High-normal Thyroid Function Research Articles

High-Normal Thyroid Function and Recurrence of Atrial Fibrillation after Catheter Ablation: A Prospective Observational Study

Background: Thyroid function is increasingly recognized as an important modifiable factor for atrial fibrillation (AF); however, it is unclear if the changes in thyroid hormones, even within the normal range, are associated with AF recurrence after catheter ablation. Methods: Consecutive paroxysmal AF patients who underwent catheter ablation were enrolled. Patients with abnormal thyroid hormones or previous thyroid illnesses were excluded. Patients were followed for 12 months or until they presented with the first episode of atrial tachyarrhythmia after a blanking period. Results: The study included 448 patients with a mean age of 61 (14) years, and 46% were women. After a 1-year follow-up, 104 (23.2%) patients experienced atrial tachyarrhythmia recurrences after an ablation procedure. Recurrence was significantly different among quartile groups of thyroid function, with highest FT₄ and FT₃ levels associated with the greatest risk of recurrence (p < 0.001 and p = 0.024, respectively). FT₄ and FT₃ levels were independent predictors of atrial tachyarrhythmia recurrence (hazard ratio 1.07 per 1 pmol/L increase in FT₄, 95% confidence interval [CI] 1.01–1.15, p = 0.036 and 1.31 per 1 pmol/L increase in FT₃, 95% CI 1.01–1.71, p = 0.032). Conclusions: High-normal FT₃ and FT₄ levels are associated with AF recurrence after catheter ablation in this Chinese population. Attention to thyroid hormones could be valuable to assist in the management of AF.

High-Normal Thyroid Function Predicts Incident Nonalcoholic Fatty Liver Disease Among Middle-Aged and Older Euthyroid Subjects

Thyroid hormones (THs) influence hepatic lipid homeostasis through multiple pathways, suggesting that THs may predict the risk of non-alcoholic fatty liver disease (NAFLD). However, prospective studies on the association between THs levels and incident NAFLD in euthyroid subjects are limited. This prospective cohort study aimed to explore whether THs were associated with the development of NAFLD in middle-aged and elderly euthyroid subjects. A total of 6,462 subjects without baseline NAFLD were included in the cohort study (~6-year follow-up period, median: 4.2 years). Chemiluminescence immunoassay was used to measure serum free triiodothyronine (FT3), free thyroxine (FT4), and thyroid-stimulating hormone (TSH), and NAFLD was diagnosed by abdominal ultrasonography. Multivariable Cox proportional hazards regression models were used to assess the association between baseline THs, TSH, and the risk of NAFLD. During the follow-up period, 1,675 subjects developed NAFLD. The incidence rate of NAFLD was 85.0 per 1000 person-years. Compared with the lowest FT3, FT4, and TSH quartiles, the multivariable-adjusted hazard ratios (95% confidence interval) of incident NAFLD for highest quartiles were 1.30 (1.12, 1.51), 1.07 (0.93, 1.23), 0.82 (0.71, 0.95) (P <0.001, =0.56, =0.01, respectively), respectively. In middle-aged and elderly euthyroid subjects, high-normal FT3 and low-normal TSH are independently associated with a higher incidence of NAFLD.

Thyroid function and risk of all-cause and cardiovascular mortality: a prospective population-based cohort study

