QT prolongation: Difference between revisions
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==Background==
==Background==
*Prolonged ventricular repolarisation → increased risk of ventricular arrythmias
[[File:SinusRhythmLabels.svg|thumb]]
[[File:Grid.png|thumb]]
*Prolonged ventricular repolarization → increased risk of ventricular arrhythmias
**Males >440-450 ms
**Males >440-450 ms
**Females >500 ms
**Females >500 ms
**Rule of thumb: Normal QT interveal is less than half of preceding RR interval
**Rule of thumb: Normal QT interval is less than half of preceding RR interval
*QT interval is from the beginning of the Q wave to the end of the T wave
*QT interval is from the beginning of the Q wave to the end of the T wave
**Rate dependent and should become proportionately shorter with increasing heart rate
**Rate dependent and should become proportionately shorter with increasing heart rate


==Clinical Features==
===List of Drugs Causing QT Prolongation===
*Most are asymptomatic
*History may include:
**[[Syncope]]
**[[Cardiac arrest]]
**Family history of long QT or sudden death
*Medication history may include QT prolonging medications
 
==Differential Diagnosis==
*Pause Dependent (Acquired)
**Drug induced
***[[Antiarrhythmics]]
***[[Phenothiazines]]
***[[TCAs]]
***[[Organophosphates]]
***[[Antihistamines]]
**[[Electrolyte Abnormalities]] ([[hypoKalemia]], [[hypoMag]], [[hypoCa]])
***[[Hypokalemia]] triad
****Long QT, ST depressions, PVCs
**[[Hypothermia]]
**Diet related (starvation, low protein)
**[[Severe Bradycardia]]/[[AV Block]]
**[[Hypothyroid]]
**Contrast injection
**[[CVA]] (intraparenchymal)
**[[Elevated intracranial pressure]] and [[Intracranial hemorrhage]]
**[[MI]]
*Adrenergic Dependent
**Congenital
***Jarvel/Lange-Nielsen
****(+deafness; AR)
***Romano-Ward syndrome
****(normal hearing; AD)
***Sporadic
***[[Mitral valve prolapse]]
**Acquired
***[[CVA]] (subarachnoid)
***Autonomic surgery (catechol excess: neck dissection, carotid endarterectomy, truncal vagotomy)
 
===Drug List===
*[[Antiarrhythmics]]
*[[Antiarrhythmics]]
**[[Amiodarone]], disopyramide, dofetilide, [[flecainide]], ibutilide, mexiletine, [[procainamide]], [[quinidine]], [[sotalol]]
**[[Amiodarone]], disopyramide, dofetilide, [[flecainide]], ibutilide, mexiletine, [[procainamide]], [[quinidine]], [[sotalol]]
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*Urinary antispasmodics
*Urinary antispasmodics
**Solifenacin
**Solifenacin
==Clinical Features==
*Most are asymptomatic
*History may include:
**[[Syncope]]
**[[Cardiac arrest]]
**Family history of long QT or sudden death
*Medication history may include QT prolonging medications
==Differential Diagnosis==
{{Syncope causes}}


==Evaluation==
==Evaluation==
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**Measure QT interval in lead II or V5-6
**Measure QT interval in lead II or V5-6
**QTc = QT /√R-R
**QTc = QT /√R-R
===Determining Cause===
*Pause Dependent (Acquired)
**Drug induced (see drug list above)
***[[Antiarrhythmics]]
***[[Phenothiazines]]
***[[TCAs]]
***[[Organophosphates]]
***[[Antihistamines]]
**[[Electrolyte Abnormalities]] ([[hypoKalemia]], [[hypoMag]], [[hypoCa]])
***[[Hypokalemia]] triad
****Long QT, ST depressions, PVCs
**[[Hypothermia]]
**Diet related (starvation, low protein)
**[[Severe Bradycardia]]/[[AV Block]]
**[[Hypothyroid]]
**Contrast injection
**[[CVA]] (intraparenchymal)
**[[Elevated intracranial pressure]] and [[Intracranial hemorrhage]]
**[[MI]]
*Adrenergic Dependent
**Congenital
***Jarvel/Lange-Nielsen
****(+deafness; AR)
***Romano-Ward syndrome
****(normal hearing; AD)
***Sporadic
***[[Mitral valve prolapse]]
**Acquired
***[[CVA]] (subarachnoid)
***Autonomic surgery (catechol excess: neck dissection, carotid endarterectomy, truncal vagotomy)


==Management==
==Management==
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*[[Hypomagnesemia]]
*[[Hypomagnesemia]]
*[[Hypermagnesemia]]
*[[Hypermagnesemia]]
== Calculators ==
{{QTc_Calculator}}


==External Links==
==External Links==
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==References==
==References==
<references/>
<references/>
[[Category:Cardiology]]
[[Category:Cardiology]]
[[Category:Toxicology]]
[[Category:Toxicology]]

Latest revision as of 15:07, 21 March 2026

Background

SinusRhythmLabels.svg
Grid.png
  • Prolonged ventricular repolarization → increased risk of ventricular arrhythmias
    • Males >440-450 ms
    • Females >500 ms
    • Rule of thumb: Normal QT interval is less than half of preceding RR interval
  • QT interval is from the beginning of the Q wave to the end of the T wave
    • Rate dependent and should become proportionately shorter with increasing heart rate

List of Drugs Causing QT Prolongation

Clinical Features

  • Most are asymptomatic
  • History may include:
  • Medication history may include QT prolonging medications

Differential Diagnosis

Syncope Causes

Evaluation

Workup

  • ECG
  • CBC
  • Chem 10

Diagnosis

Acquired QT prolongation
  • ECG
    • On visual inspection, QT takes up more than half the R-R distance
    • Measure QT interval in lead II or V5-6
    • QTc = QT /√R-R

Determining Cause

Management

Pause Dependent (precipitated by bradycardia)

Adrenergic Dependent (precipited by tachycardia)

Disposition

  • Consider admission, especially for QT >500 or if symptomatic
  • May require consultation for discontinuation of QT prolonging medications
  • Avoid prescribing medications that may contribute to prolonged QT

See Also

Calculators

Corrected QT Interval (QTc)

Corrected QT Interval (QTc)
Parameter Value
QT Interval (ms)
Heart Rate (bpm)
RR Interval (ms) — auto-calculated from HR ms
Results
QTc (Bazett's) — QT / √(RR in sec) ms
QTc (Fridericia) — QT / ∛(RR in sec) ms
Interpretation (Bazett's QTc)
<440 ms Normal QTc for males.
<460 ms Normal QTc for females.
440–500 ms Borderline/Prolonged — Monitor closely. Review medications for QT-prolonging drugs.
>500 ms Significantly prolonged — High risk for Torsades de Pointes. Discontinue offending agents. Check Mg²⁺/K⁺/Ca²⁺.
References
  • Bazett HC. An analysis of the time-relations of electrocardiograms. Heart. 1920;7:353-370.
  • Fridericia LS. Duration of systole in electrocardiogram. Acta Med Scand. 1920;53:469-486.
  • Viskin S. Long QT syndromes and torsade de pointes. Lancet. 1999;354:1625-1633. PMID 10560690.

External Links

References

  1. ↑ Simon HL, Behr ER. Pharmacological treatment of acquired QT prolongation and torsades de pointes. Br J Clin Pharmacol. 2016 Mar; 81(3): 420–427. doi: 10.1111/bcp.12726
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