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 62-year-old woman with a history of subarachnoid hemorrhage is brought to the emergency department because of shortness of breath and sharp chest pain that worsens on inspiration. She underwent surgery for a hip fracture 3 weeks ago. Her pulse is 110/min, respirations are 20/min, and blood pressure is 112/74 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 92%. The lungs are clear to auscultation and there is no jugular venous distention. A ventilation and perfusion scan shows a small perfusion defect in the left lower lung. A drug with which of the following mechanisms of action is most appropriate for this patient?

Inhibition of adenosine diphosphate receptors

Inhibition of vitamin K epoxide reductase

A 52-year-old man presents to the emergency department with sudden-onset dyspnea, tachypnea, and chest pain. He works as a long-haul truck driver, and he informs you that he recently returned to the west coast from a trip to Tennessee. His medical history is significant for gout, hypertension, hypercholesterolemia, diabetes mellitus type 2, and mild intellectual disability. He currently smokes 2 packs of cigarettes/day, drinks a 6-pack of beer/day, and he endorses a past history of injection drug use but currently denies any illicit drug use. The vital signs include: temperature 36.7°C (98.0°F), blood pressure 126/74 mm Hg, heart rate 87/min, and respiratory rate 23/min. His physical examination shows minimal bibasilar rales, but otherwise clear lungs on auscultation, grade 2/6 holosystolic murmur, and a benign abdominal physical examination. A computed tomography angiography (CTA) demonstrates a segmental pulmonary embolism (PE). Which of the following is the most appropriate treatment plan for this patient?

Initiate heparin with a bridge to warfarin

Consult interventional radiologist (IR) for IVC filter placement

Tissue plasminogen activator (tPA)

Initiate warfarin anticoagulation

A 60-year-old man presents to the emergency department with pleuritic chest pain. He recently returned from a vacation in Germany and noticed he felt short of breath and had chest pain the following morning. The patient is generally healthy but did have surgery on his ankle 3 weeks ago and has been less ambulatory. His temperature is 99.0°F (37.2°C), blood pressure is 137/88 mm Hg, pulse is 120/min, respirations are 22/min, and oxygen saturation is 96% on room air. Physical exam is notable for a warm and swollen lower extremity. The physician has high clinical suspicion for pulmonary embolism given the patient's risk factors and presentation. Which of the following findings would warrant further workup with a CT angiogram?

Decreased breath sounds over area of the lung

Increased breath sounds over area of the lung

A 33-year-old woman comes to the physician because of a 6-month history of worsening shortness of breath and fatigue. Her paternal uncle had similar symptoms and died of respiratory failure at 45 years of age. The lungs are clear to auscultation. Pulmonary function testing shows an FVC of 84%, an FEV1/FVC ratio of 92%, and a normal diffusion capacity. An ECG shows a QRS axis greater than +90 degrees. Genetic analysis shows an inactivating mutation in the bone morphogenetic protein receptor type II (BMPR2) gene. Which of the following is the most likely cause of this patient's symptoms?

Elevated pulmonary arterial pressure

Thickening of the interventricular septum

Fibrosis of the pulmonary parenchyma

Chronic intravascular hemolysis

A 28-year-old male presents to his primary care physician with complaints of intermittent abdominal pain and alternating bouts of constipation and diarrhea. His medical chart is not significant for any past medical problems or prior surgeries. He is not prescribed any current medications. Which of the following questions would be the most useful next question in eliciting further history from this patient?

"Can you tell me more about the symptoms you have been experiencing?"

"Does the diarrhea typically precede the constipation, or vice-versa?"

"Is the diarrhea foul-smelling?"

"Please rate your abdominal pain on a scale of 1-10, with 10 being the worst pain of your life"

"Are the symptoms worse in the morning or at night?"

A 24-year-old male was in a motor vehicle accident that caused him to fracture his femur and pelvis. After 2 days in the hospital, the patient became delirious, tachypneic, and a petechial rash was found in his upper extremities. Which of the following is most likely responsible for this patient’s symptoms?

