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QT IntervalAka: QT Duration, QT Prolongation, Prolonged QT
- Interpretation: Normal QT duration
- QT modifying factors
- Normal QT decreases with increasing Heart Rate
- QT is longer in leads V2 and v3
- Calculation of QTc or corrected QT (Bazett's Formula)
- QTc = QT/(sqrt RR Interval)
- QTc is normally <0.44
- Approximation of normal QT
- QT interval shortens with decreasing RR Interval
- QT = 0.5 x preceding RR Interval (if normal rate)
- Approximate normal QT Interval
- QT <= 0.38 if Heart Rate 80 bpm or greater
- Add 0.02 sec for every 10 bpm below 80
- Example: Normal QT <= 0.46 if Heart Rate 40-50
- Heart Rate determined QT
- 115 - 84 bpm: QT 0.30 to 0.37 seconds
- 83 - 72 bpm: QT 0.32 to 0.40 seconds
- 71 - 63 bpm: QT 0.34 to 0.42 seconds
- 62 - 56 bpm: QT 0.36 to 0.43 seconds
- 55 - 45 bpm: QT 0.39 to 0.46 seconds
- QT modifying factors
- Causes: Prolonged QT
- See Prolonged QT Interval due to Medication
- Familial long QT Syndrome
- Congestive Heart Failure
- Myocardial Infarction
- Hypocalcemia
- Hypomagnesemia
- Type I Antiarrhythmic drugs
- Rheumatic Fever
- Myocarditis
- Congenital Heart Disease
- Causes: Shortened QT
- Digoxin (Digitalis)
- Hypercalcemia
- Hyperkalemia
- Phenothiazines
- References
- Rollings (1984) Facts and Formulas, p. 64
- Mirvis in Braunwald (2001) Cardiovascular, p. 92-3
Prolonged QT interval (C0151878) | |
|---|---|
| Concepts | Finding (T033) |
| English | Increased Q-T interval, Increased Q-T interval -RETIRED-, Increased QT interval, Long QT, prolonged QT, Prolonged QT interval, QT INCREASED, QT INTERVAL PROLONGED |
| Spanish | aumento del intervalo QT, intervalo Q - T aumentado, intervalo Q - T prolongado - RETIRADO -, intervalo QT prolongado |
| Parent Concepts | cardiac arrhythmia (C0003811), Abnormal cardiac conduction (C0232219), [D]Electrocardiogram (ECG) abnormal (C0522055), Reason not stated concept (C1276325), QT interval - finding (C1287082), Duplicate concept (C1274013) |
| Sources | CST, DXP, NDFRT, SCTSPA, SNOMEDCT Derived from the NIH UMLS (Unified Medical Language System) |
