Congenital Coronary Anomalies

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CHAPTER 33 Congenital Coronary Anomalies

Anomalies of the coronary arteries are uncommon, but sometimes can be clinically significant. Most coronary artery anomalies are benign and clinically insignificant; however, some may lead to compromise to coronary flow causing ischemia, heart failure, and death. Clinical presentation depends on the specific anomaly.

Noninvasive imaging has emerged as the preferred way to image coronary anomalies. Electron-beam CT and MR angiography are valuable for the diagnosis of anomalous coronary arteries. More recently, multidetector CT also has been shown to be very useful in the detection and characterization of anomalous coronary arteries. This chapter reviews the appearance of the most commonly encountered coronary anomalies on noninvasive imaging using CT and MRI.

DEFINITION

Anomalous coronary arteries can be grouped into three general categories. Angelini and colleagues ¹ have written one of the most complete works on this subject, and this text can serve as an excellent reference for additional study. Anomalies generally can be divided into three general classifications: (1) anomalies of origin and course (ectopic ostium within proper sinus, ostium outside normal sinus, and absent vessel); (2) anomalies of intrinsic coronary arterial anatomy (congenital stenosis of ostium, congenital aneurysms, and myocardial bridging); and (3) anomalies of coronary termination (fistulas) (Table 33-1).

TABLE 33-1 Classification of Coronary Anomalies

Anomalies of Intrinsic Coronary Arterial Anatomy

Congenital ostial stenosis

Congenital coronary aneurysms

Myocardial bridging

Anomalies of Termination Coronary artery fistula

One of the most commonly encountered anomalies of origin and course is that of a retroaortic circumflex coronary artery that arises from the right sinus of Valsalva. This has an anomalous ectopic ostium (right sinus of Valsalva) and course (retroaortic), but terminates in the usual location (left atrioventricular groove). Myocardial bridging is a commonly encountered anomaly of intrinsic coronary anatomy. Although the artery, which is almost always the left anterior descending (LAD) artery, arises from the usual sinus and travels in the usual course (anterior interventricular groove), but it takes an unusual temporary dip into the myocardium of the anterior wall before re-emerging in the epicardial fat.

Finally, anomalies of coronary termination include coronary artery fistulas. These are coronary arteries that arise from the proper sinus, but eventually terminate in an unusual location. The coronary artery blood flow does not supply the myocardium, but may flow into the pulmonary artery, coronary sinus, cardiac chamber, or superior vena cava. Small fistulas are incidental findings; however, large fistulas may have serious hemodynamic and clinical consequences.

PREVALENCE AND EPIDEMIOLOGY

Congenital anomalies of the coronary arteries affect about 1.3% (range 0.2% to 5.6%) of individuals.²^–¹⁰ Approximately 80% of anomalies are considered benign without significant clinical sequelae; the remaining 20% can potentially cause symptoms, and may be responsible for significant disease.³

We have found a slightly higher prevalence of coronary anomalies than was previously reported. A review of 2087 coronary CT examinations (JP Earls, unpublished data) found an overall prevalence of coronary anomalies of 3.83%. Of those, 54% (or 2.1% of the total) were not previously suspected, whereas 46% (or 1.8% of the total) were either previously known or suspected based on prior imaging studies. One might expect to see anomalies in a larger percentage of clinical cases than one would believe based on epidemiologic studies.

ETIOLOGY AND PATHOPHYSIOLOGY

Coronary anomalies are congenital in origin. In many cases, blood flow to the myocardium remains intact, even in periods of high myocardial oxygen demand, and when no clinical consequences are present. In other cases, the abnormal origin or course leads to compromised blood flow either during exercise or at rest, and symptoms may develop.

The terminology used to describe coronary anomalies is not standardized and sometimes can be confusing. In addition, the actual number of different coronary anomalies is large. The most common anomalies involve variations in the origin or course of the coronary arteries themselves; examples include an artery that arises from the incorrect coronary sinus, which must travel back to its anatomically correct location before terminating in the anatomically correct region of myocardium. In most cases, anomalies are sporadic isolated findings. They may also be associated with other cardiac pathology, however, including valvular lesions, such as a bicuspid aortic valve, or congenital heart disease, such as tetralogy of Fallot or transposition of the great vessels.

