A 38-year-old woman, gravida 2, para 1, at 24 weeks' gestation comes to the physician for a routine prenatal evaluation. She has no history of major medical illness and takes no medications. Fetal ultrasonography shows a cardiac defect resulting from abnormal development of the endocardial cushions. This defect is most likely to result in which of the following?

Transposition of the great vessels

A 3-year-old boy is brought to the physician because of recurrent nosebleeds and fatigue for the past 2 months. He also frequently complains his head hurts. The patient has met all motoric milestones for his age but does not like to run because his legs start to hurt if he does. He is at the 40th percentile for both height and weight. His temperature is 37.0°C (98.6°F), pulse is 125/min, respirations are 32/min, and blood pressure in the right arm is 130/85 mm Hg. A grade 2/6 systolic murmur is heard in the left paravertebral region. Further evaluation of this patient is most likely to show which of the following findings?

Delayed pulse in lower extremities

Interarm difference in tissue oxygenation

A 1-year-old infant is brought to the emergency department by his parents because of fever and rapid breathing for the past 2 days. He had a mild seizure on the way to the emergency department and developed altered sensorium. His mother states that the patient has had recurrent respiratory infections since birth. He was delivered vaginally at term and without complications. He is up to date on his vaccines and has met all developmental milestones. His temperature is 37.0°C (98.6°F), pulse rate is 200/min, and respirations are 50/min. He is lethargic, irritable, and crying excessively. Physical examination is notable for a small head, an elongated face, broad nose, low set ears, and cleft palate. Cardiopulmonary exam is remarkable for a parasternal thrill, grade IV pansystolic murmur, and crackles over both lung bases. Laboratory studies show hypocalcemia and lymphopenia. Blood cultures are drawn and broad-spectrum antibiotics are started, and the child is admitted to the pediatric intensive care unit. The intensivist suspects a genetic abnormality and a fluorescence in situ hybridization (FISH) analysis is ordered which shows 22q11.2 deletion. Despite maximal therapy, the infant succumbs to his illness. The parents of the child request an autopsy. Which of the following findings is the most likely to be present on autopsy?

Hypertrophy of Hassall's corpuscles

Absent follicles in the lymph nodes

A 25-year-old woman, gravida 2, para 1, comes to the physician for her initial prenatal visit at 18 weeks’ gestation. She is a recent immigrant from Thailand. Her history is significant for anemia since childhood that has not required any treatment. Her mother and husband have anemia, as well. She has no history of serious illness and takes no medications. Her vital signs are within normal limits. Fundal height measures at 22 weeks. Ultrasound shows polyhydramnios and pleural and peritoneal effusion in the fetus with fetal subcutaneous edema. Which of the following is the most likely clinical course for this fetus?

Normal development with regular blood transfusion

A 74-year-old man presents with complaints of sudden severe crushing retrosternal pain. The pain radiated to his left arm shortly after it began, and he was subsequently rushed to the emergency department for evaluation. His troponins and creatine kinase-MB (CK-MB) were elevated. Unfortunately, the patient died within the next 2 hours and an autopsy was performed immediately. The gross examination of the heart will show?

White, patchy, non-contractile scar

Red granulation tissue surrounding the infarction

Congenital heart defects for USMLE Step 2 CK: High-Yield Pathology Lessons

Embryology - Heartfelt Beginnings

Cardiac Progenitor Cells in the epiblast migrate through the primitive streak, forming the primary and secondary heart fields.
Primary Heart Field (PHF): Forms atria, left ventricle.
Secondary Heart Field (SHF): Forms right ventricle, outflow tract.
Neural Crest Cells: Crucial for outflow tract septation.

⭐ Dextro-looping is the normal rightward fold; defects can cause dextrocardia (heart apex points right).

Embryonic heart tube folding and looping (23-35 days)

Acyanotic Defects - No Blue Babies

Left-to-right shunts (L→R) where oxygenated blood mixes back into pulmonary circulation. No initial cyanosis.

Ventricular Septal Defect (VSD):
- Most common congenital heart defect.
- Harsh, holosystolic murmur at the lower left sternal border.
Atrial Septal Defect (ASD):
- Wide, fixed splitting of S2.
- Ostium secundum type is most frequent.
Patent Ductus Arteriosus (PDA):
- Continuous, machine-like murmur.
- Associated with congenital rubella.
- Maintained by PGE; indomethacin promotes closure.

⭐ Eisenmenger syndrome: An uncorrected L→R shunt can lead to pulmonary hypertension, eventually reversing the shunt to R→L, causing late-onset cyanosis.

Cyanotic Defects - True Blue Trouble

Right-to-left shunts causing early cyanosis ("blue babies"). Deoxygenated blood bypasses lungs.
📌 Mnemonic: The 5 T's
- Truncus Arteriosus (1 vessel)
- Transposition of Great Arteries (2 vessels switched)
- Tricuspid Atresia (3 leaflets absent)
- Tetralogy of Fallot (4 features)
- Total Anomalous Pulmonary Venous Return (5 words)
Tetralogy of Fallot (TOF): Most common cyanotic defect.
- Features (PROVe): Pulmonary stenosis, Right ventricular hypertrophy, Overriding aorta, VSD.
- "Tet spells" (cyanosis) relieved by squatting.

⭐ Squatting improves TOF symptoms by ↑ Systemic Vascular Resistance (SVR), decreasing the right-to-left shunt and forcing more blood to the lungs.

Obstructive Lesions - Cardiac Roadblocks

Coarctation of the Aorta: Localized aortic narrowing, typically near the ductus arteriosus.
- Presents with ↑ upper extremity BP, ↓ lower extremity BP.
- Classic sign: Brachial-femoral pulse delay.
- Associated with Turner syndrome and bicuspid aortic valves.
Valvular Aortic/Pulmonary Stenosis: Obstruction of ventricular outflow.
- Causes a systolic ejection murmur.
- Can lead to concentric ventricular hypertrophy.

⭐ Look for rib notching on chest X-ray in coarctation, caused by intercostal artery enlargement from collateral circulation.

X-ray: Rib Notching in Coarctation of the Aorta

High‑Yield Points - ⚡ Biggest Takeaways

Ventricular Septal Defect (VSD) is the most common CHD.

Left-to-right shunts (VSD, ASD, PDA) are acyanotic; right-to-left shunts (e.g., Tetralogy, Transposition) are cyanotic.

Eisenmenger syndrome is the late reversal of a left-to-right shunt, causing cyanosis and pulmonary hypertension.

Tetralogy of Fallot is the most common cyanotic CHD, featuring "tet spells" relieved by squatting.

Transposition of the Great Arteries requires a shunt for viability; linked to maternal diabetes.

PDA has a continuous machine-like murmur; Coarctation shows discrepant limb BPs.

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