Acquired long QT syndrome: Clinical manifestations, diagnosis, and management

INTRODUCTION — The long QT syndrome (LQTS) is a disorder of myocardial repolarization characterized by a prolonged QT interval on the electrocardiogram (ECG) (waveform 1). This syndrome is associated with a characteristic life-threatening form of polymorphic ventricular tachycardia known as torsades de pointes (TdP) (waveform 2A-B).

LQTS may be either congenital or acquired. Acquired LQTS usually results from drug therapy (table 1), although other factors such as hypokalemia, hypomagnesemia, and bradycardia can increase the risk of drug-induced LQTS.

The clinical manifestations, diagnosis, and management of acquired LQTS will be reviewed here. The pathophysiology and causes of acquired LQTS, as well as the clinical manifestations, diagnosis, and management of congenital LQTS, are discussed elsewhere.

●(See "Acquired long QT syndrome: Definitions, pathophysiology, and causes".)

●(See "Congenital long QT syndrome: Epidemiology and clinical manifestations".)

●(See "Congenital long QT syndrome: Diagnosis".)

●(See "Congenital long QT syndrome: Treatment".)

CLINICAL PRESENTATION

Overview — Acquired LQTS should be suspected in patients who have an ECG that shows a prolonged QTc in the presence of a known QT-prolonging factor(s) such as a medication or electrolyte disturbance. The clinical presentation of acquired LQTS is variable; however, only a minority of patients experience symptoms.

Symptoms — The vast majority of patients are asymptomatic and identified solely by QT prolongation on the ECG. A small minority of patients with acquired LQTS experience an arrhythmia (usually torsades de pointes [TdP]). For these patients, the type and intensity of symptoms will vary depending upon the rate and duration of the TdP and the presence or absence of significant comorbid conditions. While TdP is frequently self-terminating, if the arrhythmia persists, patients may present with sudden cardiac arrest. The definition of TdP is provided separately. (See "Acquired long QT syndrome: Definitions, pathophysiology, and causes", section on 'Definitions'.)

Patients with TdP related to acquired LQTS who notice symptoms typically present with one or more of the following:

●Presyncope – Most commonly, symptomatic patients will be lightheaded or presyncopal and may or may not report palpitations.

●Palpitations – These may or may not be related to TdP. These can occur alone or with one or more of the other symptoms.

●Syncope – Patients presenting with syncope typically have faster and more sustained ventricular arrythmias that lead to hypotension and associated hemodynamic compromise. Patients with syncope do not always have accompanying palpitations.

●Cardiac arrest – This results from fast and sustained ventricular arrhythmia and may be a more common presentation in patients with comorbid conditions such as underlying structural or functional heart disease.

Unstable presentation — Patients present with hemodynamic compromise such as hypotension, altered mental status, chest pain, or heart failure, but they generally remain awake with a discernible pulse. Differentiation between a hemodynamically unstable versus stable patient is detailed separately. (See "Wide QRS complex tachycardias: Approach to the diagnosis", section on 'Assessment of hemodynamic stability'.)

EVALUATION — The evaluation of all patients with suspected acquired LQTS includes a 12-lead ECG and a thorough history, including medications and recent changes in medications, along with bloodwork (this usually includes serum electrolytes, particularly potassium and magnesium, as well as a toxicology screen).

ECG findings — All patients with suspected acquired LQTS should have a 12-lead ECG performed, with manual measurement of intervals.

Normal QTc ranges and general ECG principles — The sinus rhythm QT interval should be measured manually on all available ECGs (including old ECGs for comparison, when available) using multiple leads (preferably leads II and V5) and then corrected for heart rate.

The 2011 American Heart Association/American College of Cardiology (AHA/ACC) scientific statement on prevention of torsades de pointes (TdP) in hospital settings recommended that a QTc over the 99th percentile should be considered abnormally prolonged [1].

