Coronary artery anomaly

Coronary artery anomalies are variations of the coronary circulation, affecting <1% of the general population. Symptoms include chest pain, shortness of breath and syncope, although cardiac arrest may be the first clinical presentation. Several varieties are identified, with a different potential to cause sudden cardiac death.

Physiology of coronary arteries

Coronary arteries are vessels supplying blood and nutrients to the heart muscle (myocardium).

Coronary arteries arise from ostia, openings of the aorta (the largest artery in the human body) at the upper third or middle third of the sinuses of Valsalva (the first part of the big pipe coming off the main pumping chamber). The walls of coronary arteries consist of three layers: the tunica intima or inner layer (possible site of lipid deposits and fibrosis, during life), the tunica media (a smooth muscle layer whose tone is modulated by the nervous system, influencing vessel diameter and resistance) and adventitia (where nervous endings are located). Normally, the initial portion of coronary arteries lies onto the external surface of the heart (epicardium) where fat deposits tend to form during life.

In normal anatomy, three essential coronary arteries are identified: right coronary artery (RCA), left anterior descending artery (LAD) and left circumflex artery (LCx). LAD and LCx usually originate from the bifurcation of a common vessel known as left main trunk or left coronary artery (LM or LCA).

Coronary arteries are identified according to the myocardial territory they feed:

1)   the LAD supplies the anterior interventricular septum and anterior left ventricular free wall;

2)   the LCx supplies the posterolateral left ventricular free wall;

3)   the RCA supplies the right ventricular free wall;

In fact, despite a certain degree of variability in coronary artery anatomy among individuals, there is greater consistency in the ''regions'' of the heart that are supplied by the different coronary arteries.

The posterior descending artery, providing blood flow to the infero-posterior wall of the heart, originates from the RCA in 70-90% of individuals (“right coronary dominance”), whereas in 10-15% cases it originates from the LCx (“left coronary dominance”).

Coronary vessels diameter progressively decreases proceeding from their origin to the periphery. Besides the LM, LAD, LCx and RCA, arterial vessels that are large enough to be identified by clinical angiography are called “branches”, while capillaries represent the smallest peripheral vessels of the coronary tree that lack muscular tissue (and capacity to cause spasm) and are responsible for oxygen and nutrients exchange within the myocardium.

Normal variants, anomalies

Regarding coronary artery anatomy, a distinction must be provided when assessing abnormalities:

-      ''normal'': any morphological feature observed in >1% of an unselected population

-      ''normal variant'': an alternative, unusual but benign morphological feature identified in >1% of the same population (e.g. left main is absent in 1-2% of the general population with LAD and LCx originating from separate ostia - “absent left trunk” variant)

-      ''coronary artery anomaly (CAA)'': a morphological feature seen in <1% of that population, capable of causing dysfunction

The prevalence of coronary artery anomalies is inconsistent across the scientific literature, but they are considered to affect <1% of the general population. Specifically, recent data came from MRI screening of a large population (more than 5000 young children) and provided a precise estimate, suggesting that coronary artery anomalies are present in 0.45% of the US population (approximately 1.300.000 people).

Mechanism

Anomalous origin of a coronary artery from the opposite sinus are relevant on a clinical level due to a significant association with sudden cardiac death, if they are accompanied by intramural course. Indeed, the main feature responsible for adverse outcomes is the “intramural” course (sometimes improperly referred to as inter-arterial) characterized by an acute ostial angulation (tangential course), “slit-like” ostium (compressed inside the aortic wall), and a proximal or initial section penetrating into the aortic tunica media (coronary arteries normally take off at a 90 degree angle) with subsequent course reaching the “correct” side of the heart. As a consequence, lateral compression of the coronary artery leads to coronary luminal (inside opening) narrowing, with reduced supply of blood and oxygen to the depending myocardial tissue, that is phasic (worse in systole, the phase of cardiac contraction, and tachycardia). Furthermore, the intramural segment of the ectopic artery, located inside the aorta, is typically but variably “hypoplastic

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