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.) https://www.uptodate.com/contents/acquired-long-qt-syndrome-clinical-manifestations-diagnosis-and-management/print 13/33 7/6/23, 11:05 AM Acquired long QT syndrome: Clinical manifestations, diagnosis, and management - UpToDate 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. Use of UpToDate is subject to the Terms of Use. REFERENCES 1. Drew BJ, Ackerman MJ, Funk M, et al. Prevention of torsade de pointes in hospital settings: a scientific statement from the American Heart Association and the American College of https://www.uptodate.com/contents/acquired-long-qt-syndrome-clinical-manifestations-diagnosis-and-management/print 14/33 7/6/23, 11:05 AM Acquired long QT syndrome: Clinical manifestations, diagnosis, and management - UpToDate Cardiology Foundation. Circulation 2010; 121:1047. 2. Passman R, Kadish A. Polymorphic ventricular tachycardia, long Q-T syndrome, and torsades de pointes. Med Clin North Am 2001; 85:321. 3. Khan IA. Long QT syndrome: diagnosis and management. Am Heart J 2002; 143:7. 4. Kannan L, Kotus-Bart J, Amanullah A. Prevalence of Cardiac Arrhythmias in Hypothyroid and Euthyroid Patients. Horm Metab Res 2017; 49:430. 5. Al-Khatib SM, Stevenson WG, Ackerman MJ, et al. 2017 AHA/ACC/HRS Guideline for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society. J Am Coll Cardiol 2018; 72:e91. 6. Roden DM. Taking the "idio" out of "idiosyncratic": predicting torsades de pointes. Pacing Clin Electrophysiol 1998; 21:1029. 7. Kupershmidt S, Yang IC, Hayashi K, et al. The IKr drug response is modulated by KCR1 in transfected cardiac and noncardiac cell lines. FASEB J 2003; 17:2263. 8. Yang T, Roden DM. Extracellular potassium modulation of drug block of IKr. Implications for torsade de pointes and reverse use-dependence. Circulation 1996; 93:407. 9. Ridley JM, Milnes JT, Benest AV, et al. Characterisation of recombinant HERG K+ channel blockade by the Class Ia antiarrhythmic drug procainamide. Biochem Biophys Res Commun 2003; 306:388. 10. Jurkiewicz NK, Sanguinetti MC. Rate-dependent prolongation of cardiac action potentials by a methanesulfonanilide class III antiarrhythmic agent. Specific block of rapidly activating delayed rectifier K+ current by dofetilide. Circ Res 1993; 72:75. 11. Yang T, Snyders DJ, Roden DM. Ibutilide, a methanesulfonanilide antiarrhythmic, is a potent blocker of the rapidly activating delayed rectifier K+ current (IKr) in AT-1 cells. Concentration-, time-, voltage-, and use-dependent effects. Circulation 1995; 91:1799. 12. Numaguchi H, Mullins FM, Johnson JP Jr, et al. Probing the interaction between inactivation gating and Dd-sotalol block of HERG. Circ Res 2000; 87:1012. 13. Kamiya K, Nishiyama A, Yasui K, et al. Short- and long-term effects of amiodarone on the two components of cardiac delayed rectifier K(+) current. Circulation 2001; 103:1317. 14. Daleau P, Lessard E, Groleau MF, Turgeon J. Erythromycin blocks the rapid component of the delayed rectifier potassium current and lengthens repolarization of guinea pig ventricular myocytes. Circulation 1995; 91:3010. https://www.uptodate.com/contents/acquired-long-qt-syndrome-clinical-manifestations-diagnosis-and-management/print 15/33 7/6/23, 11:05 AM Acquired long QT syndrome: Clinical manifestations, diagnosis, and management - UpToDate 15. Volberg WA, Koci BJ, Su W, et al. Blockade of human cardiac potassium channel human ether-a-go-go-related gene (HERG) by macrolide antibiotics. J Pharmacol Exp Ther 2002; 302:320. 16. Roy M, Dumaine R, Brown AM. HERG, a primary human ventricular target of the nonsedating antihistamine terfenadine. Circulation 1996; 94:817. 17. Suessbrich H, Waldegger S, Lang F, Busch AE. Blockade of HERG channels expressed in Xenopus oocytes by the histamine receptor antagonists terfenadine and astemizole. FEBS Lett 1996; 385:77. 