Coronary Sinus Definition

The coronary sinus is a major vein that runs between the left ventricle and the atrium of the heart, in the atrioventricular groove (coronary sulcus). This vein gathers deoxygenated blood via many cardiac veins located throughout the heart muscle. From its origin, the coronary sinus empties into the right atrium. The coronary sinus terminates at its junction with the main cardiac vein.

Coronary Sinus Location

The knowledge of the coronary sinus needs to have a comprehension of the heart muscle and the blood vessels that surround it.

In contrast to smooth and skeletal muscle, the heart muscle is responsible for the heart’s pumping power. Myocardium, or cardiac muscle, is another name for heart muscle tissue. The myocardium is located amid the outer sac that covers the heart (epicardium) and the inner membrane (endocardium). Pacemaker cells, which replace neurons in the heart muscle, start and transmit the action potentials that produce heartbeats.

To provide a continuous energy supply, all myocardial cells contain a considerable number of mitochondria. Unlike other muscle types, the heart may be lethal if it stops for even a brief amount of time. Wave-like heart muscle contractions move blood in the appropriate path, from the upper atria to the bottom via the ventricles, providing enough blood flow into the aorta and pulmonary artery.

The myocardium is supplied with nutrients and oxygen through the coronary arteries. Numerous coronary veins provide the heart muscle with deoxygenated blood and waste products. These veins transport blood to the right atrium, where it may be absorbed into the pulmonary circulation. Due to the fact that veins also function as a reservoir system capable of modifying the flow of blood into the heart, there are twice as many coronary veins as arteries. At all times, blood must be available to supply the right and left atria.

The coronary sinus is where many of the coronary veins drain. Because of its size and closeness to the right atrium, this vein may be used for a variety of cardiac treatments, including ablation (for heart arrhythmia).

The bigger and smaller veins discharge deoxygenated blood from the myocardium. All of the coronary veins, including the great cardiac vein, the small cardiac vein, the inferior left ventricular vein, the atrial veins, and the middle cardiac vein, drain into the coronary sinus. It is part of the broader venous group.

Thebesian veins, it empties straight into the heart chambers, make up the smallest cardiac venous group.

The coronary sinus is around two to five centimetres long and has a variable diameter of one centimetre. As a result, it is the largest vein in the heart. It is located between the left atrium and ventricle, inside the heart muscle’s atrioventricular groove, which points toward the diaphragm (diaphragmatic surface). In Gray’s Anatomy, the groove between the left atrium and ventricle is concealed between the pulmonary artery and aorta. The presence and location of this groove, or sulcus, between the right atrium and ventricle is indicated by the apparent groove between them.

Coronary Sinus Function

The coronary sinus functions in conjunction with cardiac contraction: as the atria contract (atrial systole), the sinus also contracts. This is because its wall contains cardiac muscle cells that are in direct contact with the atria’s heart muscle.

Blood Reservoir

Blood is forced into the right atrium when this vein constricts. While both ventricles contract simultaneously and the valve between the atria and ventricles remains open, extra blood may travel into the right ventricle; nonetheless, the venae cavae provide the majority of blood to the right part of the heart.

Valves in the coronary sinus architecture keep blood from travelling in the incorrect direction. Between the inferior vena cava and the tricuspid valve, it keeps blood from repeating from the right ventricle into the right atrium, where the coronary sinus starts. The ostium is the name of this orifice, which is partly concealed by the Thebesian valve.

The coronary sinus is terminated by the Vieussen’s valve, which keeps blood from returning to the main heart vein.

Despite its placement between the left atrium and ventricle, the coronary sinus enters the right atrium; coronary sinus valves are located at the ostium and its confluence with the major cardiac vein.

The bundle of His is marked in red in the figure below; the blue dot indicates the location of the sinoatrial node inside the heart.

A crescent-shape protecting an aperture may be seen where the bundle of His starts, near to the inferior vena cava. The ostium is this aperture, and the Thebesian valve is the crescent.

Drainage Point

Blood is drained from several coronary veins into the coronary sinus. These veins collect deoxygenated blood from various myocardial regions.

The left ventricle sends deoxygenated blood to the major cardiac vein, the lateral marginal veins, and the inferior veins. The inferior interventricular vein, also known as the intermediate cardiac vein, empties venous blood from the myocardium’s surface. This vein ultimately merges with the great heart vein to become the great cardiac vein.

The left atrium’s oblique vein (Marshall’s vein) transfers deoxygenated blood from the heart. Finally, blood is transported from the right atrium and a portion of the right ventricle through the tiny cardiac vein. Other myocardial veins enter the heart chambers directly.

Impulse Transmission

Because it joins the right and left atriums, the coronary sinus has an electrical role. As a result, it may have a role in the development of atrial arrhythmia. This is not surprising, given that other big veins, like the superior vena cava and the pulmonary veins, may also cause this condition. A small number of cardiac muscle cells link straight to the larger veins of the heart. providing extra impulses for atrial contractions that may induce or promote an irregular heartbeat or even atrial fibrillation.

