Hyperthyroidism in Elderly Patients with Atrial Fibrillation and Normal Thyroid Hormone Measurements

Hyperthyroidism is Underdiagnosed and Undertreated in 3336 Patients: An Opportunity for Improvement and Intervention

OBJECTIVE

The aim of this study was to determine the prevalence of undiagnosed and untreated hyperthyroidism among patients with suppressed thyroid-stimulating hormone (TSH).

BACKGROUND

Hyperthyroidism can significantly diminish patient quality of life and increase the financial burden on patients and health systems. We hypothesized that many patients with hyperthyroidism remain undiagnosed because physicians fail to recognize and evaluate suppressed TSH as the first indication of disease.

METHODS

We reviewed administrative data on 174011 patients with TSH measured at a tertiary referral center between 2011 and 2017 to identify individuals with hyperthyroidism (TSH <0.05 mU/L) and their subsequent outcomes: evaluation (measurement of T4, T3, radioactive iodine (RAI) uptake scan, thyroid-stimulating immunoglobulin, thyroid peroxidase antibodies) diagnosis, referral and treatment. We used Kaplan-Meier methods and multivariable time-related parametric hazard modeling to measure our outcomes.

RESULTS

We found 3336 patients with hyperthyroidism. The mean age of our cohort was 52 ± 17 years, with 79% females and 59% whites. Only 1088 patients (33%) received any appropriate evaluation and hyperthyroidism remained undiagnosed in 37% of patients who had the appropriate workup. Among those diagnosed with hyperthyroidism, only 21% were referred for surgery and 34% received RAI. Predictors for hyperthyroidism diagnosis include lower TSH (0.01u/L), younger age, African-American race, private commercial insurance, being seen in an outpatient setting, absence of medical comorbidities, presentation with ophthalmopathy, or weight loss.

CONCLUSIONS

Hyperthyroidism is frequently unrecognized and untreated, which can lead to adverse outcomes and increased costs. Improved systems for detection and treatment of hyperthyroidism are needed to address this gap in care.

Subclinical hyperthyroidism and atrial fibrillation

Subclinical hyperthyroidism is characterized by a clearly low serum concentration of thyrotropin (TSH) and the absence of obvious symptoms of hyperthyroidism. Whether or not all persons with a low value for serum TSH can be considered subclinically hyperthyroid is uncertain, but the low serum TSH per se is a risk factor for atrial fibrillation and perhaps other cardiovascular disease. Screening all persons, even in the older age groups, for subclinical hyperthyroidism may not be justified in and of itself but such persons would likely be screened for subclinical hypothyroidism and so those with subclinical hyperthyroidism identified. There are no controlled trials that show the benefit of treatment of subclinical hyperthyroidism, thus therapy at present needs to be determined by clinical judgement, aided by monitoring the patient to see if the low serum TSH level persists and assessing the presence or absence of other determinants of therapy such as an elevated serum triiodothyronine (T3) concentration, a multinodular goiter, or the appearance of overt symptoms.

Single-channel activity and expression of atrial L-type Ca(2+) channels in patients with latent hyperthyroidism

Patients with "latent hyperthyroidism" (suppressed thyroid-stimulating hormone and normal circulating thyroid hormones) are at risk to develop atrial fibrillation. In animal models, hyperthyroidism is associated with increased cardiac L-type Ca(2+) current. Therefore, we assessed L-type channel function and expression in right atria from patients undergoing cardiac surgery. Single L-type channels were studied in the cell-attached condition. Voltage dependence of gating was similar in patients with and without latent hyperthyroidism. With use of a pulse protocol leading to maximum channel availability, single-channel activity was further analyzed. Average peak current was significantly enhanced in latent hyperthyroidism, mainly because of an increased channel availability (P < 0.05). Protein expression was analyzed by Western blot. In latent hyperthyroidism, expression of Ca(2+) channel alpha(1)-subunits was increased more than threefold (P < 0.01). In contrast, sarco(endo)plasmic reticulum Ca(2+)-ATPase and phospholamban levels were not significantly changed. We only observed a trend toward increased sarco(endo)plasmic reticulum Ca(2+)-ATPase expression (P = 0.085). Function and expression of human atrial L-type Ca(2+) channels are increased in latent hyperthyroidism. These endocrine effects on the heart may be clinically relevant.

Is idiopathic atrial fibrillation caused by occult thyrotoxicosis? A study of one hundred consecutive patients with atrial fibrillation

In this study we evaluated the possible relationship between idiopathic atrial fibrillation and occult thyrotoxicosis, diagnosed by lack of response of thyroid stimulating hormone to administration of thyrotropin releasing hormone. Three groups were compared: 25 patients with idiopathic atrial fibrillation; 52 with cardiovascular atrial fibrillation; and 27 with sinus rhythm. Patients were excluded with any clinical evidence of thyrotoxicosis or with elevated serum FT4 level, as well as those with diseases or on medications known to be associated with a diminished response to administration of the releasing hormone. A flat test (lack of response) was found in only 4% of the patients. There was no significant difference among the 3 groups. Based on these data we believe that there is no relationship between idiopathic atrial fibrillation or any other type of atrial fibrillation and occult thyrotoxicosis.

Is a more active attitude warranted in patients with subclinical thyrotoxicosis?

In 1985 one of the new sensitive thyroid stimulating hormone (TSH) assays was introduced as part of our laboratory routine for thyroid function testing. Consequently, we now routinely identify a small but not insignificant group of patients with 'subclinical thyrotoxicosis', i.e. a low serum TSH in conjunction with a normal serum free T4. We here present the results of a 2-year follow-up investigation, which includes 40 patients with subclinical thyrotoxicosis and 40 euthyroid control patients. The group with subclinical thyrotoxicosis was characterized by a mean age of 65 years and a high prevalence of nodular goitre. Twelve (30%) of the patients but none of the individuals in the control group were treated during the follow-up period because of clinical thyroid disease. Atrial fibrillation was found in 11 (28%) patients compared to four (10%) of the controls. Therapy should be considered more often than previously in patients with nodular goitre and subclinical thyrotoxicosis, particularly in conjunction with atrial fibrillation.