18. Drolet B, Khalifa M, Daleau P, et al. Block of the rapid component of the delayed rectifier potassium current by the prokinetic agent cisapride underlies drug-related lengthening of the QT interval. Circulation 1998; 97:204. 19. Dumaine R, Roy ML, Brown AM. Blockade of HERG and Kv1.5 by ketoconazole. J Pharmacol Exp Ther 1998; 286:727. 20. Tzivoni D, Banai S, Schuger C, et al. Treatment of torsade de pointes with magnesium sulfate. Circulation 1988; 77:392. 21. Neumar RW, Otto CW, Link MS, et al. Part 8: adult advanced cardiovascular life support: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation 2010; 122:S729. 22. DiSegni E, Klein HO, David D, et al. Overdrive pacing in quinidine syncope and other long QT-interval syndromes. Arch Intern Med 1980; 140:1036. 23. T tterman KJ, Turto H, Pellinen T. Overdrive pacing as treatment of sotalol-induced ventricular tachyarrhythmias (torsade de pointes). Acta Med Scand Suppl 1982; 668:28. 24. Keren A, Tzivoni D, Gavish D, et al. Etiology, warning signs and therapy of torsade de pointes. A study of 10 patients. Circulation 1981; 64:1167. 25. WASSERMAN F, BRODSKY L, KATHE JH, et al. The effect of molar sodium lactate in quinidine intoxication. Am J Cardiol 1959; 3:294. 26. Choy AM, Lang CC, Chomsky DM, et al. Normalization of acquired QT prolongation in humans by intravenous potassium. Circulation 1997; 96:2149. 27. Roden DM, Woosley RL, Primm RK. Incidence and clinical features of the quinidine- associated long QT syndrome: implications for patient care. Am Heart J 1986; 111:1088. 28. Assimes TL, Malcolm I. Torsade de pointes with sotalol overdose treated successfully with lidocaine. Can J Cardiol 1998; 14:753. 29. Takahashi N, Ito M, Inoue T, et al. Torsades de pointes associated with acquired long QT syndrome: observation of 7 cases. J Cardiol 1993; 23:99. https://www.uptodate.com/contents/acquired-long-qt-syndrome-clinical-manifestations-diagnosis-and-management/print 16/33 7/6/23, 11:05 AM Acquired long QT syndrome: Clinical manifestations, diagnosis, and management - UpToDate 30. Raehl CL, Patel AK, LeRoy M. Drug-induced torsade de pointes. Clin Pharm 1985; 4:675. 31. Vukmir RB, Stein KL. Torsades de pointes therapy with phenytoin. Ann Emerg Med 1991; 20:198. 32. Mantri N, Lu M, Zaroff JG, et al. Torsade de pointes: A nested case-control study in an integrated healthcare delivery system. Ann Noninvasive Electrocardiol 2022; 27:e12888. 33. Roden DM. Drug-induced prolongation of the QT interval. N Engl J Med 2004; 350:1013. 34. Gallo T, Heise CW, Woosley RL, et al. Clinician Responses to a Clinical Decision Support Advisory for High Risk of Torsades de Pointes. J Am Heart Assoc 2022; 11:e024338. 35. Tisdale JE, Jaynes HA, Kingery JR, et al. Development and validation of a risk score to predict QT interval prolongation in hospitalized patients. Circ Cardiovasc Qual Outcomes 2013; 6:479. Topic 116011 Version 26.0 https://www.uptodate.com/contents/acquired-long-qt-syndrome-clinical-manifestations-diagnosis-and-management/print 17/33 7/6/23, 11:05 AM Acquired long QT syndrome: Clinical manifestations, diagnosis, and management - UpToDate GRAPHICS Single-lead electrocardiogram showing a prolonged QT interval The corrected QT interval (QTc) is calculated by dividing the QT interval (0.60 seconds) by the square root of the preceding RR interval (0.92 seconds). In this case, the QTc is 0.625 seconds (625 milliseconds). Graphic 77018 Version 7.0 https://www.uptodate.com/contents/acquired-long-qt-syndrome-clinical-manifestations-diagnosis-and-management/print 18/33 7/6/23, 11:05 AM Acquired long QT syndrome: Clinical manifestations, diagnosis, and management - UpToDate Single lead electrocardiogram (ECG) showing polymorphic ventricular tachycardia (VT) This is an atypical, rapid, and bizarre form of ventricular tachycardia that is characterized by a continuously changing axis of polymorphic QRS morphologies. Graphic 53891 Version 5.0 https://www.uptodate.com/contents/acquired-long-qt-syndrome-clinical-manifestations-diagnosis-and-management/print 19/33 