Corrected QT Interval Calculator

QTc calculation using various established mathematical models.

💡 Clinical Recommendation (QRS > 120 ms):
The presence of an intraventricular conduction defect (such as left/right bundle branch block or pacemaker pacing) artificially prolongs the global QT interval. Standard formulas are heavily biased. It is recommended to use the Rautaharju (2004) or Bogossian (2014) model, which integrates the widened depolarization to estimate the true ventricular repolarization time.
Bazett (1920)
--
QT / √RR_sec
Fridericia (1920)
--
QT / ∛RR_sec
Framingham (1992)
--
QT + 154 * (1 - RR_sec)
Hodges (1983)
--
QT + 1.75 * (HR - 60)
Rautaharju (2004)
--
Adjusted HR + QRS + Sex
Bogossian (2014)
--
QTc_Bazett - (QRS - 100)
QT Interval Measurement Guide
Tangent vs. Threshold Method (Leads II or V5)
📐 Tangent Method
1. Find the steepest slope of the T-wave descending limb.
2. Draw a tangent line to this maximum slope.
3. The intersection with the isoelectric baseline (defined at QRS onset) marks the official end of the T-wave.
⚠️ U-wave Rule: If a standard T+U wave is present, the U-wave must be excluded from the measurement.
Highly Reproducible (Can shorten QTc by ~10ms)
⚖️ Threshold Method
1. Trace the terminal limb of the T-wave descending curve.
2. Determine the exact point where the T-wave joins and completely merges with the isoelectric baseline.
3. This terminal limb intersection with the baseline constitutes the end of repolarization.
⚠️ Biphasic T-waves: Unlike the U-wave, both components (T1 and T2) must be included in the measurement.
Less Consensus (No Consensus Preference)
🛡️
Expert Consensus & Best Practices: Manual measurement (using manual calipers for precise control) is strongly advised. Automated assessment algorithms frequently struggle and are unreliable with aberrant waves, particularly in patients with Long QT Syndrome (LQTS). No gold standard exists, highlighting the necessity to document the chosen method.

Credits: https://www.escardio.org/communities/councils/genomics/scientific-documents-and-publications/cardiogenomics-insights/volume-9/how-to-measure-the-qt-interval/