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REPLY
Subclinical Thyroid Dysfunction and the Heart
Bernadette Biondi, MD;
Emiliano A. Palmieri, MD;
Gaetano Lombardi, MD; and
Serafino Fazio, MD
18 November 2003 | Volume 139 Issue 10 | Pages 866-867
IN RESPONSE:
As indicated by Auer and colleagues, their large cross-sectional study (1) does have a bearing on our study. Indeed, their findings of a similar relative risk for atrial fibrillation in patients with subclinical hyperthyroidism (serum TSH level 
0.4 mU/L) and patients with overt hyperthyroidism (serum TSH level <0.03 mU/L), and an almost 3-fold (95% CI, 1.3-fold to 5.8-fold) higher risk versus euthyroid controls (P < 0.01), strengthen the concept that thyroid secretion need not increase much for atrial fibrillation to occur and that subclinical hyperthyroidism itself may precipitate atrial fibrillation and associated sequelae, especially in the elderly. We did not cite the study by Auer and colleagues because it was published when our review was at an advanced stage of the revision process. We thank Auer and colleagues for pointing out that only 187 of the 2007 older patients studied by Sawin and associates (2) could strictly be considered as having subclinical hyperthyroidism (serum TSH level 0.4 mU/L).
Turning to the observations of Drs. Sawka and Fatourechi, we believe that the literature contains information that may help clinicians manage subclinical hypothyroidism. There is now clear evidence that subclinical hypothyroidism is a mild type of tissue hypothyroidism (3) and that it may progress to overt thyroid failure, especially if associated with positive thyroid autoantibodies (4). Relevant and reversible modifications in lipid metabolism and cardiovascular function have been reported in most clinical investigations of patients with persistent subclinical hypothyroidism treated with L-thyroxine (5). In this context, until compelling evidence is provided by controlled trials, it seems morally and scientifically justifiable to consider L-thyroxine treatment on a case-by-case basis after careful evaluation of the actual risk for overt thyroid failure and cardiovascular events. However, candidates for treatment should have a favorable cardiovascular condition, a low starting dose of L-thyroxine should be used, and biochemistry should be regularly monitored to avoid overzealous hormonal dosing and iatrogenic disease associated with hyperthyroidism.
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Author and Article Information
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From University of Naples Federico II School of Medicine; 80131 Naples, Italy.
Acknowledgment: The authors thank Jean Ann Gilder for general collaboration.
1. Auer J, Scheibner P, Mische T, Langsteger W, Eber O, Eber B. Subclinical hyperthyroidism as a risk factor for atrial fibrillation Am Heart J. 2001;142:838-42. [PMID: 11685172].[Medline]
2. Sawin CT, Geller A, Wolf PA, Belanger AJ, Baker E, Bacharach P, et al. Low serum thyrotropin concentrations as a risk factor for atrial fibrillation in older persons N Engl J Med. 1994;331:1249-52. [PMID: 7935681].[Abstract/Free Full Text]
3. Andersen S, Pedersen KM, Bruun NH, Laurberg P. Narrow individual variations in serum T(4) and T(3) in normal subjects: a clue to the understanding of subclinical thyroid disease J Clin Endocrinol Metab. 2002;87:1068-72. [PMID: 11889165].[Abstract/Free Full Text]
4. Huber G, Staub JJ, Meier C, Mitrache C, Guglielmetti M, Huber P, et al. Prospective study of the spontaneous course of subclinical hypothyroidism: prognostic value of thyrotropin, thyroid reserve, and thyroid antibodies J Clin Endocrinol Metab. 2002;87:3221-6. [PMID: 12107228].[Abstract/Free Full Text]
5. Kahaly GJ. Cardiovascular and atherogenic aspects of subclinical hypothyroidism Thyroid. 2000;10:665-79. [PMID: 11014311].[Medline]
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Reviews
Effects of Subclinical Thyroid Dysfunction on the Heart
Bernadette Biondi, Emiliano A. Palmieri, Gaetano Lombardi, AND Serafino Fazio
- Annals 2002 137: 904-914.
[ABSTRACT][Full Text]
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