Blood Vessels and Nerves of the Heart

Mediastinum and the heart | Main Anatomy Index | The pericardium

Last updated 30 March 2006

Coronary Arteries

• The right and left coronary arteries (L. corona, crown) supply the myocardium, epicardium and pacemaking tissue of the heart.
• Both are branches of the ascending aorta and both give branches to the atria and ventricles as they run in the coronary sulcus.

• The right coronary artery arises from the right aortic sinus, which the left coronary artery arises from the left aortic sinus. Occasionally, the two may arise from the same sinus.
• A right coronary branch (the conus artery) may arise separately from the anterior sinus (36% of hearts), thus representing a third coronary artery.
• The left artery is larger in diameter than the right in 60% of hearts, the right is larger in 17% and the two arteries are equal in 23% of hearts.

The Right Coronary Artery

• The right coronary artery arises from the right aortic sinus, and then passes behind the pulmonary trunk to reach the atrioventricular (coronary) sulcus.
• The artery gives off several branches:

• The conus artery: this is the 1^st branch in 64% of hearts and it supplies the conus arteriosus.

• The right diagonal (ventricular) artery: this supplies the anterior aspect of the right ventricle.

• The right marginal artery: this supplies the lateral aspect of the right ventricle.

• The posterior interventricular artery: this branch is on the posterior surface of the heart (it branches from the right coronary artery after it has travelled along the coronary sulcus to the posterior surface) and runs in the posterior interventricular sulcus.

• The atrioventricular nodal artery: this branch begins opposite the origin of the posterior interventricular artery in 85% of hearts.
• It enters the posterior part of the atrioventricular groove and passes to the AV node located in the base of the interventricular septum.
• This artery supplies the AV node and bundle.

• The right coronary artery supplies the SA node in 55% of cases but the clinically important sinuatrial nodal artery may arise from the left coronary artery or its circumflex branch in 45% of cases.

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The Left Coronary Artery

• This artery usually supplies a greater volume of the myocardium than the right coronary artery.
• Its initial stem lies between the pulmonary trunk and the left auricular appendage.
• This artery divides into:

• The anterior interventricular artery: this descends in the anterior interventricular groove.

• The circumflex artery: this curves left in the coronary sulcus.

• The left diagonal artery: in 33-50% of hearts, this artery courses across the anterior aspect of the left ventricle.

• The left marginal artery: in 90% of hearts, the circumflex artery gives rises to this artery that ramifies down the left margin of the heart.

• There may be an artery to the AV node as the terminal branch of the left coronary artery in 20% of hearts.

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Areas of Distribution

The right coronary artery supplies:

• All of the right ventricle (except a small region of the anterior interventricular sulcus);
• A variable part of the left ventricular diaphragmatic surface;
• The posterior inferior 1/3 of the interventricular septum;
• All of the right atrium and part of the left;
• The conducting system as far as the proximal parts of the right and left crura.

The left coronary artery is reciprocal in distribution.

Coronary Anastomoses

• These anastomoses cannot rapidly provide collateral routes in the event of a sudden obstruction but are more effective in slowly progressive coronary obstructions.
• Anastomoses are present throughout the cardiac wall thickness.
• Several extramural intercoronary anastomoses have been identified. These are:

• The apex, between the anterior and posterior interventricular arteries.

• The anterior aspect of the right ventricle, between the anterior interventricular artery and right diagonal branches.

• The posterior aspect of the left ventricle, between the posterior interventricular artery and the circumflex branches.

• At the crux, interventricular sulci, interatrial sulci, and between the sinuatrial nodal and other atrial branches.

• Extracardiac anastomoses may connect the coronary arteries with other thoracic arteries via the pericardial arteries and arterial vasa vasorum of vessels linking the heart with the systemic and pulmonary circulations.
• These are probably of no clinical significance however.

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Cardiac Veins

• The veins draining the heart can be divided into 3 groups.

• The coronary sinus and its tributaries, returning blood to the right atrium from the whole heart including the septa, except for the anterior region of the right ventricle and small parts of the left atrium and ventricle.
• The anterior cardiac veins draining blood from the anterior aspect of the right ventricle and a region around the right cardiac border where the right marginal vein joins this group. These veins end in the right atrium.
• The venae cordis minimae (Thebesian veins) opening into the right atrium and ventricle, and to a lesser extent, the left atrium and sometimes the left ventricle.

