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Emergency And Acute Medicine – QT Syndrome, Prolonged
Prolonged QT syndrome is a disorder of myocardial repolarization characterized by prolongation of the QT interval on electrocardiogram (ECG). It reflects delayed ventricular repolarization and predisposes patients to malignant ventricular arrhythmias, particularly torsades de pointes, ventricular tachycardia, and ventricular fibrillation. These arrhythmias may cause syncope, seizures, or sudden cardiac death.
The underlying pathophysiology involves abnormalities in cardiac sodium, potassium, or calcium ion channels and may also include imbalance in sympathetic innervation. QT prolongation may be “pause-dependent,” often following a short–long–short sequence, or “adrenergic-dependent,” particularly in congenital forms triggered by exercise, emotional stress, or loud auditory stimuli. Nocturnal bradycardia can also lengthen the QT interval, leading to sleep-related events. Prolonged QT is an independent risk factor for sudden cardiac death.
Congenital long QT syndrome is linked to mutations in at least 10 genes affecting cardiac ion channels. The autosomal recessive form associated with congenital deafness is known as Jervell and Lange-Nielsen syndrome, while the autosomal dominant form without deafness is Romano-Ward syndrome. The congenital form occurs in approximately 1 in 3,000–5,000 individuals, with mortality of about 6% by age 40 if untreated. Ten to fifteen percent of gene carriers may have a normal baseline QTc. Sudden death may occur without warning symptoms in some pediatric patients.
Acquired QT prolongation is most commonly drug-induced or secondary to metabolic abnormalities. Medications associated with QT prolongation include class Ia and III antiarrhythmics, certain antibiotics (e.g., erythromycin), antifungals, psychotropic agents (e.g., haloperidol), methadone, and others. Electrolyte abnormalities such as hypokalemia, hypomagnesemia, and hypocalcemia are common causes. Cardiac conditions (bradyarrhythmias, AV block, myocarditis, ischemia), CNS disorders (subarachnoid hemorrhage, stroke), hypothyroidism, hypothermia, anorexia nervosa, and severe fasting may also contribute.
Patients may present with palpitations, lightheadedness, dizziness, syncope, or seizure-like activity. A history of syncope during exercise or emotional stress is suggestive. Family history of sudden death or syncope and congenital deafness are important clues. Medication review is essential.
Diagnosis is based on ECG findings. QTc (corrected QT) is considered prolonged when >0.44 seconds in men and >0.46 seconds in women. The QT interval is measured from the beginning of the QRS complex to the end of the T wave and averaged over several beats. The Bazett formula (QT divided by the square root of the RR interval) is most commonly used for correction. ECG may also show T-wave abnormalities, U waves, increased QT variability, torsades de pointes, or ventricular arrhythmias. Laboratory evaluation should include serum electrolytes, calcium, magnesium, and toxicology screen. Echocardiography may be performed to exclude structural heart disease. Holter monitoring, stress testing, and genetic testing may be considered in suspected congenital cases.
Initial management focuses on stabilization and arrhythmia treatment. Patients should receive supplemental oxygen, IV access, and cardiac monitoring. Hemodynamically unstable patients with torsades de pointes require immediate synchronized cardioversion or defibrillation as indicated.
Magnesium sulfate is first-line therapy for torsades de pointes, even if serum magnesium levels are normal. A typical adult dose is 2 g IV over 2–3 minutes, followed by infusion if needed. Serum potassium should be corrected to high-normal levels (4.5–5.0 mEq/L). In recurrent torsades refractory to magnesium, temporary transvenous pacing at rates of 100–120 bpm may shorten the QT interval. IV isoproterenol may be used in acquired long QT cases associated with bradycardia but is generally ineffective in congenital forms. Offending medications must be discontinued and metabolic abnormalities corrected.
For congenital long QT syndrome, β-blockers reduce the risk of arrhythmic events by approximately 70% and are recommended in symptomatic patients under cardiology guidance. High-risk patients may require pacemaker placement, implantable cardioverter-defibrillator (ICD), or surgical sympathetic denervation.
Admission is indicated for symptomatic patients, those with syncope, ventricular arrhythmias, metabolic abnormalities, or suspected ischemia. Asymptomatic patients with incidental prolonged QT may be discharged after cardiology consultation if no high-risk features are present.
Prolonged QT should be suspected in any patient presenting with unexplained syncope or seizure-like activity. Prompt correction of electrolyte abnormalities and discontinuation of QT-prolonging medications are essential. Magnesium sulfate followed by pacing remains the cornerstone of treatment for torsades de pointes. All patients with newly identified prolonged QT require cardiology follow-up.
