Electrophysiological abnormalities of the atrial muscle in patients with paroxysmal atrial fibrillation associated with hyperthyroidism

[Arrhythmias in thyroid dysfunction]

Thyroid dysfunction is associated with characteristic changes in heart rate and arrhythmias. Thyroid hormones act through genomic and non-genomic effects on myocytes and influence contractility, relaxation and action potential duration through a variety of mechanisms. Atrial fibrillation is the most common arrhythmia associated with thyroid dysfunction, it occurs in both euthyroidism and hyperthyroidism in clear association with T4 levels. Mechanistically, in the hyperthyroid state, increased automaticity and triggered activity, together with a shortened refractory period and slowing of the conduction speed, lead to the initiation and maintenance of multiple intraatrial reentry circuits. Influences from the autonomic nervous system and hemodynamics controlled by thyroid hormones act as modulators for arrhythmias, which are promoted by a corresponding substrate (significant impact of comorbidities). Concerning therapy, in addition to treating hyperthyroidism, the initial therapeutic focus is on adequate rate control and anticoagulation in patients with a high risk of thromboembolism. Ablation of atrial fibrillation can be considered later on, although there is an increased likelihood of recurrence compared to patients without hyperthyroidism.Prolongation of the QT interval and increase in QT dispersion are involved in the formation of ventricular arrhythmias. Epidemiological data suggest an association of elevated T4 levels with ventricular arrhythmias and sudden cardiac death. However, this seems to be mainly relevant for patients with underlying cardiac disease (e.g. ICD users).

Developmental changes of the fetal and neonatal thyroid gland and functional consequences on the cardiovascular system

Thyroid hormones play an important role in the development and function of the cardiac myocyte. Dysregulation of the thyroid hormone milieu affects the fetal cardiac cells via complex molecular mechanisms, either by altering gene expression or directly by affecting post-translational processes. This review offers a comprehensive summary of the effects of thyroid hormones on the developing cardiovascular system and its adaptation. Furthermore, we will highlight the gaps in knowledge and provide suggestions for future research.

The bidirectional relationship of thyroid disease and atrial fibrillation: Established knowledge and future considerations

Atrial fibrillation (AF) tends to occur frequently in patients with thyroid disease, primarily hyperthyroidism. In hyperthyroidism, increased levels of thyroid hormones, via intra- and extranuclear mechanisms, have profound effects on cardiac electrophysiology. Hypothyroidism carries a lower risk for AF and is mainly associated with the overtreatment of hypothyroid patients. New-onset AF is frequently the only manifestation of thyroid disease, which renders screening for thyroid dysfunction in that scenario clinically useful. Managing thyroid disease and comorbid AF is essential. This includes thyroid hormones control along with conventional AF therapy. However, there are several open issues with this comorbid duo. The optimal management of thyroid disease and its impact on AF burden remains obscure. There is scanty information on clear-cut benefits for therapy of subclinical thyroid disease and screening of asymptomatic patients. Furthermore, the immunogenetic overlap between the autoantibodies in Graves' disease and AF genesis may lead to novel therapeutic implications. The objective of this review is to summarize the up-to-date epidemiology, pathogenesis, pathophysiology and management of interacting thyroid disease and AF.

Hyperthyroidism With Atrial Fibrillation in Children: A Case Report and Review of the Literature

Atrial fibrillation is exceedingly rare in children with structurally and functionally normal hearts. We present a novel case of a 15-year-old female with known hyperthyroidism who subsequently developed atrial fibrillation. She had been suffering from fatigue, heat intolerance and myalgias for 6 months. Her initial TSH was 0.01mU/L, and free T4 was 75.4 pmol/L, with a free T3 of >30.8 pmol/L. An electrocardiogram showed atrial fibrillation with a ventricular rate of 141 beats per minute. An echocardiogram demonstrated an enlarged left atrium and ventricle, with mild mitral regurgitation. She was treated with methimazole and underwent synchronized cardioversion. She subsequently returned to a euthyroid state and remained in normal sinus rhythm. In this case, we discuss the physiologic and arrhythmogenic properties of thyroid hormone, with a summary of the existing literature on atrial fibrillation in hyperthyroidism in children. Current guidelines for treatment of atrial fibrillation are also outlined.

