Coronary Artery Anomalies with Focus on Anomalous Aortic Origin of a Coronary Artery (AAOCA): Definition, Pathophysiology and Anesthetic Implications

By Benjamin Kloesel, MD, MSBS; and John L. Bass, MD
Masonic Children’s Hospital, University of Minnesota
Minneapolis, MN

There is a diverse group of congenital coronary artery anomalies that can present in a variety of ways, including anomalies in coronary artery origin (absence of a coronary trunk, anomalous location of coronary ostium at improper sinus), anatomy (ostial stenosis or atresia, intramural coronary artery [muscular bridge], subendocardial coronary course) and termination (coronary fistulas, anomalous anastomoses). Some individuals with these anomalies remain asymptomatic throughout life, but others can have devastating consequences including sudden death despite the lack of cardiac risk factors in young, otherwise healthy teenagers and athletes1. Unfortunately, the low incidence, difficulties in detection and diagnosis and marked differences in risk for sudden cardiac death with coronary artery anomalies pose significant challenges in their management. These factors are illustrated by a case report from Daher et al.2 The group reports a 44 year-old female who suffered two sudden cardiac arrests during induction of general anesthesia. The patient was otherwise healthy and had no known cardiopulmonary disease. The first anesthetic was conducted emergently for a colonic perforation leading to peritonitis. During rapid sequence induction, there was marked hypotension refractory to IV fluid infusion and ephedrine. The heart rhythm rapidly progressed from sinus bradycardia to electromechanical dissociation and asystole. The patient was successfully resuscitated. No further cardiac work-up was pursued at that time and the cardiac arrest was attributed to the overall clinical picture. A year later, the patient was diagnosed with breast cancer and scheduled for a radical mastectomy. Preoperative evaluation with ECG, CXR, treadmill stress test and resting echocardiography did not show any pathology. During anesthetic induction, ventricular ectopic beats were noted, followed by ventricular tachycardia and asystole. The patient was again successfully resuscitated. Postoperative cardiac evaluation with ECG (with and without procainamide), echocardiography, myocardial scintigraphy and treadmill exercise testing were again normal. The patient was referred to a tertiary care center where a coronary angiogram revealed an anomalous origin of the left coronary artery from a single right coronary ostium.

This manuscript will focus on the entities of anomalous aortic origin of a coronary artery (AAOCA), also known as anomalous origination of a coronary artery from the opposite sinus (ACAOS). Included in this definition are anomalous aortic origin of the left coronary artery (AAOLCA)/ origination of left coronary artery from right sinus of Valsalva (L-ACAOS) and anomalous aortic origin of the right coronary artery (AAORCA)/ origination of the right coronary artery from left sinus of Valsalva (R-ACAOS). This condition, specifically AAOCA with an intramural course, was chosen for this review as it represents the most frequent cause of sudden cardiac arrest amongst all coronary artery anomalies1,3.

Incidence
The incidence of coronary artery anomalies varies tremendously depending on the method of detection (autopsy, echocardiogram, angiogram) and the definition. A prospective study utilizing angiography in 1950 patients reported a global incidence of 5.64%, with AAOCA accounting for 1.07%4. Origin of the RCA from the left sinus was more frequently observed (0.92%) compared to origin of the LCA from the right sinus (0.15%), in keeping with other reports listing a 5:1 ratio for AAORCA to AAOLCA5. Of note, this patient cohort included a large variety of coronary artery anomaly entities, many with no clinical implications that could be considered “normal variants”. Identification of high-risk coronary artery anomalies and their incidence would be helpful for the practicing clinician. In a study of 277 sudden unexpected, non-trauma related deaths of military recruits during intense physical training, 64 were attributed to cardiac causes6. Of those, 21 had AAOCA. In the general population, a study examining causes of sudden unexpected death in 162 patients revealed only one case related to coronary artery anomaly7. The American Heart Association reports that coronary artery anomalies are responsible for 19% of deaths in athletes. A contemporary study used MRA-based screening of 1836 subjects aged 11-15 years identified 24 subjects (1.3%) who had a high-risk cardiovascular condition. Amongst those, 0.7% were found to have anomalous coronary artery from the opposite sinus with an intramural course (eleven patients with AAORCA; two patients with AAOLCA)8.

Pathophysiology
Advances in imaging have improved detection and classification of this heterogeneous group of disorders. Theories about the impact of specific coronary artery anomalies on hemodynamics and myocardial perfusion have been formulated, but complete understanding is still lacking. One of the most important aspects in diagnosis and management of coronary artery anomalies is to evaluate the risk of impairing coronary artery blood flow. Coronary flow impairment may be obligatory (e.g. anomalous origination of the left coronary artery from the pulmonary artery [ALCAPA] or ostial atresia), may occur under stress (anomalies involving exceptional ischemia such as AAOCA with intramural course in the setting of strenuous exercise), or may not occur at all9.

In AAOCA, the left or right coronary artery connects with the opposite coronary cusp. The artery may cross a) retrocardiac, b) retroaortic, c) preaortic, d) intraseptal (supracristal) and e) prepulmonary (precardiac)1,10.

Increased myocardial oxygen demand coupled with a decrease in coronary artery blood flow from a coronary anomaly may lead to myocardial ischemia. Fixed obstructive coronary lesions, such as observed in patients with significant coronary artery disease, consistently produce effort-related myocardial ischemia and angina. But few congenital coronary artery anomalies behave similarly (ostial stenosis, ostial atresia, ALCAPA). In the majority of coronary artery anomalies, the occurrence of ischemia is less predictable and governed by multiple factors. In the setting of myocardial ischemia, a typical clinical pattern observed is the occurrence of bradycardia and low cardiac output, followed by either asystole or ventricular fibrillation/tachycardia2,11-13.

