Single Coronary Artery - An Overview

Introduction:

It can be defined as a single coronary artery arising from the aortic trunk from a single coronary sinus and providing perfusion to the entire myocardium regardless of its distribution. It is often associated with other congenital anomalies like septal defects, coronary artery fistula, etc.

Although the heart pumps blood to the entire body, it is still a muscle that needs its blood supply like any other organ; a pair of coronary arteries do this.

1. The right coronary artery (RCA) arises from the right aortic sinus (one of the anatomic dilations of the aortic sinus). It supplies oxygenated blood to the right side of the heart (right atrium and right ventricle).

2. The left main coronary artery (LMCA) arises from the left aortic sinus and supplies oxygenated blood to the left side of the heart (left atrium and left ventricle).

RCA and LMCA arise at the root of the aorta, the main artery that carries blood away from the heart to the rest of the body. Any anomalies in the origin and distribution of the RCA and LMCA can be considered an SCA variation.

What Are the Various Types of Single Coronary Arteries?

Single coronary artery anomalies can be classified based on the variations in the origin of the RCA and LMCA and their successive branches. They are:

1. RⅠ or LⅠ - Instead of right and left, a single solitary vessel arises for either the left or right aortic sinus and follows the course of an RCA or LMCA.

2. RⅡ or LⅡ - This can be further divided into three types based on the relationship of the SCA to the greater vessels (which include the aorta, pulmonary trunk, pulmonary vein, and vena cava); they are-

3. RⅡA or LⅡA - In this type, the SCA courses anterior to the pulmonary trunk.

4. RⅡB or LⅡB - The SCA in this variation travels between the aorta and the pulmonary trunk.

5. RⅡP or LⅡP - The SCA travels posterior to the aorta in this variation.

6. RⅢ or LⅢ - This is an extremely rare anomaly in which the LMCA is absent. Still, its successive branches, like the left anterior descending artery (LADA) and circumflex arteries, arise from the single common trunk (or RCA).

The alphabets R (right) and L(left) are used to identify the origin of the SCA; roman numerals Ⅰ, Ⅱ, and Ⅲ are used to represent the anatomical distribution of the SCA, and letters A, B, and P are used to delineate the course of the SCA with respect to the pulmonary trunk and the aorta.

What Causes Single Coronary Artery?

The exact cause for the development of SCA is not well understood. Still, according to embryologic studies, the formation of a normal coronary arterial system depends on multiple morphological features (like the formation of cardiac sinusoids, development of aortopulmonary trunk, etc.), and any malformations in this multi-step procedure will lead to the development of coronal artery anomalies including SCA.

SCA is strongly associated with the below-mentioned congenital cardiac anomalies-

1. Truncus Arteriosus - It is a congenital condition where the baby is born with one great vessel instead of the regular two (pulmonary artery and aorta).

2. Pulmonary Valve Atresia - A birth defect of the heart in which the valve (pulmonary valve) that controls blood flow from the heart to the lungs does not form.

3. Tetralogy of Fallot - It is a rare condition caused due to combination of four heart defects - pulmonary valve stenosis (narrowing of the pulmonary valve), ventricular septal defect (a hole in the septum), shifting of the aorta, and right ventricular hypertrophy (thickening of the right lower heart chamber).

4. Double Outlet Right Ventricle - It is a heart condition in which the pulmonary artery and aorta do not connect properly.

Some less frequently associated cardiac malformations seen alongside SCA are the transposition of the great arteries, the ectopic origin of the coronary sinus, left coronary artery dominance, coronary artery fistula draining into the pulmonary trunk, etc.

What Are the Symptoms of Single Coronary Artery?

Most individuals with SCA are asymptomatic, and when it does become symptomatic, the first symptom is death. However, a few suggestive symptoms of SCA are as follows:

1. In infants, SCA causes reduced blood flow to the heart, leading to myocardial infarction, manifesting as wheezing, tachypnea (rapid breathing), and episodic crying.

2. Adults' symptoms include palpitations, fatigue, fever, exertional dyspnea (shortness of breath), and angina (chest pain spreading to the arms, shoulders, and neck).

How Is Single Coronary Artery Diagnosed?

Diagnosing SCA is difficult due to its absent or irrelevant clinical manifestations. It is often diagnosed accidentally during noninvasive imaging or autopsy. If suspected, SCA can be diagnosed with different diagnostic modalities:

1. Conventional Coronary Angiography - It is the gold standard for assessing coronary artery abnormalities, including SCA; however, it is an invasive procedure with the risk of complications.

2. Coronary Computed Tomography Angiography (CCTA) - It is a noninvasive diagnostic tool with a high temporal and spatial resolution that made it emerge as the new gold standard for detecting and characterizing coronary artery anomalies.

3. Cardiac MRI (Magnetic Resonance Imaging) - It is a nonionizing test that can detect SCA and delineate the anatomy of the anomalous coronary artery.

How Is Single Coronary Artery Treated?

Surgery is the definitive treatment for individuals with SCA, but a few cases have been successfully managed with conservative management. It comprises medical therapy which restores and maintains hemodynamic status deranged by SCA. Some of the frequently used medications are:

1. Cardiac glycosides like Digoxin provide a positive ionotropic effect (alteration in the force of cardiac contractions).

2. Loop diuretics improve pulmonary and systemic cardiovascular activity by reducing cardiac output.

3. Dobutamine (beta 1- selective adrenoceptor agonist) has also been used for its positive ionotropic effect.

4. Prophylactic antibiotics should be used to prevent secondary infections.

5. Beta-adrenergic blocking agents, like Metoprolol, Atenolol, Esmolol, etc., can prevent ischemia.

Surgery is suggested to patients who do not respond to medical therapy; it can be of different types depending on the type of SCA.

Conclusion:

An SCA is a rare congenital anomaly; the condition can remain silent and asymptomatic without clinical evidence. Undiagnosed SCA has higher chances of mortality which becomes diagnosed after death. Accurate angiographic information obtained through CCTA can help manage the condition with medical therapy or surgery.