The normal range for the rate-corrected QT interval (QTc) is similar in males and females from birth until the start of adolescence, while after puberty and in adults, females have slightly longer QT intervals than males. Before puberty, a QTc <450 ms is considered normal, between 450 and 459 ms is borderline, and ≥460 ms is prolonged. After puberty in males, a QTc between 460 and 469 ms is borderline and ≥470 ms is considered prolonged. In postpubertal females, 460 to 479 ms is borderline and ≥480 ms is considered prolonged. (See "Congenital long QT syndrome: Diagnosis", section on 'QT rate correction'.)

The specific technique of measuring the QT interval, including consideration of U waves and intraventricular conduction delay, is discussed separately. (See "ECG tutorial: ST and T wave changes", section on 'Prolonged QT interval'.)

ECG findings in TdP — Typical features of TdP include an antecedent prolonged QT interval, particularly in the last heart beat preceding the onset of the arrhythmia. Additional typical features include a ventricular rate of 160 to 250 beats per minute, irregular RR intervals, and a cycling of the QRS axis through 180 degrees every 5 to 20 beats [2,3]. TdP is usually short-lived and typically terminates spontaneously. However, most patients experience multiple episodes of the arrhythmia. These episodes of TdP can recur in rapid succession, potentially degenerating to ventricular fibrillation and sudden cardiac death [2,3].

History — A careful history is important in diagnosing acquired LQTS since the diagnosis depends on the presence of a QT-prolonging factor. We collect the following history factors in patients with suspected acquired LQTS:

●Symptoms – (See 'Symptoms' above.)

●Medications – This includes the starting date, dose, and duration of use. The medication history should include all drugs (ie, prescription medications [either taken as prescribed or misused], over-the-counter medications, or supplements [including herbal medications]). (See "Acquired long QT syndrome: Definitions, pathophysiology, and causes", section on 'Specific drug regimen' and "Acquired long QT syndrome: Definitions, pathophysiology, and causes", section on 'Drugs that prolong the QT interval'.)

●Causes of electrolyte abnormalities – Specific factors underlying hypokalemia or hypomagnesemia should be obtained. Examples are recent gastroenteritis or the initiation of diuretic therapy. (See "Hypomagnesemia: Causes of hypomagnesemia" and "Causes of hypokalemia in adults".)

●Kidney or liver disease – (See "Acquired long QT syndrome: Definitions, pathophysiology, and causes", section on 'Metabolic factors' and "Acquired long QT syndrome: Definitions, pathophysiology, and causes", section on 'Metabolic abnormalities'.)

●Thyroid disease – The association with LQTS has been described but is not well established [4]. If abnormal thyroid function is found, a second electrolyte or rate-related phenomena (hysteresis) may underlie TdP.

●Hypothermia – This includes accidental and iatrogenic hypothermia from targeted temperature management in patients who have had a postcardiac arrest. (See "Accidental hypothermia in adults", section on 'Electrocardiographic changes' and "Intensive care unit management of the intubated post-cardiac arrest adult patient", section on 'Adverse effects' and "Intensive care unit management of the intubated post-cardiac arrest adult patient", section on 'Electrocardiography and echocardiography'.)

●Bradycardia and bradyarrhythmia – (See "Acquired long QT syndrome: Definitions, pathophysiology, and causes", section on 'Bradyarrhythmias'.)

●Family history – Taking a careful family and genetic history is important because congenital LQTS is important to distinguish from acquired LQTS given differing management strategies. In this regard, screening of family members is also important. (See 'Screening of family members' below.)

●History of eating disorders such as anorexia – (See "Anorexia nervosa in adults and adolescents: Medical complications and their management", section on 'Functional changes'.)

Laboratory tests — Basic metabolic panel including serum electrolytes (eg, potassium and magnesium) with liver and kidney function tests should be obtained. If illicit drug or medication misuse is suspected, toxicology testing can be obtained.