Fat microglobules in the microvasculature

Thrombotic clot in the pulmonary artery

Aspiration of oropharyngeal contents

Alveolar foamy exudates with disc shaped cysts seen with methenamine silver stain

Type I and type II pneumocyte damage due to neutrophils

Pulmonary vascular disorders for USMLE Step 1: High-Yield Pathology Lessons

Pulmonary Embolism - The Clot Thickens

Pathophysiology: Occlusion of pulmonary artery → ↑ pulmonary vascular resistance → RV strain. Creates ventilation/perfusion (V/Q) mismatch (ventilated, not perfused).
Origin: >95% from deep vein thrombosis (DVT) in lower extremities.
Risk Factors (Virchow's Triad): Stasis, hypercoagulability, endothelial injury.
Clinical Features: Sudden-onset dyspnea, pleuritic chest pain, tachypnea, tachycardia. May have hemoptysis.

⭐ V/Q Scan: Shows perfusion defects with normal ventilation. The "gold standard" if CTPA is contraindicated (e.g., renal failure, contrast allergy).

Management: Anticoagulation (heparin, DOACs). Thrombolysis or embolectomy if hemodynamically unstable (massive PE).
Non-Thrombotic Emboli: 📌 FAT BAT: Fat, Air, Thrombus, Bacteria, Amniotic fluid, Tumor.

Pulmonary Hypertension - Pressure Overload

Definition: Mean pulmonary arterial pressure (mPAP) > 20 mmHg at rest.
Pathophysiology: Endothelial dysfunction → ↑ vasoconstrictors (e.g., endothelin) & ↓ vasodilators (e.g., NO, prostacyclin) → vascular remodeling, smooth muscle hypertrophy, & intimal fibrosis.
WHO Classification Groups:
- 1: Pulmonary Arterial Hypertension (PAH) (idiopathic, heritable, drugs)
- 2: Due to left heart disease (e.g., mitral stenosis)
- 3: Due to chronic lung disease/hypoxia (e.g., COPD, OSA)
- 4: Chronic thromboembolic (CTEPH)
- 5: Multifactorial
Presentation: Exertional dyspnea, fatigue, syncope on exertion. Loud P2, right ventricular heave.
Diagnosis: Echocardiogram (screening) → Right Heart Catheterization (gold standard).

Plexiform lesions in severe pulmonary hypertension

⭐ Plexiform lesions, representing tufts of capillary formations, are pathognomonic for severe, long-standing Group 1 PAH (idiopathic/heritable).

Other Emboli - Unwanted Guests

Fat Embolism Syndrome (FES):
- Cause: Long bone fractures (femur), orthopedic surgery, liposuction.
- Pathophysiology: Mechanical obstruction & inflammatory response to free fatty acids.
- Classic Triad:
  - Hypoxemia
  - Neurologic dysfunction (e.g., confusion)
  - Petechial rash (axilla/chest) - often delayed.
- Diagnosis: Clinical; fat in urine/sputum.
Air Embolism:
- Cause: Iatrogenic (central lines), trauma, barotrauma (diving).
- Effect: Obstructs RV outflow tract → acute right heart failure.
- Management: Left lateral decubitus position.
Amniotic Fluid Embolism:
- Pathophysiology: Fetal material enters maternal circulation.
- Presentation: Abrupt cardiogenic shock, respiratory failure, & DIC during/after labor.

⭐ High-Yield: Amniotic fluid embolism is a clinical diagnosis of exclusion, often presenting with sudden cardiovascular collapse and coagulopathy during or shortly after childbirth. It carries a very high mortality rate.

Pulmonary embolism (PE) most commonly originates from deep vein thrombosis (DVT).

Suspect PE with sudden-onset dyspnea, pleuritic chest pain, and tachypnea.

CT pulmonary angiography is the gold standard for PE diagnosis; use V/Q scan if contraindicated.

Pulmonary hypertension (mean PAP >20 mmHg) leads to cor pulmonale (RV hypertrophy and failure).

Idiopathic pulmonary arterial hypertension is classically linked to a BMPR2 gene mutation.

Fat embolism syndrome triad (post-long bone fracture): neurologic changes, petechial rash, and respiratory distress.

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