The relationship between history of thyroid diseases and risk of in-hospital cardiovascular outcomes in patients with atrial fibrillation: Findings From the CCC-AF (Improving Care for Cardiovascular Disease in China-Atrial Fibrillation) Project

BACKGROUND

Atrial fibrillation (AF) has the close relation to thyroid dysfunction and these two diseases lead to poor cardiovascular outcomes. But the prognostic value of thyroid diseases in AF remains unclear. We aimed to determine whether history of thyroid diseases is associated with risk of in-hospital cardiovascular outcomes in AF.

METHODS

Based on the data from the CCC-AF (Improving Care for Cardiovascular Diseases in China-Atrial Fibrillation) project, 31,486 inpatients with a definitive diagnosis of AF and record of history of thyroid diseases were included. Logistic regression analysis was performed to investigate the relationship between history of thyroid diseases and risk of in-hospital major adverse cardiovascular events (MACE) in AF.

RESULTS

Among AF patients, 503 (1.6%) had a history of hypothyroidism, 642 (2.0%) had a history of hyperthyroidism and 30,341 (96.4%) had no thyroid dysfunction. During this hospitalization, 5146 (16.3%) AF patients suffered from MACE. The incidence was 13.1% in hypothyroidism, 16.3% in euthyroidism and 19.0% in hyperthyroidism, in which there was a significant difference among three groups (p=0.028). Multivariable logistic regression analysis revealed that history of hypothyroidism decreased but history of hyperthyroidism increased the risk of in-hospital MACE in AF patients (adjusted odds ratio [OR]=0.603; 95% confidence interval [CI], 0.449-0.811; p=0.001 versus adjusted OR=1.327; 95% CI, 1.060-1.661; p=0.013).

CONCLUSION

History of hypothyroidism was an independent protective factor, whereas history of hyperthyroidism was an independent risk factor for in-hospital cardiovascular outcomes in AF. Our study indicated that hyperthyroidism should be treated aggressively in order to improve the prognosis of AF.

Pro-Arrhythmic Signaling of Thyroid Hormones and Its Relevance in Subclinical Hyperthyroidism

A perennial task is to prevent the occurrence and/or recurrence of most frequent or life-threatening cardiac arrhythmias such as atrial fibrillation (AF) and ventricular fibrillation (VF). VF may be lethal in cases without an implantable cardioverter defibrillator or with failure of this device. Incidences of AF, even the asymptomatic ones, jeopardize the patient's life due to its complication, notably the high risk of embolic stroke. Therefore, there has been a growing interest in subclinical AF screening and searching for novel electrophysiological and molecular markers. Considering the worldwide increase in cases of thyroid dysfunction and diseases, including thyroid carcinoma, we aimed to explore the implication of thyroid hormones in pro-arrhythmic signaling in the pathophysiological setting. The present review provides updated information about the impact of altered thyroid status on both the occurrence and recurrence of cardiac arrhythmias, predominantly AF. Moreover, it emphasizes the importance of both thyroid status monitoring and AF screening in the general population, as well as in patients with thyroid dysfunction and malignancies. Real-world data on early AF identification in relation to thyroid function are scarce. Even though symptomatic AF is rare in patients with thyroid malignancies, who are under thyroid suppressive therapy, clinicians should be aware of potential interaction with asymptomatic AF. It may prevent adverse consequences and improve the quality of life. This issue may be challenging for an updated registry of AF in clinical practice. Thyroid hormones should be considered a biomarker for cardiac arrhythmias screening and their tailored management because of their multifaceted cellular actions.