DIAGNOSIS

Diagnostic criteria — The diagnosis of acquired LQTS can be made in a patient with sufficient QT prolongation on an ECG who is taking a medication or has another cause of QT prolongation (ie, hypokalemia, hypomagnesemia, ischemia, hypothermia). Ideally, the diagnosis is made following review of a full 12-lead ECG. Sometimes a single-lead rhythm strip is adequate if a full 12-lead ECG cannot be obtained. The acquired QT prolongation is typically reversed once the underlying etiology is removed or treated, such as discontinuation of an offending medication or correction of electrolyte derangements.

Differential diagnosis — The main differential diagnosis for acquired LQTS is congenital LQTS. Therefore, a careful family and genetic history is important. Acquired and congenital LQTS may be related since some patients who develop acquired LQTS have an inherited predisposition. Although these patients have abnormalities in repolarization, they do not have enough criteria to meet the definition of congenital LQTS. The diagnosis of congenital LQTS is discussed in detail separately. (See "Congenital long QT syndrome: Diagnosis".)

INITIAL MANAGEMENT — In all patients with acquired LQTS, we identify and treat any reversible underlying causes of long QT. The management of patients without torsades de pointes (TdP) differs from patients with TdP in terms of urgency of treatment.

All patients — The cornerstone of the management of patients with acquired LQTS is addressing the underlying cause of QT prolongation. This includes identifying and stopping a precipitating drug(s) and aggressive correction of any metabolic abnormalities, such as hypokalemia or hypomagnesemia [5]. Drugs that prolong the QT interval (see also www.crediblemeds.org/) should be avoided. These drugs typically inhibit IKr [6-19]. Therefore, in addition to stopping the QT-prolonging drug, correcting hypokalemia is important because a low serum potassium concentration enhances the degree of drug-induced inhibition of IKr, thereby increasing the QT interval [8].

For patients with multiple self-terminating episodes of TdP, the same therapies are utilized as for patients with a single episode (ie, intravenous [IV] magnesium, correction of metabolic/electrolyte derangements, and/or removal of any inciting medications), along with additional interventions to regularize the heart rate, which include overdrive atrial pacing and/or IV isoproterenol infusion. Other antiarrhythmics are not commonly used for TdP. Specific therapies used are detailed below.

Specific therapy for TdP (the ventricular arrhythmia typically seen in acquired LQTS) differs from congenital LQTS due to pathophysiologic differences between the two forms (table 2). As an example, bradycardia is usually associated with TdP in acquired LQTS, whereas catecholamine surges trigger TdP in some types of congenital LQTS (figure 1). (See "Congenital long QT syndrome: Epidemiology and clinical manifestations", section on 'Triggers of arrhythmia'.)

Asymptomatic patients — If the patient is on a medication that prolongs the QT interval, we make efforts to switch the patient to an alternative agent. If the patient has a strong medical requirement to be on the QT-prolonging medication, if they are truly asymptomatic (eg, no palpitations, presyncope, or syncope), and if they only have mild QT prolongation (QTc <500 ms and <60 ms increase from baseline, if available) without TdP, we may choose to monitor them in an outpatient setting. Specific protocols for such management have not been established, but we suggest intermittent monitoring with ECGs and Holter recordings, particularly at times of dose changes.

Asymptomatic patients with long QT intervals should also have laboratory testing to evaluate for electrolyte abnormalities (eg, potassium, magnesium). Such abnormalities should be corrected as necessary.

Patients with palpitations — The cause of palpitations in a patient with LQTS should be quickly identified with careful history taking and Holter monitoring. If the patient is found to have TdP, management of this malignant arrythmia is discussed below. (See 'Patients with acute TdP' below.)

Patients with presyncope or syncope — Patients with prolonged QT with syncope (without documented TdP) or ECG signs of instability (ventricular ectopy, T wave alternans, atrioventricular block, or QRS widening) should be admitted for telemetry observation during withdrawal of the toxic agent (with immediate availability of an external defibrillator) and treatment of arrhythmias if indicated. In addition, admission and monitoring during drug withdrawal is suggested for patients with markedly prolonged QTc (>500 milliseconds) or an increase in QTc of at least 60 milliseconds compared with the predrug baseline value [1].

