Brief Summary
This video provides a comprehensive lecture on coronary artery disease, angina, and myocardial infarction (MI). It covers the anatomy of coronary arteries, the causes and types of angina, diagnostic methods including ECG and stress tests, and treatment strategies ranging from lifestyle modifications to medications and surgical interventions. The lecture also addresses potential complications of MI and their management.
- Anatomy of coronary arteries and their function
- Causes, types, and diagnosis of angina
- Diagnostic methods for coronary artery disease
- Treatment strategies for angina and myocardial infarction
- Potential complications of MI and their management
Coronary Artery Anatomy
The lecture begins by describing the anatomy of the coronary arteries. The aorta has an aortic valve, followed by an expansion called the sinus of Valsalva. The right coronary artery originates from the right sinus, and the left coronary artery originates from the left sinus. The left coronary artery divides into the left anterior descending (LAD) artery and the circumflex artery. The LAD supplies the anterior portion of the heart, while the circumflex supplies the left atrium and the posterior left ventricle. The right coronary artery supplies the right ventricle and the posterior part of the heart. Coronary artery dominance varies among individuals, with most people having right dominance, some left dominance, and others a balanced supply.
Causes of Ischaemia
Ischaemia occurs when there is an imbalance between the supply of oxygen to the heart and the heart's demand for oxygen. This imbalance can arise from either a decrease in supply or an increase in demand. Reduced supply can be due to decreased quantity (e.g., stenosis or obstruction) or decreased quality of blood (e.g., anaemia or hypoxaemia). Increased demand can result from conditions such as hypertension, tachycardia, or hyperthyroidism. Problems with the aortic valve or increased blood viscosity can also contribute to ischaemia.
Coronary Artery Disease
The lecture identifies several causes of coronary artery disease, including congenital abnormalities, acquired conditions, and inflammatory diseases like Kawasaki disease. A common issue is atherosclerosis, where plaque builds up in the arteries, reducing blood flow. This can lead to ischaemia and myocardial infarction. The process involves LDL cholesterol accumulating in the artery walls, becoming oxidised, and triggering an inflammatory response. Foam cells form, leading to plaque formation and potential rupture, causing thrombus formation and acute coronary syndrome.
Risk Factors for Atherosclerosis
Risk factors for atherosclerosis are categorised into modifiable, non-modifiable, and partially modifiable factors. Non-modifiable factors include age, gender, and family history. Modifiable factors include smoking, hypertension, and diabetes. Partially modifiable factors include hypercholesterolaemia and dyslipidaemia. Dyslipidaemia involves imbalances in lipoproteins, specifically VLDL, LDL, and HDL. High LDL and low HDL levels increase the risk of atherosclerosis. Personality type (ambitious, competitive), stress, and obesity also contribute to the risk.
Types of Angina
Angina is classified into stable, unstable, variant (Prinzmetal's), and microvascular angina. Stable angina is predictable and occurs with exertion, resolving with rest or medication. Unstable angina is new, worsening, or occurs at rest, indicating a higher risk of myocardial infarction. Variant angina is caused by coronary artery spasm, often occurring at rest and associated with ST-segment elevation. Microvascular angina involves dysfunction of small coronary arteries.
Stable Angina
Stable angina is chest pain or discomfort that occurs predictably with exertion or emotional stress and is relieved by rest or medication (e.g., nitroglycerin). The pain is typically described as a squeezing, pressure, or tightness in the chest, located behind the sternum (retrosternal) or in front of the heart (precordial). It may radiate to the left arm, shoulder, jaw, or back. The duration is usually brief, lasting a few minutes, and rarely exceeds 20 minutes. Factors that can trigger stable angina include exercise, cold weather, heavy meals, and emotional stress. Treatment involves rest, nitroglycerin, and lifestyle modifications.
Unstable Angina
Unstable angina is characterised by new-onset angina, increasing frequency or severity of existing angina, or angina occurring at rest. It is a high-risk condition that can lead to myocardial infarction. Unlike stable angina, it may not be relieved by rest or nitroglycerin.
Variant (Prinzmetal's) Angina
Variant angina, also known as Prinzmetal's angina, is caused by coronary artery spasm, leading to temporary reduction in blood flow to the heart. It often occurs at rest, particularly at night or in the early morning. ECG findings during an episode typically show ST-segment elevation. Unlike typical angina, it is not usually associated with atherosclerosis. The exact cause of coronary artery spasm is not fully understood, but it may involve endothelial dysfunction, increased thromboxane A2 production, or smooth muscle hyperreactivity. Beta-blockers are generally avoided in the treatment of variant angina, as they can exacerbate the spasms.
Microvascular Angina
Microvascular angina is chest pain caused by dysfunction of the small blood vessels of the heart. It is more common in women and is often associated with other conditions such as diabetes, hypertension, and hyperlipidaemia. The diagnosis can be challenging, as the coronary arteries appear normal on angiography.
Clinical Examination for Angina
During an angina attack, physical examination may reveal signs of left ventricular dysfunction, such as a displaced apex beat or a gallop rhythm (S3 or S4). Auscultation may reveal a paradoxical splitting of the second heart sound (S2), where the aortic component is delayed due to ischaemia. However, the clinical examination is often normal between angina episodes.
Diagnostic Tests for Angina
Diagnostic tests for angina include ECG, exercise stress testing, stress echocardiography, myocardial perfusion imaging (MPI), and coronary angiography. ECG may show ST-segment depression, T-wave inversion, or other abnormalities during an angina episode. Exercise stress testing involves monitoring the ECG and blood pressure while the patient exercises on a treadmill or stationary bike. Stress echocardiography combines exercise stress testing with echocardiography to assess left ventricular function. MPI uses radioactive tracers to assess blood flow to the heart muscle. Coronary angiography is the gold standard for diagnosing coronary artery disease, as it allows direct visualisation of the coronary arteries.
