Coronary Circulation Overview

Coronary Circulation

• The left main coronary artery and the right coronary artery branch from the aorta, just after the aortic valve.
• The left main coronary artery divides into:
  • The left anterior descending artery: supplies the front of the left ventricle, the apex, and the front of the septum.
  • The circumflex artery: supplies the back of the left ventricle and the lower surface.
• The right coronary artery: supplies the right atrium, the right ventricle, and the inferior posterior part of the left ventricle.
  • In most people, the right coronary artery supplies the posterior descending artery.
  • In some people, the left circumflex artery supplies the posterior descending artery.
• The sinoatrial node is supplied by the right coronary artery in about 60% of people, and the atrioventricular node in 90%.
• The venous system mainly follows the coronary arteries and drains into the coronary sinus, which then empties into the right atrium.

Coronary Artery Disease (CAD)

• CAD is also known as ischemic heart disease (IHD) and is usually caused by atherosclerosis of a coronary artery.
• IHD describes a group of syndromes where there is an imbalance between myocardial blood supply and demand.

Stable CAD (Chronic Coronary Syndrome)

• Characterized by stable angina pectoris.
• It is characterized by chest pain that:
  • Builds up quickly (within 30 seconds) and disappears gradually (within 5 to 15 minutes).
  • Feels like tightness, squeezing, or constriction.
  • Can feel like an ache, discomfort, indigestion, or burning pain.
  • Is usually located behind the breastbone (retrosternal).
  • Radiates to the left shoulder, arm, back, neck, jaw, teeth, or epigastrium.
  • Is caused by exertion, emotions, or sexual activity.
  • Is relieved by rest and sublingual nitroglycerin.
• Other characteristics:
  • Nocturnal angina: chest pain that occurs during sleep.
  • Postprandial angina: chest pain that develops after meals.
  • Angina equivalents: chest pain may not be present, instead experiencing shortness of breath, dizziness, fatigue, or faintness, especially common in diabetics.

Diagnosing Stable CAD

• Physical examination may be normal, but may reveal signs of risk factors.
• Electrocardiogram (ECG):
  • May be normal in 50% of cases.
  • During episodes of angina: ST segment depression, T wave inversion, and ventricular tachyarrhythmias may be observed.
• Continuous ECG monitoring:
  • Helps detect silent ischemia.
• Provocative testing: Used to confirm the presence of ischemia if resting ECG is normal.
  • Stress ECG (treadmill test): Records the 12-lead ECG before, during, and after exercise.
    • Discontinued if the patient experiences chest discomfort, severe dyspnea, dizziness, fatigue, fall in systolic blood pressure > 10 mmHg, ST segment depression > 0.2 mV, or ventricular tachyarrhythmias.
  • Cardiac radionuclide imaging: Utilizes thallium 201 to show areas of absent perfusion during exercise.
  • Echocardiogram: Assesses ventricular function.
    • Reduced left ventricular ejection fraction (LVEF) may indicate reduced heart function.
    • Regional wall motion abnormalities may suggest ischemia or old infarction.
  • Stress echocardiography: After intravenous dobutamine (pharmacological challenge) or exercise, it shows areas of regional wall motion abnormality (akinesia) in the left ventricle due to persistent ischemia or myocardial infarction.
  • Multislice CT coronary angiography: Emerging as the most reliable noninvasive method for assessing coronary artery disease.
    • Detects and defines coronary anatomy, identifying flow-limiting atherosclerotic lesions, coronary plaques, and significant obstructive coronary lesions.
    • Can confirm or exclude the diagnosis of ischemia.
    • Used for patients who are still experiencing ischemia despite medical treatment.
  • Positron emission tomography (PET): Used for assessing myocardial perfusion.
    • Intravenous pharmacologic challenge is used for patients who cannot exercise.
    • Aims to create a "steal" by temporarily increasing flow in non-diseased coronary segments, at the expense of diseased segments.
    • Uses dipyridamole or adenosine to identify myocardial ischemia.
    • Transient perfusion defects with radionuclides like thallium or 99mTc can help detect myocardial ischemia.
  • Cardiac magnetic resonance (CMR) stress testing: Evolving as an alternative to radionuclide, PET, or echocardiographic stress imaging.
    • Performed with dobutamine infusion.
    • Helps assess wall motion abnormalities associated with ischemia.
  • Multislice MR imaging and myocardial perfusion CMR: Provide a more comprehensive ventricular evaluation.
  • Coronary angiography: Invasive diagnostic method that shows narrowing of the coronary artery lumen.
    • Helps assess the severity of obstruction in the coronary arteries.
    • Can confirm or exclude the diagnosis of ischemia.
    • Used for patients experiencing severe symptoms despite medical treatment.
    • Used for patients with severe ischemia demonstrated in non-invasive tests.
    • Used for high-risk patients, including those with left ventricular dysfunction.

Treatment for Stable CAD

• Goal of treatment:
  • Slow down the progression of atherosclerosis.
  • Decrease future events, including myocardial infarction.
  • Decrease mortality.
• Treatments implemented:
  • Medical therapy: includes non-pharmacological and lifestyle measures.
  • Revascularization: includes percutaneous coronary intervention (PCI) or coronary artery bypass graft surgery (CABG).
• Control of risk factors and associated disorders:
  • Stop smoking.
  • Manage hypertension, diabetes, anemia, infection, and chronic kidney disease.
  • Lower LDL cholesterol.

This quiz covers the essential aspects of coronary circulation, focusing on the roles of the left and right coronary arteries. You'll learn about the branches of these arteries and their significance in supplying blood to the heart. Test your knowledge on the anatomy and function of coronary blood vessels.