A 43-year-old woman presents to her primary care provider with shortness of breath. She reports a 4-month history of progressively worsening difficulty breathing with associated occasional chest pain. She is a long-distance runner but has had trouble running recently due to her breathing difficulties. Her past medical history is notable for well-controlled hypertension for which she takes hydrochlorothiazide. She had a tibial osteosarcoma lesion with pulmonary metastases as a child and successfully underwent chemotherapy and surgical resection. She has a 10 pack-year smoking history but quit 15 years ago. She drinks a glass of wine 3 times per week. Her temperature is 98.6°F (37°C), blood pressure is 140/85 mmHg, pulse is 82/min, and respirations are 18/min. On exam, she has increased work of breathing with a normal S1 and loud P2. An echocardiogram in this patient would most likely reveal which of the following?

Right ventricular hypertrophy with a dilated pulmonary artery

Biventricular dilatation with a decreased ejection fraction

Left ventricular dilatation with an incompetent aortic valve

Left atrial dilatation with mitral valve stenosis

Left ventricular hypertrophy with a bicuspid aortic valve

A 72-year-old African American man presents with progressive fatigue, difficulty breathing on exertion, and lower extremity swelling for 3 months. The patient was seen at the emergency department 2 times before. The first time was because of back pain, and the second was because of fever and cough. He took medications at the emergency room, but he refused to do further tests recommended to him. He does not smoke or drink alcohol. His family history is irrelevant. His vital signs include a blood pressure of 110/80 mm Hg, temperature of 37.2°C (98.9°F), and regular radial pulse of 90/min. On physical examination, the patient looks pale, and his tongue is enlarged. Jugular veins become distended on inspiration. Pitting ankle edema is present on both sides. Bilateral basal crackles are audible on the chest auscultation. Hepatomegaly is present on abdominal palpation. Chest X-ray shows osteolytic lesions of the ribs. ECG shows low voltage waves and echocardiogram shows a speckled appearance of the myocardium with diastolic dysfunction and normal appearance of the pericardium. Which of the following best describes the mechanism of this patient’s illness?

Deposition of an extracellular fibrillar protein that stains positive for Congo red in the myocardium

Thickening of the parietal pericardium with dystrophic calcification

Calcification of the aortic valve orifice with obstruction of the left ventricular outflow tract

Concentric hypertrophy of the myocytes with thickening of the interventricular septum

Diastolic cardiac dysfunction with reciprocal variation in ventricular filling with respiration

A 49-year-old man presents to his physician complaining of weakness and fatigue. On exam, you note significant peripheral edema. Transthoracic echocardiogram is performed and reveals a preserved ejection fraction with impaired diastolic relaxation. A representative still image is shown in Image A. Which of the following is likely the cause of this patient's symptoms?

Heavy, long-term alcohol consumption

History of myocardial infarction

History of a recent viral infection

Previous treatment with doxorubicin

A 14-year-old boy who has been otherwise healthy presents to his doctor complaining of feeling easily winded and light-headed at basketball practice. He has never felt this way before and is frustrated because he is good enough to make varsity this year. He denies smoking, alcohol, or recreational drug use. His mother is very worried because her oldest son and brother had both died suddenly while playing sports despite being otherwise healthy. The transthoracic echocardiogram confirms the suspected diagnosis, which demonstrates a preserved ejection fraction and systolic anterior motion of the mitral valve. The patient is advised that he will need to stay hydrated and avoid intense exercise, and he will likely need an ICD due to his family history. Which of the following physical exam findings is consistent with this patient’s most likely diagnosis?

Systolic ejection murmur that worsens with the Valsalva maneuver

Systolic ejection murmur that radiates to the carotids

A 51-year-old man comes to the physician because of progressively worsening dyspnea on exertion and fatigue for the past 2 months. Cardiac examination shows no murmurs or bruits. Coarse crackles are heard at the lung bases bilaterally. An ECG shows an irregularly irregular rhythm with absent p waves. An x-ray of the chest shows globular enlargement of the cardiac shadow with prominent hila and bilateral fluffy infiltrates. Transthoracic echocardiography shows a dilated left ventricle with an ejection fraction of 40%. Which of the following is the most likely cause of this patient's condition?

Tachycardia-induced cardiomyopathy secondary to atrial fibrillation

Deposition of misfolded proteins

Inherited β-myosin heavy chain mutation

Uncontrolled essential hypertension

A 16-year-old boy is brought to the emergency department 20 minutes after collapsing while playing basketball. There is no personal or family history of serious illness. On arrival, there is no palpable pulse and no respiratory effort is seen. He is declared dead. The family agrees to an autopsy. Which of the following is most likely to be found in this patient?

Interventricular septal hypertrophy

Postductal narrowing of the aorta

A 73-year-old man with coronary artery disease and hypertension is brought to the emergency department by ambulance 90 minutes after the acute onset of substernal chest pain and dyspnea. He has smoked 2 packs of cigarettes daily for 52 years. Shortly after arriving at the hospital, he loses consciousness and is pulseless. Despite attempts at cardiopulmonary resuscitation, he dies. Examination of the heart at autopsy shows complete occlusion of the left anterior descending artery with a red thrombus overlying a necrotic plaque. Which of the following pathophysiologic mechanisms is most likely responsible for this patient's acute coronary condition?