7/6/23, 11:05 AM Acquired long QT syndrome: Clinical manifestations, diagnosis, and management - UpToDate Single lead electrocardiogram (ECG) showing torsades de pointes The electrocardiographic rhythm strip shows torsades de pointes, a polymorphic ventricular tachycardia associated with QT prolongation. There is a short, preinitiating RR interval due to a ventricular couplet, which is followed by a long, initiating cycle resulting from the compensatory pause after the couplet. Graphic 73827 Version 4.0 https://www.uptodate.com/contents/acquired-long-qt-syndrome-clinical-manifestations-diagnosis-and-management/print 20/33 7/6/23, 11:05 AM Acquired long QT syndrome: Clinical manifestations, diagnosis, and management - UpToDate Some reported causes and potentiators of the long QT syndrome Congenital Jervell and Lange-Nielsen syndrome (including "channelopathies") Romano-Ward syndrome Idiopathic Acquired Metabolic disorders Other factors Androgen deprivation therapy Hypokalemia Myocardial GnRH agonist/antagonist therapy ischemia or infarction, Hypomagnesemia Bilateral surgical orchiectomy Hypocalcemia Diuretic therapy via electrolyte disorders especially with Starvation particularly hypokalemia and hypomagnesemia prominent T-wave inversions Anorexia nervosa Herbs Liquid protein diets Cinchona (contains quinine), iboga (ibogaine), licorice extract in overuse via electrolyte disturbances Intracranial disease Hypothyroidism Bradyarrhythmias HIV infection Sinus node dysfunction Hypothermia Toxic exposure: Organophosphate insecticides AV block: Second or third degree Medications* High risk Adagrasib Cisaparide Lenvatinib Selpercatinib (restricted availability) Ajmaline Levoketoconazole Sertindole Amiodarone Methadone Sotalol Delamanid Arsenic trioxide Mobocertinib Terfenadine Disopyramide Astemizole Papavirine Vandetanib Dofetilide (intracoronary) Bedaquline Vernakalant Dronedarone Procainamide Bepridil Ziprasidone Haloperidol (IV) Quinidine Chlorpromazine Ibutilide Quinine Ivosidenib Moderate risk Amisulpride (oral) Droperidol Inotuzumab ozogamacin Propafenone Azithromycin Encorafenib Propofol Isoflurane Capecitabine Entrectinib Quetiapine Carbetocin Erythromycin Ribociclib https://www.uptodate.com/contents/acquired-long-qt-syndrome-clinical-manifestations-diagnosis-and-management/print 21/33 7/6/23, 11:05 AM Acquired long QT syndrome: Clinical manifestations, diagnosis, and management - UpToDate Certinib Escitalopram Levofloxacin Risperidone (systemic) Chloroquine Etelcalcetide Saquinavir Lofexidine Citalopram Fexinidazole Sevoflurane Meglumine Clarithromycin Flecainide Sparfloxacin antimoniate Clofazimine Floxuridine Sunitinib Midostaurin Clomipramine Fluconazole Tegafur Moxifloxacin Clozapine Fluorouracil Terbutaline Nilotinib (systemic) Crizotinib Thioridazine Olanzapine Flupentixol Dabrafenib Toremifene Ondansetrol (IV > Gabobenate dimeglumine Dasatinib Vemurafenib oral) Deslurane Voriconazole Osimertinib Gemifloxacin Domperidone Oxytocin Gilteritinib Doxepin Pazopanib Halofantrine Doxifluridine Pentamidine Haloperidol (oral) Pilsicainide Imipramine Pimozide Piperaquine Probucol Low risk Albuterol Fingolimod Mequitazine Ranolazine (due to bradycardia) Alfuzosin Fluoxetine Methotrimeprazine Relugolix Amisulpride (IV) Fluphenazine Metoclopramide (rare reports) Rilpivirine Amitriptyline Formoterol Metronidazole (systemic) Romidepsin Anagrelide Foscarnet Roxithromycin Apomorphine Fostemsavir Mifepristone Salmeterol Arformoterol Gadofosveset Mirtazapine Sertraline Artemether- Glasdegib Mizolastine lumefantrine Siponimod Goserelin Nelfinavir Asenapine Solifenacin Granisetron Norfloxacin Atomoxetine Sorafenib Hydroxychloroquine Nortriptyline Benperidol (rare reports) Sulpiride Ofloxacin (systemic) Bilastine Hydroxyzine Tacrolimus Olodaterol (systemic) Bosutinib Iloperidone Osilodrostat Tamoxifen Bromperidol Indacaterol Oxaliplatin Telavancin Buprenorphine Itraconazole Ozanimod Telithromycin Buserelin Ketoconazole (systemic) Pacritinib Teneligliptin Ciprofloxacin (Systemic) Lacidipine Paliperidone Tetrabenazine Cocaine (Topical) Lapatinib Panobinostat Trazodone Degarelix Lefamulin Pasireotide Triclabendazole https://www.uptodate.com/contents/acquired-long-qt-syndrome-clinical-manifestations-diagnosis-and-management/print 22/33 7/6/23, 11:05 AM Acquired long QT syndrome: Clinical manifestations, diagnosis, and management - UpToDate Desipramine Leuprolide Pefloxacin Triptorelin Deutetrabenazine Leuprolide- Periciazine Tropisetron norethindrone Dexmedetomidine** Pimavanserin Vardenafil Levalbuterol Dolasetron Pipamperone Vilanterol Levomethadone Donepezil Pitolisant Vinflunine Lithium Efavirenz Ponesimod Voclosporin Loperamide overdose in Eliglustat Primaquine Vorinostat Eribulin Promazine Zuclopenthixol Lopinavir Ezogabine Radotinib Macimorelin Mefloquine This is not a complete list of all corrected QT interval (QTc)-prolonging drugs and does not include drugs with either a minor degree or isolated association(s) with QTc prolongation that appear to be safe in most patients but may need to be avoided in patients with congenital long QT syndrome depending upon clinical circumstances. A more complete list of such drugs is available at the CredibleMeds website. For clinical use and precautions related to medications and drug interactions, refer to the UpToDate topic review of acquired long QT syndrome discussion of medications and the Lexicomp drug interactions tool. AV: atrioventricular; IV: intravenous; QTc: rate-corrected QT interval on the electrocardiogram. Classifications provided by Lexicomp according to US Food & Drug Administration guidance: Clinical Evaluation of QT/QTc Interval Prolongation and Proarrhythic Potential for Non-Antiarrhythmic Drugs Questions and Answers; Guidance for Industry US Food and Drug Administration, June 2017 (revision 2) available at: https://www.fda.gov/downloads/Drugs/GuidanceComplianceRegulatoryInformation/Guidances/UCM 073161.pdf with additional data from CredibleMeds QT drugs list criteria may lead to some agents being classified differently by other sources. [1,2] . The use of other classification Not available in the United States. In contrast with other class III antiarrhythmic drugs, amiodarone is rarely associated with torsades de pointes; refer to accompanying text within UpToDate topic reviews of acquired long QT syndrome. Withdrawn from market in most countries due to adverse cardiovascular effects. IV amisulpride antiemetic use is associated with less QTc prolongation than the higher doses administered orally as an antipsychotic. Other cyclic antidepressants may also prolong the QT interval; refer to UpToDate clinical topic on cyclic antidepressant pharmacology, side effects, and separate UpToDate topic on tricyclic antidepressant poisoning. The "low risk" category includes drugs with limited evidence of clinically significant QTc prolongation or TdP risk; many of these drugs have label warnings regarding possible QTc effects or recommendations to avoid use or increase ECG monitoring when combined with other QTc prolonging drugs. https://www.uptodate.com/contents/acquired-long-qt-syndrome-clinical-manifestations-diagnosis-and-management/print 23/33 7/6/23, 11:05 AM Acquired long QT syndrome: Clinical manifestations, diagnosis, and management - UpToDate Rarely associated with significant QTc prolongation at usual doses for treatment of opioid use disorder, making buprenorphine a suitable alternative for patients with methadone-associated QTc prolongation. Refer to UpToDate clinical topic reviews. * The United States FDA labeling for the sublingual preparation of dexmedetomidine warns against use in patients at elevated risk for QTc prolongation. Both intravenous (ie, sedative) and sublingual formulations of dexmedetomidine have a low risk of QTc prolongation and have not been implicated in TdP. Over-the-counter; available without a prescription. Not associated with significant QTc prolongation in healthy persons. Refer to UpToDate clinical topic for potential adverse cardiovascular (CV) effects in patients with CV disease. Data from: 1. Lexicomp Online. Copyright 1978-2023 Lexicomp, Inc. All Rights Reserved. 