ECG in Angina
A resting ECG may be normal in patients with stable angina. However, during an angina episode, the ECG may show ST-segment depression, T-wave inversion, or ST-segment elevation (in variant angina). Exercise ECG involves monitoring the ECG during exercise. A positive test is indicated by ST-segment depression, chest pain, or other symptoms.
Myocardial Perfusion Imaging (MPI)
MPI involves injecting a radioactive tracer into the bloodstream and using a gamma camera to assess blood flow to the heart muscle. Images are taken at rest and during exercise or pharmacological stress (e.g., with adenosine or dipyridamole). Areas of reduced blood flow during stress that improve at rest indicate ischaemia, while areas of reduced blood flow at rest and during stress indicate infarction. Dipyridamole causes vasodilation in healthy arteries but not in diseased arteries, creating a "steal" effect that highlights areas of ischaemia.
Coronary Angiography
Coronary angiography involves inserting a catheter into the coronary arteries and injecting contrast dye to visualise the arteries on X-ray. It is the gold standard for diagnosing coronary artery disease and allows assessment of the location and severity of stenosis. It is indicated for patients with unstable angina, significant ischaemia on non-invasive testing, or symptoms that are not well-controlled with medical therapy.
Pre-Hospital and In-Hospital Management of Acute Coronary Syndrome
Pre-hospital management of acute coronary syndrome (ACS) involves rapid transport to the hospital, oxygen administration, aspirin, nitroglycerin, and pain relief with morphine. In-hospital management includes admission to a coronary care unit (CCU), continuous ECG monitoring, oxygen administration, aspirin, nitroglycerin, beta-blockers, and anticoagulation.
Medical Treatment for Angina
Medical treatment for angina aims to reduce myocardial oxygen demand and increase coronary blood flow. Medications used include antiplatelet agents (e.g., aspirin, clopidogrel), beta-blockers, nitrates, calcium channel blockers, and ACE inhibitors. Lifestyle modifications, such as smoking cessation, weight loss, and regular exercise, are also important.
Nitrates
Nitrates cause vasodilation, reducing preload and afterload, and increasing coronary blood flow. They are available in various forms, including sublingual tablets, oral tablets, transdermal patches, and intravenous infusions. Common side effects include headache and hypotension. Tolerance to nitrates can develop with prolonged use, so intermittent dosing is recommended.
Beta-Blockers
Beta-blockers reduce myocardial oxygen demand by decreasing heart rate, blood pressure, and contractility. They are contraindicated in patients with acute heart failure, bradycardia, or severe peripheral vascular disease.
Calcium Channel Blockers
Calcium channel blockers cause vasodilation and reduce myocardial contractility. They are useful for treating angina, particularly variant angina.
ACE Inhibitors
ACE inhibitors reduce blood pressure and improve endothelial function. They are recommended for patients with angina and other cardiovascular risk factors, such as hypertension, diabetes, or heart failure.
Revascularisation Procedures
Revascularisation procedures, such as percutaneous coronary intervention (PCI) and coronary artery bypass grafting (CABG), are used to restore blood flow to the heart muscle. PCI involves inserting a catheter into the coronary artery and using a balloon to open the stenosis, followed by placement of a stent to keep the artery open. CABG involves grafting a blood vessel from another part of the body to bypass the blocked coronary artery.
ECG Changes in Myocardial Infarction
ECG changes in myocardial infarction (MI) evolve over time. The earliest change is hyperacute T waves, followed by ST-segment elevation, Q-wave formation, and T-wave inversion. The location of the ST-segment elevation and Q waves can help identify the affected coronary artery.
Cardiac Enzymes in Myocardial Infarction
Cardiac enzymes, such as creatine kinase (CK), CK-MB, troponin I, and myoglobin, are released into the bloodstream following myocardial infarction. Troponin I is the most specific marker for myocardial damage.
Management of ST-Elevation Myocardial Infarction (STEMI)
Management of ST-elevation myocardial infarction (STEMI) involves rapid reperfusion therapy, either with thrombolytic agents or primary percutaneous coronary intervention (PCI). Thrombolytic agents, such as streptokinase and tissue plasminogen activator (tPA), dissolve the blood clot and restore blood flow to the heart muscle. Primary PCI involves inserting a catheter into the coronary artery and using a balloon to open the stenosis, followed by placement of a stent.
Complications of Myocardial Infarction
Complications of myocardial infarction include heart failure, arrhythmias, cardiogenic shock, ventricular septal rupture, papillary muscle rupture, and left ventricular aneurysm. Heart failure occurs when the heart is unable to pump enough blood to meet the body's needs. Arrhythmias are abnormal heart rhythms that can be life-threatening. Cardiogenic shock is a severe form of heart failure that occurs when the heart is unable to pump enough blood to maintain blood pressure. Ventricular septal rupture is a tear in the wall between the ventricles. Papillary muscle rupture is a tear in the muscle that supports the mitral valve. Left ventricular aneurysm is a bulge in the wall of the left ventricle.
Post-Hospital Management of Myocardial Infarction
Post-hospital management of myocardial infarction involves lifestyle modifications, such as smoking cessation, weight loss, and regular exercise, as well as medications to prevent further cardiovascular events. Medications used include antiplatelet agents (e.g., aspirin, clopidogrel), beta-blockers, ACE inhibitors, and statins.
