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Revision as of 14:17, 3 January 2018



  • <a href="#Long_QT_.28LQT.29_Syndrome">1 Long QT (LQT) Syndrome</a>
    • <a href="#Diagnosis">1.1 Diagnosis</a>
    • <a href="#Treatment">1.2 Treatment</a>
    • <a href="#Drugs_and_Circumstances_to_Avoid">1.3 Drugs and Circumstances to Avoid</a>
    • <a href="#Genetics">1.4 Genetics</a>
    • <a href="#Prevalence_and_Population_Frequencies">1.5 Prevalence and Population Frequencies</a>
    • <a href="#Genetic_Counselling_Considerations">1.6 Genetic Counselling Considerations</a>
    • <a href="#Support">1.7 Support</a>
    • <a href="#References">1.8 References</a>

Long QT (LQT) Syndrome[<a href="/index.php?title=Course:MEDG550/Student_Activities/Long_QT&action=edit&section=1" title="Edit section: Long QT (LQT) Syndrome">edit</a>]

<a href="/File:Long_QT2.png" class="image"><img alt="" src="//wiki.ubc.ca/images/thumb/7/78/Long_QT2.png/180px-Long_QT2.png" width="180" height="110" class="thumbimage" srcset="//wiki.ubc.ca/images/thumb/7/78/Long_QT2.png/270px-Long_QT2.png 1.5x, //wiki.ubc.ca/images/thumb/7/78/Long_QT2.png/360px-Long_QT2.png 2x" /></a>
<a href="/File:Long_QT2.png" class="internal" title="Enlarge"><img src="/skins/common/images/magnify-clip.png" width="15" height="11" alt="" /></a>
Normal ECG contrasted with an ECG of an individual with Long QT

LQT is characterized by a prolonged QT interval, on an <a rel="nofollow" class="external text" href="http://www.nhlbi.nih.gov/health/health-topics/topics/ekg/">electrocardiogram</a> (ECG), syncope (fainting spells) and sudden death, leading to 3,000 – 4,000 deaths per year in the United States. These deaths usually occur suddenly in young people. The QT interval may be elongated due to mutations in the proteins that form, or interact, with cardiac ion channels and delay re-polarization <a href="#cite_note-two-1">[1]</a>.

The condition itself may be inherited, with a genetic cause or may be acquired, usually drug-induced. Certain medications, including antibiotics, antihistamines, diabetes medications and cholesterol-lowering drugs may lengthen the QT interval. Individuals with drug-induced long QT may also have genetic changes that make them more susceptible to this condition; however this document will focus on the inherited form of long QT, which has a population frequency of 1 in 2,500 individuals. It has variable penetrance, as 40% of individuals with a known genetic change, do not show any symptoms <a href="#cite_note-one-2">[2]</a> <a href="#cite_note-three-3">[3]</a>

Arrhythmic events could be triggered by a number events, consisting of emotional and physical stress, such as: physical (example: swimming), emotional (example: anger) or startling noises (example: alarm clocks).

There are two 'types' of long QT: Romano-Ward syndrome and Jervell and Lange-Nielsen syndrome. Romano-Ward syndrome is a clinical term that describes the autosomal dominant form of Long QT, where individuals do not have hearing loss. Jervell and Lange-Nielsen syndrome describes the autosomal recessive form of Long QT, characterized by Long QT symptoms and bilateral congenital hearing loss. Only the KCNQ1 and KCNE1 genes have been implicated with this subtype of Long QT.

Diagnosis[<a href="/index.php?title=Course:MEDG550/Student_Activities/Long_QT&action=edit&section=2" title="Edit section: Diagnosis">edit</a>]

The diagnosis of LQT can often come up when an individual has an unexplained syncope episode, which then initiates further cardiac investigations for a number of conditions. Another route that a diagnosis may arise is when investigations are initiated by a family history of sudden unexplained death or syncope. However, many people do not receive a diagnosis because they do not have any indications. Methods of diagnosis include:

<a rel="nofollow" class="external text" href="http://www.nhlbi.nih.gov/health/health-topics/topics/ekg/">Electrocardiogram (ECG)</a> - A test which detects and records electrical activity in the heart. It would be able to show a long QT interval, and this test can be the first clue towards reaching the diagnosis. A QT of over 470 milliseconds in males, and 480 milliseconds in females, indicates a strong likelihood for LQT.