Atrial fibrillation and hyperthyroidism: A literature review

Atrial fibrillation is the most common arrhythmia worldwide with increasing frequency noted with age. Hyperthyroidism is a well-known cause of atrial fibrillation with a 16%–60% prevalence of atrial fibrillation in patients with known hyperthyroidism Ross et al. (2016). While hyperthyroidism as a causative factor of atrial fibrillation is well established, this literature review aims to answer several questions on this topic including:

1. The relationship of atrial fibrillation to hyperthyroidism

2. Atrial fibrillation as a predictor of hyperthyroidism

3. The pathophysiology of thyrotoxic atrial fibrillation

4. Subclinical hyperthyroidism and the relationship with atrial fibrillation

5. Cardioversion and Catheter ablation of hyperthyroid patients with atrial fibrillation

6. Thrombotic risk of hyperthyroid patients with atrial fibrillation

7. Management of Thyrotoxic Atrial fibrillation

8. Pharmacological rhythm control in patients with hyperthyroidism and atrial fibrillation

9. Treatment of Hyperthyroidism to prevent atrial fibrillation

10. Clinical Implications of Hyperthyroidism and Atrial Fibrillation

Impact of Free Thyroxine on the Outcomes of Left Atrial Ablation Procedures

The prevalence of atrial fibrillation (AF) is increased in hyperthyroidism. The degree to which thyroid hormones affect the outcomes of left atrial (LA) ablation is still unclear. From September 2010 to September 2013, 1,095 patients who underwent LA ablation (59.7% paroxysmal AF, 32.3% persistent AF, and 8.0% LA tachycardia) had their serum thyroid-stimulating hormone (TSH) and free thyroxine (FT4) levels measured in the 48 hours before the procedure. Patients were followed until they presented the first AF relapse after a blanking period of 3 months. TSH and FT4 were assessed as predictors of arrhythmia relapse and were adjusted for possible confounders. During a mean follow-up of 12.5 ± 7.9 months, 28.9% of patients presented an atrial arrhythmia relapse. TSH was not a predictor of relapse. In contrast, after adjustment, FT4 (median = 11.8 ng/L and interquartile range 10.6 to 14.6 ng/L) remained a predictor of relapse with 15% increase per quartile (hazard ratio 1.15, 95% confidence interval 1.03 to 1.29, p = 0.014). In conclusion, FT4 levels influence the success rate of LA ablation procedures, even when in the normal range.

Wenxin Keli versus Sotalol for Paroxysmal Atrial Fibrillation Caused by Hyperthyroidism: A Prospective, Open Label, and Randomized Study

We aimed to compare effectiveness of Wenxin Keli (WK) and sotalol in assisting sinus rhythm (SR) restoration from paroxysmal atrial fibrillation (PAF) caused by hyperthyroidism, as well as in maintaining SR. We randomly prescribed WK (18 g tid) or sotalol (80 mg bid) to 91 or 89 patients. Since it was not ethical not to give patients antiarrhythmia drugs, no control group was set. Antithyroid drugs were given to 90 patients (45 in WK group, 45 in sotalol group); ¹³¹I was given to 90 patients (46 in WK group, 44 in sotalol group). Three months later, SR was obtained in 83/91 or 80/89 cases from WK or sotalol groups (P = 0.762). By another analysis, SR was obtained in 86/90 or 77/90 cases from ¹³¹I or ATD groups (P = 0.022). Then, we randomly assigned the successfully SR-reverted patients into three groups: WK, sotalol, and control (no antiarrhythmia drug was given) groups. After twelve-month follow-up, PAF recurrence happened in 1/54, 2/54, and 9/55 cases, respectively. Log-Rank test showed significant higher PAF recurrent rate in control patients than either treatment (P = 0.06). We demonstrated the same efficacies of WK and sotalol to assist SR reversion from hyperthyroidism-caused PAF. We also showed that either drug could maintain SR in such patients.

Cardiovascular morbidity and mortality in surgically treated hyperthyroidism - a nation-wide cohort study with a long-term follow-up

OBJECTIVE

Previous studies suggest that patients with hyperthyroidism remain at an increased risk of cardiovascular morbidity even after restoring euthyroidism. The mechanisms of the increased risk and its dependency on the different treatment modalities of hyperthyroidism remain unclear. The aim of this long-term follow-up study was to compare the rate of hospitalizations for cardiovascular causes and the mortality in hyperthyroid patients treated surgically with an age- and gender-matched reference population.