Prolonged QT syndrome is a disorder of myocardial repolarization characterized by prolongation of the QT interval on electrocardiogram (ECG). It reflects delayed ventricular repolarization and predisposes patients to malignant ventricular arrhythmias, particularly torsades de pointes, ventricular tachycardia, and ventricular fibrillation. These arrhythmias may cause syncope, seizures, or sudden cardiac death.
The underlying pathophysiology involves abnormalities in cardiac sodium, potassium, or calcium ion channels and may also include imbalance in sympathetic innervation. QT prolongation may be “pause-dependent,” often following a short–long–short sequence, or “adrenergic-dependent,” particularly in congenital forms triggered by exercise, emotional stress, or loud auditory stimuli. Nocturnal bradycardia can also lengthen the QT interval, leading to sleep-related events. Prolonged QT is an independent risk factor for sudden cardiac death.
Congenital long QT syndrome is linked to mutations in at least 10 genes affecting cardiac ion channels. The autosomal recessive form associated with congenital deafness is known as Jervell and Lange-Nielsen syndrome, while the autosomal dominant form without deafness is Romano-Ward syndrome. The congenital form occurs in approximately 1 in 3,000–5,000 individuals, with mortality of about 6% by age 40 if untreated. Ten to fifteen percent of gene carriers may have a normal baseline QTc. Sudden death may occur without warning symptoms in some pediatric patients.
Acquired QT prolongation is most commonly drug-induced or secondary to metabolic abnormalities. Medications associated with QT prolongation include class Ia and III antiarrhythmics, certain antibiotics (e.g., erythromycin), antifungals, psychotropic agents (e.g., haloperidol), methadone, and others. Electrolyte abnormalities such as hypokalemia, hypomagnesemia, and hypocalcemia are common causes. Cardiac conditions (bradyarrhythmias, AV block, myocarditis, ischemia), CNS disorders (subarachnoid hemorrhage, stroke), hypothyroidism, hypothermia, anorexia nervosa, and severe fasting may also contribute.
Patients may present with palpitations, lightheadedness, dizziness, syncope, or seizure-like activity. A history of syncope during exercise or emotional stress is suggestive. Family history of sudden death or syncope and congenital deafness are important clues. Medication review is essential.
Diagnosis is based on ECG findings. QTc (corrected QT) is considered prolonged when >0.44 seconds in men and >0.46 seconds in women. The QT interval is measured from the beginning of the QRS complex to the end of the T wave and averaged over several beats. The Bazett formula (QT divided by the square root of the RR interval) is most commonly used for correction. ECG may also show T-wave abnormalities, U waves, increased QT variability, torsades de pointes, or ventricular arrhythmias. Laboratory evaluation should include serum electrolytes, calcium, magnesium, and toxicology screen. Echocardiography may be performed to exclude structural heart disease. Holter monitoring, stress testing, and genetic testing may be considered in suspected congenital cases.
Initial management focuses on stabilization and arrhythmia treatment. Patients should receive supplemental oxygen, IV access, and cardiac monitoring. Hemodynamically unstable patients with torsades de pointes require immediate synchronized cardioversion or defibrillation as indicated.
Magnesium sulfate is first-line therapy for torsades de pointes, even if serum magnesium levels are normal. A typical adult dose is 2 g IV over 2–3 minutes, followed by infusion if needed. Serum potassium should be corrected to high-normal levels (4.5–5.0 mEq/L). In recurrent torsades refractory to magnesium, temporary transvenous pacing at rates of 100–120 bpm may shorten the QT interval. IV isoproterenol may be used in acquired long QT cases associated with bradycardia but is generally ineffective in congenital forms. Offending medications must be discontinued and metabolic abnormalities corrected.
For congenital long QT syndrome, β-blockers reduce the risk of arrhythmic events by approximately 70% and are recommended in symptomatic patients under cardiology guidance. High-risk patients may require pacemaker placement, implantable cardioverter-defibrillator (ICD), or surgical sympathetic denervation.
Admission is indicated for symptomatic patients, those with syncope, ventricular arrhythmias, metabolic abnormalities, or suspected ischemia. Asymptomatic patients with incidental prolonged QT may be discharged after cardiology consultation if no high-risk features are present.
Prolonged QT should be suspected in any patient presenting with unexplained syncope or seizure-like activity. Prompt correction of electrolyte abnormalities and discontinuation of QT-prolonging medications are essential. Magnesium sulfate followed by pacing remains the cornerstone of treatment for torsades de pointes. All patients with newly identified prolonged QT require cardiology follow-up.
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