<a rel="nofollow" class="external text" href="http://www.nhlbi.nih.gov/health/health-topics/topics/holt/">Holter monitor</a> - This device can measure electrical activity from the heart for a longer period of time than the ECG, up to 48 hours. This is useful if an individual has cardiac changes for short periods throughout the day, and may not occur while being monitored by ECG.

<a rel="nofollow" class="external text" href="http://www.nhlbi.nih.gov/health/health-topics/topics/stress/">Stress Test</a> - Many individuals only have cardiac changes during physical exertion, or when excited. A stress test allows for the heart to be monitored during an activity which causing physical excitement, or stress, when the heart is beating harder and faster than at a resting state <a href="#cite_note-four-4">[4]</a>.

<a rel="nofollow" class="external text" href="http://ghr.nlm.nih.gov/handbook/testing/genetictesting">Genetic Testing</a> - This route is commonly used to confirm a diagnosis of an individual that has a long QT interval. The testing may provide a clearer picture as to the most effective treatment to use. As well, testing may lead to cascade screening to their family members to identify additional individuals who may be at risk. There is a 75% detection rate, meaning that the genetic test for an unknown mutation (called a gene panel), detects 75% of cases. <a href="#cite_note-three-3">[3]</a>

Autopsy - Sadly, some cases of LQT are only diagnosed after there has been sudden unexplained death of an individual.

Treatment[<a href="/index.php?title=Course:MEDG550/Student_Activities/Long_QT&action=edit&section=3" title="Edit section: Treatment">edit</a>]

There are many different treatments available for those with long QT. Those offered depend several factors including the degree of risk for sudden death and medication tolerance.

Beta-Blockers - a tablet-type of medication that target receptors found on the muscles of the heart and can manage the cardiac arrhythmia. These have been used to maintain LQT for roughly 30 years, and effectively prevent LQT-related arrhythmias - depending on which gene is affected. This medication can also be used along side of other treatments <a href="#cite_note-six-5">[5]</a>

Potassium Channel Openers - this is a tablet-type medication that targets the potassium channels in the heart, and facilitates transport. Some examples of this are: Diazoxide and Nicorandil.

Potassium Supplements - An oral supplement to increase the potassium in their body, and then provide more potassium to the heart for transport. It can be found in many foods, such as bananas, or potatoes, or in tablet form.

Sodium Channel Blockers - a tablet-type of medication that slows the sodium going into the cells of the heart by two routes. The first is by binding to the sodium channel on the outside of the cells, and the second is by binding the sodium channel from the inside of the cell. This can control an irregular heartbeat, like that seen in LQT.

Calcium Channel Blockers - a tablet-type of medication that slows the calcium intake in the heart, and can then control irregular heartbeats, such as a long QT interval. Examples would be Nisoldipine (Sular) or Amlodipine (Norvasc)

<a rel="nofollow" class="external text" href="https://www.nhlbi.nih.gov/health/health-topics/topics/icd/">Implantable Cardioverter Defibrillator (ICD)</a> - a device that is surgically placed into the heart or abdomen, and control arrhythmias by using electrical pulses. This treatment option is commonly used if the patient is responding poorly to beta-blockers.

Left Cardiac Sympathetic Denervation (LCSD)- surgery in which specific nerves in the chest are removed. This surgery significantly reduces the risk of sudden death, and is usually offered only to individuals who are at risk of sudden death, do not tolerate their medications or have fainting spells despite medications. Individuals with an implanted ICD may also receive this surgery, which may reduce the frequency of ICD shocks.

