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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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Syncope in a Patient With Cervical Tumor and Prolonged QT Interval - Letter to the Editor
From CHEST, 3/1/01 by Oscar Aramburu-Bodas

To the Editor:

Long QT syndromes can be congenital or acquired. Acquired cases have been described in association with severe bradycardia, hypokalemia, and with the use of antiarrhythmic drugs of class IA, IC, and III; antihistaminic agents; cisapride; and pentamidine, among others. A proposed pathogenic mechanism for this syndrome is a disproportionate activity of the left cervical sympathetic ganglions. In fact, pharmacologic blockade of the left stellate ganglion[1] or left cervical sympathectomy[2] have been successfully used in patients not responding to [Beta]-blockers. Moreover, prolongation of the QT interval has been noted in various studies of patients with extensive surgical neck dissection[3] or thoracic surgery.[4] In these cases, no association with ventricular malignant arrhythmias has been described.

We report a case of a 79-year-old man admitted to our hospital in October 1998 because of a sudden loss of consciousness with sphincter relaxation, while cycling, and no other accompanying symptoms. The patient had been a heavy smoker (60 cigarettes per day) until 3 years before. He was taking no medication. He had felt healthy until 2 months before admission, when he noticed a painless nodule in the right area of the tongue base and a progressively enlarging mass in the right submandibular and cervical area, with dysphagia for solid food and weight loss (6 kg).

Physical examination was unremarkable except for the cervical mass affecting the tongue base as well as the right submandibular and cervical area (which was hard, uneven, and painless), and an arrhythmic pulse. The blood cell count, biochemical parameters, and urine test results were normal, An ECG recorded on admission showed sinus rhythm with ventricular premature complexes and a long QT interval (0.52 s). The QTc was 0.54 s (QTc = QT/[square root of R-R]). A 24-h ECG monitoring disclosed frequent ventricular and atrial premature complexes, short episodes of supraventricular and ventricular tachycardia, some of them with torsade de pointes appearance. A CT scan of the neck showed a nonuniform mass in the right cervical area, affecting the internal jugular lymph nodes and the internal jugular vein, reaching the parotid gland and the fight mandibular branch, together with swelling of right oropharynx and tongue base. A biopsy specimen of the mass was indicative of squamous carcinoma.

The patient was treated with magnesium, 2 g by the day (IV at first and orally thereafter), with normalization of the QT interval and disappearance of arrhythmias. Radiotherapy (cobalt) was given in the right cervical area, which produced clinical improvement and disappearance of the tumoral mass and the lymph nodes. Oral magnesium was discontinued once radiotherapy had concluded. Neither prolongation of the QT interval nor arrhythmias occurred, and the patient did not present any further syncope. Six months later, the tumor regrew in the tongue base and right tonsil, but the right cervical area was not affected, and the ECG was normal. The patient died due to bronchopneumonia in January 2000. In summary, our patient presented syncope with a long QT interval and torsade de pointes ventricular tachycardia, and a squamous carcinoma of the tongue, infiltrating adjacent neck structures and affecting the right lateral cervical sympathetic ganglions.

We are not aware of reported cases of sympathetic cervical ganglion infiltration by a tumor with long QT interval and ventricular arrhythmias. In our patient, the tumor affected the area surrounding the right jugular vein and probably some of the right sympathetic cervical ganglions. This could have caused a disbalanced sympathetic enervation of the heart, the exact opposite effect of left sympathectomy,[5] thereby originating prolongation of the QT interval. Treatment with IV magnesium during ventricular tachycardia episodes has proved effective,[6] although there are no reported references of chronic treatment with oral magnesium. Our patient was treated with oral magnesium until radiotherapy was finished, with disappearance of the tumoral mass affecting the right sympathetic cervical ganglions. The QT interval was normal thereafter, and there was no occurrence of arrhythmias and syncopes during this period.

Oscar Aramburu-Bodas, MD Antonio Cayon-Blanco, MD Juan Carlos Garcia-Rubira, MD Ramon Perez-Cano, MD Virgen Macarena University Hospital Seville, Spain

Correspondence to: Oscar Aramburu-Bodas, MD, C/Espinosa y Carcel, n [degrees] 57, 10 [degrees]-A, 41005-Sevilla, Spain; e-mail: oaramburub@ nexo.es

REFERENCES

[1] Hoepp HW, Eggeling T, Hombach V. Pharmacologic blockade of the left stellate ganglion using a drug-reservoir-pump system. Chest 1990; 97:250-251

[2] Coyer BH, Pryor R, Kirsch WM, et al. Left stellectomy in the long QT syndrome. Chest 1978; 74:584-586

[3] Acquadro MA, Nghiem TX, Beach TP, et al. Acquired QT interval changes and neck dissections. J Clin Anesth 1995; 7:54-57

[4] Dorian P, Newman D, Hughes W, et al. Torsade de pointes ventricular tachycardia following right pneumonectomy: insights into the relation between right cardiac sympathetic nerve damage, QT intervals, and arrhythmias. Int J Cardiol 1994; 46:292-296

[5] Schwartz PJ, Locati EH, Moss AJ, et al. Left cardiac sympathetic denervation in the therapy of congenital long QT syndrome: a worldwide report. Circulation 1991; 84:503-511

[6] Perticone F, Adinolfi L, Bonaduce D. Efficacy of magnesium sulfate in the treatment of torsade de pointes. Am Heart J 1986; 112:847-849

COPYRIGHT 2001 American College of Chest Physicians
COPYRIGHT 2001 Gale Group

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