Coronary Circulation and Ischemic Heart Disease

Arterial Supply of the Heart

The heart is supplied by the right and left coronary arteries.

Most of the myocardium receives its blood supply through the coronary circulation. Only the innermost 75–100 μm of the endocardial region can obtain nutrients directly by diffusion from blood within the cardiac chambers.

Features of Coronary Arteries

1. The right and left coronary arteries arise from the ascending aorta, immediately above the aortic valve.
2. They originate from the corresponding right and left aortic sinuses.
3. Coronary arteries are considered functional end arteries because their anastomoses are usually insufficient to maintain adequate blood flow when a major branch is suddenly occluded. Anatomically, however, they are not true end arteries.
4. Coronary blood flow occurs predominantly during ventricular diastole, particularly in the left coronary circulation.
5. Coronary arteries are especially susceptible to atherosclerosis, which may narrow or obstruct their lumen and reduce myocardial blood supply.

Right Coronary Artery

Origin

The right coronary artery (RCA) arises from the right coronary sinus of the ascending aorta, immediately above the aortic valve. The right coronary artery is generally smaller than the left coronary artery.

Course

The course of the right coronary artery may be described in two segments:

1. First segment
   • From its origin, the artery passes forward and to the right between the pulmonary trunk and the right auricle.
   • It then descends in the right atrioventricular groove toward the inferior border of the heart.
2. Second segment
   • The artery curves around the inferior border of the heart and enters the posterior part of the right atrioventricular groove.
   • It continues posteriorly and terminates by anastomosing with the circumflex branch of the left coronary artery.

Branches

The right coronary artery gives rise to the following branches:

1. Conus artery (arteria coni arteriosi)
   • Usually the first branch of the right coronary artery.
   • Supplies the infundibulum, or outflow tract, of the right ventricle.
2. Anterior ventricular branches
   • Usually three to four in number.
   • Supply the anterior surface of the right ventricle.
3. Right marginal artery
   • Usually the largest ventricular branch of the right coronary artery.
   • Runs along the inferior margin of the heart toward the apex.
   • Supplies much of the sternocostal surface of the right ventricle.
4. Atrial branches
   • Usually two to three in number.
   • Include anterior, lateral, and posterior atrial branches that supply the right atrium.
5. Sinoatrial nodal artery
   • Supplies the sinoatrial node.
   • In about 60% of individuals, it arises from the right coronary artery; in the remaining cases, it most commonly arises from the circumflex branch of the left coronary artery.
6. Posterior ventricular branches
   • Usually two to three in number.
   • Arise from the posterior part of the right coronary artery.
   • Supply the diaphragmatic surface of the right ventricle.
7. Posterior interventricular artery
   • In most individuals with right coronary dominance, it arises from the right coronary artery.
   • Descends in the posterior interventricular groove toward the apex and anastomoses with the anterior interventricular artery.
   • It gives rise to:
     • Septal branches, which supply the posterior one-third of the interventricular septum.
     • Atrioventricular nodal branch, which commonly supplies the AV node.
     • Ventricular branches, which supply adjacent parts of the inferior surfaces of the right and left ventricles.

Area of Distribution

The right coronary artery typically supplies:

1. Right atrium
2. Most of the right ventricle, except the region near the anterior interventricular groove
3. A small part of the left ventricle near the posterior interventricular groove
4. Posterior one-third of the interventricular septum
5. Much of the cardiac conduction system, including the SA and AV nodes in most individuals

Left Coronary Artery

Origin

The left coronary artery (LCA) arises from the left coronary sinus of the ascending aorta, immediately above the aortic valve.

It is generally larger than the right coronary artery. After a short course, the main trunk usually divides into:

1. Anterior interventricular artery, also called the left anterior descending (LAD) artery
2. Circumflex artery

Course

Main trunk

• The left coronary artery passes to the left between the pulmonary trunk and the left auricle. It then divides into the anterior interventricular and circumflex arteries.

