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Long QT Syndrome


Presentation

The majority of patients that have a LQTS may not present with any signs and symptoms. These cases are incidentally discovered during routine electrocardiogram. Patients who are symptomatic of LQTS may commonly present with the following signs and symptoms:

  • Fainting: This is the most common of symptomatology associated with LQTS. Fainting spells or syncope happens when the heart temporarily beats erratically which are often times triggered by severe emotional or physical stress.
  • Seizure: This is a result of the inadequate blood supply to the brain from an incompetently beating heart. 
  • Sudden death: LQTS patients may progress to dysrhythmia which may succumb to sudden death if no electric defibrillation is done soon.
Agonal Respiration
  • We encountered a 15-year-old female student with LQTs who had prolonged QTc and multiple episodes of syncope or agonal respiration during sleep.[ncbi.nlm.nih.gov]
Respiratory Insufficiency
  • Mutations in BAG3 and aberrations in its expression cause fulminant myopathies, presenting with progressive limb and axial muscle weakness, and respiratory insufficiency and neuropathy.[ncbi.nlm.nih.gov]
Tachycardia
  • KEYWORDS: head-up tilt testing; long QT syndrome; loss of consciousness; postural orthostatic tachycardia syndrome; vasovagal syncope[ncbi.nlm.nih.gov]
  • The patient received an implantable cardioverter-defibrillator due to polymorphic ventricular tachycardia under beta-blocker therapy.[ncbi.nlm.nih.gov]
  • One was on amiodarone for suspected supraventricular tachycardia and hydrops. Five had serial fMCGs.[ncbi.nlm.nih.gov]
  • Polymorphic ventricular extrasystolies and episodes of polymorphic non‐sustained ventricular tachycardia were confirmed by Holter ECG monitoring.[oadoi.org]
Heart Disease
  • Patreon Help with Search Health Conditions and Diseases Cardiovascular Disorders Heart Disease Arrhythmia Long QT Syndrome 0 Long QT syndrome is a cardiac ion channel disease that predisposes its carriers to lethal ventricular arrhythmias.[curlie.org]
  • As inherited congenital heart disease may be a risk factor for sudden unexpected death in epilepsy (SUDEP), attention to all specific genetic markers in a young patient with QT prolongation and a first seizure could guide the use of anti-seizure medication[ncbi.nlm.nih.gov]
  • There have been sporadic reports of LQTS coexisting with more common forms of congenital heart disease (CHD).[ncbi.nlm.nih.gov]
  • disease MANAGEMENT beta-blockade avoidance of increased sympathetic tone cardiac pacing treat cause ICD About Dr Chris Nickson An oslerphile emergency physician and intensivist suffering from a bad case of knowledge dipsosis.[lifeinthefastlane.com]
  • An additional 16 carriers were identified, including 2 with structural heart disease: one with cardiomyopathy resulting in sudden death and the other with congenital heart disease. For all carriers of this variant, the average QTc was 475 ms ( 40).[ncbi.nlm.nih.gov]
Myopathy
  • Herein, we report a sporadic case of a 15-years old girl with symptoms of myopathy, demyelinating polyneuropathy and asymptomatic long QT syndrome.[ncbi.nlm.nih.gov]

Workup

The following test and diagnostic modalities are implored among patients with high suspicion of Long QT syndrome:

