Long QT syndrome and Torsade de pointes

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Long QT syndrome and Torsade de pointes

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Chapter 27 Ventricular Tachycardia LONG QT SYNDROME (LQTS) osms.it/long-qt-syndrome PATHOLOGY & CAUSES ▪ Cardiac rhythm disorder characterized by prolonged ventricular repolarization ▪ Characterized by abnormally long QT interval ▫ QT interval: total time from ventricular depolarization (QRS complex) to complete repolarization (T wave); measured from beginning of QRS to end of T wave ▫ QTc (corrected) accounts for changes in heart rate: QTc = QT interval ÷ √RR interval (in sec); AKA Bazett formula ▫ Adult normal = 420 ± 20 msec ▪ Results in ↑ risk of polymorphic ventricular arrhythmias (TdP), which can deteriorate into ventricular ﬁbrillation TYPES Inherited ▪ Caused by mutations in genes associated with cardiac potassium, sodium channels ▪ Triggered by exertion, emotional events, stress, postpartum events, noise ▪ ≥ 13 types identiﬁed; associated with mutations in genes encoding myocyte ion channels ▪ KCNQ1, KCNH2, KCNE1, KCNE2 affect potassium channels → ↓ outward potassium current ▪ SCN5A affects sodium channels → ↑ inward sodium current ▫ Two distinct LQT phenotypes due to mutant alleles in same locus: ▫ Romano–Ward syndrome: autosomal dominant; LQTS without hearing loss ▫ Jervell and Lange–Nielsen syndrome: autosomal recessive; LQTS with congenital sensorineural hearing loss Acquired ▪ Usually caused by certain drugs (e.g. antiinfectives, psychotropics, antiarrhythmics, antineoplastics, bronchodilators, gastric motility agents) ▫ Common mechanism involves blockage of rapidly activating potassium channels (IKr) current in potassium channel encoded by KCNH2 gene RISK FACTORS ▪ Electrolyte imbalances (e.g. hypokalemia, hypomagnesemia, hypocalcemia) ▪ Underlying heart disease (e.g. HF, hypertrophic left ventricle, history of myocardial infarction) ▪ Bradyarrhythmias ▪ Biological females > biological males ▪ ↑ age ▪ Inherited genetic mutation ▪ Postpartum period ▫ Related to physiologic stress, altered sleep patterns ▪ Anorexia nervosa COMPLICATIONS ▪ Malignant arrhythmias (TdP, VF), syncope, seizures, sudden death SIGNS & SYMPTOMS ▪ Palpitations, lightheadedness, hypotension DIAGNOSIS LAB RESULTS ▪ Serum electrolytes ▫ Hypokalemia, hypomagnesemia, hypocalcemia may be present OSMOSIS.ORG 187

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Long QT syndrome and Torsade de pointes

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A 26-year-old woman comes to the emergency department after fainting at work and hitting her head. She is conscious, alert, and in pain as she sustained a deep laceration above her right orbit. When asked about prior fainting episodes, she says that she has had them since childhood, but she felt it was "nothing serious". She also says she has frequent palpitations, shortness of breath, nausea, and at times, chest pain and attributes this to "working too hard." Physical examination shows tachycardia and mild hypotension. The patient's electrocardiogram is obtained. Which of the following drugs is the best choice for first line treatment of the patient's condition?

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