Anterior interventricular artery

• The anterior interventricular artery descends in the anterior interventricular groove toward the apex of the heart. It may curve around the apex onto the diaphragmatic surface and anastomose with the posterior interventricular artery.

Circumflex artery

• The circumflex artery runs to the left in the atrioventricular groove. It curves around the left border of the heart and continues posteriorly in the atrioventricular groove. Its extent varies according to coronary dominance, and it may anastomose with branches of the right coronary artery near the crux of the heart.

Branches

1. Anterior Interventricular Artery

The anterior interventricular artery gives rise to the following branches:

1. Anterior ventricular branches: Supply adjacent parts of the right and left ventricles on the sternocostal surface.
2. Diagonal branches: Run obliquely over the anterior surface of the left ventricle and supply its myocardium. Occasionally, an additional branch may arise near the bifurcation of the left coronary artery.
3. Conus branch: Supplies part of the right ventricular outflow tract and may contribute to arterial anastomoses around the pulmonary conus.
4. Septal branches: Penetrate the interventricular septum and supply its anterior two-thirds.

2. Circumflex Artery

The circumflex artery gives the following branches:

1. Ventricular branches: Supply the left and posterolateral surfaces of the left ventricle and may extend onto its diaphragmatic surface.
2. Atrial branches: Supply the adjacent part of the left atrium.
3. Sinoatrial nodal artery: Arises from the circumflex artery in a substantial proportion of individuals.
4. Left marginal artery: Runs along the left border of the heart toward the apex and supplies the left ventricle.
5. Posterior interventricular artery: In a left-dominant circulation, the circumflex artery gives rise to the posterior interventricular artery.
6. Kugel artery: An atrial arterial branch that may form an anastomotic connection between branches of the right and left coronary circulations.

Area of Distribution

The left coronary artery typically supplies:

1. Left atrium
2. Most of the left ventricle
3. Part of the right ventricle adjacent to the anterior interventricular groove
4. Anterior two-thirds of the interventricular septum
5. Most of the atrioventricular bundle and its bundle branches, particularly the left bundle branch

Cardiac dominance

Cardiac dominance, also termed coronary dominance, is determined by the coronary artery that gives rise to the posterior interventricular artery.

Types of cardiac dominance

1. Right dominance: The posterior interventricular artery arises from the right coronary artery. This is the most common pattern.
2. Left dominance: The posterior interventricular artery arises from the circumflex branch of the left coronary artery.
3. Co-dominant or balanced circulation: Both the right coronary and circumflex arteries contribute significantly to the arterial supply of the inferior and posterior aspects of the heart. Typically, the posterior interventricular artery arises from the right coronary artery, while substantial posterolateral branches arise from the circumflex artery.

Coronary Anastomoses

Coronary vessels form several types of vascular communications:

1. Interarterial anastomoses
2. Arteriovenous communications
3. Arteriosinusoidal communications

Anatomical anastomoses exist between branches of the coronary arteries, but under normal conditions they are usually too small to provide adequate collateral circulation after sudden occlusion of a major coronary artery. Acute interruption of coronary blood flow may therefore produce myocardial ischemia or infarction.

Collateral coronary channels may enlarge gradually when arterial narrowing develops slowly, thereby providing an alternative route for myocardial perfusion.

Small extracardiac anastomoses may also occur between coronary branches and vessels such as the internal thoracic, bronchial, pericardiophrenic, and esophageal arteries.

Ischemic Heart Disease

Ischemic heart disease (IHD) refers to a group of conditions caused by inadequate blood flow to the myocardium, resulting in an imbalance between myocardial oxygen supply and demand. Coronary artery disease (CAD), particularly atherosclerotic narrowing of the coronary arteries, is the most common underlying cause.

Causes

The principal cause of ischemic heart disease is coronary atherosclerosis. Progressive narrowing or acute obstruction of a coronary artery reduces myocardial perfusion and may produce ischemia or infarction.