  • Electrocardiogram (ECG): This test may be taken at rest or during a treadmill stress test. ECG may be taken while standing to increase sympathetic tone where QT interval prolongation is usually observable [5]. A positive standing test may continually show a prolonged QT after resting and even when the heart returns to normal rate [6]. 
  • Ambulatory ECG monitoring: This test is also called Holter monitoring which is a portable device attached to the patient to monitor heart rhythm within an extended period of up to 24 hours. Prolonged QT intervals may then be spotted by the attending cardiologist during the whole day stretch of cardiac monitoring.
  • Event ECG monitoring: This is similar to the Holter monitor which may be used in a period of days and weeks. An access button may be provided for the patient to activate in case of any cardiac event to record the actual rhythm real-time for analysis. 
  • A diagnostic criteria for the identification of risk for LQTS was developed which includes parameters like QT interval, presence of torsade de pointe and familial history of LQTS [7].
Prolonged QT Interval
  • […] is characterized by episodes of fainting (syncope) and varying degree of ventricular arrhythmia as indicated by the prolonged qt interval.[icd9data.com]
  • A prolonged QT interval in the surface electrocardiogram is the sine qua non of the LQTS and is a surrogate measure of the ventricular action potential duration (APD).[ncbi.nlm.nih.gov]
  • (ECG): To confirm prolonged QT intervals Stress test with ECG: To provide better resolution of prolonged QT intervals during strenuous exercise Treatment of Long QT Syndrome LQTS Treatments for LQTS include: Lifestyle changes, such as reducing exercise[utswmedicine.org]
  • BACKGROUND: The congenital Long QT syndrome (LQTS) is a hereditary cardiac channelopathy that is characterized by a prolonged QT interval, syncope, ventricular arrhythmias, and sudden death.[ncbi.nlm.nih.gov]
  • Prolonged QT interval may be associated with torsades de pointes and lead to sudden cardiac death.[ncbi.nlm.nih.gov]
Torsades De Pointes
  • KEYWORDS: Digenic mutation; Epinephrine test; Long QT syndrome; Torsade de pointes[ncbi.nlm.nih.gov]
  • The prolongation of the q-t interval combined with torsades de pointes manifests as several different forms; some may be acquired or congenital; some may lead to serious arrhythmia and sudden cardiac death Prolongation of q-t interval combined with torsades[icd9data.com]
  • Prolonged QT interval may be associated with torsades de pointes and lead to sudden cardiac death.[ncbi.nlm.nih.gov]
  • Abstract Acquired long QT syndrome (LQTS) is a disorder of cardiac repolarization most often due to specific drugs, hypokalemia, or hypomagnesemia that may precipitate torsade de pointes and cause sudden cardiac death.[ncbi.nlm.nih.gov]
T Wave Alternans
  • We report a case with type 3 congenital long QT syndrome, who exhibited a sudden paradoxical QT-interval prolongation during a progressive increase in heart rate, which exacerbated T-wave alternans. 2014 Wiley Periodicals, Inc.[ncbi.nlm.nih.gov]
  • Macro T wave alternans was observed in 4 patients. The QT interval was not different in patients with VF( ) and VF(-) episodes, 633 60 and 639 57, respectively.[ncbi.nlm.nih.gov]
  • Catecholamine provoked microvoltage T wave alternans in genotyped long QT syndrome. Pacing & Clinical Electrophysiology. 2003;26(8):1660–7. Google Scholar 104. Nemec J, Hejlik JB, Shen WK, Ackerman MJ.[doi.org]
  • […] the ECG, syncope, and sudden death as a result of ventricular tachyarrhythmias. 1 2 3 4 Other repolarization abnormalities identified in the syndrome include increased QT-interval dispersion on the 12-lead ECG, 5 6 7 abnormal ST-T–wave morphology, 8 9 T-wave[doi.org]

Treatment

The main treatment options in LQTS are beta-blockers, permanent pacing, stellectomy, implantable cardioverter-defibrillator (ICD), or a combination [8]. The use of anti-arrhythmic drugs like beta-blockers [9] in combination with mexiletine slows down heart rate and reduces the risk of cardiac dysrhythmias. Patients who presents with recurrent syncope in the face of an LQTS may benefit from theophylline and hydralazine medications that may improve these signs of bradycardia.

A healthy diet rich in potassium and omega 3 fatty acids (fish oil) may stabilize abnormal cardiac rhythms in high risk individuals. Strenuous exercise should be avoided. 