The Coronary Sinus and its Tributaries

• This lies in the posterior coronary sulcus and opens into the right atrium between the IVC opening and the right atrioventricular orifice.
• Its opening has a valve of the coronary sinus to prevent regurgitation of blood.
• It receives blood from the following veins; all except the last have valves at their orifices:

• Great cardiac vein (anterior interventricular vein), lying in the anterior interventricular sulcus.
• Small cardiac vein lies in the posterior coronary sulcus between the right atrium and ventricle and joints the coronary sinus near its atrial opening.
• Middle cardiac vein (posterior interventricular vein), lying in the posterior interventricular sulcus.
• Posterior vein of the left ventricle lies to the left of the middle cardiac vein.
• Oblique vein of the left atrium lies on the back of the left atrium. It is continuous with the ligament of the left vena cava.

The Anterior Cardiac Veins

• There are usually 3 in number.
• The right marginal vein courses along the right cardiac border and may drain into the right atrium, the anterior cardiac veins or the coronary sinus.

The Venae Cordis Minimae

• These are found in most chambers but are rare in the left atrium and ventricle.
• They open directly in the heart chambers.

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The Pacemaking and Conducting System of the Heart

• The normal heart rate is about 60 to 100 beats per minute.

The Sinuatrial Node

• This is regarded as the initiator of each cardiac cycle.
• It lies at the superior limits of the crista terminalis in the wall of the right atrium.
• Described as a flat ellipsoid, it is 10 to 20 mm in length, 1 mm thick and 3 mm at its maximum lateral convexity.
• It receives the artery of the sinuatrial node.

• The SA node is said by some authors to be connected to the AV node by several internodal tracts.
• The anterior internodal tract (with includes the interatrial tract of Bachmann), the middle internodal tract, and the posterior internodal tract, have all been claimed to exist on the basis of dissection and microscopy.

The Atrioventricular Node

• This is oval (7 mm by 3 mm by 1 mm) and lies under the right atrial endocardium, 1 cm above the septal margin of the orifice of the coronary sinus.
• Its anteroinferior end becomes the common atrioventricular bundle.
• The AV node is probably responsible for the atrioventricular conduction delay.

The Atrioventricular Bundle (Bundle of His)

• This courses from the AV node along the posterior inferior margin of the membranous part of the interventricular septum to the muscular part.
• The bundle then divides into the right and left branches.

• The right branch continues subendocardially to the septomarginal trabecula, which it traverses to reach the base of the anterior papillary muscle of the right ventricle.
• From there it goes to the rest of the right ventricle.

• The left branch is actually several separate fascicles (separately ensheathed), which forms a flattened sheet over the subendocardium.
• This covers the muscular part of the interventricular septum and distributes to the left ventricle.

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Autonomic Innervation of the Heart

Sympathetic

• This contains afferent and efferent fibres.
• This is from the cardiac fibres (postganglionic fibres) from the superior, middle and inferior cervical ganglia.
• Also, sympathetic innervation is from the thoracic cardiac nerves from T1 to T4 segments of the spinal cord (preganglionic) and then via the sympathetic trunk (postganglionic).

• The pain sensory fibres probably pass back to the CNS with the sympathetic fibres (T1 to T4).

Parasympathetic

• The efferent and afferent fibres (preganglionic) are from the cardiac branches of the vagus nerve.
• Sensory receptors in the atria and ascending parts of the great vessels (baroreceptors) send impulses via the vagus nerve to the brainstem.
• These nerves form several cardiac plexuses.

• The superficial cardiac plexus (ventral) lies below the arch of the aorta, anterior to the right pulmonary artery, and near the ligamentum arteriosum.

• The deep cardiac plexus (dorsal) lies at the back of the aorta, in front of the tracheal bifurcation.

• The left coronary plexus (accompanies the left coronary artery) receives branches from the deep plexus and supplies the left atrium and ventricle.

• The right coronary plexus (accompanies the right coronary artery) receives branches from the superior and deep plexuses and gives branches to the right atrium and ventricle.

Function of the ANS supply to the Heart

Stimulation of the vagus nerve (parasympathetic) will:

• Slow the heart
• Reduce the blood pressure
• Constrict the coronary arteries

Stimulation of the sympathetic nerves (sympathetic) will:

• Raise the blood pressure
• Raise the heart rate
• Vasodilate the coronary arteries
• Increase the force and speed of contraction of cardiac muscle.

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