PATIENTS AND MEASUREMENTS

A population-based cohort study was conducted among 4334 hyperthyroid patients (median age 46 years) treated with thyroidectomy in 1986-2007 in Finland and among 12,991 reference subjects. Firstly, the hospitalizations due to cardiovascular diseases (CVD) were analysed until thyroidectomy. Secondly, the hazard ratios for any new hospitalization due to CVDs after the thyroidectomy were calculated in Cox regression analysis adjusted with the prevalent CVDs at the time of thyroidectomy.

RESULTS

The risk of hospitalization due to all CVDs started to increase already 5 years before the thyroidectomy, and by the time of the operation, it was 50% higher in the hyperthyroid patients compared to the controls (P < 0·001). After the thyroidectomy, the hospitalizations due to all CVDs (HR 1·15), hypertension (HR 1·23), heart failure (HR 1·17) and valvular diseases or cardiomyopathies (HR 1·55) remained more frequent among the patients than among the controls for 20 years after thyroidectomy. The increased morbidity was not clearly related to the aetiology of hyperthyroidism. Despite the increased CVD morbidity among the patients, there was no difference in cardiovascular mortality.

CONCLUSIONS

The present study shows that hyperthyroidism increases the risk of hospitalization due to CVDs and the risk is sustained up to two decades after effective surgical treatment. However, there was no excess CVD mortality in the middle-aged patient cohort studied.

Contrast Induced Thyrotoxicosis in a Patient with New onset Atrial Fibrillation: A Case Report and Review

The development of thyrotoxicosis following the administration of iodinated contrast is a rare occurrence. The effect, referred to as the Jod-Basedow effect, is often observed in patients with underlying thyroid disease who develop thyrotoxicosis subsequent to the exposure of exogenous iodide. An example of an iatrogenic cause for this event may be seen when a large iodide load is given intravenously for studies or procedures. Thyrotoxicosis can also lead to cardiac arrhythmias including atrial fibrillation. This is a case presentation of a 74 year old female who developed thyrotoxicosis as well as new onset atrial fibrillation approximately one week after receiving iodinated contrast dye for a diagnostic CT of the abdomen. We further review the prior published literature in regard to atrial fibrillation and thyrotoxicosis.

Evaluation of atrial electromechanical delay and diastolic functions in patients with hyperthyroidism

AIM

Hyperthyroidism is a well-known cause of atrial fibrillation (AF) which is associated with increased morbidity and mortality. Atrial electromechanical delay (EMD) is a significant predictor of AF. The aim of this study was to assess the atrial EMD and diastolic functions in subclinical and overt hyperthyroidism by using tissue Doppler imaging (TDI).

METHODS AND RESULTS

The study population consisted of 3 groups: group I (30 healthy subjects), group II (38 patients with subclinical hyperthyroidism), and group III (25 patients with overt hyperthyroidism). Atrial electromechanical coupling was measured with TDI. Standard echocardiographic measurements and parameters of diastolic function were obtained by conventional echocardiography and TDI. Intra- and inter-atrial EMD were significantly prolonged in subclinical and overt hyperthyroidism compared with control group (P = 0.03 and P < 0.001 for intra-atrial EMD; P < 0.001 for inter-atrial EMD). In groups II and III, mitral A velocity (P = 0.005 and P = 0.001) and mitral E-wave deceleration time (P < 0.001 and P = 0.02) were significantly increased, and mitral E/A ratio (P = 0.005 and P = 0.001) was significantly decreased compared with the control group. The lateral mitral Em /Am ratio in group II and group III was significantly lower than controls (P = 0.001). Mitral Em /Am ratio (β = -0.32, P = 0.002) and thyroid stimulating hormone (TSH) level (β = -0.27, P = 0.009) were negatively and independently correlated with inter-atrial EMD.