2. CredibleMeds QT drugs list website sponsored by Science Foundation of the University of Arizona. Available at http://crediblemeds.org/. Graphic 57431 Version 142.0 https://www.uptodate.com/contents/acquired-long-qt-syndrome-clinical-manifestations-diagnosis-and-management/print 24/33 7/6/23, 11:05 AM Acquired long QT syndrome: Clinical manifestations, diagnosis, and management - UpToDate Treatment of torsades de pointes due to long QT syndrome Acquired LQTS Pharmacologic Magnesium sulfate Isoproterenol Lidocaine Phenytoin Sodium bicarbonate (for quinidine-related arrhythmia) Nonpharmacologic Temporary pacing (atrial or ventricular) Congenital LQTS Pharmacologic Beta blockers Mexiletine Nonpharmacologic Permanent dual chamber pacemaker Left cardiac sympathetic denervation (cardiothoracic sympathectomy) Implantable cardioverter-defibrillator Graphic 70083 Version 1.0 https://www.uptodate.com/contents/acquired-long-qt-syndrome-clinical-manifestations-diagnosis-and-management/print 25/33 7/6/23, 11:05 AM Acquired long QT syndrome: Clinical manifestations, diagnosis, and management - UpToDate Triggers for cardiac events in long QT syndrome are related to genotype In a study of 670 patients with long QT syndrome and known genotype, all symptomatic (syncope, aborted cardiac arrest, or sudden death), the occurrence of a lethal cardiac event (n = 110) provoked by a specific trigger (exercise, emotion, and sleep/rest without arousal) differed according to genotype. LQT1 patients experienced most of their events (90%) during exercise or emotion. These percentages were almost reversed among LQT2 and LQT3 patients who had most of their events during rest or sleep (63 and 80%, respectively); by contrast, they were at almost no risk of major events during exercise (arrows), which is explained by their having a normal I current. Ks ACA: aborted cardiac arrest; SCD: sudden cardiac death. Modi ed from: Schwartz PJ, Priori SG, Spazzolini C, et al. Genotype-phenotype correlation in the long-QT syndrome: gene-speci c triggers for life-threatening arrhythmias. Circulation 2001; 103:89. Graphic 64239 Version 3.0 https://www.uptodate.com/contents/acquired-long-qt-syndrome-clinical-manifestations-diagnosis-and-management/print 26/33 7/6/23, 11:05 AM Acquired long QT syndrome: Clinical manifestations, diagnosis, and management - UpToDate Adult cardiac arrest algorithm https://www.uptodate.com/contents/acquired-long-qt-syndrome-clinical-manifestations-diagnosis-and-management/print 27/33 7/6/23, 11:05 AM Acquired long QT syndrome: Clinical manifestations, diagnosis, and management - UpToDate https://www.uptodate.com/contents/acquired-long-qt-syndrome-clinical-manifestations-diagnosis-and-management/print 28/33 7/6/23, 11:05 AM Acquired long QT syndrome: Clinical manifestations, diagnosis, and management - UpToDate Reprinted with permission. Highlights of the 2020 American Heart Association Guidelines for CPR and ECC. Copyright 2020 American Association, Inc. Graphic 129983 Version 9.0 https://www.uptodate.com/contents/acquired-long-qt-syndrome-clinical-manifestations-diagnosis-and-management/print 29/33 7/6/23, 11:05 AM Acquired long QT syndrome: Clinical manifestations, diagnosis, and management - UpToDate Acute management of torsades de pointes All patients with TdP should be treated with IV magnesium. TdP: torsades de pointes; IV: intravenous; ACLS: Advanced Cardiac Life Support; ECG: electrocardiogram. Refer to UpToDate content on ACLS in adults. Optimal timing of magnesium administration relative to cardioversion has not been determined. The rate o slower when the patient has a pulse, as rapid magnesium infusion can cause hypotension and