Published: 2019-09-23

Evaluation of the QTc internal and QT dispersion in patients with newly detected clinical hypothyroidism

Aravind G. N., Archita R.


Background: Thyroid hormones play an important role in the orchestration of various metabolic functions in the body and thus thyroid dysfunction can produce dramatic cardiovascular effects. Electrocardiographic changes such as bradycardia, low voltage complexes, and varying degrees of heart block are commonly recognized in hypothyroid patients. Hypothyroidism has been found to be associated with increased cardiovascular morbidity and mortality. Hence, it is important to investigate the ECG  profile in these patients. The present study was aimed at evaluating the QTc interval and QT dispersion, an indicator of inhomogeneity of ventricular repolarisation and cardiac autonomic modulation in patients with newly detected clinical hypothyroidism.

Methods: 50 patients with newly detected clinical hypothyroidism and 50 healthy controls were included in the study. The ECG was recorded and the heart-rate, QTc interval and QT dispersion were calculated.

Results: The mean heart-rate was found to be significantly (p <0.05) reduced in hypothyroid patients when compared to healthy controls. The mean QTc interval and QT dispersion were significantly increased in hypothyroid patients when compared to controls. QTmin and QTmax of cases and controls also showed a statistically significant  difference.

Conclusion: Thus, the present study confirms the role of thyroid hormones on the cardiovascular system, particularly on ventricular repolarisation and cardiac autonomic modulation. Hence, early and prompt therapy with levothyroxine may help to prevent the adverse events resulting from cardiovascular dysfunction.


Hypothyroidism, Heart-rate, QTc interval, QT dispersion

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J Larry Jameson, Susan J Mandel, Anthony P Weitzman. Thyroid gland physiology and testing. In: Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson JL, Loscalzo J, eds. Harrison's principles of internal medicine. 20th Ed; Vol 2 EB: McGraw Hill Professional.

Unnikrishnan AG, Menon UV. Thyroid disorders in India: An epidemiological perspective. Ind J endocrinol and metabolism. 2011 Jul;15(2):S78.

Galetta F, Franzoni F, Fallahi P, Rossi M, Carpi A, Rubello D, et al. Heart rate variability and QT dispersion in patients with subclinical hypothyroidism. Biomedicine and pharmacotherapy. U.S. National Library of Medicine; 2006 Sep 1;60(8):425-30.

Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson JL, Loscalzo J. Harrison's principles of internal medicine 19E Vol 2 EB. McGraw Hill Professional; 2012 Nov 8.

Crowley Jr WF, Ridgway EC, Bough EW, Francis GS, Daniels GH, Kourides IA, et al. Noninvasive evaluation of cardiac function in hypothyroidism: response to gradual thyroxine replacement. New England J Med. 1977 Jan 6;296(1):1-6.

Van Noord C, van der Deure WM, Sturkenboom MC, Straus SM, Hofman A, Visser TJ, et al. High free thyroxine levels are associated with QTc prolongation in males. J Endocrinol. 2008 Jul 1;198(1):253-60.

Cacciatori V, Gemma ML, Bellavere F, Castello R, De Gregori ME, Zoppini G, et al. Power spectral analysis of heart rate in hypothyroidism. Eur J Endocrinol. 2000 Sep 1;143(3):327-33.

Manhem P, Bramnert M, Hallengren B, Lecerof H, Werner R. Increased arterial and venous plasma noradrenaline levels in patients with primary hypothyroidism during hypothyroid as compared to euthyroid state. J Endocrinol Investigation. 1992 Nov 1;15(10):763-5.

Polikar R, Kennedy B, Maisel A, Ziegler M, Dittrich H, Nicod P. Decreased adrenergic sensitivity in patients with hypothyroidism. J Am College of Cardiol. 1990 Jan 1;15(1):94-8.

Dillmann WH. Cellular action of thyroid hormone on the heart. Thyroid. 2002 Jun 1;12(6):447-52.

Inukai T, Kobayashi I, Kobayashi T, Ishii A, Yamaguchi T, Yamaguchi Y, et al. Parasympathetic nervous system activity in hypothyroidism determined by R‐R interval variations on electrocardiogram. J Inte Med. 1990 Nov;228(5):431-4.

Karademir S, Akçam M, Kuybulu AE, Olgar S, Oktem F. Effects of fluorosis on QT dispersion, heart rate variability and echocardiography parameters in children/Cocuklarda QT dispersiyonu, kalphizidegiskenligiveekokardiyografikparametrelereflorozisinetkileri. Anatolian J Cardiol. 2011 Mar 1;11(2):150-6.

Unal O, Erturk E, Ozkan H, Kiyici S, Guclu M, Ersoy C, et al. Effect of levothyroxine treatment on QT dispersion in patients with subclinical hypothyroidism. Endocrine Practice. 2007 Nov 1;13(7):711-5.

Altun A, Altun G, Özbay G. QT dispersion in hypothyroidism. Int J Cardiol. 1999 Dec 15;72(1):93-5.

Klein I, Danzi S. Cardiovascular involvement in general medical conditions. Circulation. 2007 Oct 9;116:1725-35.