CORRESPONDENCE: LETTER TO THE EDITOR
Inherited Long QT Syndromes: Be Mindful of the Potassium Level
John R. Kapoor, MD, PhD*
* Division of Cardiology, Stanford University, 300 Pasteur Drive, Stanford, California 94305 (Email: jkapoor{at}stanford.edu).
Management of inherited channelopathies has benefited a great deal from advances in our understanding of the pathophysiological basis of associated arrhythmogenesis. The hereditary long-QT syndrome (LQTS) is no exception, being one of the most studied of the inherited channelopathies. Mechanistically, alterations in the balance of membrane ion currents can affect action potential repolarization, hence predisposing to lethal arrhythmias. Indeed, the utility of beta-blockers, implantable cardioverter defibrillators, and left cervicothoracic sympathetic denervation in this condition cannot be understated (1). Mutations leading to a reduction in the outward potassium current underlie certain subtypes of LQTS. It would therefore seem logical that increasing this outward potassium current might have some therapeutic value. It is noteworthy that merely maintaining a serum K+ well above baseline has the effect of reducing the resting corrected QT (QTc) interval, because of the resultant increase in conductance through both Ikr and IK1 (2). Administration of oral potassium to patients with long QT syndrome type 2 (LQT2) to increase plasma concentration by 1.5 mEq/l above the baseline resulted in a 24% reduction in resting QTc interval (from 617 ± 92 ms to 469 ± 23 ms, p = 0.004) compared with a 4% reduction in control subjects (from 425 ± 25 ms to 410 ± 45 ms, p > 0.05) (2). It also normalized QT dispersion and led to an improved T-wave morphology and QT-RR relationship (2). The improvement in the repolarization abnormality was also seen when patients with LQT2 were subjected to longer-term oral potassium administration (3). An increase in serum K+ from 4.0 ± 0.3 mEq/l to 5.2 ± 0.3 mEq/l was found to be safe and resulted in a decrease in the QTc interval from 526 ± 94 ms to 423 ± 36 ms and improvement in both QT dispersion and T-wave morphology (3). Patients with the LQT2 subtype have the highest incidence of a cardiac event (46%) before age 40 years, and the QTc interval has been found to be an independent predictor of events (4). This would suggest that rectifying the repolarization abnormalities in these patients would lead to improved outcomes. Although well-controlled long-term trials are needed to determine its efficacy in arrhythmia prevention, supplemental potassium seems to be a promising addition to the treatment armamentarium in congenital LQTS.
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1. Goldenberg I, Moss AJ. Long QT syndrome J Am Coll Cardiol 2008;51:2291-2300.[Abstract/Free Full Text]2. Compton SJ, Lux RL, Ramsey MR, et al. Genetically defined therapy of inherited long-QT syndrome. Correction of abnormal repolarization by potassium. Circulation 1996;94:1018-1022.[Abstract/Free Full Text] 3. Etheridge SP, Compton SJ, Tristani-Firouzi M, Mason JW. A new oral therapy for long QT syndrome: long-term oral potassium improves repolarization in patients with HERG mutations J Am Coll Cardiol 2003;42:1777-1782.[Abstract/Free Full Text] 4. Priori SG, Schwartz PJ, Napolitano C, et al. Risk stratification in the long-QT syndrome N Engl J Med 2003;348:1866-1874.[Abstract/Free Full Text]
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- Ilan Goldenberg and Arthur J. Moss
J. Am. Coll. Cardiol. 2008 52: 1605-1606.
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