Classification

Ischemic heart disease may present as:

1. Stable angina
2. Acute coronary syndrome, including unstable angina and myocardial infarction
3. Ischemic heart failure
4. Cardiac arrhythmias
5. Sudden cardiac death

Angina pectoris

Angina pectoris is chest discomfort caused by transient myocardial ischemia without irreversible necrosis of cardiac muscle.

• It usually presents as episodic substernal or precordial discomfort.
• The pain is commonly described as pressure, heaviness, tightness, squeezing, or constriction.
• It is typically retrosternal and may radiate to the left shoulder, medial aspect of the arm and forearm, neck, jaw, or back.

Stable angina

Stable angina is usually precipitated by exertion, emotional stress, or other situations that increase myocardial oxygen demand. It typically improves with rest or appropriate medication.

Unstable angina

Unstable angina is characterized by new-onset, increasingly frequent or severe angina, or chest discomfort occurring at rest or with minimal exertion. It forms part of the acute coronary syndrome and requires urgent clinical assessment.

Myocardial infarction (heart attack)

Myocardial infarction (MI), commonly called a heart attack, occurs when prolonged myocardial ischemia causes irreversible necrosis of cardiac muscle. It most commonly results from acute thrombotic obstruction of a coronary artery following disruption of an atherosclerotic plaque.

Common manifestations include:

• Persistent chest pain or pressure
• Pain radiating to the upper limb, shoulder, neck, jaw, or back
• Shortness of breath
• Sweating
• Nausea or vomiting
• Weakness, dizziness, or syncope

The coronary arteries most frequently involved are:

1. Anterior interventricular artery or left anterior descending (LAD) artery
2. Right coronary artery
3. Circumflex branch of the left coronary artery

The frequency of involvement varies among populations and according to the type and location of myocardial infarction.

Cardiac arrest

Cardiac arrest is the sudden cessation of effective cardiac mechanical activity, resulting in loss of systemic circulation.

Acute myocardial infarction is an important cause, usually by precipitating a serious cardiac arrhythmia such as ventricular fibrillation.

Typical features include:

• Sudden loss of consciousness
• Absence of normal breathing or presence of agonal gasping
• Absence of a palpable central pulse

Cardiac arrest is a medical emergency requiring immediate cardiopulmonary resuscitation (CPR) and, when indicated, defibrillation.

Investigations

Electrocardiography (ECG)

Echocardiography uses ultrasound to examine the structure and function of the heart.

It can assess:

• Dimensions and thickness of cardiac chambers
• Ventricular contraction and ejection
• Regional wall motion
• Valve structure and function
• Pericardial abnormalities

Echocardiography

Echocardiography uses ultrasound to examine the structure and function of the heart.

It can assess:

• Dimensions and thickness of cardiac chambers
• Ventricular contraction and ejection
• Regional wall motion
• Valve structure and function
• Pericardial abnormalities

Doppler echocardiography

Doppler echocardiography evaluates the direction and velocity of blood flow through the heart and major vessels.

It is particularly useful for assessing:

• Valvular stenosis and regurgitation
• Intracardiac shunts
• Septal defects
• Pressure gradients across valves and vessels

Coronary angiography

Coronary angiography is an invasive imaging procedure used to visualize the lumen of the coronary arteries and identify sites of narrowing or obstruction.

A catheter is commonly introduced through the radial or femoral artery and advanced under imaging guidance to the ascending aorta and coronary ostia.

When the femoral route is used, the catheter passes through:

Femoral artery → external iliac artery → common iliac artery → abdominal aorta → thoracic aorta → arch of the aorta → ascending aorta

Iodinated contrast medium is injected into the coronary arteries, and their course and lumen are visualized using fluoroscopic imaging.

Treatment

Coronary angioplasty

Coronary angioplasty, usually performed as part of percutaneous coronary intervention (PCI), is used to restore blood flow through a narrowed or obstructed coronary artery. A catheter carrying a balloon is advanced to the affected segment. The balloon is inflated to widen the narrowed lumen. In most procedures, a coronary stent, consisting of an expandable mesh framework, is deployed to maintain patency of the artery. PCI is generally performed by an interventional cardiologist.

