A 52-year-old man with a 15-year history of poorly controlled hypertension (BP 160/100 mmHg) presents with dyspnea on exertion. Physical examination reveals a sustained apical impulse and an S4 gallop. Echocardiography shows left ventricular wall thickness of 16 mm (normal <11 mm) with normal cavity size and preserved ejection fraction. The clinician suspects concentric left ventricular hypertrophy secondary to chronic pressure overload. Which investigation would be most appropriate to assess the degree of myocardial fibrosis and confirm the adaptive response to sustained hypertension?

Explanation

## Investigation of Choice for Myocardial Fibrosis in Hypertensive LVH ### Clinical Context The patient has concentric left ventricular hypertrophy (LVH) secondary to chronic hypertension. While echocardiography confirms wall thickening and preserved function, it does not quantify myocardial fibrosis—a key component of the adaptive response to sustained pressure overload. Fibrosis represents the transition from compensatory hypertrophy to potential maladaptation and diastolic dysfunction. ### Why Cardiac MRI with T1 Mapping and Extracellular Volume (ECV) Quantification? **Key Point:** Cardiac MRI with T1 mapping is the gold standard non-invasive technique for quantifying myocardial fibrosis. It measures: - **Native T1 relaxation time:** Reflects myocardial composition (fibrosis, edema, infiltration) - **Extracellular volume (ECV):** Directly quantifies the proportion of interstitial space occupied by fibrosis - **Post-contrast T1 mapping:** Allows calculation of ECV = (1 − hematocrit) × (ΔR1 myocardium / ΔR1 blood) **High-Yield:** In hypertensive LVH, elevated ECV (>28%) indicates: - Replacement fibrosis (myocyte loss and collagen deposition) - Reactive fibrosis (perivascular and interstitial collagen) - Prognostic marker for diastolic dysfunction and heart failure progression ### Comparison with Other Investigations | Investigation | Utility | Limitation | |---|---|---| | **Cardiac MRI with T1 mapping & ECV** | Quantifies myocardial fibrosis non-invasively; prognostic; no radiation | Contraindicated in pacemakers (older devices); requires gadolinium contrast | | **TTE with Tissue Doppler** | Assesses diastolic function (E/e' ratio, S' velocity); detects diastolic dysfunction | Does not quantify fibrosis; operator-dependent; indirect measure of fibrosis | | **Serum biomarkers (BNP, troponin, galectin-3)** | Reflect myocardial stress and remodeling; prognostic | Non-specific; elevated in many conditions; do not directly quantify fibrosis; cannot localize fibrosis | | **Chest X-ray with CTR** | Screens for cardiomegaly; simple, low-cost | Insensitive; does not assess wall thickness or fibrosis; poor specificity | **Clinical Pearl:** T1 mapping has emerged as a superior tool for detecting early myocardial fibrosis before clinical heart failure develops. In hypertensive LVH, rising ECV predicts progression to diastolic dysfunction and eventual systolic failure, making it valuable for risk stratification and guiding intensity of antihypertensive therapy. ### Pathophysiology of Hypertensive LVH Chronic pressure overload triggers: 1. **Myocyte hypertrophy** (increased sarcomere number in parallel) 2. **Reactive fibrosis** (perivascular and interstitial collagen deposition) 3. **Replacement fibrosis** (myocyte apoptosis and collagen replacement) 4. **Diastolic dysfunction** (increased stiffness from fibrosis) T1 mapping directly quantifies steps 2–3, making it the most specific investigation for assessing the degree of fibrotic remodeling. [cite:Robbins 10e Ch 1; Harrison 21e Ch 238]