PurposeAlthough thyroid hormones are irrefutably implicated in cardiovascular physiology, the impact of within-reference range variations of thyroid function on cardiovascular disease (CVD) remains unclear. Elucidating this is important, since it could foster preventive treatment and reduce global CVD burden. We therefore investigated the impact of within-reference range variations of thyroid function on all-cause and cardiovascular mortality.MethodsWe included community-dwelling individuals aged 28–75 years from a prospective cohort study, without known use of thyroid-affecting therapy and with thyrotropin within reference range. Associations of thyroid function with mortality were quantified using Cox models and adjusted for sociodemographic and cardiovascular risk factors.ResultsMean (SD) age of the 6,054 participants (52.0% male) was 53.3 (12.0) years. During 47,594 person-years of follow-up, we observed 380 deaths from all causes and 103 from CVDs. Although higher thyrotropin was not associated with all-cause mortality (adjusted HR 1.02, 95% CI 0.92–1.14), point estimates for cardiovascular mortality diverged toward increased risk in younger (<72 years) participants (1.31, 1.00–1.72) and decreased risk in elderly (≥72 years) (0.77, 0.56–1.06). Higher free thyroxine (FT4) was associated with all-cause mortality (1.18, 1.07–1.30) and with cardiovascular mortality only in elderly (1.61, 1.19–2.18), but not in younger participants (1.03, 0.78–1.34). Higher free triiodothyronine (FT3) was associated with all-cause mortality in females only (1.18, 1.02–1.35). FT3 was not associated with cardiovascular mortality (0.91, 0.70–1.18).ConclusionsCommunity-dwelling elderly individuals with high-normal thyroid function are at increased risk of all-cause and cardiovascular mortality, reinforcing the need of redefining the current reference ranges of thyroid function.

Thyroid function and life expectancy with and without noncommunicable diseases: Apopulation-based study.

BackgroundVariations in thyroid function within reference ranges are associated with increased risk of diseases and death. However, the impact of thyroid function on life expectancy (LE) with and without noncommunicable diseases (NCDs) remains unknown. We therefore aimed to investigate the association of thyroid function with total LE and LE with and without NCD among euthyroid individuals.Methods and findingsThe study was embedded in the Rotterdam Study, a prospective population-based study carried out in the Netherlands. In total, 7,644 participants without known thyroid disease and with thyroid-stimulating hormone (TSH) and free thyroxine (FT4) levels within reference ranges were eligible. NCDs were defined as presence of cardiovascular disease, diabetes mellitus type 2, or cancer. We used the demographic tool of multistate life tables to calculate LE estimates at the age of 50 years, using prevalence, incidence rates, and hazard ratios for three transitions (healthy to NCD, healthy to death, and NCD to death). The total LE and LE with and without NCD among TSH and FT4 tertiles were calculated separately in men and women. Analyses were adjusted for sociodemographic and cardiovascular risk factors. The mean (standard deviation) age of the participants was 64.5 (9.7) years, and 52.3% were women. Over a median follow-up of 8 years (interquartile range 2.7–9.9 years), 1,396 incident NCD events and 1,422 deaths occurred. Compared with those in the lowest TSH tertile, men and women in the highest TSH tertile were expected to live 1.5 years (95% confidence interval [CI] 0.8–2.3, p < 0.001) and 1.5 years (CI 0.8–2.2, p < 0.001) longer, respectively, of which 1.4 years (CI 0.5–2.3, p = 0.002) and 1.3 years (CI 0.3–2.1, p = 0.004) with NCD. Compared with those in the lowest FT4 tertile, the difference in LE for men and women in the highest FT4 tertile was −3.7 years (CI −5.1 to −2.2, p < 0.001) and −3.3 years (CI −4.7 to −1.9, p < 0.001), respectively, of which −1.8 years (CI −3.1 to −0.7, p = 0.003) and −2.0 years (CI −3.4 to −0.7, p = 0.003) without NCD. A limitation of the study is the observational design. Thus, the possibility of residual confounding cannot be entirely ruled out.ConclusionsIn this study, we found that people with low–normal thyroid function (i.e., highest tertile of TSH and lowest tertile of FT4 reference ranges) are expected to live more years with and without NCD than those with high–normal thyroid function (i.e., lowest tertile of TSH and highest tertile of FT4 reference ranges). These findings provide support for a re-evaluation of the current reference ranges of thyroid function.