Patients with acute TdP

Initial measures — Patients with TdP should have an immediate assessment of the symptoms, vital signs, and level of consciousness to determine if they are hemodynamically stable or unstable. While the assessment of hemodynamic status is being performed by a clinician, other members of the healthcare team should to the following:

●Attach the patient to a continuous cardiac monitor

●Establish IV access

●Obtain a 12-lead ECG

●Administer supplemental oxygen

●Send blood for appropriate initial studies

Unstable patients — In unstable patients, emergency management is required (algorithm 1), and treatment should be promptly administered (algorithm 2). In parallel, underlying etiology and treatment for precipitating factors should be determined. (See 'Unstable presentation' above.)

Stable patients — Patients with TdP who are initially stable may rapidly become unstable, particularly in the setting of extremely rapid heart rates (greater than 200 beats per minute) or significant underlying cardiac comorbidities. Emergency management should be anticipated in these patients in case it becomes necessary to rapidly deliver it. Such patients should remain in a monitored setting during evaluation and management.

Magnesium therapy — For all patients with TdP, IV magnesium sulfate is first-line therapy since it is highly effective for both the treatment and prevention of recurrence of long QT-related ventricular ectopic beats or TdP [2,3,20]. We usually administer this prior to cardioversion, but it can also be given afterwards. Evidence supporting the specific timing of magnesium is lacking. Treatment with magnesium is effective even without shortening of the QT interval and is beneficial even in patients with normal serum magnesium concentrations at baseline. The rate of magnesium infusion is slower when the patient has a pulse, as rapid magnesium infusion can cause hypotension and asystole.

●Adults with TdP and pulse – The standard regimen for an adult is a 1 to 2 g IV bolus of magnesium sulfate (2 to 4 mL of 50% solution [500 mg/mL]) mixed with D5W to a total volume of 10 mL or more (eg, 50 to 100 mL over 15 minutes) [20,21]. If no response is seen or TdP recurs, the magnesium sulfate dose may be repeated immediately to a total of 4 grams in one hour. Use of continuous infusion (as an adjunct to bolus dosing) varies among clinicians. Some clinicians administer a continuous infusion of 0.5 to 1 g/hour (8 to 16 mg/min) if TdP persists after one or more bolus doses.

●Adults with TdP and no pulse – Magnesium is administered in conjunction with electrical cardioversion/defibrillation. A dose of 1 to 2 g magnesium sulfate (2 to 4 mL of 50% solution [500 mg/mL]) is diluted in 10 mL D5W and administered as a bolus over one to two minutes; the intraosseous route is used if IV is not available. If Tdp recurs or the QTc remains prolonged, some experts administer up to two additional 2 g bolus doses as needed (total maximum dose of 6 g).

●Children – The bolus dose in children is 25 to 50 mg/kg; there are no published data on IV maintenance dosing in children.

For patients with a single episode of TdP, treatment with IV magnesium along with correction of metabolic/electrolyte derangements and/or removal of any inciting medications may be sufficient. The patient should be carefully monitored until electrolytes are normalized and the QT interval nearly normalizes.

Patients who do not respond to magnesium

●Pacing – For patients with long QT related TdP who do not respond to IV magnesium, we use temporary transvenous overdrive pacing (atrial or ventricular) [2,3]. In patients with a pre-existing permanent pacemaker, we may reprogram the device to increase the pacing rate. In patients with a pre-existing implantable cardioverter-defibrillator (ICD), we may have the ICD reprogrammed to a prolonged detection time, thereby delaying ICD shock for episodes of TdP that may self-terminate. When the patient is stabilized with the temporary wire, we lower the pacing rate and watch for any return of TdP. Usually, the temporary wire will not be needed for longer than one to two days. If the patient requires temporary pacing in order to suppress TdP for longer than two days, this is usually an indication that the patient will need a permanent pacemaker.

