An Introduction to Long QT Syndrome

Long QT syndrome (LQTS) is the most common of the potentially lethal inherited arrhythmias causing sudden cardiac death in the younger population. While it can be detected on ECG, mandatory screening is not routinely performed, allowing congenital long QT syndrome to remain undiscovered in many children.¹

Pathophysiology of LQTS

LQTS is an inherited genetic disorder by which abnormal ion channels within the cellular structure of the myocardium produce electrical disruption within the myocardium’s conduction system.² Ions like potassium, sodium, calcium, and chloride move back and forth, crossing over cell membranes via these ion channels. During the movement of these ion channels, depolarization and repolarization occur, thereby producing the electrical activity within the myocardium. The electrical change produces myocardial contractions. The ECG is our objective observation of this electrical activity within the myocardium. 

Potassium, the most abundant intracellular cation, and sodium, the most abundant extracellular cation, are two of the ion channels affected in LQTS. The result of these ion channel abnormalities extends the repolarization phase along with the QT interval, placing patients at risk for certain arrhythmias. Basically, LQTS is a malfunction in the electrical phase of the reloading process of the myocardium.²

Evaluation of the QT Interval 

The prolonged repolarization phase of LQTS can be distinguished by measuring the QT interval. As represented on the ECG, the QT interval occurs from the start of ventricular depolarization to the end of repolarization.²

Prolongation of the QT interval subsequently produces the risk of potentially fatal lengthy ventricular dysrhythmias.³ The measurement should be taken from the beginning of the Q wave to end of the T wave. If there is no Q wave, the measurement will begin with the R wave. Use the lead that produces the longest QT interval on the 12-lead, as it has the highest sensitivity.⁴ 

Because heart rate can affect the QT interval—bradycardia lengthens it, tachycardia shortens it—it is recommended to calculate a rate-corrected QT interval, or QTc. There are several formulas for this. In boys a QTc greater than 450-460 milliseconds and in girls 460-470 milliseconds is a valuable measurement for the diagnosis of LQTS.² This exceedingly long repolarization phase is concerning because it will place the child at risk for polymorphic ventricular tachycardia, also known as torsades de pointes, and possible sudden cardiac death. 

LQTS is usually inherited due to a DNA abnormality in one of the child’s parents.² Congenital LQTS has been linked with children who are deaf. LQTS can also be acquired, resulting from the effects of medications.⁵ 

Assessment, Treatment, and Transport

Assessment and history-taking of the child are important when evaluating for possible LQTS. Syncope, near syncope, seizures, palpitations and orthostatic vital sign changes are among the objective presentations prolonged QT syndrome can produce. The syncopal episodes that occur with LQTS usually happen without preceding signs. They generally occur during or after active play, expressing enthusiasm, or acute sounds that produce arousal.² 

Obtain a thorough history on your pediatric patient prior to administering any medication that may further prolong their QT interval. For instance, the child may be taking medications for depression or antibiotics. If the child is taking beta blockers, the preventive treatment for LQTS, it’s a red flag.² Parents and guardians of LQTS children should ensure the children receive their daily medication—the primary reason for a cardiac event while undergoing pharmacological treatment is either missing a dose or discontinuing a medication.² Prehospital providers should be aware of these prescriptions prior to transport and realize they may impact medications administered during transport.

Note that 11% of Americans age 12 and above are taking some form of antidepressant. If the child has depression and is taking citalopram (Celexa), a dose of 20 mg can prolong the QT interval up to 8.5 milliseconds.⁶ Escitalopram (Lexapro) is a selective serotonin reuptake inhibitor also known to prolong the QT interval. If the patient is taking a dose of 10 mg, this will prolong the QT interval by 4.5 milliseconds, and a dose of 20 mg will prolong it by 6.6.³ 

Azithromycin, a medication used to treat a variety of bacterial infections, is frequently used to treat pediatric patients and another medication known to prolong the QT interval.⁷ 

During transport of a pediatric patient, complaints of nausea or active emesis are common. Most EMS crews carry the antiemetic ondansetron hydrochloride (Zofran). Administration at a dose of 8 mg can prolong the QT interval up to 6 milliseconds.⁸ 

Should a child be in a tachyarrhythmia requiring pharmacological intervention, protocols allow for treatment with antiarrhythmics; however, poor selection can result in patient decline. Amiodarone, an antiarrhythmic used to treat pediatric patients, produces QT prolongation. Avoid it due to the risk of potentially producing an R-on-T phenomenon or prolonging the QT interval to the point of producing polymorphic ventricular tachycardia.⁹ 

When your pediatric patient with LQTS presents with an unstable tachyarrhythmia, recommended treatment may include beta blocker or sodium channel blocker therapy.³ Beta blocker therapy is the primary pharmacological treatment in certain types of LQTS, but not all beta blockers are effective or used in every patient, as they have different mechanisms of action. Certain beta-adrenergic receptor blockers may be indicated for treatment of LQTS types 1 and 2 (see sidebar), whereas sodium channel blocker therapy may be utilized in type 3.¹⁰ 

Prior to the administration of any medication to a stable child with suspected LQTS, the provider can always contact a physician who specializes in pediatrics at the receiving hospital. When a child presents with LQTS in transport, always have the ECG monitor on with limb leads and combo pads in place should the need arise for cardioversion, defibrillation, or pacing. Treat the unstable child following PALS guidelines. 