Drugs and Circumstances to Avoid[<a href="/index.php?title=Course:MEDG550/Student_Activities/Long_QT&action=edit&section=4" title="Edit section: Drugs and Circumstances to Avoid">edit</a>]

In addition to the treatments listed above, there are drugs and circumstances that individuals with LQT can avoid to further decrease their risk of an arrhythmic event. Not all of these changes will be useful for all individuals with LQT, so it is helpful to discuss these suggestions with a health professional.

Drugs that prolong the QT interval - It is very important for all patients diagnosed with LQT to avoid certain drugs that can prolong the QT interval. A list of drugs to avoid is available at <a rel="nofollow" class="external text" href="http://www.qtdrugs.org">www.qtdrugs.org</a>.

Exercise and sports - While physical activity can be beneficial for overall health, individuals with LQT are advised to avoid intense exercise or competitive sports. Swimming alone should also be avoided.

Startling noises and stressful situations - Loud and/or sudden noises are known to be a trigger of arrhythmia for some individuals with LQT. These risks can be reduced by turning down devices such as alarm clocks and phones, and eliminating other alarming sounds when possible. Emotional stress can also be a trigger of arrhythmia for some individuals with LQT, and should be avoided. Examples of emotionally-stressfull events include amusement park rides and jumping into cold water<a href="#cite_note-gene_reviews-6">[6]</a>.

Genetics[<a href="/index.php?title=Course:MEDG550/Student_Activities/Long_QT&action=edit&section=5" title="Edit section: Genetics">edit</a>]

There are multiple types of LQT, with each type having a gene associated with it. Usually a single change or point mutation occurs in the gene; however more severe forms have been reported with large pieces of gene missing or duplicated. The genetic testing for the following genes allows for the identification of potentially unique triggers of events, responses to the treatment or severity of the condition. Certain point mutations have been associated with specific physiological changes, which is why genetic testing may help identify which treatments may work better than others for a particular individual.

LQT1 - The most common type of LQT, accounting for ~50% of cases. It is associated with genetic mutations, or changes, in the gene KCNQ1. This mutation leads to the slowing of the potassium channel in the heart muscle, which in turn results in the longer QT interval. The arrhythmic events for this type are attributed to emotional or physical stress (eg. swimming). Treatment with B-blockers shows a great improvement in the interval. Hearing loss may also be present.

LQT2 - The second most common type of LQT, accounting for ~40% and caused by changes in the KCNH2 gene. This gene is similar to KCNQ1 in that it also affects the potassium channels.

LQT3 - This type of LQT only accounts for 5-10% of the cases, and are caused by mutations in the SCN5A gene. Mutations in this gene affect the sodium channels, which then cause the repolarization of the heart to slow, lengthening the QT interval.

The other types of LQT account for <5% of the LQT cases <a href="#cite_note-seven-7">[7]</a>

LQT Type Associated Gene

Prevalence and Population Frequencies[<a href="/index.php?title=Course:MEDG550/Student_Activities/Long_QT&action=edit&section=6" title="Edit section: Prevalence and Population Frequencies">edit</a>]

The prevalence of LQT is 1/3000-1/7000 individuals <a href="#cite_note-gene_reviews-6">[6]</a>. LQT occurs in individuals of all ethnic backgrounds, although it may occur less frequently in individuals of African descent. Other populations appear to have a much higher frequency of certain LQT-causing mutations.

For instance, a particular KCNQ1 mutation has been found in Finnish families with LQT, which has not been seen in other populations. This mutation accounts for up to 30% of Finnish cases, and is thought to be the result of a "founder effect" <a href="#cite_note-Piippo-8">[8]</a>. A founder effect occurs when a small number of individuals (founders) expands to form a new, larger population. A mutation present in one or more of the founders may occur at a high frequency in individuals descended from this small gene pool.

A founder effect is also thought to have occurred in the Gitxsan First Nations community in Northern BC, in which the prevalence of LQT is 1/250 or higher <a href="#cite_note-Arbour-9">[9]</a>. A novel alteration in the KCNQ1 gene has been found to be a common mutation in this community, and a screening strategy is being implemented.

