|
|
| (57 intermediate revisions by 7 users not shown) |
| Line 2: |
Line 2: |
| {{Infobox_Disease | | | {{Infobox_Disease | |
| Name = Long QT syndrome | | | Name = Long QT syndrome | |
| Image = SinusRhythmLabels.png | | | Image =Long QT Syndrome.PNG| |
| Caption = Schematic representation of normal ECG trace ''([[sinus rhythm]]),'' with waves, segments, and intervals labeled. | | | Caption = Type 3 Long QT Syndrome | |
| DiseasesDB = 11104 | | | DiseasesDB = 11104 | |
| ICD10 = {{ICD10|I|45|8|i|30}} | | | ICD10 = {{ICD10|I|45|8|i|30}} | |
| Line 10: |
Line 10: |
| OMIM = | | | OMIM = | |
| MedlinePlus = | | | MedlinePlus = | |
| eMedicineSubj = |
| |
| eMedicineTopic = |
| |
| MeshID = D008133 | | | MeshID = D008133 | |
| }} | | }} |
| {{Long QT Syndrome}} | | {{Long QT Syndrome}} |
| {{WikiDoc Cardiology Network Infobox}}
| |
|
| |
|
| {{CMG}}; '''Associate Editor(s)-In-Chief:''' {{CZ}}
| | '''For patient information, click [[Long QT syndrome (patient information)|here]].''' |
|
| |
|
| ==Mechanism of arrhythmia generation==
| | '''Long QT syndrome is one of the many causes of [[QT prolongation]]. For a complete review of [[QT prolongation]] in general, click [[QT prolongation|here]].''' |
|
| |
|
| All forms of the long QT syndrome involve an abnormal repolarization of the heart. The abnormal repolarization causes differences in the "refractoriness" of the [[myocyte]]s. After-depolarizations (which occur more commonly in LQTS) can be propagated to neighboring cells due to the differences in the [[refractory period|refractory periods]], leading to re-entrant ventricular arrhythmias.
| | {{CMG}} |
|
| |
|
| It is believed that the so-called early after-depolarizations (EADs) that are seen in LQTS are due to re-opening of L-type calcium channels during the plateau phase of the [[cardiac action potential]]. Since [[adrenergic]] stimulation can increase the activity of these channels, this is an explanation for why the risk of sudden death in individuals with LQTS is increased during increased adrenergic states (ie exercise, excitement) -- especially since repolarization is impaired. Normally during adrenergic states, repolarizing currents will also be enhanced to shorten the action potential. In the absence of this shortening and the presence of increased L-type calcium current, EADs may arise.
| | {{SK}} LQTS; long QT; congenital long QT; congenital long QT interval |
|
| |
|
| The so-called delayed after-depolarizations (DADs) are thought to be due to an increased Ca<sup>2+</sup> filling of the [[sarcoplasmic reticulum]]. This overload may cause spontaneous Ca<sup>2+</sup> release during repolarization, causing the released Ca<sup>2+</sup> to exit the cell through the 3Na<sup>+</sup>/Ca<sup>2+</sup>-exchanger which results in a net depolarizing current.
| | == [[Long QT Syndrome overview|Overview]] == |
|
| |
|
| == Diagnosis == | | == [[Long QT Syndrome historical perspective|Historical Perspective]]== |
|
| |
|
| The diagnosis of LQTS is not easy since 2.5% of the healthy population have prolonged QT interval, and 10% of LQTS patients have a normal QT interval. A commonly used criterion to diagnose LQTS is the LQTS "diagnostic score" <ref>Schwartz PJ, Moss AJ, Vincent GM, Crampton RS. Diagnostic criteria for the long QT syndrome. An update. Circulation. 1993 Aug;88(2):782-4. PMID 8339437.</ref>. Its based on several criteria giving points to each. With 4 or more points the probability is high for LQTS, and with 1 or less point the probability is low. Two or 3 points indicates intermediate probability.
| | == [[Long QT Syndrome classification|Classification]] == |
|
| |
|
| * QTc (Defined as QT interval / square root of RR interval)
| | == [[Long QT Syndrome pathophysiology|Pathophysiology]] == |
| ** >= 480 msec - 3 points
| |
| ** 460-470 msec - 2 points
| |
| ** 450 msec and male gender - 1 point
| |
| * [[Torsades de Pointes]] ventricular tachycardia - 2 points
| |
| * [[T wave alternans]] - 1 point
| |
| * Notched T wave in at least 3 leads - 1 point
| |
| * Low heart rate for age (children) - 0.5 points
| |
| * Syncope (one cannot receive points both for syncope and Torsades de pointes)
| |
| ** With stress - 2 points
| |
| ** Without stress - 1 point
| |
| * Congenital deafness - 0.5 points
| |
| * Family history (the same family member cannot be counted for LQTS and sudden death)
| |
| ** Other family members with definite LQTS - 1 point
| |
| ** Sudden death in immediate family (members before the age 30) - 0.5 points
| |
|
| |
|
| ==Treatment options== | | == [[Long QT Syndrome differential diagnosis|Differentiating Long QT Syndrome from other Diseases]] == |
| There are two treatment options in individuals with LQTS: arrhythmia prevention, and arrhythmia termination.
| |
|
| |
|
| ===Arrhythmia prevention=== | | == [[Long QT Syndrome epidemiology and demographics|Epidemiology and Demographics]]== |
| Arrhythmia suppression involves the use of medications or surgical procedures that attack the underlying cause of the arrhythmias associated with LQTS. Since the cause of arrhythmias in LQTS is after depolarizations, and these after depolarizations are increased in states of adrenergic stimulation, steps can be taken to blunt adrenergic stimulation in these individuals. These include:
| |
| * Administration of [[beta blocker|beta receptor blocking agents]] which decreases the risk of stress induced arrhythmias. Beta blockers are the first choice in treating Long QT syndrome.
