Long QT Syndrome

I am dr. Jason Johnson one of the pediatric cardiology fellows at Duke University this is the voice annotated presentation on long QT syndrome with emphasis on this disease in the pediatric population this presentation will go over how to measure the QT interval I will discuss the incidents and characteristics of long QT syndrome I will speak briefly about the genetics of the disease and then explain how the genetics of the disease can have a specific phenotype with specific clinical manifestations I will end with discussion about the diagnosis and treatment options for these patients I will start by defining the QT interval and review how to measure that on the electrocardiogram knowing how to correctly measure the QT interval is very important in diagnosing long QT syndrome the QT interval varies with age and there are established norms typically lead to and v5 is the best for measuring the QT interval a normal QT interval is less than zero point four four to zero point four six seconds the QT is usually the longest in v2 and v3 to account for increased heart rates and children the corrected QT interval where the QT C is calculated the formula at the top right of the slide is a formula to calculate the corrected QT interval the QT interval divided by the square root of the preceding RR interval is called the pizzette formula it is very important to remember to keep the measurements in seconds and not milliseconds where the equation will be wrong also please become familiar with how to measure the QT interval the image on the bottom right depicts the correct way to measure the QT interval the QT interval is defined from the beginning of the Q wave to the end of the T wave the incidence of long QT syndrome is one in ten thousand live births this syndrome is caused by a genetic abnormality that causes delayed repolarization of the heart this creates a prolonged action potential seen as a prolonged QT interval on the ECG long QT syndrome is caused by abnormalities and specific ion channels the figure on the right of the slide shows an ECG from a single contraction with the QRS complex and a T wave the initial depolarization of cardiac myocytes through gap junctions or cell-to-cell connections activates the inward sodium current that depolarizes the myocytes rapidly which is the phase zero of the depolarization seen at the bottom right of the slide transient outward potassium current during phase one creates a notch during the early phase of repolarization balance of the inward depolarizing calcium current and outward rectifier potassium currents IKS and IKR form a plateau phase or phase two the activation of the inward current and increase of the outward current complete repolarization phase 3 and the membrane potential returns to its resting potential phase 4 it is important to know some of the ion channels as these are adversely affected in long QT syndrome the genetics of long QT syndrome is complicated and occurs at different sites there are multiple known mutations in over eight gene loci the most common types are listed here with their associated gene defect kc in q1 leads to long QT type 1 and causes a loss of function in the i KS channel Casey in h2 leads to long QT type 2 and causes a loss of function in the IKr channel SC n5a leads to long QT type 3 and causes a gain of function in the sodium channel types one through three account for 90% of long QT syndrome however you should remember Romana Ward syndrome which is an autosomal dominant form of long QT syndrome with variable penetrants also remember Ravel and laying Neilson as it is associated with sensory neural deafness with long QT syndrome the clinical manifestations are not specific to long QT syndrome the most common presentation is one of syncope brought on by exercise fright or a sudden startled patients can be seen with seizures pre syncope or palpitations however it is important to realize that 10% initially present with cardiac arrest the interesting aspect of the genetics of long QT syndrome is that the type can have a phenotypic appearance the typical phenotypic presentation of cardiac arrest or syncope based upon the genetic subtypes are as follows in patients with type 1 cardiac arrest or syncope typically presents with exercise specifically swimming and emotion is associated as well emotion auditory startled and somewhat exercised are associated with long QT type too for type-3 it is actually rest sleep and then less emotion that causes cardiac arrest or syncope the diagnosis of long QT syndrome is mainly established with electrocardiogram criteria typically if patients have a QT C greater than 480 milliseconds they have long QT syndrome however one can't rely only on the ECG in fact 33 % of mutation positive patients are patients with known genetic long QT syndrome have a QT C less than 480 milliseconds therefore the Schwartz criteria developed to diagnose long QT syndrome it uses a point system to help diagnose long QT syndrome most of the points are related to ECG findings but clinical history and family history play a role patients with more than three points have a high probability of having long QT syndrome therefore a patient with acute EC greater than 480 milliseconds and an uncle with known long QT syndrome would have four points three for the ECG findings and one for the family history they would have a high probability of having long QT syndrome this is a 12-lead electrocardiogram of a patient with type 2 long QT syndrome his history is one of a seven-year-old boy who presented to the emergency department with a syncopal episode the episode occurred when he was surprised by an unannounced visit from his grandparents his corrected QT interval on this ECG is 550 milliseconds he later had genetic testing to confirm a defect in the KC nh-2 gene leading to loss of function of the I K R ion channel consistent with long QT type 2 torsades the points is a form of polymorphic ventricular tachycardia with characteristic beat by beat change or twisting around the baseline in the QRS complex and occurs frequently in patients with long QT syndrome toursad de pointes is literally translated twisting of the points this can cause syncope and degenerate into ventricular fibrillation resulting in sudden death torsades de pointes is typically preceded by frequent premature ventricular complexes the figure at the bottom of the slide depicts what happens in a patient with long QT syndrome type 2 who experiences an alarming auditory stimuli there are multiple premature ventricular complexes that eventually lead to to sod the points at the end of the electrocardiogram the treatment of long QT syndrome is somewhat limited there is no definitive cure typically one would start with lifestyle modifications based upon the type of long QT syndrome there is no competitive sports participation allowed in all types in patients with type 1 long QT syndrome only supervised swimming is allowed in patients with type 2 long QT syndrome there are no alarm clocks or phones allowed in the patient's bedroom beta blockers have shown to decrease syncope and incidence of cardiac arrest beta-blockers have not been found effective in patients with long QT syndrome type 3 and typically these patients are placed on mix illa teen if patients have previous cardiac arrest an implantable cardioverter-defibrillator is added to beta-blocker therapy and that would be the standard of care I will end by reviewing the genetics clinical features therapy and electrocardiogram of each of the different types of long QT syndrome long QT syndrome type 1 is caused by a gene abnormality of the kcn q1 that causes a loss of function of the i KS channel type 1 is the most common type and is associated with syncope during exercise specifically swimming the sudden death rate is 0.3 per year and the median age to first cardiac arrest is 9 years old beta blockers are very effective in his patient population long QT syndrome type 2 is caused by a gene abnormality of kcn h2 that causes a loss of function of the IKr channel type 2 is the second most common and is associated with syncope with auditory stimuli or emotions the sudden death rate is 0.6 per year and the median age to first arrest is 12 years old beta blockers are effective in this patient population long QT syndrome type 3 is caused by a gene abnormality of SC and 5a that leads to a gain of function in the sodium channel this type is uncommon with a low incidence of symptoms type 3 is associated with cardiac arrest during sleep the sudden death rate is 0.6 per year with the median age 2 first event at 16 years old miksa lutein and beta blockers are minimally effective in preventing cardiac arrest and these patients often get implantable cardiac defibrillators the different types of long QT syndrome have characteristic types of ECGs you would not be expected to know this I put these different examples in this presentation to show you that all the types have a prolonged QT interval these are references to book chapters and great review article in The Lancet where most of the figures originated thank you for your time

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Keywords: lit, learning in 10, cardiology, dukenus, duke, Long QT Syndrome, long qt syndrome treatment, long qt syndrome symptoms, long qt syndrome drugs to avoid, long qt syndrome diagnosis, long qt syndrome life expectancy, long qt syndrome type 1, long qt syndrome foods to avoid, long qt syndrome pathophysiology

Id: xek-npOpJog

Length: 12min 23sec (743 seconds)

Published: Sun Apr 26 2020