Genetic Counselling Considerations[<a href="/index.php?title=Course:MEDG550/Student_Activities/Long_QT&action=edit&section=7" title="Edit section: Genetic Counselling Considerations">edit</a>]

<a href="/File:Autosomal_dominant_1.png" class="image"><img alt="" src="//wiki.ubc.ca/images/thumb/2/29/Autosomal_dominant_1.png/180px-Autosomal_dominant_1.png" width="180" height="110" class="thumbimage" srcset="//wiki.ubc.ca/images/thumb/2/29/Autosomal_dominant_1.png/270px-Autosomal_dominant_1.png 1.5x, //wiki.ubc.ca/images/thumb/2/29/Autosomal_dominant_1.png/360px-Autosomal_dominant_1.png 2x" /></a>
<a href="/File:Autosomal_dominant_1.png" class="internal" title="Enlarge"><img src="/skins/common/images/magnify-clip.png" width="15" height="11" alt="" /></a>
Autosomal dominant inheritance. One gene with a mutation is enough to cause the condition. An individual with an autosomal dominant condition has 50% chance of having a child with the condition.
<a href="/File:Autosomal_recessive.jpg" class="image"><img alt="" src="//wiki.ubc.ca/images/thumb/4/4b/Autosomal_recessive.jpg/180px-Autosomal_recessive.jpg" width="180" height="113" class="thumbimage" srcset="//wiki.ubc.ca/images/thumb/4/4b/Autosomal_recessive.jpg/270px-Autosomal_recessive.jpg 1.5x, //wiki.ubc.ca/images/thumb/4/4b/Autosomal_recessive.jpg/360px-Autosomal_recessive.jpg 2x" /></a>
<a href="/File:Autosomal_recessive.jpg" class="internal" title="Enlarge"><img src="/skins/common/images/magnify-clip.png" width="15" height="11" alt="" /></a>
Autosomal recessive inheritance. Both genes need to have a mutation in order to cause the condition.

Recurrence risk - LQT is inherited in either an autosomal dominant (see figure) or an autosomal recessive manner. The de novo mutation rate, meaning that condition-causing mutations are more-likely to be inherited within the family than to occur as a new change.

  • in autosomal dominant inheritance, an individual with LQT has a 50% chance of having a child with the condition.
  • in autosomal recessive inheritance, an individual with LQT has a 50% chance of having a child with the condition, only if the partner is a carrier (has one mutation). If the partner does not carry a mutation, then none of the children will be affected but all will be carriers and unaffected. If both parents are carriers, there is a 25% chance of having a child with the condition.

Penetrance - LQT shows variability in the condition's appearance between families, but also within families, even if the genetic changes are within the same gene. There is no guarantee that an individual with a mutation will show any symptoms of LQT, meaning that it has incomplete penetrance. ~50% of individuals with the gene have no signs or symptoms of LQT.

Prenatal diagnosis - Prenatal testing is able to be done for LQT if the familial mutation is known. It can be done with chorionic villi sampling (CVS), amniocentesis, or pre-implantation diagnosis.

Predictive testing - Many patients that come in for genetic testing have a clear clinical diagnosis of LQT, and so testing allows the ability to provide cascade screening to their family members. If a mutation is identified, the asymptomatic family members can be offered screening to determine risk.

Support[<a href="/index.php?title=Course:MEDG550/Student_Activities/Long_QT&action=edit&section=8" title="Edit section: Support">edit</a>]

Living with, or having a family member who is living with or passed away from LQT may be extremely challenging. Support groups may provide further information on the condition and tips for management. They are an excellent source for support, allowing families to interact locally and globally.

