Ventricular Wall Stretch as the Trigger Signal
Increased wall tension is the mechanical trigger for peptide release.
- Wall tension: Trigger (Volume/pressure overload)
- Cardiomyocytes: Source cells (mainly ventricular)
- Stretch receptors: Sensing (mechanosensitive)
- Minutes: Onset (rapid transcription)
Mechanism of stretch sensing
Wall stretch activates gene transcription for natriuretic peptides.
Release of BNP and NT-proBNP Into Circulation
ProBNP is cleaved into active BNP and inactive NT-proBNP fragments.
- proBNP-108: Precursor (cleaved by corin)
- BNP-32: Active form (short half-life ~20min)
- NT-proBNP: Inactive form (half-life ~120min)
- 1:1 molar: Ratio (equimolar cleavage)
Cleavage and clearance
Longer half-life makes NT-proBNP a more stable lab marker.
Interpreting Normal Ranges by Patient Age
Normal thresholds rise with age due to natural cardiac changes.
- <450 pg/mL: Age <50 (normal cutoff)
- <900 pg/mL: Age 50-75 (normal cutoff)
- <1800 pg/mL: Age >75 (normal cutoff)
- Fibrosis/renal: Reason (age-related decline)
Why age matters
Renal clearance and stiffness both raise baseline levels with age.
Diagnostic Threshold for Heart Failure
Levels above the age-adjusted threshold raise heart failure likelihood.
- <300 pg/mL: Rule-out (NT-proBNP, acute setting)
- Age-based: Rule-in (450/900/1800 pg/mL)
- High: Sensitivity (good for ruling out)
- Renal, obesity: Confounders (shift interpretation)
Threshold caveats
Obesity lowers levels; renal impairment raises them independent of HF.
Trend Interpretation Across Serial Measurements
Change over time often matters more than a single value.
- Worsening: Rising trend (decompensation risk)
- Improving: Falling trend (therapy response)
- >30-50%: Significant Δ (biologic variability)
- HF titration: Use case (guides therapy)
Trend over single value
Serial trends help guide diuretic and therapy adjustments.
Placeholder: track the trend, not just one number.