CONCLUSION

This study showed that intra- and inter-atrial electromechanical intervals were prolonged and diastolic function was impaired in both overt and subclinical hyperthyroidism. TSH level and mitral Em /Am ratio were found as independent predictors of atrial EMD.

Association of inflammation with atrial fibrillation in hyperthyroidism

Objectives

The aim of this study was to evaluate the relationship between inflammation and development of atrial fibrillation (AF) in patients with hyperthyroidism.

Methods

A total of 65 patients with newly diagnosed hyperthyroidism, 35 of whom were in sinus rhythm and 30 of whom in AF. Thirty five age- and gender-matched patients in a control group were included in the study. Factors associated with the development of AF were evaluated by multivariate regression analysis.

Results

Factors associated with AF in multivariate analysis included high sensitivity C reactive protein (HsCRP) [odds ratio (OR): 11.19; 95% confidence interval (95% CI): 1.80-69.53; P = 0.003], free T4 (OR: 8.76; 95% CI: 2.09–36.7; P = 0.003), and left atrial diameter (OR: 1.25; 95% CI: 1.06–1.47; P = 0.008).

Conclusions

The results of the present study suggest that HsCRP, an indicator of inflammation, free T4 and left atrial diameter are associated with the development AF in patients with hyperthyroidism.

P-wave dispersion in endogenous and exogenous subclinical hyperthyroidism

BACKGROUND

The aim of this study was to measure maximum P wave duration (Pmax) and P wave dispersion (PWD), which can be indicators for the risk of paroxysmal atrial fibrillation when increased, and to reveal their relationship with thyroid hormone levels in patients with endogenous and exogenous subclinical hyperthyroidism.

METHODS

Seventy-one patients with sublinical thyrotoxicosis (34 endogenous, 37 exogenous) and 69 healthy individuals were enrolled in the study. Pmax and minimum P wave duration (Pmin) on electrocardiogram recordings were measured and PWD was calculated as Pmax-Pmin.

RESULTS

Pmax (p<0.001) and PWD (p<0.001) values were significantly higher in patients with endogenous subclinical hyperthyroidism compared with the control group. Pmax (p<0.001) and PWD (p<0.001) values were significantly higher in patients with exogenous subclinical thyrotoxicosis compared with the control group. Pmax (p=0.710) and PWD (p=0.127) were not significantly different in patients with endogenous subclinical hyperthyroidism compared with exogenous subclinical hyperthyroid patients. Pmax and PWD negatively associated with TSH in endogenous and exogenous subclinical hyperthyroidism.

CONCLUSION

In the present study, we observed that Pmax and PWD were longer in patients with endogenous and exogenous subclinical hyperthyroidism. Lack of a difference in Pmax and PWD between patients with endogenous and exogenous subclinical hyperthyroidism seems to support the idea that hormone levels rather than the etiology of thyrotoxicosis affect the heart.

Comparison of atrial fibrillation recurrence rates after successful electrical cardioversion in patients with hyperthyroidism-induced versus non-hyperthyroidism-induced persistent atrial fibrillation

Hyperthyroidism-induced atrial fibrillation (AF) often spontaneously reverts to sinus rhythm after the return of euthyroid state, but a significant number of patients remain in persistent AF, which requires electrical cardioversion. The long-term outcome of hyperthyroidism-induced persistent AF after successful cardioversion remains unclear. The study group consisted of 58 patients with hyperthyroidism-induced persistent AF (mean age 57 +/- 2 years, 72% men) who had undergone successful electrical cardioversion. The AF recurrence rate was prospectively studied and compared with age- and gender-matched controls with persistent AF of nonthyroid origins. After a 24-month follow-up period, 34 patients (59%) had developed AF recurrence, significantly fewer than among controls (83%) (hazard ratio 0.64, 95% confidence interval 0.39 to 0.97, p = 0.04). Cox regression analysis showed that long AF duration was the only predictor of AF recurrence in patients with hyperthyroidism-induced persistent AF. In conclusion, hyperthyroidism-induced persistent AF carries a lower recurrence rate after conversion to sinus rhythm than non-hyperthyroidism-induced persistent AF, and early electrical cardioversion should be considered.