P3414Differences in total life expectancy and life expectancy with and without non-communicable diseases within the reference range of thyroid function

Abstract Background Variations in thyroid function within the reference ranges are associated with an increased risk of diseases and death. However, the impact of thyroid function on life expectancy (LE) and the number of years lived with and without non-communicable diseases (NCD) remains unknown. Purpose We aimed to investigate the association of thyroid function with total LE and LE with and without NCD among euthyroid subjects. Methods Participants of the Rotterdam Study without known thyroid disease and with thyroid-stimulating hormone (TSH) and free thyroxine (FT4) levels within the reference ranges were eligible. NCD were defined as the presence of cardiovascular disease, diabetes mellitus type 2, or cancer. We used multistate life tables to calculate the total LE and LE with and without NCD among TSH and FT4 tertiles, in men and women. LE estimates were obtained using prevalence, incidence rates and hazard ratios for three transitions (healthy to NCD, healthy to death and NCD to death). Analyses were adjusted for sociodemographic and cardiovascular risk factors. Results The mean (standard deviation) age of 7644 participants was 64.5 (9.7) years and 52.2% were women. Over a median follow-up of 8 years, we observed 1396 incident NCD events and 1422 deaths. Compared with those in the lowest tertile, men and women in the highest TSH tertile lived 1.5 (95% confidence interval [CI], 0.8; 2.3) and 1.5 (95% CI, 0.8; 2.2) years longer, respectively; of which 1.4 (95% CI, 0.5; 2.3) and 1.3 (95% CI, 0.3; 2.1) years with NCD. Compared with those in the lowest tertile, the difference in LE for men and women in the highest FT4 tertile was −3.7 (95% CI, −5.1 to −2.2) and −3.3 (95% CI, −4.7; −1.9), respectively; of which −1.8 (95% CI, −3.1 to −0.7) and −2.0 (95% CI, −3.4 to −0.7) years without NCD. Life expectancy in TSH and FT4 tertiles Conclusions There are meaningful differences in total LE, LE with and without NCD within the reference ranges of thyroid function. People with low-normal thyroid function live more years with and without NCD than those with high-normal thyroid function. These findings support a reevaluation of the current reference ranges of thyroid function.

High-Normal Thyroid Function and Recurrence of Atrial Fibrillation after Catheter Ablation: A Study Related to Dietary Structure and Iodine Intake

Background: Thyroid function is increasingly recognized as an important modifiable factor for atrial fibrillation (AF); however, it is unclear if the changes in thyroid hormones, even within the normal range, are associated with AF recurrence after catheter ablation. Thus, we investigated the relationship between thyroid hormones and AF recurrence. Methods: A total of 388 consecutive AF patients (mean [standard deviation] age, 59*9 [9*7] years; 240 males [61.9%]) who underwent catheter ablation were enrolled and had thyroid functions measured before the procedure. Patients were followed for 12 months or until they presented with the first AF episode after a blanking period. Findings: After a 1-year follow-up, 104 (26*8%) patients experienced AF recurrences after an ablation procedure. Kaplan-Meier analysis revealed that patients with high-normal free tetraiodothyronine (FT4) or free triiodothyronine (FT3) levels had a lower recurrence-free survival compared to the low-normal groups (P = 0*037 and P = 0*035, respectively), and those trends were more prominent in younger patients (P = 0*028 and P = 0*031, respectively). Although higher tetraiodothyronine (T4) levels were not associated with higher AF recurrence rates in the general population, there was a significant difference in AF recurrences between higher and lower T4 levels in younger and male populations (P = 0*004 and P = 0*003, respectively). After multivariate adjustment, patients in both the high-normal FT4 and FT3 groups had an increased risk of recurrence (hazard ratio 1*70; 95% confidence interval, 1*14-2*53, P < 0*01). Interpretation: Both high-normal FT3 and FT4 levels are associated with AF recurrence, especially in younger populations, which suggests a low daily intake of iodine, especially in some iodine-abundant areas. Trial Registration: This study was registered at chictr.org.cn (identifier ChiCTR1800017465). Funding Statement: National Key R&D Program of China (Grant no.2016YFC1301003), the National Science Foundation of China (Grant no. 81873484), National Key R&D Program of China (Grant no. 2016YFC1301003), the National Science Foundation of China (Grant nos. 30900612, 81800231 and 81873484), the Clinical Research Fund of Zhejiang Provincial Medical Association (Grant nos.2015ZYC-A16 and 2018ZYC-A11), the Nature Science Foundation of Zhejiang Province (Grant no. LZ16H020001), Medical Science Research Foundation of Zhejiang Province (Grant no. 2018ZD017), the Zhejiang Provincial Natural Science Foundation (Grant no. LY15H020002 and Y17H020020), the Department of Science and Technology, Zhejiang Province (Grant no. LGF19H020011), People's Republic of China. Declaration of Interests: The authors declare no competing interests. Ethics Approval Statement: This study was approved by our hospital Institutional Review Board and all of the patients gave informed consent.