Although the incidence of AAORCA is higher than AAOLCA, the risk for sudden cardiac death is greater with AAOLCA. Data gathered from coronary angiography, CT/cardiac MRA and intravascular ultrasonography suggest that the underlying cause of sudden cardiac death is related to an intramural course of the coronary artery with a degree of stenosis, hypoplasia of the intramural segment and lateral compression that increases during systole and exercise1,9,14,15. In a case of a woman with AAOLCA whose postoperative course after surgical translocation of the coronary ostium from the right to the left sinus of Valsalva was complicated by low cardiac output and new myocardial infarction that improved after coronary artery bypass, intravascular ultrasound revealed an intrinsic deformity in the intramural segment of the coronary artery that caused the initial cardiovascular collapse. This finding illustrates that ostial location by itself was not the main factor triggering myocardial ischemia16. Intravascular ultrasound has so far only confirmed the intraluminal coronary abnormality in AAOCA with preaortic intramural course, but not in AAOCA with prepulmonic, intraseptal, retroaortic, or retrocardiac courses15,16.

Diagnosis
The majority of patients with AAOCA are asymptomatic, and the condition may be present in young athletes or military recruits who are otherwise in excellent health. Some patients with AAOCA have symptoms such as dyspnea on exertion, syncope, chest pain and palpitations.

Guidelines for coronary artery anomaly testing are lacking. The gold-standard for delineating the coronary anatomy remains coronary angiography. Echocardiography is a good screening tool when imaging is adequate as it is non-invasive, yet able to visualize the proximal left and right coronary arteries in about 95% of young athletes. Most coronary artery anomalies of clinical significance can be detected with adequate image resolution and technical skill. Nevertheless, echocardiography has shortcomings: false-negative results may occur, especially in AAORCA1. Multidetector computed tomography and coronary magnetic resonance angiography have proven to be excellent alternatives (the latter avoids radiation exposure but provides less clarity of small details)17-20. Those modalities provide anatomic information but do not allow functional assessment. Treadmill stress testing and stress echocardiography using exercise, dobutamine or adenosine/ dipyridamole yield false-positive and false-negative results15,21. Nuclear stress testing, if positive, may provide a clear justification for intervention, but often fails to detect reversible ischemia9,22.

For suspected AAOCA, testing should include an electrocardiogram, Holter monitor and echocardiography. Identification of two normally located coronary ostia makes presence of AAOCA unlikely and additional testing is only needed if there are clinical or other indications that strongly suggest myocardial ischemia. If the coronary ostia are not clearly visualized, advanced imaging with computed tomography or magnetic resonance imaging can establish the diagnosis. Additional testing may include nuclear stress imaging and coronary angiography.

Management
For high-risk AAOCA, medical management is focused on close observation combined with exercise restriction and beta-blockade. The interventional approach utilizes coronary angioplasty with stent deployment into the obstructed intramural part of the coronary artery; this approach is less frequently used compared to surgery and its overall role in regards to patient selection and outcomes is under investigation23. Surgical correction is associated with excellent outcomes24,25 and can involve unroofing of the intramural segment of the ectopic coronary artery, re-implantation of the ectopic coronary artery at the aortic root or translocation of the pulmonary artery3,10,26.

Anesthetic implications
In essence, the pathophysiologic cascade leading to cardiac arrest in patients with AAOCA starts with a combination of increased myocardial oxygen demand from positive chronotropy/inotropy and blood flow impairment from stenosis and lateral compression resulting in myocardial ischemia. An important and conditional factor is the transition from normal coronary blood flow to coronary blood flow obstruction which shares a lot of similarities with coronary artery disease (the exception being that the former is dynamic while the latter is fixed). Anesthetic interventions should be directed at optimization of coronary artery blood flow, reduction of myocardial oxygen demand and preparedness for resuscitation per ACLS protocol with specific attention to defibrillation/cardioversion of malignant arrhythmias. Induction of anesthesia should focus on maintaining contractility and systemic vascular resistance while avoiding excessive increases in heart rate. Short-acting beta-blockers (esmolol) should be readily available, and an adequate depth of anesthesia with blunting of sympathetic response to intubation needs to be ensured. The same applies for significant intraoperative stimuli such as incision or sternotomy. Beat-to-beat arterial blood pressure monitoring is beneficial to closely adjust perioperative hemodynamics, avoiding hypertension or hypotension. Hypertension in particular can result in elevated aortic pressures that can distend the ascending aorta and cause compression of a coronary artery between the ascending aorta and pulmonary artery (preaortic course). ECG monitoring of leads II and V5 should be utilized along with ST segment analysis. Triggers for perioperative tachycardia including pain, hypovolemia, anemia, hyperthermia, shivering and nausea/ emesis should be avoided or promptly addressed. The occurrence of a supraventricular tachycardia must be addressed with antiarrhythmics or cardioversion in a timely manner.

Conclusion
Coronary artery anomalies are a heterogeneous group, not only in regards to their anatomic presentation, but also in their disease severity and potential for devastating outcomes. While many patients with an incidental discovery of a coronary artery anomaly are asymptomatic, others can present with sudden cardiac arrest. Despite an incomplete knowledge of risk factors and pathomechanism, advances in imaging techniques and review of prior cases have provided us with a better understanding of this disease entity. Amongst coronary artery anomalies, anomalous aortic origin of a coronary artery (AAOCA) with intramural course is a high-risk lesion that requires appropriate evaluation and management. The anesthesiologist will likely encounter patients in two settings: in the critical care unit after successful resuscitation of a sudden cardiac arrest event and in the operating room or cardiac catheterization laboratory after diagnosis of a high-risk lesion with the plan for surgical or interventional correction.

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