Prognosis

The prognosis of LQTS with current treatment with the anti-arrhythmic medications like beta blockers is good. Episodes associated with torsade de pointes are usually self-limiting in patients with LQTS where only 4-5% may conclude with a fatal cardiac event.

Patients with recurrent bouts or episodes of aborted cardiac arrest and other cardiac events despite medications have a very high risk for sudden cardiac death. The total deaths in the US caused by LQTS reaches 4000 in number per year. The presence of neurologic deficits in aborted cardiac arrest after a successful resuscitation may further complicate the prognosis of long QT syndrome in patients.

Complications

Patients suffering from long QT intervals may progress to life threatening complications after an emotional induction. The more common LQTS complications are identified as follows:

  • Torsades de pointes: Otherwise referred to as the “twisting of the points”. This type of arrhythmia is caused by the rapid depolarization of the ventricles causing the electrocardiogram readings to appear twisted. The uncontrolled rapid contraction of the heart makes it an inefficient pump to supply the brain with adequate blood supply that may cause sudden fainting. 
  • Ventricular fibrillation: This condition can virtually complicate from torsade de pointes characterized as a rapid ventricular contraction that later leads to quivering of the heart muscles and is unable to pump out any blood. When ventricular fibrillation is not defibrillated soon enough, this may lead to brain death or eventual death if left unchecked. 

Etiology

The long QT syndrome is either inherited or acquired. There are at least two forms of inherited that has been identified so far:

  • Romano-Ward syndrome: This LQTS form is the more common genetic variant that occurs in people who inherit a single genomic variant from one of his parent.
  • Jervell and Lange-Nielsen syndrome: This LQTS is more severe and rare than the other variant. This variant is inherited from both parents and are usually eminent in children who are born deaf.

Majority of acquired LQTS is induced by the intake of certain medications that tend to prolong the QT intervals among patients. These medications include certain antibiotics, antidepressants, cholesterol-lowering agents, diuretics, antipsychotics, antifungal medications, antihistamine, oral hypoglycemic and some heart medications. Researchers have identified that people who suffer from drug induced LQTS are genetically predisposed or at risk of LQTS when exposed to certain drugs.

Epidemiology

In the United States, the incidence of long QT syndrome is estimated to reach a ratio of 1 case in 10,000 population. This incidence ratio and prevalence rate for LQTS are similar internationally. Female patients are more predisposed with a more than 2:1 ratio compared to the male counterpart. Although young men carries a higher mortality rate than women for LQTS.

Women during menopause are more predisposed to LQTS with cardiac events in up to 2 to 8 folds increase compared to female counterparts that are still in their reproductive years [1]. The more common cardiac events associated with LQTS in adolescents and adults includes syncope, aborted cardiac arrest, and sudden cardiac deaths.

Sex distribution
Age distribution

Pathophysiology

In patients with LQTS that is inherited, primary defects in the cardiac sodium, potassium and calcium channel are the common pathophysiologic defect seen. Ion channels may inherently be obstructed or may cause an opening delay causing an imbalance in the ionic gradients of the heart.

Channel protein defects in the caveolae have been recognized in the increased sodium flux type of LQTS found in LQTS3 genetic phenotype [2]. Functional studies have demonstrated that late sodium channel dysfunction associated with LQTS is implicated in sudden infant death syndrome (SIDS) among infants [3]. However, a gain in sodium channel conduction is demonstrated in LQTS associated with a genetic missense mutation with the alpha 1 synthropin gene [4].

External stimuli like loud noises, exercise, emotion and swimming may trigger an adrenergic response and elicit a long QT period in high risk patients.

Drug-induced LQTS are basically in direct relation to cardiac ion channels especially potassium that may be blocked by the therapeutic drug. Further genetic mutations may predispose patients to prolonged exposure to the drug due to its inherent poor metabolism and excretion.

Prevention

Patients who inherit LQTS from either parent should take extra precaution in taking medications that may trigger LQTS like common antibiotics like erythromycin. Illicit drug use with amphetamine and cocaine may increase the risk of LQTS and sudden cardiac deaths for those who have concurrent risk factors.

