Table 4: Risk factors contributing to QTc interval prolongation and torsades de pointes.

Risk factorCauses/implications

Sex (female)QT intervals longer in women than in men
QT interval longer during first half of menstrual cycle

Age (elderly)Comorbid coronary artery diseases
Multiple medications
Pharmacokinetic/pharmacodynamic changes

Electrolyte imbalance
Hypokalemia, hypomagnesemia
Hypocalcemia
Diuretic use
Excessive vomiting or diarrhea
Postprandial hypokalemia

Congenital long QT syndromeAssociated with torsade and sudden death

Cardiac disease with history of acute or chronic myocardial ischemia, CHF, cardiac arrhythmias, and bradycardiaIncreased risk of cardiac arrhythmias

Drugs known to prolong QTc intervalMay potentiate QTc prolongation

Medication overdose with drugs that prolong the QTc intervalQTc prolongation generally dose dependent

Concomitant medications, liver diseaseAdverse events with cytochrome P-450 enzyme system inhibition, leading to increased drug levels that can increase QT interval

Endocrine/metabolic disorders
Diabetes, obesity
Hypothyroidism, pituitary insufficiency
Via electrolytes or cardiovascular disease

Injury to the central nervous system
Stroke, infection, and trauma
Via autonomic nervous system dysfunction