QCM : Overview of Coronary Artery Disease — 36 questions

Explication

At rest, myocardial oxygen demand and supply are balanced at approximately 3 Oxygen/sec. During exercise, demand increases to about 9 Oxygen/sec, and under normal conditions, coronary blood flow (supply) compensates accordingly. These values highlight the heart’s ability to adapt its blood flow to meet increased oxygen requirements during physical activity.

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The sheet states that atherosclerosis causes 95% of coronary stenosis, making it the main cause. The other percentages are not supported by this specific data.

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A significant mismatch where oxygen demand exceeds supply indicates myocardial ischemia. This imbalance can be caused by decreased coronary blood flow, such as with stenosis or vasospasm, or by increased demand, such as with tachycardia or hypertrophy. It is a hallmark of conditions like ischemic heart disease.

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Stable angina is exertional, relieved by rest or nitrates, and typically lasts less than 20 minutes, unlike unstable angina or MI which are more prolonged and unpredictable.

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The main cause of myocardial ischemia in ischemic heart disease is a reduction in coronary blood flow due to atherosclerotic stenosis of the coronary arteries. This organic stenosis, often caused by atherosclerosis, reduces oxygen delivery to the myocardium during increased demand such as exercise.

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Troponin is highlighted as a biomarker that rises during MI but not in stable angina, making it useful for diagnosis of myocardial necrosis.

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T wave inversion on ECG is most characteristic of myocardial ischemia, indicating subendocardial hypoxia. Deep Q waves are more indicative of myocardial infarction (necrosis), and ST elevation suggests injury.

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T wave inversion indicates ischemia. ST elevation is associated with injury, and Q waves with necrosis. PEAK T wave is not a standard indicator.

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Organic stenosis in atherosclerosis is predominantly caused by the accumulation of lipids, fibrous tissue, and cellular debris within the arterial wall, leading to thickening and narrowing of the artery. Vasospasm is a functional, non-organic constriction, and embolism or dissection are different pathological processes.

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The left coronary artery (LCA) includes the LAD and LCX and supplies the left side of the heart, whereas RCA supplies the right heart.

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Stable angina is typically characterized by chest pain that occurs on exertion or stress, is constrictive or pressure-like, lasts less than 20 minutes, and is relieved by rest or nitroglycerin. Persistent pain at rest suggests unstable angina or myocardial infarction.

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Stable angina involves partial stenosis and is predictable, while MI results from plaque rupture and thrombosis causing complete occlusion, consistent with the table.

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Functional vasospasm is caused by transient, abnormal contraction of the smooth muscle in the coronary artery wall, leading to temporary narrowing. Unlike organic stenosis, it does not involve plaque or thrombus formation, but rather a hyperreactivity or spasmodic contraction of the vessel.

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Coronary vasospasm typically presents as episodes of chest pain occurring unpredictably, often at rest, and sometimes at night. It is not necessarily related to exertion and can cause transient ischemia without physical activity, distinguishing it from stable angina.

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The left anterior descending (LAD) artery supplies the anterior wall of the left ventricle. It runs down the anterior interventricular groove and gives off diagonal branches to the anterior wall and septum. It is a critical artery in coronary circulation and commonly involved in coronary artery disease.

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The right coronary artery (RCA) primarily supplies the right atrium, right ventricle, and the posterior interventricular septum. A key feature is its role in supplying the posterior part of the heart, including the posterior interventricular artery (posterior descending artery), which typically originates from the RCA in right-dominant systems. The RCA also arises from the right aortic sinus, but its defining role is in supplying the right-sided and posterior myocardial regions.

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Stable angina typically lasts less than 20 minutes and is relieved by rest or administration of nitroglycerin. It occurs during exertion or stress and subsides with rest, distinguishing it from unstable angina or myocardial infarction.

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T wave inversion on ECG is a common transient change seen during myocardial ischemia, indicating repolarization abnormalities. Deep Q waves suggest necrosis, and persistent ST elevation usually indicates ongoing injury or infarction. ECG can often be normal between episodes in stable angina.

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The hallmark of plaque rupture in acute coronary syndrome is the thinning and rupture of the fibrous cap that covers a lipid-rich atherosclerotic plaque. This rupture exposes thrombogenic material within the plaque to the bloodstream, leading to thrombus formation and potential sudden occlusion of the coronary artery.

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Sudden onset of chest pain with evidence of intracoronary thrombus strongly suggests plaque rupture, which leads to acute coronary syndrome. Plaque rupture causes thrombus formation that acutely occludes the coronary artery, manifesting as sudden, severe chest pain not relieved by nitrates, unlike stable angina.

