Which statement is true about MS severity thresholds?

• A. Mild MS is defined by PHT 150-219 ms.
• B. Severe MS is defined by PHT ≥ 220 ms.
• C. Moderate MS mean gradient is > 10 mmHg.
• D. PHT cannot be used to grade MS severity.

Answer: (B)

Understanding how pressure half-time (PHT) relates to mitral stenosis severity shows why a longer PHT signals more severe narrowing. PHT is the time it takes for the transmitral pressure gradient to drop by half. In mitral stenosis, a longer PHT means a smaller mitral valve area (MVA). There’s an approximate relationship: MVA ≈ 220 / PHT (with PHT in milliseconds and MVA in square centimeters). So when PHT reaches about 220 ms or more, the MVA is around 1.0 cm² or less, which corresponds to severe mitral stenosis. That’s why defining severe MS as PHT ≥ 220 ms is the true statement.

PHT is indeed used to grade severity because it directly reflects how restricted the valve is. The other statements don’t fit standard interpretations: a PHT range of 150–219 ms doesn’t uniquely define mild MS, it sits in a mid-range between mild and moderate; a moderate MS mean gradient is typically in a lower range (often around 5–10 mmHg, with exact cutoffs varying by guideline), not strictly greater than 10 mmHg; and PHT can be used to assess severity, so saying it cannot is inaccurate.