An electrical defect in the atria may be seen in the electrocardiogram (ECG) below. The P wave, QRS complex, and T wave are all present in a normal ECG. The P wave in the figure below is made up of several, unequal waves rather than a single curve (atrial systole). This indicates that the electrical impulses responsible for atrial systole are not coordinated; impulses might originate from several parts of the atrium, not simply the sinoatrial node. Some of these aberrant impulses may be delivered or transferred via the sinus wall by cardiac muscle cells.

Coronary Sinus Pathology

Heart disease may be present at birth or develop over time. The coronary sinus does not generate fatty deposits (atherosclerosis) since it is a vein; nonetheless, it might dilate owing to arterial hypertension. A massive coronary sinus with a diameter of 4.5 cm has been discovered.

Unroofed Coronary Sinus Defect

ASDs (atrial septal defects) are often referred to as “heart holes.” When an opening (septum) in the wall between the right and left atria remains open after delivery, it is called an ASD. This hole often closes immediately before or shortly after delivery. The foramen ovale is the name of the opening.

The foramen ovale does not seal entirely or at all in an atrial septal defect, permitting deoxygenated blood from the right atrium to enter the left atrium’s oxygenated blood and vice versa.

A real type of ASD is not a coronary sinus atrial defect. In this situation, the hole lies between the (unroofed) coronary sinus and the left atrium, not in the septum. This space between the right and left atrium may allow deoxygenated and oxygenated blood to mingle. This pathology has symptoms that are comparable to ASD.

Sinus coronary If the septum’s foramen ovale remains open and the wall between the sinus and atria remains intact,

ASD occurs. This defect is known as an “unroofed sinus” because it does not have a flaw in the foramen ovale.

 n unroofed coronary sinus defect (UCSD) is virtually invariably congenital and highly uncommon, with symptoms that resemble those of an ASD. Shortness of breath, edoema (swelling of the limbs and belly), weariness, and heart palpitations are all symptoms. These symptoms may be absent if the abnormality is minor.

UCSD and ASD are diagnosed via an echocardiogram, EKG, MRI, and/or CT scan. Previously, an unroofed coronary sinus defect was often misdiagnosed as an ASD.

Coronary Sinus Arrhythmia

Another probable condition is coronary sinus arrhythmia, since the sinus wall also contains cardiac muscle cells. The presence of cardiac muscle in or near the sinus transmits impulses, and the pressure from a dilated coronary sinus (see next heading) modifies the electrical pathways of the right atrium. The most common treatment is ablation therapy, which includes cauterising the areas outside of the sinoatrial node that generate action potentials.

Ischemic heart failure and/or dilated cardiomyopathy are often associated with dilatation of the coronary veins (a left ventricle that is swollen and overworked). Increased blood flow is almost invariably the cause of a dilated vein.

Increased blood flow to the coronary sinus is produced by either increased volume reaching the heart via the venae cavae or regurgitation from the right ventricle to the right atrium as a result of a faulty tricuspid valve. This inhibits the sinus from emptying properly and places strain on the sinus’s elastic walls. When a vein is blown beyond a certain point, it is unable to return to its normal shape—it stays dilated and unable to contract as vigorously as before.

If a dilated coronary sinus is detected, a cardiologist will immediately assume a right ventricular issue.

The diameter of the vein (seen below) may be used to determine if surgery is necessary.

Coronary Sinus Diverticulum

Diverticulum is another disorder that is defined by a projection in the vessel wall that affects the vein and results in gradual dilatation throughout its extent. While coronary veins are not subjected to the high pressures seen in the arteries closest to the heart, there is a chance that the weaker wall may leak. This is a very unusual event. The muscular walls of the coronary sinus, on the other hand, when dilated, are difficult to constrict or perform an efficient reservoir role.

The most serious complication of this disease is the development of blood clots. The smooth inside walls of the vein enable blood to flow freely through it. Turbulence occurs while the vessel wall bubbles outwards as a result of the shape shift. Small blood clots may develop as a result of turbulence. Clots go from the coronary sinus to the right atrium, where they pass via the right ventricle and into the lungs through the pulmonary artery. Blood clots may lodge in the arterioles and capillaries of the lungs, obstructing blood flow and causing major complications (pulmonary embolism).

References

• Wilson A, Bhutta BS. (Updated 2020). Anatomy, Thorax, Coronary Sinus. Treasure Island (FL), StatPearls Publishing. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK557566/
• Park IS (Ed). (2019). An Illustrated Guide to Congenital Heart Disease: From Diagnosis to Treatment – From Fetus to Adult. Singapore, Springer Nature.
• Foster T, Shen J. (2019) Crash Course Cardiology: Fifth Edition. Oxford, Elsevier Ltd.