Thyroid Function and Cardiovascular Disease: The Mediating Role of Coagulation Factors.

Mechanisms linking high and high-normal thyroid function to increased cardiovascular risk remain unclear. Hypothetically, coagulation can play a role. To investigate (i) the association of thyroid function with coagulation factors and (ii) whether coagulation factors mediate the association of thyroid function with cardiovascular disease (CVD). Rotterdam Study, a population-based prospective study. In 5918 participants (mean age, 69.1 years), we measured TSH, free T4 (FT4), and coagulation factors [von Willebrand factor antigen (VWF:Ag), ADAMTS13 activity, fibrinogen]. Participants were followed up for the occurrence of cardiovascular events and deaths. Associations of thyroid function with coagulation factors (standardized z scores) and CVD were assessed through linear regression and Cox proportional hazards models, adjusted for potential confounders. We performed causal mediation analyses to evaluate whether the effect of thyroid function on CVD is mediated by coagulation. Higher FT4 levels were associated with higher VWF:Ag (β = 0.34; 95% CI = 0.22, 0.47), lower ADAMTS13 activity (β = -0.22; 95%CI = -0.35, -0.09), and higher fibrinogen (β = 0.26; 95% CI = 0.13, 0.39); 857 incident cardiovascular events and 690 cardiovascular deaths occurred. FT4 levels were positively associated with cardiovascular events and deaths. The effect of FT4 on incident cardiovascular events was minimally mediated by fibrinogen (1.6%) but not by VWF:Ag and ADAMTS13. VWF:Ag and fibrinogen together mediated 10.0% of the effect of FT4 on cardiovascular deaths. Higher FT4 levels were associated with higher VWF:Ag, lower ADAMTS13 activity, and higher fibrinogen levels, indicating a procoagulant state. VWF:Ag and fibrinogen explained up to 10% of the link between FT4 and CVD.

Association of Thyroid Function With Life Expectancy With and Without Cardiovascular Disease

Variations in thyroid function within reference ranges are associated with an increased risk of cardiovascular disease (CVD) and mortality. However, the impact of thyroid function on life expectancy (LE) and the number of years lived with and without CVD remains unknown. To investigate the association of thyroid function with total LE and LE with and without CVD among euthyroid individuals. The Rotterdam Study, a population-based, prospective cohort study. We included participants without known thyroid disease and with thyrotropin and free thyroxine (FT4) levels within the reference ranges. Multistate life tables were used to calculate total LE and LE with and without CVD among thyrotropin and FT4 tertiles. Life expectancy estimates in men and women aged 50 years and older were obtained using prevalence, incidence rates, and hazard ratios for 3 transitions (healthy to CVD, healthy to death, and CVD to death), adjusting for sociodemographic and cardiovascular risk factors. The mean (SD) age of the 7785 participants was 64.7 (9.8) years, and 52.5% were women. Over a median follow-up of 8.1 (interquartile range, 2.7-9.9) years, we observed 789 incident CVD events and 1357 deaths. Compared with those in the lowest tertile, men and women in the highest thyrotropin tertile lived 2.0 (95% CI, 1.0 to 2.8) and 1.4 (95% CI, 0.2 to 2.4) years longer, respectively, of which, 1.5 (95% CI, 0.2 to 2.6) and 0.9 (95% CI, -0.2 to 2.0) years longer without CVD. Compared with those in the lowest tertile, the difference in life expectancy for men and women in the highest FT4 tertile was -3.2 (95% CI, -5.0 to -1.4) and -3.5 (95% CI, -5.6 to -1.5) years, respectively, of which, -3.1 (95% CI, -4.9 to -1.4) and -2.5 (95% CI, -4.4 to -0.7) years without CVD. At the age of 50 years, participants with low-normal thyroid function live up to 3.5 years longer overall and up to 3.1 years longer without CVD than participants with high-normal thyroid function. These findings provide supporting evidence for a reevaluation of the current reference ranges of thyroid function and can help inform preventive and clinical care.