Secretion of matrix metalloproteinases

Influx of lipids into the endothelium

Release of platelet-derived growth factor

Proliferation of smooth muscle cells

Myocarditis and cardiomyopathies for USMLE Step 1: High-Yield Pathology Lessons

Myocarditis - The Inflamed Heart

Etiology: Inflammation of myocardium, often leading to myocyte necrosis and cardiac dysfunction.
- Viral: Most common cause (e.g., Coxsackie B, Adenovirus, Parvovirus B19).
- Non-Infectious: Autoimmune (SLE), drug hypersensitivity (clozapine), toxins (cocaine).
Clinical Features: Highly variable; can mimic acute coronary syndrome. Chest pain, dyspnea, fatigue, arrhythmias. Often preceded by a viral prodrome.
Diagnosis:
- Labs: ↑ Troponin, ↑ CK-MB, ↑ ESR/CRP.
- ECG: May show diffuse ST elevation or T-wave inversions.
- Gold Standard: Endomyocardial biopsy showing inflammatory infiltrate and myocyte necrosis.

⭐ Fulminant myocarditis can cause cardiogenic shock, while chronic myocarditis is a key cause of dilated cardiomyopathy.

Acute vs. Healing Lymphocytic Myocarditis Histopathology

Dilated Cardiomyopathy - Big, Boggy Heart

Pathophysiology: Most common cardiomyopathy. Characterized by ventricular chamber enlargement and systolic dysfunction (↓ contractility), leading to a dilated, flabby, heavy heart.
Etiologies: 📌 ABCCCD
- Alcohol abuse
- Beriberi (wet, thiamine/B1 deficiency)
- Coxsackie B virus
- Cocaine use
- Chagas disease (T. cruzi)
- Doxorubicin toxicity
- Also: Hemochromatosis, Sarcoidosis, Peripartum.
Clinical: Presents as systolic heart failure (left, right, or both). S3 gallop, mitral/tricuspid regurgitation murmurs, arrhythmias.
Diagnosis: Echocardiogram shows four-chamber dilation and ↓ ejection fraction (< 40%).

⭐ Familial Dilated Cardiomyopathy is common (20-50% of cases), most frequently caused by an autosomal dominant mutation in the Titin (TTN) gene.

Hypertrophic Cardiomyopathy - Dangerously Thick Muscle

Etiology: Autosomal dominant mutation in sarcomere protein genes (e.g., β-myosin heavy chain).
Pathophysiology: Asymmetric hypertrophy, usually of the interventricular septum, leading to diastolic dysfunction and potential left ventricular outflow tract (LVOT) obstruction.
Clinical: Dyspnea, angina, syncope, often post-exertion. Major cause of sudden cardiac death (SCD) in young athletes.
Auscultation: Harsh crescendo-decrescendo systolic murmur.
- ↑ Intensity: Valsalva, abrupt standing (↓ preload).
- ↓ Intensity: Squatting, handgrip (↑ afterload/preload).
Diagnosis: Echocardiogram showing septal wall thickness > 1.5 cm.
Management:
- Meds: β-blockers, verapamil.
- Avoid: Dehydration, diuretics, vasodilators.
- Surgical: Septal myectomy or alcohol ablation for refractory symptoms.

⭐ The murmur of HCM is one of the few systolic murmurs that increases in intensity with maneuvers that decrease venous return (Valsalva, standing).

Restrictive Cardiomyopathy - Stiff, Rigid Prison

Pathophysiology: Rigid, noncompliant ventricles impair diastolic filling, leading to backup pressure. Systolic function is often preserved until late stages.
Etiologies: Think "Puppy Leash": Post-radiation fibrosis, Loeffler endocarditis, Endomyocardial fibrosis, Amyloidosis, Sarcoidosis, Hemochromatosis.
Clinical: Resembles constrictive pericarditis. Dyspnea, Kussmaul sign (paradoxical ↑ JVP with inspiration). Prominent right heart failure signs.
Diagnosis:
- ECG: Low-voltage QRS, especially with amyloidosis.
- Echocardiogram: Symmetrically thickened walls, diastolic dysfunction, biatrial enlargement.
- Endomyocardial biopsy is definitive.

⭐ In cardiac amyloidosis, the classic diagnostic clue is the combination of low voltage on ECG despite a thickened myocardium seen on echocardiography.

Cardiac amyloidosis with Congo red stain and birefringence

High‑Yield Points - ⚡ Biggest Takeaways

Myocarditis is most often viral (Coxsackie B), presenting with chest pain after a URI; histology shows lymphocytic infiltrate.

Dilated cardiomyopathy, the most common type, is linked to alcohol and doxorubicin, causing systolic dysfunction.

Hypertrophic cardiomyopathy is an autosomal dominant disorder causing asymmetric septal hypertrophy and risk of sudden death in athletes.

Restrictive cardiomyopathy results from infiltrative diseases like amyloidosis, leading to diastolic dysfunction.

Chagas disease (T. cruzi) is a classic infectious cause of dilated cardiomyopathy.

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