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Short QT syndrome

Short QT syndrome is a genetic disease of the electrical system of the heart. It consists of a constellation of signs and symptoms, consisting of a short QT interval interval on EKG (≤ 300 ms) that doesn't significantly change with heart rate, tall and peaked T waves, and a structurally normal heart. Short QT syndrome appears to be inherited in an autosomal dominant pattern, and a few affected families have been identified. more...

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Symptoms and signs

Individuals with short QT syndrome frequently complain of palpitations and may have syncope (loss of consciousness) that is unexplained. Due to the autosomal dominant inheritance pattern, most individuals will have family members with a history of unexplained or sudden death at a young age (even in infancy), palpitations, or atrial fibrillation.

Short QT syndrome is associated with an increased risk of sudden cardiac death, most likely due to ventricular fibrillation.

Diagnosis

The diagnosis of short QT syndrome consists of characteristic history and findings on EKG and electrophysiologic testing. There are currently no set guidelines for the diagnosis of short QT syndrome.

Electrocardiogam

The characteristic findings of short QT syndrome on EKG are a short QT interval, typically ≤ 300 ms, that doesn't significantly change with the heart rate. Tall, peaked T waves may also be noted. Individuals may also have an underlying atrial rhythm of atrial fibrillation.

Electrophysiologic Studies

In the electrophysiology lab, individuals with short QT syndrome are noted to have short refractory periods, both in the atria as well as in the ventricles. Also, ventricular fibrillation is frequently induced on programmed stimulation.

Etiology

The etiology of short QT syndrome is unclear at this time. A current hypothesis is that short QT syndrome is due to increased activity of outward potassium currents in phase 2 and 3 of the cardiac action potential. This would cause a shortening of the plateau phase of the action potential (phase 2), causing a shortening of the overall action potential, leading to an overall shortening of refractory periods and the QT interval.

In the families afflicted by short QT syndrome, two different missense mutations have been described in the human ether-a-go-go gene (HERG). These mutations result in expression of the same amino acid change in the cardiac IKr ion channel. This mutated IKr has increased activity compared to the normal ion channel, and would theoretically explain the above hypothesis.

Treatment

Currently, the only effective treatment option for individuals with short QT syndrome is implantation of an implantable cardioverter-defibrillator (ICD).

A recent study has suggested that the use of certain antiarrhythmic agents, particularly quinidine, may be of benefit in individuals with short QT syndrome due to their effects on prolonging the action potential and by their action on the IK channels1. While the use of these agents alone is not indicated at present, there may be benefit of adding these agents to individuals who have already had ICD implantation to reduce the number of arrhythmic events.

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Electrocardiography. 5th ed
From Critical Care Nurse, 12/1/04 by Linda Bell

Electrocardiography. 5th ed.

Mosby's Pocket Guide Series. Mary Boudreau Conover, St. Louis, Mo: Mosby: 2004.

337 pages; $26.95.

This pocket sized reference is composed of 31 chapters--each devoted to a different aspect of electrocardiography (ECG). Each chapter is relatively short and packed with easy-to-use reference information and illustrations. As with previous books by Conover, this volume provides the appropriate level of information for the target audience.

[ILLUSTRATION OMITTED]

Electrocardiography begins with the basics of monitoring and 12-lead ECG placement; then proceeds through the normal cardiac electrical information and mechanisms of arrhythmias. The classic information of ECG analysis is addressed, that is, systematic evaluation of waveforms and determination of axis.

The arrhythmia sections are devoted to single topics such as atrial fibrillation and flutter and continue on to ventricular ectopy. Topics of interest to anyone evaluating ECG rhythms are included, such as aberration versus ectopy, drug-and electrolyte-induced changes, and specific changes that can be expected in the athlete or during cardiac-related conditions. Additions to this edition are The Athlete's ECG, Congenital Long QT Syndrome, and Brugada Syndrome.

This book would be of value to anyone needing a quick reference at hand, whether he or she is working in a cardiac unit and sees frequent challenging arrhythmias, or is a less sophisticated user needing a helpful resource.

Electrocardiography is not a reference for in-depth analysis; there are many resources available on the market for that purpose. This is the quick reference, something that can be carried in the pocket of a scrub jacket or lab coat, and that will assist in the immediate analysis of ECG rhythms. It will be as helpful for the nurse or monitor technician new to the world of ECG analysis as to the advanced practitioner needing a teaching tool. For example, each arrhythmia analysis section includes a rhythm strip with a brief description, ECG recognition criteria, the mechanism of the arrhythmia (including illustrations as appropriate), clinical implications, emergency and long-term treatment, and patient education requirements. Additional information that would have been helpful is the documentation and additional monitoring requirements.

Reviewed by Linda Bell, RN, MSN

Linda Bell is a Clinical Practice Specialist at the American Association of Critical-Care Nurses in Aliso Viejo, Calif.

COPYRIGHT 2004 American Association of Critical-Care Nurses
COPYRIGHT 2004 Gale Group

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