Simple electrocardiographic markers for the prediction of paroxysmal atrial fibrillation in hyperthyroidism

BACKGROUND

Hyperthyroidism is a major cause of paroxysmal atrial fibrillation (AF). The purpose of this study was to evaluate the predictors of AF in the patients with clinical and subclinical hyperthyroidism.

METHODS AND RESULTS

The study population consisted of four groups: group I (57 euthyroid healthy persons), group II (33 patients with subclinical hyperthyroidism), group III (69 patients with overt hyperthyroidism) and group IV (31 patients with overt hyperthyroidism and documented paroxysmal AF). The maximum P wave duration (P maximum) in group IV (114 +/- 8 ms) was significantly higher than group I (102 +/- 7 ms, p < 0.001), group II (106 +/- 7 ms, p < 0.001) and group III (108 +/- 9 ms, p0.005). The P wave dispersion (PWD) was measured as 46 +/- 9 ms in group IV and this was significantly higher than group I (29 +/- 8 ms, p < 0.001), group II (36 +/- 9 ms, p < 0.001) and grup III (38 +/- 8 ms, p = 0.001). The P maximum and PWD were higher in the patients with subclinical hyperthyroidism compared to healthy individuals. Univariate regression analysis revealed that age, P maximum and PWD, multivariate analysis showed that P maximum and PWD were significant predictors of paroxysmal AF. A PWD value of 37.5 ms separated group IV from others with a sensitivity of 90%, specificity of 85%, and positive predictive accuracy of 77%.

CONCLUSION

Simply measuring P maximum and PWD values, we could identify the patients with high risk for the development of AF and these simple ECG parameters may help in clinical judgement to determine the requirement for treatment in the patients with subclinical hyperthyroidism.

A novel implantable cardiac telemetry system for studying atrial fibrillation

Atrial fibrillation (AF) is the most common arrhythmia in clinical practice. Most in vivo experimental research on AF is performed in a surgical setting, on animals instrumented by external devices, or using commercial implantable pacemakers. This paper describes a novel implantable cardiac telemetry system, which allows the study of AF remotely in conscious and ambulatory animals over a few month period. To validate this concept, the system was built and implanted in a sheep for 3 months. During this period, the system was used to deliver chronic rapid atrial pacing for AF induction, and to record and measure atrial electrograms and atrial effective refractory period (AERP) daily. During the course of AF induction the AERP decreased, confirming the progression of the electrical remodeling process in the atria. Episodes of paroxysmal AF were successfully induced in the animal. Burst pacing therapy was delivered with the system, however, no AF termination was observed. Result shows that this telemetry-based pacing and monitoring system can be used to study AF in a conscious animal non-invasively for an extended period of time, making this system a unique research tool.

Effects of intravenous nifekalant, a class III antiarrhythmic drug, on atrial vulnerability parameters in patients with paroxysmal atrial fibrillation

Nifekalant, a class III antiarrhythmic drug, has been shown to suppress ventricular tachyarrhythmias, but its effects on AF are unclear. The aim of this study was to clarify the effects of nifekalant on the atrial vulnerability parameters in patients with paroxysmal AF. The study included 18 patients with paroxysmal AF who underwent electrophysiological study before and after intravenous infusion of nifekalant. The atrial electrophysiological parameters including the atrial effective refractory period (AERP), maximum intraatrial conduction delay, and wavelength index, calculated as the ratio of AERP to the maximum conduction delay, were quantitatively measured at baseline and during nifekalant infusion. The mean AERP was significantly prolonged from 214 +/- 27 ms at baseline to 242 +/- 39 ms after nifekalant (P < 0.001). Although earlier studies have shown that nifekalant does not affect the atrial conduction time, the mean maximum conduction delay of the study patients was significantly prolonged from 59 +/- 19 ms at baseline to 72 +/- 28 ms after nifekalant (P = 0.015). There was no significant difference in the wavelength index at baseline (4.1 +/- 1.7) and after nifekalant (4.1 +/- 2.5). However, when the differences of AERP and wavelength index were defined as each parameter during nifekalant infusion minus that at baseline, the difference of AERP showed a direct positive correlation with that of the wavelength index (P = 0.013). In conclusion, nifekalant may be effective in the prevention of AF due to prolongation of the AERP. However, in those patients who have a lesser degree of prolongation of the AERP by nifekalant, the wavelength index tended to be decreased, suggesting that the drug might augment the propensity for AF.