| |
|
| |
|
| In 2004 it has been shown that genotype and QT interval duration are independent predictors of recurrence of life-threatening events during beta-blockers therapy. Specifically the presence of QTc >500ms and LQT2 and LQT3 genotype are associated with the highest incidence of recurrence. In these patients primary prevention with ICD (Implantable Cardioverster Defibrilator) implantaion can be considered.<ref>Priori SG, Napolitano C, Schwartz PJ, Grillo M, Bloise R, Ronchetti E, Moncalvo C, Tulipani C, Veia A, Bottelli G, Nastoli J. Association of long QT syndrome loci and cardiac events among patients treated
| | == [[Long QT Syndrome risk stratification|Risk Stratification]] == |
| with beta-blockers. JAMA. 2004 Sep 15;292(11):1341-4. [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=15367556&query_hl=26&itool=pubmed_docsum PMID: 15367556]</ref>
| |
|
| |
|
| * Potassium supplementation. If the potassium content in the blood rises, the action potential shortens and due to this reason it is believed that increasing potassium concentration could minimize the occurrence of arrhythmias. It should work best in LQT2 since the HERG channel is especially sensible to potassium concentration, but the use is experimental and not evidence based.
| | == [[Long QT Syndrome screening|Screening]]== |
| * [[Mexiletine]]. A sodium channel blocker. In LQT3 the problem is that the sodium channel does not close properly. Mexiletine closes these channels and is believed to be usable when other therapies fail. It should be especially effective in LQT3 but there is no evidence based documentation.
| |
| * Amputation of the [[cervical sympathetic chain]] (left [[Stellate ganglion|stellectomy]]). This may be used as an add-on therapy to beta blockers but modern therapy mostly favors ICD implantation if beta blocker therapy fails.
| |
|
| |
|
| ===Arrhythmia termination=== | | == [[Long QT Syndrome natural history, complications and prognosis|Natural History, Complications and Prognosis]] == |
| Arrhythmia termination involves stopping a life-threatening arrhythmia once it has already occurred. The only effective form of arrhythmia termination in individuals with LQTS is placement of an [[implantable cardioverter-defibrillator]] (ICD). ICD are commonly used in patients with syncopes despite beta blocker therapy, and in patients who have experienced a cardiac arrest.
| |
|
| |
|
| With better knowledge of the genetics underlying the long QT syndrome, more precise treatments will be readily available.<ref>Compton SJ, Lux RL, Ramsey MR, Strelich KR, Sanguinetti MC, Green LS, Keating MT, Mason JW. Genetically defined therapy of inherited long-QT syndrome. Correction of abnormal repolarization by potassium. Circulation. 1996 Sep 1;94(5):1018-22. PMID 8790040</ref>
| | == Diagnosis == |
| | | [[Long QT Syndrome history and symptoms|History and Symptoms]] | [[Long QT Syndrome electrocardiogram|Electrocardiogram]] | [[Long QT Syndrome genetic studies|Genetic Studies]] | [[Long QT Syndrome other diagnostic studies|Other Diagnostic Studies]] |
| == Risk stratification == | |
|
| |
|
| The risk for untreated LQTS patients having events (syncopes or cardiac arrest) can be predicted from their genotype (LQT1-8), gender and corrected QT interval.<ref>Risk Stratification in the Long-QT Syndrome: N Engl J Med 2003; 349:908-909, Aug 28, 2003. PMID 12944579.</ref>
| | == Treatment == |
|
| |
|
| * High risk (>50%)
| | ===Medical Therapy=== |
|
| |
|
| QTc>500 msec LQT1 & LQT2 & LQT3(males)
| | ===Surgery=== |
|
| |
|
| * Intermediate risk (30-50%)
| | ===Primary Prevention=== |
|
| |
|
| QTc>500 msec LQT3(females)
| | ===Secondary Prevention=== |
|
| |
|
| QTc<500 msec LQT2(females)& LQT3
| | ====Contraindicated medications==== |
| | {{MedCondContrAbs|MedCond = Long QT syndrome|Dofetilide}} |
|
| |
|
| * Low risk (<30%)
| | ==Case Studies== |
|
| | :[[Long QT Syndrome case study one|Case #1]] |
| QTc<500 msec LQT1 & LQT2 (males)
| |
|
| |
|
| ==References== | | ==Related Chapters== |
| <references/>
| |
| | |
| ==See also==
| |
| * [[Cardiac action potential]] | | * [[Cardiac action potential]] |
| * [[Short QT syndrome]] | | * [[Short QT syndrome]] |
|
| |
| ==External links==
| |
|
| |
| * [http://videos.med.wisc.edu/videoInfo.php?videoid=266 VIDEO - Mechanistic Insight into a Rare Cardiovascular Disease: Congenital Long QT Syndrome 2007]
| |
| * {{DMOZ|Health/Conditions_and_Diseases/Cardiovascular_Disorders/Heart_Disease/Arrhythmia/Long_QT_Syndrome/}}
| |
|
| |
|
| {{Electrocardiography}} | | {{Electrocardiography}} |
| Line 100: |
Line 67: |
|
| |
|
|
| |
|
| | | [[Category:Best pages]] |
| [[Category:Cardiology]] | | [[Category:Cardiology]] |
| [[Category:Electrophysiology]] | | [[Category:Electrophysiology]] |