asystole. https://www.uptodate.com/contents/acquired-long-qt-syndrome-clinical-manifestations-diagnosis-and-management/print 30/33 7/6/23, 11:05 AM Acquired long QT syndrome: Clinical manifestations, diagnosis, and management - UpToDate Tests include basic metabolic panel (eg, serum electrolytes, potassium, and magnesium) with liver and kidn drug or medication misuse is suspected, toxicology testing can be obtained. Reduce the rate and watch for any recurrent TdP. Discontinue the pacing wire if there is no recurrent TdP (u Refer to UpToDate content for further information. The initial dose of isoproterenol in adults is 2 mcg/min and in children is 0.05 to 0.1 mcg/kg/min (maximum the dose is then titrated to achieve a heart rate of 100 beats per minute. Especially if TdP is secondary to quinidine. Graphic 140279 Version 2.0 https://www.uptodate.com/contents/acquired-long-qt-syndrome-clinical-manifestations-diagnosis-and-management/print 31/33 7/6/23, 11:05 AM Acquired long QT syndrome: Clinical manifestations, diagnosis, and management - UpToDate ACC/AHA/HRS guideline summary: Indications for pacing to prevent tachycardia Class I - There is evidence and/or general agreement that pacing should be used to prevent tachycardia in the following setting: Sustained pause-dependent ventricular tachycardia (VT), with or without QT prolongation. (Level of Evidence: C) Class IIa - The weight of evidence or opinion is in favor of the usefulness of pacing to prevent tachycardia in the following setting: High-risk patients with congenital long QT syndrome. (Level of Evidence: C) Class IIb - The weight of evidence or opinion is less well established for the usefulness of pacing to prevent tachycardia in the following setting: Prevention of symptomatic, drug-refractory, recurrent atrial fibrillation in patients with coexisting sinus node dysfunction. (Level of Evidence: B) Class III - There is evidence and/or general agreement that pacing to prevent tachycardia is not useful in the following settings: Frequent or complex ventricular ectopic activity without sustained VT in the absence of the long QT syndrome. (Level of Evidence: C) Torsade de pointes VT due to reversible causes. (Level of Evidence: A) Adapted from Epstein AE, DiMarco JP, Ellenbogen KA, et al. ACC/AHA/HRS 2008 Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the ACC/AHA/NASPE 2002 Guideline Update for Implantation of Cardiac Pacemakers and Antiarrhythmia Devices): developed in collaboration with the American Association for Thoracic Surgery and Society of Thoracic Surgeons. Circulation 2008; 117:e350. Graphic 80487 Version 2.0 https://www.uptodate.com/contents/acquired-long-qt-syndrome-clinical-manifestations-diagnosis-and-management/print 32/33 7/6/23, 11:05 AM Acquired long QT syndrome: Clinical manifestations, diagnosis, and management - UpToDate Contributor Disclosures Charles I Berul, MD Patent Holder: PeriCor LLC [Pacemakers/defibrillators]. Grant/Research/Clinical Trial Support: Medtronic Inc [Pacemakers/defibrillators]. All of the relevant financial relationships listed have been mitigated. Samuel Asirvatham, MD Grant/Research/Clinical Trial Support: Medtronic [Defibrillators]; St Jude's [Sudden Cardiac Death]. Consultant/Advisory Boards: BioTronik [Defibrillators]; Boston Scientific [Sudden Cardiac Death]. All of the relevant financial relationships listed have been mitigated. Nisha Parikh, MD, MPH No relevant financial relationship(s) with ineligible companies to disclose. Contributor disclosures are reviewed for conflicts of interest by the editorial group. When found, these are addressed by vetting through a multi-level review process, and through requirements for references to be provided to support the content. Appropriately referenced content is required of all authors and must conform to UpToDate standards of evidence. Conflict of interest policy https://www.uptodate.com/contents/acquired-long-qt-syndrome-clinical-manifestations-diagnosis-and-management/print 33/33