Tp-Te Interval Calculation and Clinical Applications
How Tp-Te is Calculated
The Tp-Te (T peak to T end) interval is measured as the distance from the peak of the T wave to the end of the T wave on the electrocardiogram 1, 2, 3. This measurement reflects transmural dispersion of ventricular repolarization—the time difference between epicardial and endocardial repolarization completion.
Measurement Technique
- Identify the T wave peak: The highest point of the T wave
- Identify the T wave end: Where the T wave returns to the isoelectric baseline (TP segment)
- Measure the interval: The time between these two points, typically in milliseconds
The measurement should be performed in precordial leads V2-V5, with lead V5 being particularly reliable 2, 4. When measuring from multiple leads, the longest Tp-Te interval should be used, similar to QT interval measurement principles.
Normal Reference Values
- Normal Tp-Te interval: Approximately 66-79 ms in adults 2, 3
- In children: 85 ms (98th percentile) in first 5 years, increasing to 92 ms in adolescence 4
- Values vary with age, body mass index, body surface area, and left ventricular parameters 2
Formulas Using Tp-Te Interval
1. Tp-Te/QT Ratio
Calculated by dividing the Tp-Te interval by the QT interval 1, 3:
- Formula: Tp-Te/QT = Tp-Te interval ÷ QT interval
- Normal range: 0.17-0.19 in healthy adults 2, 3
- Advantage: Less heart rate-dependent than Tp-Te alone 5
- Clinical significance: Values >0.21 suggest increased arrhythmic risk 3
2. Tp-Te/QTc Ratio
Calculated by dividing the Tp-Te interval by the corrected QT interval 1, 3:
- Formula: Tp-Te/QTc = Tp-Te interval ÷ QTc interval
- Normal range: 0.16-0.19 in healthy adults 2, 3
- QTc calculation: Typically uses Bazett's formula (QT/√RR) or Fridericia's formula (QT/∛RR)
- Note: In children, Fridericia correction is preferred over Bazett's, which overcorrects at higher heart rates 4
3. Tp-Te Dispersion
Calculated as the difference between the maximum and minimum Tp-Te values across all measured ECG leads 2, 6:
- Formula: Tp-Te dispersion = Maximum Tp-Te - Minimum Tp-Te (across all leads)
- Normal range: Approximately 10-20 ms 2
- Clinical significance: Tp-Te dispersion >17 ms predicts ventricular arrhythmias with 71% sensitivity and 76% specificity 6
- Superior to single-lead measurements for predicting ventricular tachycardia/fibrillation 6
4. Tp-Te/JT Ratio
Calculated by dividing Tp-Te by the JT interval (QT interval minus QRS duration) 4:
- Formula: Tp-Te/JT = Tp-Te interval ÷ (QT - QRS)
- Clinical note: Higher in younger children due to greater QT shortening at faster heart rates 4
Clinical Applications and Pitfalls
Key Clinical Uses
- Arrhythmia risk stratification: Prolonged Tp-Te predicts ventricular arrhythmias in multiple conditions 1, 3, 7, 8
- Disease monitoring: Elevated in diabetes, hyperparathyroidism, cardiac amyloidosis, and vasovagal syncope 1, 3, 7, 8
- Structural heart disease: Correlates with left ventricular diameter and volume in dilated cardiomyopathy 5
Important Caveats
- Lead selection matters: Tp-Te in leads II and V5 correlate well; use V2-V5 for most reliable measurements 2, 4
- Heart rate correction: Tp-Te/QT and Tp-Te/QTc ratios are more heart rate-independent than raw Tp-Te 5
- Multi-lead assessment: Tp-Te dispersion (multi-lead evaluation) is superior to single-lead measurements for arrhythmia prediction 6
- Age and gender: No gender differences in children; Tp-Te lengthens with age as heart rate decreases 4
- Measurement challenges: Difficult when T and U waves merge; use leads without prominent U waves (aVR, aVL) in such cases