery (ALCAPA), typically presents during infancy with signs and symptoms of myocardial ischemia like sweating, dyspnea, pallor, and failure to thrive. In ALCAPA, coronary blood will tend to reverse flow from the high-resistance coronary artery system into the lower resistance pulmonary artery (rather than into the coronary capillary bed), and therefore a steal phenomenon develops. This rare condition occurs in 1:300,000 live births. ALCAPA, also known as Bland-Garland-White syndrome, is 90% fatal in the first year of life if not surgically corrected with reimplantation of the anomalous coronary artery.
An anomalous coronary artery may arise from the systemic arterial circulation, but the contralateral or incorrect coronary sinus or cusp. This includes the right coronary artery (RCA) arising from the left coronary sinus, the left coronary artery arising from the right coronary sinus, and the left circumflex artery (LCX) arising for the right coronary sinus. The origin of the right coronary artery from the left sinus is three times more common than the origin of the left coronary artery from the right cusp but is less often clinically significant by a factor of 3:1. The anomalous artery may originate directly from the aorta (e.g., two separate coronary ostia, one native and one anomalous, arise from the same coronary cusp of the aorta) or as a branch of the native coronary artery of that incorrect cusp (e.g., the RCA originates normally from the right coronary cusp, but the first branch of the RCA is an anomalous LCX).
The hemodynamic significance of these particular anomalies depends not only upon the course the anomalous artery takes before it reaches the myocardium but also upon the effect of the abnormal course on the shape of the artery and its ostium. If the course of the anomalous artery is entirely anterior to the pulmonary artery (pre-pulmonic) or entirely posterior to the aorta (retro-aortic), hemodynamic compromise does not occur. However, if the course of the anomalous artery is between the pulmonary artery and the aorta, known as an inter-arterial course, flow compromise may occur if there is an adverse effect on the coronary artery ostium or lumen. However, an interarterial course is not always associated with arterial compromise. Flow compromise may be suspected if an acute angle of origin of the anomalous artery causes non-atherosclerotic ostial stenosis. This kind of ostial stenosis is visible on CCTA. Luminal compromise may also occur due to the anomalous artery traveling within the wall of the aorta, known as an intramural course. The elliptical shape of the vessel lumen suggests the presence of an intramural course. If an inter-arterial anomaly has an intramural course, an intramural coronary artery height to width ratio of greater than 1.3 (i.e., the coronary artery lumen is oblong in cross-section) has been shown to successfully predict the presence of hemodynamic compromise with 100% sensitivity and specificity. These hemodynamically significant anomalies can sufficiently alter myocardial perfusion to cause chest pain, myocardial infarction, congestive heart failure (CHF), or even sudden cardiac death. A 25-year review of autopsies of 6.3 million military recruits found that the left coronary artery arising from the right coronary cusp was the most common cause of sudden non-traumatic death, accounting for 33% of cases.
Not all inter-arterial anomalies are hemodynamically significant. If an inter-arterial anomalous coronary artery travels inferior or caudal to the level of the pulmonary valve, known as a trans-septal course, then, similar to pre-pulmonic or retro-aortic anomalies, arterial compromise does not occur, and the anomaly is considered hemodynamically non-significant.
Coronary artery fistulas are rare congenital anomalies. They include abnormal communication between a coronary artery and a venous structure (coronary-venous fistula) or abnormal communication between a coronary artery and a cardiac chamber (coronary-cameral fistula) without the presence of an intervening capillary bed. Combined, they have an incidence of 0.2% to 0.6%. Coronary artery fistulas usually drain into a right heart structure, most commonly the right ventricle, right atrium, pulmonary artery, or coronary sinus. Left coronary artery fistulas account for 50% of fistulas, right coronary artery fistulas account for 38%, and 12% of fistulas arise from both right and left coronary arteries. Fistulas may present in infancy with a continuous auscultatory murmur and may be confirmed by echocardiography. However, presentation is more common in adulthood (60-75%) with symptoms that include chest pain, shortness of breath, and dysrhythmia. Similar to ALCAPA, symptoms occur because of the steal phenomenon; however, blood flow is antegrade bypassing the myocardial capillary bed and flowing into the lower resistance vein or cardiac chamber. Besides steal syndrome, complications also include aneurysm, thrombosis, coronary rupture, infective endocarditis, and pulmonary hypertension.
