Practice 18 structured short- and long-answer medical questions on Heart Disease: Must Knows. Review model answers for exam revision.
Answer: Heart disease encompasses various conditions that impair the heart's ability to effectively pump blood. Heart failure can arise from six primary mechanisms, including pump failure (systolic or diastolic), obstruction to flow, regurgitant flow, shunted flow, conduction disorders, or rupture. Congestive Heart Failure (CHF) is defined by the heart's inability to meet metabolic demands, often due to systolic or diastolic dysfunction, and triggers compensatory mechanisms like the Frank-Starling law, neurohumoral activation, and hypertrophy. While these initially maintain output, chronic hypertrophy can be pathological and lead to increased oxygen demand and sudden cardiac death. Left-sided heart failure typically presents with pulmonary congestion (dyspnea, orthopnea) and is often caused by ischemic heart disease (IHD) or hypertension, leading to "heart failure cells" in the lungs. Right-sided heart failure, frequently secondary to left-sided failure or pulmonary hypertension (cor pulmonale), manifests as systemic venous congestion, including peripheral edema and "nutmeg liver." Ischemic Heart Disease (IHD), primarily caused by coronary atherosclerosis, represents an imbalance between myocardial oxygen supply and demand and is a leading cause of death worldwide. Its pathogenesis involves plaque formation, thrombosis following plaque disruption (often in plaques previously deemed non-critical), and vasospasm. "Vulnerable plaques" with large lipid cores and thin fibrous caps are prone to rupture, leading to acute coronary syndromes like unstable angina, acute myocardial infarction (MI), and sudden cardiac death. Stable angina, Prinzmetal angina, and chronic IHD are other clinical manifestations. Understanding these mechanisms, clinical presentations, and morphological changes is crucial for managing heart disease, which often progresses to biventricular CHF in its advanced stages. ## Key Points - **Pump failure**: Impaired cardiac output due to weak contraction (systolic) or impaired relaxation (diastolic). - **Congestive Heart Failure (CHF)**: Heart cannot generate sufficient output for metabolic needs, or only at elevated filling pressures. - **Forward failure**: Decreased cardiac output, almost always accompanied by backward failure (venous congestion). - **Concentric hypertrophy**: Sarcomeres added in parallel, caused by pressure overload (e.g., hypertension, valve stenosis). - **Eccentric/dilated hypertrophy**: Sarcomeres added in series, caused by volume overload (e.g., regurgitation, shunts). - **Heart failure cells**: Hemosiderin-laden macrophages found in the lungs, indicative of chronic left-sided CHF and pulmonary edema. - **Nutmeg liver**: Gross appearance of the liver in right-sided CHF, characterized by centrilobular congestion. - **Cor pulmonale**: Right ventricular hypertrophy and dilation due to pulmonary hypertension, an isolated right-sided pathology. - **Ischemic Heart Disease (IHD)**: Imbalance between coronary blood supply and myocardial oxygen demand, primarily due to coronary atherosclerosis. - **Critical stenosis**: >70% occlusion of a coronary artery, typically causing symptoms with exertion (stable angina). - **Vulnerable plaque**: Atherosclerotic plaque with a large lipid core, thin fibrous cap, and high macrophage load, prone to rupture. - **Acute coronary syndrome**: A spectrum of conditions including unstable angina, acute myocardial infarction, and sudden cardiac death, often initiated by plaque disruption and thrombosis. ## Detailed Notes ### OVERVIEW: 6 MECHANISMS OF HEART FAILURE
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Answer: ### CONGESTIVE HEART FAILURE (CHF) **Definition:** Heart cannot generate sufficient output to meet metabolic demands — OR can only do so at elevated filling pressures **Epidemiology:** ~5 million affected in USA; >1 million hospitalizations/year; 300,000 deaths/year **Causes:** - Systolic dysfunction (most common) — ischemic heart disease, hypertension - Diastolic dysfunction — LV hypertrophy, fibrosis, amyloid, constrictive pericarditis; more common in elderly, diabetics, women; accounts for **40–60% of CHF** - High-output failure — hyperthyroidism, anemia **Key concept:** Forward failure (↓ output) is almost always accompanied by backward failure (venous congestion) #### Compensatory Mechanisms | Mechanism | Details | | :---------------- | :--------------------------------------------------------------- | | Frank-Starling | ↑ end-diastolic volume → ↑ stretch → ↑ contraction force | | Neurohumoral | Norepinephrine (↑ HR, contractility); RAAS (salt/water retention); ANP (counters RAAS) | | Hypertrophy | Pressure overload → concentric hypertrophy (sarcomeres added in parallel); Volume overload → eccentric/dilated (sarcomeres in series) | **Compensated vs Decompensated:** When the dilated ventricle maintains output = compensated; when it can no