Only in rare circumstances, if transvenous pacing is not readily available, transcutaneous pacing may be performed as a temporizing measure. However, the patient must be fully sedated, as transcutaneous pacing is very painful in a patient who is awake.

For children over age 5 and adults, pacing at rates of approximately 100 beats per minute will decrease the dispersion of refractoriness, decrease the development of early afterdepolarizations, and may shorten the surface QT interval, especially if there is an associated bradycardia.

The efficacy of overdrive pacing was illustrated in a report of nine patients with life-threatening ventricular arrhythmias and drug-induced LQTS [22]. Acceleration of the heart rate produced immediate suppression of all arrhythmias, with a reduction in the QT interval from 0.65 to 0.50 seconds. Similar findings were noted in another small series [23].

●Isoproterenol – Although we favor placement of a temporary pacemaker in the treatment of most cases of TdP that do not respond to magnesium, isoproterenol can be used as a temporizing measure prior to pacing. Isoproterenol increases the sinus rate and decreases the QT interval [2,3,24]. It should be noted that if ventricular tachycardia is misdiagnosed as TdP, isoproterenol will worsen the ventricular tachycardia by increasing the heart rate.

The initial dose of isoproterenol is 0.05 to 0.1 mcg/kg/min in children and 2 mcg/min in adults, then titrated to achieve a heart rate of 100 beats per minute.

Other therapy — Alkalinization of the plasma via the administration of sodium bicarbonate is useful when TdP is due to quinidine [25]. (See "Major side effects of class I antiarrhythmic drugs", section on 'Cardiovascular toxicity' and "Enhanced elimination of poisons", section on 'Urinary alkalinization'.)

Therapies with less evidence supporting their use

●Potassium – In a single study, an IV infusion of potassium was shown to be beneficial even in patients with normal serum potassium. This was illustrated in a report of 20 normokalemic patients with QT prolongation due to quinidine or heart failure [26]. The administration of IV potassium (0.5 mEq/kg to a maximum of 40 mEq) raised the plasma potassium concentration by 0.7 mEq/L, reversed QT prolongation and QT morphologic changes (U waves and bifid T waves), and decreased QT dispersion. It is uncertain, however, if this therapy is effective for preventing or reversing TdP; therefore, we reserve using these medications for selected patients with clinically refractory TdP and would not give IV potassium if the serum level was in the normal range.

●Class IB antiarrhythmic drugs – Medications such as lidocaine and phenytoin shorten the action potential duration and, based upon small case series, may be effective in the acute management of TdP and ventricular fibrillation [27-31]. They appear to be less predictably effective than pacing or isoproterenol [3,27]. Therefore, we reserve using these medications for selected patients with clinically refractory TdP.

LONG-TERM MANAGEMENT — Patients with acquired LQTS should be educated about the culprit drugs, other QT-prolonging drugs (including being provided with a list, available at www.crediblemeds.org/), and potential drug-drug interactions [1]. Additional information can also be found using the drug interactions program. In some patients, drug-associated LQTS appears to represent a concealed form of congenital LQTS in which a pathogenic variant in one of the LQTS genes is clinically inapparent until the patient is exposed to a particular drug or other predisposing factor (eg, hypokalemia or hypomagnesemia). If appropriate, the patient should be referred for genetic testing. (See "Congenital long QT syndrome: Pathophysiology and genetics".)

A permanent pacemaker may be required in the occasional patient with a chronic bradyarrhythmia (due to sinus node dysfunction or atrioventricular block) who has bradycardia- or pause-dependent TdP (table 3). (See "Permanent cardiac pacing: Overview of devices and indications".)

PROGNOSIS OF TDP — Among patients with TdP, the in-hospital and one-year mortality rates are relatively high. In a nested case control study from a genetics cohort of over 110,000 patients from an integrated health system, 56 patients with TdP were studied; their in-hospital and one-year mortality rates were 11 and 25 percent, respectively [32].

