Page 98 - Critical Care Notes

4223_Tab02_045-106 29/08/14 10:00 AM Page 92

CV
■ Radiofrequency ablation
■ Pacemaker
■ If arrhythmia converts to pulseless VT or VF → defibrillate
■ Implantable cardioverter defibrillator (ICD), if indicated

QTc Prolongation
■ Acquired drug-induced cardiac conduction abnormality causing delayed
repolarization of ventricular myocardium.
■ Normal QT interval is <440 msec. QT intervals 440–460 msec considered
borderline for men and 440–470 msec for women. Greater values for each
gender are considered a prolonged QT interval.
■ QT interval shortens with tachycardia and lengthens with bradycardia. A
rate corrected (QTc) is then calculated. No one best method to calculate.
QTc interval >510 msec is clinically significant. Quick calculation method:
preceding RR interval ÷ 2. A calculator for corrected QT interval can be
found at http://www.mdcalc.com/corrected-qt-interval-qtc/ or http://www.
medical-calculator.nl/calculator/QTc/.
■ Criteria for QT monitoring (at least one must be met)
■ Use of a QT-prolonging medication
■ Presence of cardiac arrhythmias causing severe bradycardia or long
pauses
■ Patients with hypomagnesemia or hypokalemia
Causes
■ Select antimicrobials: macrolides, fluoroquinolones, azole antifungals
■ Select antiarrhythmics: classes Ia, Ic, III
■ Select antipsychotics: haloperidol, risperidone, and others
■ Select antidepressants
■ Select amphetamines and anticholinergics
■ Select sympathomimetics and vasodilators
■ Methadone and oxycodone
■ Phenothiazines and protease inhibitors
■ Benadryl and nonsedating antihistamines; select decongestants
■ Select diuretics
■ Select antiemetics: ondansetron (Zofran), cisapride, prochlorperazine, and
metoclopramide (Reglan)
■ Hypokalemia and hypomagnesemia
■ Bradycardia, complete heart block, and long sinus pauses
■ SAH and stroke
■ HF
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