<a rel="nofollow" class="external text" href="http://www.sads.ca/">The Canadian SADS Foundation</a>

<a rel="nofollow" class="external text" href="http://www.phsa.ca/AgenciesAndServices/Agencies/Cardiac/bc-inherited-arrhythmia/default.htm">BC Inherited Arrhythmia Program</a>

References[<a href="/index.php?title=Course:MEDG550/Student_Activities/Long_QT&action=edit&section=9" title="Edit section: References">edit</a>]

  1. <a href="#cite_ref-two_1-0">↑</a> Morita, H., Wu, J., & Zipes, D. P. (2008). The QT syndromes: long and short. Lancet. 372:750 63 <a rel="nofollow" class="external free" href="http://www.ncbi.nlm.nih.gov/pubmed/18761222">http://www.ncbi.nlm.nih.gov/pubmed/18761222</a>
  2. <a href="#cite_ref-one_2-0">↑</a> Aatre, R. D., Day, S. M. (2011). Psychological issues in genetic testing for inherited cardiovascular diseases. Circulation Cardiovascular Genetics. 4: 81-90 <a rel="nofollow" class="external free" href="http://circgenetics.ahajournals.org/content/4/1/81.full.pdf+html">http://circgenetics.ahajournals.org/content/4/1/81.full.pdf+html</a>
  3. <a href="#cite_ref-three_3-0">3.0</a> <a href="#cite_ref-three_3-1">3.1</a> Gollob, M. H. (2011). Recommendations for the use of genetic testing in the clinical evaluation of inherited cardiac arrhythmias associated with sudden cardiac death: canadian cardiovascular society/Canadian heart rhythm society joint position paper. Canadian Journal of Cardiology 27: 232-245 <a rel="nofollow" class="external free" href="http://download.journals.elsevierhealth.com/pdfs/journals/0828-282X/PIIS0828282X10000942.pdf">http://download.journals.elsevierhealth.com/pdfs/journals/0828-282X/PIIS0828282X10000942.pdf</a>
  4. <a href="#cite_ref-four_4-0">↑</a> <a rel="nofollow" class="external free" href="http://www.sads.org/SADS/media/pdf/Long-QT--3-2011.pdf">http://www.sads.org/SADS/media/pdf/Long-QT--3-2011.pdf</a>
  5. <a href="#cite_ref-six_5-0">↑</a> Viskin, S., Halkin, A. (2009). Treating the long-QT syndrome in the era of implantable defibrillators. Circulation. 119: 204-206 <a rel="nofollow" class="external free" href="http://circ.ahajournals.org/content/119/2/204.full.pdf+html">http://circ.ahajournals.org/content/119/2/204.full.pdf+html</a>
  6. <a href="#cite_ref-gene_reviews_6-0">6.0</a> <a href="#cite_ref-gene_reviews_6-1">6.1</a> Alders M, Mannens MMAM. Romano-Ward Syndrome. 2003 Feb 20 [Updated 2012 May 31]. In: Pagon RA, Adam MP, Ardinger HH, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2015. Available from: <a rel="nofollow" class="external free" href="http://www.ncbi.nlm.nih.gov/books/NBK1129/">http://www.ncbi.nlm.nih.gov/books/NBK1129/</a>
  7. <a href="#cite_ref-seven_7-0">↑</a> Udo, E.O., Baars, H.F., Winter, J.B., Wilde, A.A.M. (2007). Not just any ICD device in patients with long-QT syndrome. Neth Heart J. 15: 418-421 <a rel="nofollow" class="external free" href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2213451/">http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2213451/</a>
  8. <a href="#cite_ref-Piippo_8-0">↑</a> Piippo K, Swan H, Pasternack M, Chapman H, Paavonen K, Viitasalo M, Toivonen L, Kontula K. (2001). A founder mutation of the potassium channel KCNQ1 in long QT syndrome: implications for estimation of disease prevalence and molecular diagnostics. J Am Coll Cardiol. 37(2):562-8.
  9. <a href="#cite_ref-Arbour_9-0">↑</a> Arbour L, Rezazadeh S, Eldstrom J, Weget-Simms G, Rupps R, Dyer Z, Tibbits G, Accili E, Casey B, Kmetic A, Sanatani S, Fedida D. A KCNQ1 V205M missense mutation causes a high rate of long QT syndrome in a First Nations community of northern British Columbia: a community-based approach to understanding the impact. (2008). Genetics in Medicine. 10(7):545.

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