I am going to answer the sample USMLE Step 1 Questions with Explanation. These questions are available at USMLE.org
A 52-year-old woman comes to the office because of a 6-month history of intermittent headaches. Sometimes the pain improves when the patient lies down in a quiet room. Her temperature is 37.5°C (99.5°F), pulse is 86/min, respirations are 16/min, and blood pressure is 154/100 mm Hg. The lungs are clear. Cardiac examination shows the point of maximal impulse displaced to the left and occasional skipped beats; there are no murmurs or rubs. There is no S3. Resting electrocardiography shows left axis deviation with R waves greater than 30 mm in leads V5 through V6. Which of the following processes best explains the development of the left ventricular abnormalities in this patient?
(A) Excessive accumulation of glycogen
(B) Fibrosis of intraventricular conduction pathways
(C) Increased synthesis of contractile filaments
(D) Misfolding and aggregation of cytoskeletal proteins
(E) Myocyte hyperplasia as a result of induction of embryonic genes
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Answer
The patient’s presentation suggests left ventricular hypertrophy (LVH), which is characterized by increased left ventricular wall thickness and/or mass. Several features point to this diagnosis:
- Elevated blood pressure (154/100 mm Hg): Hypertension is a common cause of LVH, leading to increased workload on the heart.
- Electrocardiogram findings: The presence of tall R waves (>30 mm) in leads V5-V6 and left axis deviation are classic findings associated with LVH.
- Displaced point of maximal impulse (PMI): This finding suggests an enlarged heart, often due to LVH.
Pathophysiology:
In response to chronic pressure overload from hypertension, cardiac myocytes undergo hypertrophy, characterized by an increase in the size of the cells rather than the number (hyperplasia). The process involves:
- Increased synthesis of contractile filaments (actin and myosin) to generate more force and compensate for the increased workload.
- Reorganization of the sarcomeres within the myocytes, resulting in increased wall thickness of the left ventricle.
The correct answer is C