Prevalence of right atrial non-pulmonary vein triggers in atrial fibrillation patients treated with thyroid hormone replacement therapy.

Thyroid hormone (TH) is known to enhance arrhythmogenicity, and high-normal thyroid function is related with an increased recurrence of atrial fibrillation (AF) after catheter ablation. However, the impact of thyroid hormone replacement (THR) on AF ablation is not well known. This study evaluated 1163 consecutive paroxysmal AF patients [160 (14%) on THR and 1003 (86%) without THR] undergoing their first catheter ablation. A total of 146 patients on THR and 146 controls were generated by propensity matching, based on calculated risk factor scores, using a logistic model (age, sex, body mass index, and left atrium size). The presence of non-pulmonary vein (PV) triggers was disclosed by a high-dose isoproterenol challenge (up to 30μg/min) after PV isolation. Clinical characteristics were not different between the groups. When compared to the control, non-PV triggers were significantly greater in the THR patients [112 (77%) vs. 47 (32%), P < 0.001], and most frequently originated from the right atrium (95 vs. 56%, P < 0.001). Other sources of non-PV triggers were the interatrial septum (25 vs. 11%, P = 0.002), coronary sinus (70 vs. 52%, P = 0.01), left atrial appendage (47 vs. 34%, P = 0.03), crista terminalis/superior vena cava (11 vs. 8%, P = 0.43), and mitral valve annulus (7 vs. 5%, P = 0.45) (THR vs. control), respectively. After mean follow-up of 14.7 ± 5.2months, success rate was lower in patients on THR therapy [94 (64.4%)] compared to patients not receiving THR therapy [110 (75.3%), log-rank test value = 0.04]. Right atrial non-PV triggers were more prevalent in AF patients treated with THR. Elimination of non-PV triggers provided better arrhythmia-free survival in the non-THR group.

Thyroid function and the risk of dementia: The Rotterdam Study.

To study the role of thyroid function in dementia, cognitive function, and subclinical vascular brain disease with MRI. Analyses were performed within the Rotterdam Study (baseline 1997), a prospective, population-based cohort. We evaluated the association of thyroid-stimulating hormone (TSH) and free thyroxine with incident dementia using Cox models adjusted for age, sex, cardiovascular risk factors, and education. Absolute risks were calculated accounting for death as a competing risk factor. Associations of thyroid function with cognitive test scores and subclinical vascular brain disease (white matter lesions, lacunes, and microbleeds) were assessed with linear or logistic regression. Additionally, we stratified by sex and restricted analyses to normal thyroid function. We included 9,446 participants with a mean age of 65 years. During follow-up (mean 8.0 years), 601 participants had developed dementia. Higher TSH was associated with lower dementia risk in both the full and normal ranges of thyroid function (hazard ratio [HR] 0.90, 95% confidence interval [CI] 0.83-0.98; and HR 0.76, 95% CI 0.64-0.91, respectively). This association was independent of cardiovascular risk factors. Dementia risk was higher in individuals with higher free thyroxine (HR 1.04, 95% CI 1.01-1.07). Absolute 10-year dementia risk decreased from 15% to 10% with higher TSH in older women. Higher TSH was associated with better global cognitive scores (p = 0.021). Thyroid function was not related to subclinical vascular brain disease as indicated by MRI. High and high-normal thyroid function is associated with increased dementia risk. Thyroid function is not related to vascular brain disease as assessed by MRI, suggesting a role for thyroid hormone in nonvascular pathways leading to dementia.

