Prolonged Ventricular Repolarization Measured by Corrected QT Interval (QTc) in Subclinical Hyperthyroidism

Abstract

Overt hyperthyroidism and hypothyroidism exert a major effect on cardiac function and on ECG. The influence of subclinical hyperthyroidism on the circulatory system is still under debate. Few studies examined the effect of thyroid hormones on ventricular repolarization measured by corrected QT interval (QTc). Longer QTc is associated with increased risk of arrhythmia and cardiac mortality. The aim of this study was to examine the influence of subclinical hyperthyroidism on ventricular repolarization measured by corrected QTc in a standard 12-lead electrocardiogram. The examined group consisted of thirty-two patients with subclinical hyperthyroidism; the controls were thirty-nine healthy individuals. In the group with subclinical hyperthyroidism, we observed a significant increase in heart rate (80.3 ± 10.59 vs. 73.7 ± 11.37 bpm, p < 0.05). The mean corrected QTc was 0.434 ± 0.0207 seconds and 0.414 ± 0.0208 in the examined groups and in controls, respectively (p < 0.001). QTc did not correlate with free thyroxin concentrations (p = 0.5084). Conclusion: Corrected QT intervals were significantly longer in patients with subclinical hyperthyroidism.

Key words

Thyroid - ECG - heart - thyroxine

References

• 1 Klein I, Ojamaa K. Thyroid hormone and the cardiovascular system.  N Engl J Med. 2001;  344 501-509
• 2 Sarma J S, Venkataraman K, Nicod P, Polikar R, Smith J, Schoenbaum M P, Singh B N. Circadian rhythmicity of rate-normalized QT interval in hypothyroidism and its significance for development of class III antiarrhythmic agents.  Am J Cardiol. 1990;  66 959-963
• 3 Belfiore A, Sava L, Runello F, Tomaselli L, Vigneri R. Solitary autonomously functioning thyroid nodules and iodine deficiency.  J Clin Endocrinol Metab. 1983;  56 283-287
• 4 Elte J W, Bussmaker J K, Haak A. The natural history of euthyroid multinodular goiter.  Postgrad Med J. 1990;  66 186-190
• 5 Montanez A, Ruskin J N, Hebert P R, Lamas G A, Hennekens C H. Prolonged QTc interval and risks of total and cardiovascular mortality and sudden death in the general population: a review and qualitative overview of the prospective cohort studies.  Arch Intern Med. 2004;  164 943-948
• 6 Bazett H C. An analysis of the time relations of electrocardiograms.  Heart. 1920;  7 353-370
• 7 Marqusee E, Haden S T, Utiger R D. Subclinical thyrotoxicosis.  Endocrinol Metab Clin North Am. 1998;  27 37-49
• 8 Cooper D S. Subclinical thyroid disease: a clinician’s perspective.  Ann Intern Med. 1998;  129 135-138
• 9 Biondi B, Fazio S, Carella C, Amato G, Cittadini A, Lupoli G, Sacca L, Bellastella A, Lombardi G. Cardiac effects of long term thyrotropin-suppressive therapy with levothyroxine.  J Clin Endocrinol Metab. 1993;  77 334-338
• 10 Fazio S, Biondi B, Carella C, Sabatini D, Cittadini A, Panza N, Lombardi G, Sacca L. Diastolic dysfunction in patients on thyroid-stimulating hormone suppressive therapy with levothyroxine: beneficial effect beta-blockade.  J Clin Endocrinol Metab. 1995;  80 2222-2226
• 11 Biondi B, Fazio S, Cuocolo A, Sabatini D, Nicolai E, Lombardi G, Salvatore M, Sacca L. Impaired cardiac reserve and exercise capacity in patients receiving long-term thyrotropin suppressive therapy with levothyroxine.  J Clin Endocrinol Metab. 1996;  81 4224-4228
• 12 Shapiro L E, Sievert R, Ong L, Ocampo E L, Chance R A, Lee M, Nanna M, Ferrick K, Surks M I. Minimal cardiac effects in asymptomatic athyreotic patients chronically treated with thyrotropin-suppressive doses of L-thyroxin.  J Clin Endocrinol Metab. 1997;  82 2592-2595
• 13 Sawin C T, Geller A, Wolf P A, Belanger A J, Baker E, Bacharach P, Wilson P W, Benjamin E J, D’Agostino R B. Low serum thyrotropin concentration as a risk factor for atrial fibrillation in older persons.  N Engl J Med. 1994;  331 1249-1252
• 14 Kahn J K, Sisson J C, Vinik A I. QT interval prolongation and sudden cardiac death in diabetic autonomic neuropathy.  J Clin Endocrinol Metab. 1987;  64 751-754
• 15 Moss A J, Zareba W, Hall W J, Schwartz P J, Crampton R S, Benhorin J, Vincent G M, Locati E H, Priori S G, Napolitano C, Medina A, Zhang L, Robinson J L, Timothy K, Towbin J A, Andrews M L. Effectiveness and limitations of beta-blocker therapy in congenital long-QT syndrome.  Circulation. 2000;  101 616-623
• 16 Farhangi V, Sansone R A. QTc prolongation due to propranolol overdose.  Int J Psychiatry Med. 2003;  33 201-202
• 17 Viskin S, Fish R, Roth A, Schwartz P J, Belhassen B. QT or Not QT?.  New Engl J Med. 2000;  343 352-356
• 18 Colzani R M, Emdin M, Conforti F, Passino C, Scarlattini M, Iervasi G. Hyperthyroidism is associated with lengthening of ventricular repolarization.  Clin Endocrinol (Oxf). 2001;  55 27-32
• 19 Bosch R F, Wang Z, Li G R, Nattel S. Electrophysiological mechanisms by which hypothyroidism delays repolarization in guinea pig hearts.  Am J Physiol. 1999;  277 211-220
• 20 Le Bouter S, Demolombe S, Chambellan A, Bellocq C, Aimond F, Toumaniantz G, Lande G, Siavoshian S, Baro I, Pond A L, Nerbonne J M, Leger J J, Escande D, Charpentier F. Microarray analysis reveals complex remodeling of cardiac ion channel expression with altered thyroid status: relation to cellular and integrated electrophysiology.  Circ Res. 2003;  92 234-242
• 21 Venditti P, Puca A, Di Meo S. Effects of thyroid state on H₂O₂ production by rat heart mitochondria: sites of production with complex I- and complex II-linked substrates.  Horm Metab Res. 2003;  35 55-61