MANIFESTATIONS OF DISEASE

Clinical Presentation

Presentation depends greatly on the specific anomaly. Most coronary artery anomalies are benign and never have any clinical symptoms. These are usually detected as incidental findings. Other anomalies are potentially significant and are sometimes ominously termed malignant or potentially lethal; these increase the risk of myocardial ischemia and sudden death because their position or orientation may lead to coronary flow compromise.¹¹^–¹⁵ Although anomalies are uncommon, they can have a substantial impact on premature cardiac morbidity and mortality among young adults. Eckart and associates¹⁶ found coronary anomalies present in more than 30% of sudden nontraumatic deaths in young individuals.

Imaging Indications and Algorithm

Noninvasive imaging has emerged as the preferred way to diagnose and evaluate coronary anomalies. Echocardiography can often detect anomalous origins and even some anomalous courses or, as in the case of larger fistulas, anomalous terminations. Electron-beam CT and MR angiography are useful for the comprehensive diagnosis of anomalous coronary arteries.¹⁷^–²² More recently, multidetector CT has proved to be useful in the detection and characterization of anomalous coronary arteries.²³^–²⁸

IMAGING TECHNIQUE AND FINDINGS

Computed Tomography

Cardiac multidetector CT using contrast-enhanced technique is capable of detecting and characterizing coronary artery anomalies. Most anomalies are incidental findings and are frequently detected when the coronary arteries are being evaluated for atherosclerotic stenoses. The same CT angiographic technique is used when imaging coronary anomalies and atherosclerotic coronary artery disease. This technique is discussed in depth in Chapter 9.

With the exception of anomalous coronary arteries arising from the pulmonary artery, anomalous arteries fill with contrast material at the same time as anatomically normal arteries. Timing of contrast administration and data acquisition for the examination should not be altered. If anomalous origin from the pulmonary artery is suspected, a longer contrast infusion may be appropriate. In situations where the anomalies are seen in conjunction with other cardiac conditions, such as transposition of the great vessels, the amount of imaged anatomy in the z-axis may be increased from the standard heart and aortic root only selection.

Magnetic Resonance Imaging

MRI has been used for a long time to image potential coronary anomalies. It has the advantage of not using ionizing radiation, and has many different pulse sequences to help identify and evaluate the anomalous artery. MRI has been especially used in children and young adults to minimize radiation dose because this population is more susceptible to radiation-induced malignancies owing to their young age. Techniques vary widely and include bright blood and dark blood sequences, contrast-enhanced and non–contrast-enhanced sequences, and breath-hold and non–breath-hold sequences. No single technique has yet emerged as the dominant coronary MRI technique for coronary analysis. MRI sometimes can be less reliable, however, than its newer competitor, multidetector CT. MRI does not expose patients to the higher risks of ionizing radiation and of iodinated contrast agents. The relatively small amount of radiation exposure and of need for an intravenous catheter are particular advantages for imaging children.

DIFFERENTIAL DIAGNOSIS

Anomalies of Origin and Course

Anomalous Origin of a Coronary Artery from the Opposite Sinus of Valsalva

One of the most commonly encountered potentially serious anomalies involves the anomalous origination of a coronary artery from the opposite sinus of Valsalva. Either the right coronary artery (RCA) or the left coronary artery (LCA) can arise from the opposite sinus, and then traverse across the heart to resume a normal position. Alternatively, a single branch of the LCA, the LAD artery, or the left circumflex artery can arise from the opposite sinus, whereas the remainder of the LCA may arise from the correct sinus.

There are several potential courses for an anomalous LCA arising from the right sinus of Valsalva or the RCA (Fig. 33-1). Diagnosis of the exact course is important because it determines if intervention is necessary. There are four possible pathways for the anomalous LCA: (1) between the aortic root and the pulmonary artery (interarterial course), (2) a transseptal (intraseptal or subpulmonic) course, (3) anterior to the right ventricular outflow tract (anterior or prepulmonic course), and (4) posterior to the aortic root (retroaortic course). Although the anterior, posterior, and septal (subpulmonic) courses are benign, an interarterial course carries a high risk for sudden cardiac death.²⁹^,³⁰