SCREENING OF FAMILY MEMBERS — In addition to treating the underlying cause, thorough history and ECG screening of immediate family members are recommended because of the potential for unmasking an inherited form and, therefore, the potential for other family members to harbor mutations causing congenital LQTS. (See "Congenital long QT syndrome: Diagnosis" and "Acquired long QT syndrome: Definitions, pathophysiology, and causes", section on 'Underlying pathogenic variant in a long QT syndrome gene'.)

PRECAUTIONS FOR ANY PATIENT STARTING QT-PROLONGING DRUGS — For any patient who is treated with drugs that have been associated with LQTS (table 1) (see also www.crediblemeds.org/), the following recommendations have been made [33]:

●Risk factors

•Caution should be used when prescribing a drug that prolongs the QT interval in patients with one or more risk factors (eg, diuretic therapy, electrolyte abnormalities, kidney disease, etc). Decisions regarding use of a QT-prolonging drug should be based upon an individualized risk-benefit analysis. Alternative agents that do not prolong the QT interval should be considered.

•The use of more than one QT-prolonging drug should be avoided whenever possible, as this is a common risk factor for drug-induced TdP. (See "Acquired long QT syndrome: Definitions, pathophysiology, and causes", section on 'Risk factors for drug-induced long QT syndrome'.)

●ECG monitoring

•A baseline ECG to detect prolongation of the QT interval should be obtained prior to the administration of the drug and during the course of treatment. The 2011 American Heart Association/American College of Cardiology (AHA/ACC) scientific statement on prevention of TdP suggests a strategy of documenting the QTc interval before and at least every 8 to 12 hours after the initiation, increased dose, or overdose of QT-prolonging drugs [1]. If QTc prolongation is observed, more frequent measurements are recommended. (See 'ECG findings' above.)

•The duration of QTc monitoring depends upon the duration of treatment with the QT-prolonging drug and the drug half-life. Once the patient is on a steady state of the drug, an ECG should be done to measure their QTc.

●Educating patients – Patients who are taking QT-prolonging drugs should be instructed to promptly report any new symptoms including palpitations, syncope, or near-syncope. They should also report clinical changes that could lead to hypokalemia, such as gastroenteritis or the initiation of diuretic therapy. Any identified electrolyte abnormalities should be promptly corrected in order to minimize the risk of arrhythmias.

TDP DECISION SUPPORT TOOL — A study showed that a clinical decision support tool programmed to appear when prescribers attempt to order medications for patients with risk factors for TdP may help identify high-risk patients and lead to clinical responses that could potentially prevent TdP [34]. The decision support tool was embedded in the electronic medical record system of a large healthcare system in 30 hospitals. The tool included a risk advisory that was programmed to appear when prescribers attempted to order medications with a known risk of TdP in such patients with a modified Tisdale QT risk score ≥12 (The modified Tisdale is a validated TdP risk score based on patient demographic and clinical and ECG characteristics) [35]. The advisory presented the clinician with the patient's QT risk score, delineated factors contributing to the score, and then presented relevant single‐click management options. Over an eight-month period, 7794 advisories were issued. The study reported the following findings with respect to risk advisories issued:

●Antibiotics most frequently triggered the advisory (in 33 percent of advisories).

●More than one management action was taken for 35 percent of the advisories.

●The most common action was ordering an ECG (in 20 percent of all advisories).

●Medication orders were canceled in 10 percent of patients with an advisory.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Inherited arrhythmia syndromes" and "Society guideline links: Ventricular arrhythmias" and "Society guideline links: Cardiac implantable electronic devices".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topic (see "Patient education: Long QT syndrome (The Basics)")

SUMMARY AND RECOMMENDATIONS

●Background – Acquired long QT syndrome (LQTS) is a disorder of myocardial repolarization characterized by a prolonged QT interval on the electrocardiogram (ECG) (waveform 1). It usually results from drug therapy, hypokalemia, and/or hypomagnesemia (table 1). (See "Acquired long QT syndrome: Definitions, pathophysiology, and causes", section on 'Definitions'.)