longer meet body needs = decompensated **Cost of hypertrophy:** - ↑ O₂ demand without proportional capillary expansion → ischemia risk - Fetal gene re-expression (myosin heavy chain changes) - Myocyte apoptosis, cytoskeletal changes, ↑ ECM deposition - Pathologic hypertrophy = independent risk factor for sudden cardiac death - Physiologic hypertrophy (aerobic exercise) = ↑ capillary density, ↓ resting HR/BP → protective #### Left-Sided Heart Failure **Causes:** IHD, hypertension, mitral/aortic valve disease, cardiomyopathy **Clinical features:** - Dyspnea on exertion (earliest symptom) - Orthopnea → paroxysmal nocturnal dyspnea - Cardiomegaly, tachycardia, S3 heart sound - Fine basal rales - Mitral regurgitation (papillary muscle displacement) → systolic murmur - Atrial fibrillation → "irregularly irregular" pulse + thrombus risk → stroke - Prerenal azotemia, hypoxic encephalopathy in severe cases **Morphology:** - Heart: LV hypertrophy ± dilation; interstitial fibrosis - Lungs: Heavy, boggy; alveolar edema; **heart failure cells** (hemosiderin-laden macrophages from extravasated RBCs) - Pleural effusion from ↑ hydrostatic pressure #### Right-Sided Heart Failure **Causes:** Most commonly secondary to left heart failure; also cor pulmonale (severe pulmonary hypertension), primary pulmonic/tricuspid disease **Cor pulmonale:** RV hypertrophy + dilation due to pulmonary hypertension; isolated right-sided pathology **Clinical features:** Peripheral edema, hepatomegaly, splenomegaly, ascites, pleural effusion — minimal respiratory symptoms in pure right-sided failure **Morphology:** - Liver: Congestive hepatomegaly; **nutmeg liver** (centrilobular congestion); cardiac cirrhosis in chronic severe cases - Portal hypertension → congestive splenomegaly; bowel wall edema (impairs drug/nutrient absorption) - Peripheral edema (pedal/pretibial); anasarca in severe cases - Pleural/pericardial/peritoneal transudates — low protein, no inflammatory cells Most patients present with **biventricular CHF** in chronic disease ### ISCHEMIC HEART DISEASE (IHD) **Definition:** Imbalance between coronary blood supply and myocardial O₂/nutritional demand **Cause:** >90% due to coronary atherosclerosis (CAD) **Epidemiology:** Leading cause of death in USA + developed nations; 7 million deaths/year worldwide; mortality has declined ~50% since 1963 peak #### Pathogenesis **Critical stenosis:** >70% occlusion → symptoms with exertion (stable angina); ≥90% → symptoms at rest **Key point:** Two-thirds of ruptured plaques had <50% stenosis pre-rupture; 85% had <70% stenosis → most MI-causing plaques were not previously symptomatic **Three contributing mechanisms:**
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Answer: **Vulnerable plaque features:** - Large atheromatous core - Thin fibrous cap - Fissures at cap-normal vessel junction (highest mechanical stress) - High macrophage load, few smooth muscle cells **Statins:** Benefit beyond cholesterol lowering — reduce plaque inflammation, ↑ plaque stability **Circadian pattern:** MI incidence highest 6 AM–12 noon (adrenergic surge on awakening) **Collateral circulation:** Slowly progressive stenosis → collateral remodeling → protection from MI even with complete occlusion; acute blockage → no time for collaterals → infarction #### Clinical Syndromes of IHD | Syndrome | Key Features | | :------------------ | :--------------------------------------------------------------------------------------------------------------------------------------------------- | | Stable angina | >70% fixed stenosis; predictable with exertion; relieved by rest/nitroglycerin | | Prinzmetal angina | Coronary spasm at rest; responds to vasodilators + calcium channel blockers | | Unstable angina | Plaque disruption + thrombus; increasing frequency/less exertion; harbinger of MI | | Acute MI | Sufficient ischemia to cause cardiomyocyte death | | Chronic IHD/CHF | Cumulative ischemic insults → pump failure | | Sudden cardiac death | Most commonly lethal arrhythmia without myocyte necrosis | **Acute coronary syndrome** = unstable angina + acute MI + sudden cardiac death **Pain mechanism:** Ischemia → adenosine + bradykinin release → autonomic afferent stimulation → crushing/squeezing substernal pain radiating to left arm/jaw ### HIGH-YIELD ASSOCIATIONS SUMMARY | Finding | Association | | :-------------------------- | :------------------------------------------- | | Heart failure cells | Left-sided CHF → pulmonary edema | | Nutmeg liver | Right-sided CHF | | Cardiac cirrhosis | Chronic severe right-sided CHF | | Concentric hypertrophy | Pressure overload (HTN, stenosis) | | Eccentric/dilated hypertrophy | Volume overload (regurgitation, shunts) | | Physiologic hypertrophy | Aerobic exercise — protective | | Pathologic hypertrophy | ↑ risk sudden cardiac death | | S3 heart sound | Volume overload/CHF | | Paroxysmal nocturnal dyspnea | Left-sided CHF | | Anasarca | Severe right-sided CHF | ## Practice Questions
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