A 32-year-old woman from rural Maharashtra presents with progressive dyspnea on exertion and palpitations for 8 months. She has a history of severe anemia (Hb 6.5 g/dL) due to chronic blood loss from heavy menstrual bleeding. On examination, she has tachycardia (HR 110/min), a systolic flow murmur at the apex, and an enlarged cardiac silhouette on chest X-ray. Echocardiography shows uniform increase in left ventricular wall thickness and chamber diameter with preserved ejection fraction (EF 60%). Which cellular adaptation is primarily responsible for the cardiac changes observed in this patient?

Explanation

## Cellular Adaptation in Chronic Anemia-Induced Cardiac Stress ### Pathophysiology Chronic severe anemia causes chronic hypoxia and increased cardiac workload (increased stroke volume and heart rate needed to maintain oxygen delivery). This sustained hemodynamic stress triggers **eccentric hypertrophy** — individual cardiomyocytes increase in size through accumulation of contractile proteins (actin, myosin) and organelles, NOT through cell division. ### Key Findings in This Case - **Uniform wall thickening + chamber dilation** = eccentric hypertrophy (wall thickness increases proportionally less than chamber size) - **Preserved ejection fraction** = adaptation is still compensatory - **Systolic flow murmur** = increased flow across mitral valve due to increased stroke volume - **No cell proliferation** = true hypertrophy, not hyperplasia ### Distinction: Hypertrophy vs. Hyperplasia | Feature | Hypertrophy | Hyperplasia | |---------|-------------|-------------| | **Cell number** | Unchanged | Increased | | **Cell size** | Increased | Normal or decreased | | **Mechanism** | Increased protein synthesis | Cell division (mitosis) | | **Cardiomyocytes** | Can undergo (post-mitotic) | Cannot undergo (terminally differentiated) | | **Reversibility** | Partial (if stimulus removed) | Partial | **Key Point:** Adult cardiomyocytes are terminally differentiated and cannot divide; they respond to chronic stress exclusively by **hypertrophy** (increase in cell size), not hyperplasia. ### Clinical Pearl Eccentric hypertrophy (as in chronic anemia, aortic regurgitation, or high-output states) is initially compensatory but can progress to dilated cardiomyopathy and heart failure if the stimulus persists. **High-Yield:** The distinction between eccentric (volume overload) and concentric (pressure overload) hypertrophy is critical: - **Eccentric:** wall thickness ↑ < chamber diameter ↑ (anemia, AR, mitral regurgitation) - **Concentric:** wall thickness ↑ > chamber diameter ↑ (hypertension, aortic stenosis) [cite:Robbins 10e Ch 3]