●Clinical presentation – The clinical presentation of acquired LQTS is variable; many patients are asymptomatic and identified solely by QT prolongation on the ECG, while a minority are symptomatic and present with presyncope, palpitations, syncope, and/or sudden cardiac arrest. (See 'Clinical presentation' above.)

●Evaluation – The evaluation of all patients with suspected acquired LQTS includes a 12-lead ECG, a thorough history, and laboratory testing. (See 'Evaluation' above.)

The history should include medications, recent medications changes, kidney or liver dysfunction symptoms, family history, and bloodwork (See 'History' above and 'Laboratory tests' above.)

●Diagnosis – The diagnosis of acquired LQTS can be made in a patient with sufficient QT prolongation on the surface ECG in association with a medication or other clinical scenario (ie, hypokalemia or hypomagnesemia). In general, the cutpoints for abnormal QTc are the 99th percentile QTc values (470 ms in postpubertal males and 480 ms in postpubertal females). (See 'Diagnosis' above.)

●Precautions when starting a QT-prolonging medication – It may be necessary to obtain a baseline and follow-up QT interval. We educate the patient on potential symptoms and ask them to report the symptoms should they arise. (See 'Precautions for any patient starting QT-prolonging drugs' above.)

●Management of patients without active torsades de pointes (TdP)

•Asymptomatic patients – In such patients, we identify and treat any reversible underlying causes of long QT such as electrolyte disturbances and kidney or hepatic dysfunction. Any QT-prolonging medications should be stopped. (See 'Asymptomatic patients' above.)

•Palpitations – In such patients, the cause of palpitations should be quickly identified with careful history taking and Holter monitoring. If the patient is found to have TdP, management of this malignant arrythmia is discussed elsewhere. (See 'Patients with palpitations' above.)

•Syncope – If there is presyncope or syncope (without documented TdP) or ECG signs of instability (ventricular ectopy, T wave alternans, atrioventricular block, or QRS widening), the patient should be admitted for telemetry observation during withdrawal of the toxic agent (with immediate availability of an external defibrillator) and treatment of arrhythmias if indicated. (See 'Patients with presyncope or syncope' above.)

●Management of patients with acute TdP – The initial management of patients with TdP varies depending on the hemodynamic stability of the patient. Emergency management is required in unstable patients (algorithm 1), while additional time may be spent determining the etiology and treating any underlying precipitating factors in patients who are hemodynamically stable (algorithm 2). (See 'Patients with acute TdP' above.)

•Hemodynamically unstable patients – These patients are generally severely symptomatic or become pulseless. They require prompt emergency treatment (algorithm 1). Initial treatment with antiarrhythmic medications, with the exception of intravenous (IV) magnesium, is not indicated for hemodynamically unstable or pulseless patients. Subsequent therapy is similar to that of hemodynamically stable patients with TdP. (See 'Unstable patients' above.)

•Hemodynamically stable patients – These patients may become unstable rapidly and without warning. As such, therapy should be promptly provided to most patients. Initial therapy for patients with a single episode of TdP is IV magnesium along with correction of metabolic/electrolyte derangements and/or removal of any inciting medications. For patients with subsequent, multiple, self-terminating episodes of TdP, we use the same therapies as for patients with a single episode, along with additional interventions to slow the heart rate. These include overdrive atrial pacing and/or IV isoproterenol infusion. (See 'Initial measures' above and 'Patients who do not respond to magnesium' above.)

●Long-term management – Patients with acquired LQTS should be educated about the culprit drugs, other QT-prolonging drugs (including being provided with a list, available at www.crediblemeds.org/), and potential drug-drug interactions. (See 'Long-term management' above.)

ACKNOWLEDGMENT — The editorial staff at UpToDate acknowledge Stephen Seslar MD, PhD, and the late Mark E. Josephson, MD, who contributed to an earlier version of this topic review.