Coronary artery bypass grafting

Coronary artery bypass grafting (CABG) is a surgical procedure that creates an alternative route for blood to reach the myocardium beyond a significantly narrowed or obstructed coronary artery.

A vascular graft is connected so that blood bypasses the diseased coronary segment.

Commonly used conduits include:

1. Internal thoracic artery
2. Great saphenous vein
3. Radial artery

The procedure is performed by a cardiothoracic surgeon.

Great Saphenous Vein as a Bypass Graft

The great saphenous vein has traditionally been used for coronary artery bypass grafting because:

1. It is long and can provide grafts for multiple coronary vessels.
2. It is readily accessible and relatively easy to harvest.
3. Its caliber is suitable for coronary bypass grafting.
4. When used as a graft, the vein is usually reversed or its valves are rendered functionally ineffective so that they do not obstruct arterial blood flow.

The internal thoracic artery, particularly the left internal thoracic artery, is often preferred for important coronary targets because of its superior long-term patency.

Venous Drainage of Heart

Venous blood from the myocardium is returned mainly through three sets of veins:

1. Coronary sinus and its tributaries
2. Anterior cardiac veins
3. Venae cordis minimae (Thebesian veins)

Most cardiac venous blood reaches the right atrium through the coronary sinus. Smaller amounts drain directly into the right atrium through the anterior cardiac veins and into the cardiac chambers through the venae cordis minimae.

Coronary Sinus

The coronary sinus is the principal venous channel of the heart.

• Length: Approximately 2–3 cm
• Location: Posterior part of the atrioventricular groove
• Development: Mainly derived from the left horn of the sinus venosus.

Beginning

The coronary sinus begins as the continuation of the great cardiac vein in the left part of the posterior atrioventricular groove.

Termination

The coronary sinus opens into the right atrium. Its opening lies between the orifice of the inferior vena cava and the right atrioventricular orifice.

The opening is guarded by a small, usually functionally insignificant fold called the valve of the coronary sinus (Thebesian valve).

Tributaries

The coronary sinus receives the following major tributaries:

1. Great cardiac vein
   • Begins near the apex of the heart.
   • Ascends in the anterior interventricular groove with the anterior interventricular artery.
   • Enters the left atrioventricular groove and passes around the left border of the heart.
   • Continues into the coronary sinus.
   • Usually receives the left marginal vein.
2. Middle cardiac vein
   • Begins near the apex.
   • Ascends in the posterior interventricular groove.
   • Opens into the coronary sinus near its right end.
3. Small cardiac vein
   • Runs in the right atrioventricular groove.
   • Drains into the right end of the coronary sinus.
   • Commonly receives the right marginal vein.
4. Posterior vein of the left ventricle
   • Drains the posterior and diaphragmatic surfaces of the left ventricle.
   • Opens into the coronary sinus, usually to the left of the middle cardiac vein.
5. Oblique vein of the left atrium (vein of Marshall)
   • A small vein descending over the posterior surface of the left atrium.
   • Opens into the left end of the coronary sinus.
   • It is an embryological remnant associated with the left common cardinal venous system.
6. Right marginal vein
   • Runs along the inferior margin of the heart.
   • Usually drains into the small cardiac vein but may open directly into the right atrium.
7. Left marginal vein
   • Ascends along the left border of the heart.
   • Usually drains into the great cardiac vein or directly into the coronary sinus.

Anterior Cardiac Veins (3–4 in number)

The anterior cardiac veins are usually three or four small veins that drain the anterior wall of the right ventricle, particularly the region of the infundibulum.

Unlike most cardiac veins, they do not drain into the coronary sinus. Instead, they open directly into the right atrium.

Venae Cordis Minimae (Thebesian Veins)

The venae cordis minimae, or Thebesian veins, are numerous minute veins within the myocardium.

They open directly into the cardiac chambers through small openings called foramina venarum minimarum. They are most numerous in the right atrium and right ventricle and are less abundant in the left-sided chambers.

Click to see: Medical Disclaimer and Copyright Notice