Additional measurement of hCG distinguishes physiological high-normal thyroid function and reveals large differences in the risk of developing preeclampsia

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Association of maternal thyroid function during early pregnancy with offspring IQ and brain morphology in childhood: a population-based prospective cohort study

Thyroid hormone is involved in the regulation of early brain development. Since the fetal thyroid gland is not fully functional until week 18-20 of pregnancy, neuronal migration and other crucial early stages of intrauterine brain development largely depend on the supply of maternal thyroid hormone. Current clinical practice mostly focuses on preventing the negative consequences of low thyroid hormone concentrations, but data from animal studies have shown that both low and high concentrations of thyroid hormone have negative effects on offspring brain development. We aimed to investigate the association of maternal thyroid function with child intelligence quotient (IQ) and brain morphology. In this population-based prospective cohort study, embedded within the Generation R Study (Rotterdam, Netherlands), we investigated the association of maternal thyroid function with child IQ (assessed by non-verbal intelligence tests) and brain morphology (assessed on brain MRI scans). Eligible women were those living in the study area at their delivery date, which had to be between April 1, 2002, and Jan 1, 2006. For this study, women with available serum samples who presented in early pregnancy (<18 weeks) were included. Data for maternal thyroid-stimulating hormone, free thyroxine, thyroid peroxidase antibodies (at weeks 9-18 of pregnancy), and child IQ (assessed at a median of 6·0 years of age [95% range 5·6-7·9 years]) or brain MRI scans (done at a median of 8·0 years of age [6·2-10·0]) were obtained. Analyses were adjusted for potential confounders including concentrations of human chorionic gonadotropin and child thyroid-stimulating hormone and free thyroxine. Data for child IQ were available for 3839 mother-child pairs, and MRI scans were available from 646 children. Maternal free thyroxine concentrations showed an inverted U-shaped association with child IQ (p=0·0044), child grey matter volume (p=0·0062), and cortex volume (p=0·0011). For both low and high maternal free thyroxine concentrations, this association corresponded to a 1·4-3·8 points reduction in mean child IQ. Maternal thyroid-stimulating hormone was not associated with child IQ or brain morphology. All associations remained similar after the exclusion of women with overt hypothyroidism and overt hyperthyroidism, and after adjustment for concentrations of human chorionic gonadotropin, child thyroid-stimulating hormone and free thyroxine or thyroid peroxidase antibodies (continuous or positivity). Both low and high maternal free thyroxine concentrations during pregnancy were associated with lower child IQ and lower grey matter and cortex volume. The association between high maternal free thyroxine and low child IQ suggests that levothyroxine therapy during pregnancy, which is often initiated in women with subclinical hypothyroidism during pregnancy, might carry the potential risk of adverse child neurodevelopment outcomes when the aim of treatment is to achieve high-normal thyroid function test results. The Netherlands Organisation for Health Research and Development (ZonMw) and the European Community's Seventh Framework Programme.

State of the art paper Hyperthyroidism and cardiovascular complications: a narrative review on the basis of pathophysiology

Cardiovascular complications are important in hyperthyroidism because of their high frequency in clinical presentation and increased mortality and morbidity risk. The cause of hyperthyroidism, factors related to the patient, and the genetic basis for complications are associated with risk and the basic underlying mechanisms are important for treatment and management of the disease. Besides cellular effects, hyperthyroidism also causes hemodynamic changes, such as increased preload and contractility and decreased systemic vascular resistance causes increased cardiac output. Besides tachyarrythmias, impaired systolic ventricular dysfunction and diastolic dysfunction may cause thyrotoxic cardiomyopathy in a small percentage of the patients, as another high mortality complication. Although the medical literature has some conflicting data about benefits of treatment of subclinical hyperthyroidism, even high-normal thyroid function may cause cardiovascular problems and it should be treated. This review summarizes the cardiovascular consequences of hyperthyroidism with underlying mechanisms.