Pacemakers and internal cardioverter/defibrillators, the long-term solution, are implanted in children to control their heart rhythms. The growing child may have issues with outgrowing their device and need replacement.¹⁰ This could be an indirect reason for calling EMS. 

Summary

In conclusion, LQTS, though detectable through noninvasive ECG assessment, often remains undiagnosed in children until a potentially tragic event occurs. EMS providers must maintain keen skills in pediatric resuscitation to provide necessary treatment. For children previously diagnosed, thorough assessment, complete medical history, and understanding the pathophysiology of LQTS remain invaluable.  

Sidebar: Types of LQTS

Most people with long QT syndrome have the inherited form. Of the known types of inherited LQTS, the most common are types 1, 2, and 3.

With Type 1, the heart’s potassium ion channels don’t function properly, disrupting the heart’s electrical activity. Emotional stress or physical exercise, particularly swimming, can trigger arrhythmias. Torsades de pointes occurs more often in people with LQT1.

Type 2 results from insufficient potassium ion activity in the heart. This prevents proper electrical function and leads to arrhythmia. Emotional stress and surprise can cause arrhythmias; a common trigger is sudden loud noises.

Type 3 occurs when too little sodium flows through the heart’s ion channels. This can trigger an arrhythmia. People with LQT3 often develop arrhythmias during sleep or rest due to their slow heart rate. 

—Source: Stanford Healthcare

References

1. Rodday AM, Triedman JK, Alexander ME, at al. Electrocardiogram Screening for Disorders That Cause Sudden Cardiac Death in Asymptomatic Children: A Meta-Analysis. Pediatrics, 2012 Apr; 129(4): e999–1,010.

2. SADS Foundation. Long QT Syndrome, www.sads.org/Library/Long-QT-Syndrome#.XuEyBUVKg2w. 

3. Thome J. Congenital and Acquired Long QT Syndrome: A Pharmacist’s Perspective. U.S. Pharmacist, 2014 May 16; www.uspharmacist.com/article/congenital-and-acquired-long-qt-syndrome-a-pharmacists-perspective. 

4. Lux RL, Sower CT, Allen N, et al. The application of root mean square electrocardiography (RMS ECG) for the detection of acquired and congenital long QT syndrome. PLoS One, 2014 Jan 15; 9(1): e85689. 

5. Van Noord C, Eijgelsheim M, Stricker BHC. Drug- and non-drug-associated QT interval prolongation. Br J Clin Pharmacol, 2010 Jul; 70(1): 16–23. 

6. U.S. Food & Drug Administration. FDA Drug Safety Communication: Revised recommendations for Celexa (citalopram hydrobromide) related to a potential risk of abnormal heart rhythms with high doses, www.fda.gov/drugs/drug-safety-and-availability/fda-drug-safety-communication-revised-recommendations-celexa-citalopram-hydrobromide-related. 

7. U.S. Food & Drug Administration. FDA Drug Safety Communication: Azithromycin (Zithromax or Zmax) and the risk of potentially fatal heart rhythms, www.fda.gov/drugs/drug-safety-and-availability/fda-drug-safety-communication-azithromycin-zithromax-or-zmax-and-risk-potentially-fatal-heart. 

8. U.S. Food & Drug Administration. FDA Drug Safety Communication: New information regarding QT prolongation with ondansetron (Zofran), www.fda.gov/drugs/drug-safety-and-availability/fda-drug-safety-communication-new-information-regarding-qt-prolongation-ondansetron-zofran. 

9. Hamilton D, Nandkeolyar S, Lan S, et al. Amiodarone: A Comprehensive Guide for Clinicians. Am J Cardiovasc Drugs, 2020 Mar 13 [epub ahead of print]. 

10. National Heart, Lung, and Blood Institute. Long QT Syndrome, https://www.nhlbi.nih.gov/health-topics/long-qt-syndrome. 

Roger L. Layell, FP-C, CCP-C, CCEMT-P, NRP,  is a flight and critical care paramedic at Wake Forest Baptist Health AirCare in Winston-Salem, N.C. He has 15 years of experience in the field as a paramedic and 10 of critical care experience in the HEMS environment.  

Kory A. Lane, MEd, NRP, CCEMT-P, NCEE,  is a doctoral candidate at North Carolina State University and a paramedic at Cone Health CareLink Mobile Critical Care in Greensboro, N.C. He has over 20 years of experience in EMS and teaches extensively for PreMed Training Group.