Medical conditions like vomiting and diarrhea that may potentially lower the serum levels of potassium should be averted to prevent the occurrence of LQTS in hypokalemic states. Patients with concurrent illness like hypertension may be prescribed with diuretics that can potentially lower potassium levels.

Genetic testing may predict the risk among the offspring of the defective gene carriers; thus genetic counselling is an effective modality in the prevention of LQTS [10].

Summary

Long QT syndrome or LQTS is a dysrhythmic heart disorder associated with fast and chaotic heartbeats. The intermittent occurrence of these dysrhythmias may cause syncope and seizure attacks in afflicted patients. An increased duration in the dysrhythmia can result to sudden death in some patients.

Long QT syndrome is treatable and preventable, the intake of certain anti-arrhythmic drugs may avert its dysrhythmic complications. LQTS may also be treated with cardiac surgery and may be controlled with the use of implantable devices.

Patient Information

Definition

Long QT syndrome (LQTS) is a dysrhythmic heart disorder associated with fast and chaotic heartbeats that may potentially cause sudden death.

Cause

LQTS is either inherited (genetics) or acquired. 

Symptoms

Symptoms inculde fainting, seizure or sudden death.

Diagnosis

Electrocardiography, Holter monitoring, and event ECG monitoring may be necessary to diagnose LQTS.

Treatment and follow-up

Pacemaker implantation, defibrillation, beta-blockers, vitamin D and omega 3 fatty acids are used to treat the disorder.

References

Article

  1. Buber J, Mathew J, Moss AJ, et al. Risk of Recurrent Cardiac Events After Onset of Menopause in Women With Congenital Long-QT Syndrome Types 1 and 2. Circulation. Jun 21 2011; 123(24):2784-91.
  2. Vatta M, Ackerman MJ, Ye B, Makielski JC, Ughanze EE, Taylor EW, et al. Mutant caveolin-3 induces persistent late sodium current and is associated with long-QT syndrome. Circulation. Nov 14 2006; 114(20):2104-12.
  3. Border WL, Benson DW. Sudden infant death syndrome and long QT syndrome: the zealots versus the naysayers. Heart Rhythm. Feb 2007; 4(2):167-9.
  4. Wu G, Ai T, Kim JJ, et al. Alpha-1-Syntrophin Mutation and the Long QT Syndrome: a disease of sodium channel disruption. Circulation. May 28, 2008.
  5. Viskin S, Postema PG, Bhuiyan ZA, Rosso R, Kalman JM, Vohra JK, et al. The Response of the QT Interval to the Brief Tachycardia Provoked by Standing A Bedside Test for Diagnosing Long QT Syndrome. J Am Coll Cardiol. Jan 22 2010.
  6. Adler A, van der Werf C, Postema PG, Rosso R, Bhuiyan ZA, Kalman JM, et al. The phenomenon of "QT stunning": The abnormal QT prolongation provoked by standing persists even as the heart rate returns to normal in patients with long QT syndrome. Heart Rhythm. Jun 2012; 9(6):901-8.
  7. Schwartz PJ, Moss AJ, Vincent GM. Diagnostic criteria for the long QT syndrome: an update. Circulation. 1993; 88:782-4.
  8. Zipes DP, Camm AJ, Borggrefe M, et al. ACC/AHA/ESC 2006 Guidelines 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 and the European Society of Cardiology Committee for Practice Guidelines (writing committee to develop Guidelines for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death): developed in collaboration with the European Heart Rhythm Association and the Heart Rhythm Society. Circulation. Sep 5 2006; 114(10):e385-484.
  9. Roden DM. Long QT Syndrome. N Engl J Med. Jan 2008; 358(2):169-76.
  10. Ching CK, Tan EC. Congenital long QT syndromes: clinical features, molecular genetics and genetic testing.Expert Rev Mol Diagn. May 2006; 6(3):365-74.

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Last updated: 2018-06-22 08:25