Thyroid Function and Risk of Atrial Tachyarrhythmia Occurrence after Pulmonary Vein Isolation in Patients with Paroxysmal Atrial Fibrillation

Backgrounds: Recent evidence demonstrated that serum free thyroxine (FT4) concentration was independently associated with the development of atrial fibrillation (AF), even in euthyroid persons with TSH levels in the normal range. We examined the impact of thyroid function on the risk of recurrent and newly developed atrial tachyarrythmias after catheter ablation for AF. Methods: This study included 156 consecutive patients with paroxysmal AF who underwent initial pulmonary vein antral isolation with elimination of dormant conduction induced by isoproterenol and adenotriphosphate injection. Patients with prior or current thyroid dysfunction were excluded. We examined the occurrence of documented recurrent or newly developed atrial tachyarrhythmia after the ablation. Results: After a mean follow-up of 27 months, 12.2% (19/156) of the studied subjects had AF recurrence. Although the AF recurrence rates of the highest FT4 quartile tended to be higher, there was no significant difference in recurrence rates among those quartiles. Patients with newly developed atrial tachycardia/flutter had significantly higher serum FT4 level and lower serum thyroid-stimulating hormone. The higher FT4 level was significantly associated with newly documented atrial tachycardia/flutter. Conclusions: Patients with high-normal thyroid function were not at an increased risk of AF recurrence but associated with newly developed atrial tachycardia/flutter after catheter ablation.

E0574 High-normal thyroid function and risk of recurrence of atrial fibrillation after catheter ablation

BackgroundIt has been shown that serum free thyroxine (FT4) concentration is independently associated with atrial fibrillation (AF) even in euthyroid persons. This study aimed to testify the impact of high-normal...

High-Normal Thyroid Function and Risk of Recurrence of Atrial Fibrillation After Catheter Ablation

It has been shown that the concentration of serum free thyroxine (FT(4)) is independently associated with atrial fibrillation (AF), even in euthyroid persons. This study investigated the effect of a high-normal level of FT(4) on recurrence after catheter ablation of AF. The 244 consecutive patients with paroxysmal AF and who underwent circumferential pulmonary vein isolation (PVI) were prospectively enrolled. Exclusion criteria included prior or current thyroid dysfunction on admission, amiodarone medication for 3 months before admission. After a mean follow-up of 416+/-204 (91-856) days, the recurrence rates were 14.8%, 23.0%, 33.3%, 38.7% from the lowest FT(4) quartile to the highest FT(4) quartile, respectively (P=0.016). After adjustment for age, sex, left atrial diameter, and PVI, there was an increased risk of recurrence in the subjects with the highest FT(4) quartile compared with those with the lowest quartile (hazard ratio 3.31, 95% confidence interval 1.45-7.54, P=0.004). As a continuous variable, FT(4) was also an independent predictor of recurrence (hazard ratio 1.10, 95% confidence interval 1.02-1.18, P=0.016). Patients with high-normal thyroid function were at an increased risk of AF recurrence after catheter ablation.

High-Normal Thyroid Function and Risk of Atrial Fibrillation

Overt and subclinical hyperthyroidism are both well-known independent risk factors for atrial fibrillation. We aimed to investigate the association of high-normal thyroid function with the development of atrial fibrillation in a prospective population-based study in the elderly. The association between thyroid-stimulating hormone (TSH) levels and atrial fibrillation was examined in 1426 subjects with TSH levels in the normal range (0.4-4.0 mU/L) and without atrial fibrillation at baseline. In 1177 of the 1426 persons in this group, we also examined the association between free thyroxine levels within the normal range (0.86-1.94 ng/dL [to convert to picomoles per liter, multiply by 12.871]) and atrial fibrillation. During a median follow-up of 8 years, 105 new cases of atrial fibrillation were identified. Hazard ratios (HRs) were calculated with 95% confidence intervals (CIs) using Cox proportional hazards models after adjustment for age, sex, current smoking, former smoking, body mass index, systolic blood pressure, hypertension, history of myocardial infarction, presence of heart failure, left ventricular hypertrophy on the electrocardiogram, diabetes mellitus, total cholesterol level, and time of the drawing of blood samples. The risk of atrial fibrillation was associated with the TSH level. The multivariate adjusted HR was 1.94 (95% CI, 1.13-3.34, lowest vs highest quartile; P for trend, .02). The multivariate adjusted level of free thyroxine showed a graded association with risk of atrial fibrillation (HR, 1.62; 95% CI, 0.84-3.14, highest vs lowest quartile; P for trend, .06). Within the normal range of thyroid parameters, persons with high-normal thyroid function are at an increased risk of atrial fibrillation.