Thyroid disease

Evaluation and treatment of thyroid disease is a common feature of primary care medicine. Nevertheless, the dose of thyroid hormone used to treat hypothyroidism is frequently not titrated to normalize the TSH, engendering the risks of under- or overtreatment. Other hypothyroid patients remain symptomatic even with normalized TSH on levothyroxine alone. Some of these patients improve symptomatically when liothyronine is added to the treatment regimen. Subclinical hypothyroidism and hyperthyroidism are also relatively common in primary care medical practice, and appropriately selected patients probably benefit from treatment. In the follow-up of patients treated for thyroid cancer, the use of rhTSH improves patient comfort considerably while allowing sensitive screening for persistent or recurrent cancer.

Thyroid hormone regulates mRNA expression and currents of ion channels in rat atrium

Atrial fibrillation is one of the common arrhythmias associated with hyperthyroidism. This study examined the effects of thyroid hormone (T3) on mRNA expression and currents of major ionic channels determining the action potential duration (APD) in the rat atrium using the RNase protection assay and the whole-cell patch-clamp technique, respectively. T3 increased the Kv1.5 mRNA expression and decreased the L-type calcium channel mRNA expression, while the Kv4.2 mRNA expression did not change. APD was shorter in hyperthyroid than in euthyroid myocytes. The ultrarapid delayed rectifier potassium currents were remarkably increased in hyperthyroid than in euthyroid myocytes, whereas the transient outward potassium currents were unchanged. L-type calcium currents were decreased in hyperthyroid than in euthyroid myocytes. T3 shifted the current-voltage relationship for calcium currents negatively. In conclusion, T3 increased the outward currents and decreased the inward currents. The resultant changes of ionic currents shortened APD, providing a substrate for atrial fibrillation.

Prevalence of thyroid dysfunction in patients with acute atrial fibrillation attended at a cardiology emergency room

CONTEXT

Atrial fibrillation occurs frequently in patients with thyrotoxicosis, while it has low prevalence in adults of the general population. The prevalence of thyroid dysfunction in subjects with atrial fibrillation is 0 to 24%, a wide variation that is attributed to the different methodologies applied. However, continuous use of amiodarone in patients with previous atrial fibrillation may interfere with these prevalence rates.

OBJECTIVE

In this study, we present the prevalence of thyroid dysfunction in adult patients who presented at a cardiac emergency room with acute atrial fibrillation, using a sensitive thyroid-stimulating hormone (TSH) assay and triiodothyronine (T3) and thyroxine (T4) determination.

TYPE OF STUDY

Cross-sectional study.

SETTING

Emergency room of a tertiary care facility.

PARTICIPANTS

A total of 72 patients with atrial fibrillation who presented at the emergency room not more than 48 hours after its onset.

PROCEDURES

A standardized questionnaire and 12-lead electrocardiogram were applied, and T3, T4 and TSH were determined.

MAIN MEASUREMENTS

TSH, T3 and T4 determination.

RESULTS

Among these patients, 16.6% had altered thyroid function tests: 6.9% had hyperthyroidism, 5.6% hypothyroidism and 4.2% had increased T4 levels, by means of amiodarone use.

CONCLUSION

The high prevalence of thyroid dysfunction in our study, especially hyperthyroidism, suggests that routine thyroid testing with sensitive thyroid-stimulating hormone assay is required in patients with acute atrial fibrillation.