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Background
- Prolonged ventricular repolarisation → increased risk of ventricular arrythmias
- Males >440-450 ms
- Females >500 ms
- Rule of thumb: Normal QT interveal 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
Clinical Features
- Most are asymptomatic
- History may include:
- Medication history may include QT prolonging medications
Differential Diagnosis
- Pause Dependent (Acquired)
- Adrenergic Dependent
- Congenital
- Acquired
- CVA (subarachnoid)
- Autonomic surgery (catechol excess: neck dissection, carotid endarterectomy, truncal vagotomy)
Drug List
- Antiarrhythmics
- Antibiotics
- Antidepressants
- Antiemetics
- Antifungals
- Antihypertensives
- Antineoplastics
- Lapatinib, nilotinib, sunitinib, tamoxifen
- Antimalarials
- Antipsychotics
- Chlorpromazine, clozapine, galantamine, haloperidol, lithium, paliperidone, pimozide, quetiapine, risperidone, thioridazine, ziprasidone
- Antivirals
- Diuretics
- Immune suppressants
- Opiates
- Phosphodiesterase inhibitors
- Skeletal muscle relaxants
- Urinary antispasmodics
Evaluation
Workup
Diagnosis
- 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
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
External Links
References