Intrinsic coronary artery anomalies include an intramyocardial course, subendocardial course, and coronary artery ectasia or aneurysms. Coronary artery aneurysms are uncommon, usually incidental, and are associated with atherosclerotic disease 50% of the time. In children, Kawasaki disease is the most common cause of coronary artery aneurysm as a result of an acute vasculitis of the coronary arteries. Coronary artery ectasia or aneurysm can also be congenital, for example, with compensatory ectasia of the right coronary artery in the setting of ALCAPA.
The majority of coronary artery anomalies will be occult on physical examination. Those that cause transient adverse blood flow will present with signs and symptoms of myocardial ischemia such as chest pain, shortness of breath, dyspnea, and rarely sudden cardiac death. High flow anomalies, such as coronary artery fistulas or anomalous left coronary artery from the pulmonary artery (ALCAPA), may also present with an audible continuous murmur.
CCTA has become the reference standard for the evaluation of coronary artery anomalies and is deemed appropriate for the evaluation of coronary artery anomalies by the American College of Cardiology Foundation. CCTA has the advantage of speed and accuracy of diagnosis at the cost of exposure to ionizing radiation. Cardiac MRI has slightly lower spatial resolution than CCTA, but does not expose the patient to radiation and is also deemed appropriate for the evaluation of suspected coronary artery anomalies.
The majority of coronary artery anomalies are benign, incidental findings that require no treatment. For symptomatic anomalies, treatment is dictated by the nature of the specific anomaly.
ALCAPA treatment in infants requires surgical reimplantation of the anomalous artery to restore a two coronary circulation. In ALCAPA in adults, surgical free survival is possible if the condition results in moderate, chronic ischemia.
Treatment of hemodynamically significant interarterial coronary artery anomalies, such as an origin from the contralateral coronary sinus with an intramural course, involves surgical unroofing of the intramural portion of the anomalous artery or coronary artery bypass grafting.
Coronary artery fistulas have a spontaneous closure rate of only 1% to 2%. Transcatheter therapy is effective, has a lower morbidity and complication rate, and is preferred over surgery. Transcatheter treatments include coil embolization, occlusion devices such as the Amplatzer occluder, and implantable balloons. Surgical repair is reserved for cases that fail or are not amenable to transcatheter options.
Intrinsic anomalies, including an intramyocardial course and a subendocardial course, generally do not require treatment.
Coronary artery anomalies can cause signs and symptoms of myocardial ischemia in adults but are far less common than atherosclerotic coronary lesions that induce ischemia. Rarely, a transseptal course of an interarterial anomaly can be associated with dysrhythmia. Sudden cardiac death in athletes and young adults can occur secondary to a coronary artery anomaly but is less common a cause than is hypertrophic cardiomyopathy induced fatal ventricular dysrhythmia.
Since most anomalies are not clinically significant, the prognosis for the vast majority of patients is good. Patients with ischemia inducing anomalies should be referred to centers with experience in treating these conditions.
Most coronary artery anomalies and variants are not hemodynamically significant and are incidental findings on CCTA. However, flow-limiting anomalies can cause signs and symptoms of myocardial ischemia including chest pain, shortness of breath, and sudden cardiac death. Coronary artery anomalies such as ALCAPA and coronary artery fistula can present in infancy with failure to thrive, chest pain when crying or eating, as well as sweating, dyspnea, and pallor.
Coronary artery anomalies are rare entities that are usually incidental and benign. The key to identifying a flow-limiting anomaly is the analysis of the vessel shape, in particular, ostial narrowing and vessel cross-section.
Some anomalies, such as intramyocardial course, subendocardial course, as well as pre-pulmonic, retro-aortic, and trans-septal anomalies, are almost always benign based on course alone. ALCAPA and coronary artery fistula cause a steal phenomenon, which may induce myocardial ischemia.
Coronary artery anomalies are more frequently encountered with the increasing use of CCTA in the evaluation of patients with acute chest pain. Outcomes in patients will be improved by an understanding of the significance of the anomaly by the healthcare team so that unnecessary treatment does not occur.
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