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QT prolongation
From WikEM
Contents
Background
- Prolonged ventricular repolarisation → increased risk of ventricular arrythmias
- QT interval is from the beginning of the Q wave to the end of the T wave; it is rate dependent and should become proportionately small with increasing rate rate
- An abnormal QT is >440-450 ms (males) and >460-470 ms (females); >500 may result in torsades
Clinical Features
- Most are asymptomatic
- History may or may not include
- Syncope, cardiac arrest, family history of long QT or sudden death
- Medication history should always be obtained especially so to avoid interactions and further QT prolongation.
Differential Diagnosis
- Pause Dependent (Aquired)
- Drug induced
- Antidyrhythmics
- Phenothiazines
- TCAs
- Organophosphates
- Antihistamines
- Electrolyte Abnormalities (hypoKalemia, hypoMag, hypoCa)
- Hypokalemia triad
- Long QT, ST depressions, PVCs
- Hypokalemia triad
- Hypothermia
- Diet related (starvation, low protein)
- Severe Bradycardia/AV Block
- Hypothyroid
- Contrast injection
- CVA (intraparenchymal)
- Elevated intracranial pressure and Intracranial hemorrhage
- MI
- Drug induced
- Adrenergic Dependent
- Congenital
- Jarvel/Lange-Nielsen
- (+deafness; AR)
- Romano-Ward synd
- (nl hearing; AD)
- Sporatic
- Mitral valve prolapse
- Jarvel/Lange-Nielsen
- Acquired
- CVA (subarachnoid)
- Autonomic surg (catechol excess: neck dissection, carotid endarterect, truncal vagotomy)
- Congenital
Drug List
- Antiarrhythmics
- Amiodarone, disopyramide, dofetilide, flecainide, ibutilide, mexiletine, procainamide, quinidine, sotalol
- Antibiotics
- Macrolide
- Azithromycin, erythromycin, clarithromycin
- Fluoroquinolone
- Ciprofloxacin, gatifloxacin (most common), gemifloxacin, levofloxacin, moxifloxacin, ofloxacin
- Other
- Pentamidine, telithromycin, trimethoprim-sulfamethoxazole
- Macrolide
- Antidepressants
- Amitriptyline, citalopram, doxepin, fluoxetine, nortriptyline, paroxetine, sertraline, venlafaxine
- Antiemetics
- Dolasetron, droperidol, granisetron, ondansetron
- Antifungals
- Fluconazole, itraconazole, ketoconazole, voriconazole
- Antihypertensives
- Nicardipine
- Antineoplastics
- Lapatinib, nilotinib, sunitinib, tamoxifen
- Antimalarials
- Chloroquine, halofantrine
- Antipsychotics
- Chlorpromazine, clozapine, galantamine, haloperidol, lithium, paliperidone, pimozide, quetiapine, risperidone, thioridazine, ziprasidone
- Antivirals
- Amantadine, atazanavir, foscarnet
- Diuretics
- Indapamide
- Immune suppressants
- Tacrolimus
- Opiates
- Methadone
- Phosphodiesterase inhibitors
- Sildenafil, vardenafil
- Skeletal muscle relaxants
- Tizanidine
- Urinary antispasmodics
- Solifenacin
Evaluation
- ECG
- quick/imprecise measure: QT takes up more than half the R-R distance
- Measure QT interval in lead II or V5-6
- QTc = QT /√R-R
- Long QT: QTc >440 (male), >460 (female)
- >500 = real concern (may result in torsades)
Management
Pause Dependent (precipitated by bradycardia)
- Unstable/sustained torsades→ defibrilation (unsynchronized)
- Stable
- Treat underlying prob
- Increase HR (isoproterenol or overdrive pacing)
- Magnesium sulfate IV
- Consider amiodarone
Adrenergic Dependent (precipited by tachycardia)
- Unstable/sustained torsades→ defibrilation (unsynchronized)
- Stable
- Slow HR (beta-blockers)
- May consider magnesium sulfate
Disposition
- Highly consider admission, especially for QT >500