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T wave inversion is a characteristic ECG change during myocardial ischemia, reflecting repolarization abnormalities due to inadequate oxygen supply. ST segment elevation indicates injury, while deep Q waves suggest infarction. Persistent ST depression might also occur but T wave inversion is more specific for ischemia.

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ST segment elevation on ECG, often with Q waves developing later, is a hallmark of acute myocardial infarction, indicating ongoing myocardial injury. Other options either represent ischemia without infarction or are normal findings.

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Troponin I is the most specific and sensitive biomarker for myocardial necrosis because it is released specifically from cardiac muscle damage. Elevated troponin levels are used widely in diagnosing acute myocardial infarction. CK, while more sensitive, is less specific, and AST and LDH are less specific and less sensitive for cardiac injury.

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Following myocardial necrosis, cardiac enzymes like CK and troponin increase within hours (CK rises within 4-6 hours; troponin within 3-4 hours) and remain elevated for days, helping to confirm myocardial injury. They do not decrease immediately nor take weeks to peak.

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Coronary CTA is a non-invasive imaging technique that provides detailed visualization of coronary artery anatomy, allowing detection of stenoses, plaques, and coronary anomalies. Echocardiography primarily assesses cardiac function and structures but is limited in visualizing coronary arteries directly. Chest X-ray is not suitable for detailed coronary visualization. MRI is used for myocardial tissue characterization but is less commonly employed specifically for coronary artery imaging compared to CTA.

Explication

Exercise stress testing, such as ergometry, monitors ECG and symptoms during controlled physical exertion to detect ischemia-induced changes in real-time. Resting ECG may appear normal despite ischemia; coronary angiography visualizes anatomical stenosis but doesn't assess ischemia dynamically. Echocardiography at rest does not evaluate ischemia triggered by exertion; stress echocardiography can be used, but the question specifically asks about exertion testing in general, making ergometry the most useful tool.

Explication

Nitrates, such as nitroglycerin, are vasodilators that relax vascular smooth muscle, leading to dilation of coronary and peripheral vessels. This reduces myocardial oxygen demand and provides symptomatic relief in angina. Beta-blockers decrease myocardial oxygen demand by lowering heart rate and contractility but do not act primarily as vasodilators. Calcium channel blockers also vasodilate but are not the primary agents used acutely for symptom relief, unlike nitrates. ACE inhibitors mainly affect the renin-angiotensin system and are used for long-term management rather than immediate symptom relief.

Explication

Nitrates relax vascular smooth muscle, leading to venodilation, which decreases preload and myocardial wall stress. This reduction in preload decreases myocardial oxygen demand, alleviating anginal symptoms. Although nitrates can cause some dilation of coronary arteries, their primary effect in symptom relief is through decreasing preload and myocardial oxygen demand, not directly increasing oxygen supply. They do not significantly reduce heart rate or systemic vascular resistance as their main action.

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PTCA aims to mechanically dilate a narrowed coronary artery using a balloon catheter, thereby restoring blood flow through the affected artery. It is not for removing clots directly, dissolving plaque chemically, or performing surgical bypass.

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A known complication of PTCA is coronary artery dissection or perforation due to the mechanical dilation process. Infection is less common, and PTCA does not cause new plaques or directly affect systemic blood pressure.

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CABG aims to improve blood supply to ischemic heart tissue by creating a new pathway for blood flow around blocked or narrowed coronary arteries, typically using a graft from another vessel, such as the saphenous vein or internal mammary artery.

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CABG is generally indicated in patients with multi-vessel coronary artery disease and significant ischemia, especially when lesions are not suitable for percutaneous interventions, to restore adequate blood flow and improve clinical outcomes.

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Typical angina pain often radiates to the left side of the body, including the axilla, arm, shoulder, and jaw. This radiation pattern is characteristic of myocardial ischemia due to the way pain signals are transmitted via visceral afferent fibers accompanying autonomic nerves.

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Myocardial ischemic pain is typically felt in the retrosternal or precordial area, reflecting the heart's location within the chest. The pain may radiate to other regions but is usually localized to the chest area.

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The main cause of flow reduction in ischemic heart disease is organic stenosis caused by atherosclerosis, which narrows the coronary arteries and impairs blood flow, especially during increased demand like exercise.

Explication

In significant coronary artery stenosis, the damage impairs the increase in blood flow during exercise, resulting in decreased oxygen supply relative to the increased demand, leading to ischemia.