The effects of L-thyroxine treatment on QT dispersion in primary hypothyroidism

A Prolonged QTc Interval Leads to the Diagnosis of Hyperthyroidism in an Adolescent Boy

BACKGROUND

Syncope is a common cause of pediatric emergency department visits and carries a broad differential diagnosis, which includes a few rare but critical cardiac conditions.

CASE REPORT

We review the case of an adolescent boy who presented to the emergency department after a syncopal event. He was found to have a prolonged QTc interval on electrocardiogram (ECG), without personal or family history or known risk factors. He was screened for thyroid dysfunction on a second ED visit for presyncope and was subsequently diagnosed with hyperthyroidism. The patient was treated with methimazole for 2 weeks and a repeat ECG showed normalization of the QTc interval with a QTc reduction of more than 100 ms; routine thyroid studies showed correction of thyroid stimulating hormone and free thyroxine levels shortly thereafter. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: This case and review of the medical literature should raise awareness for the emergency physician to consider evaluation of thyroid function in pediatric patients with QT interval prolongation and vice versa, potentially averting dangerous dysrhythmias.

Thyroid hormones regulate cardiac repolarization and QT-interval related gene expression in hiPSC cardiomyocytes

Prolongation of cardiac repolarization (QT interval) represents a dangerous and potentially life-threatening electrical event affecting the heart. Thyroid hormones (THs) are critical for cardiac development and heart function. However, little is known about THs influence on ventricular repolarization and controversial effects on QT prolongation are reported. Human iPSC-derived cardiomyocytes (hiPSC-CMs) and multielectrode array (MEA) systems were used to investigate the influence of 3,3',5-triiodo-L-Thyronine (T3) and 3,3',5,5'-tetraiodo-L-Thyronine (T4) on corrected Field Potential Duration (FPDc), the in vitro analog of QT interval, and on local extracellular Action Potential Duration (APD). Treatment with high THs doses induces a significant prolongation of both FPDc and APD, with the strongest increase reached after 24 h exposure. Preincubation with reverse T3 (rT3), a specific antagonist for nuclear TH receptor binding, significantly reduces T3 effects on FPDc, suggesting a TRs-mediated transcriptional mechanism. RNA-seq analysis showed significant deregulation in genes involved in cardiac repolarization pathways, including several QT-interval related genes. In conclusion, long-time administration of high THs doses induces FPDc prolongation in hiPSC-CMs probably through the modulation of genes linked to QT-interval regulation. These results open the way to investigate new potential diagnostic biomarkers and specific targeted therapies for cardiac repolarization dysfunctions.

Left Frontal Lobe Tumor-Induced Intraoperative Premature Ventricular Beats

In the absence of cardiac pathology, premature ventricular contractions (PVCs) in neurosurgical patients frequently accompany subarachnoid hemorrhage, intracerebral hemorrhage, traumatic brain injury, or raised intracranial pressure. PVCs detected during preanesthesia assessment prompts detailed cardiac evaluation. Our 57-year-old patient, a case of left frontal meningioma, with controlled hypertension, diabetes and hypothyroidism, had normal preoperative ECG and potassium. However, immediately on anesthesia induction, she developed multiple refractory to treatment PVCs but with normal blood pressure. Anesthesia, which was maintained with sevoflurane and fentanyl, was deepened to exclude light anesthesia as the cause, without useful outcome. Two lignocaine boluses (100 mg each), followed by its infusion, also proved ineffective. Her blood gases and potassium, checked twice, were normal. Throughout, her hemodynamics remained stable. As soon as tumor was removed, the PVCs disappeared not to return. Her postoperative recovery was uneventful with normal ECG.

Association of thyroid-stimulating hormone with corrected QT interval variation: A prospective cohort study among patients with type 2 diabetes

BACKGROUND

Patients with type 2 diabetes mellitus (T2DM) have a prolonged QT interval and are at high risk of sudden cardiac death. A prolonged QT interval, indicative of impaired ventricular repolarization, is a risk factor for lethal ventricular arrhythmias, such as torsades-de-pointes (TdP).

AIMS

To identify key clinical and biochemical covariates associated with Fridericia's corrected QT interval (QTcF) among euthyroid patients with T2DM, and to describe the temporal relationship between these factors and QTcF.

METHODS

We performed prospective, clinical, biochemical and electrocardiographic measurements among patients with T2DM enrolled in the DIACART study at Pitié-Salpêtrière Hospital, at T1 (baseline) and T2 (follow-up), with a median interval of 2.55 years.

RESULTS

Mean age (63.9±8.5 years), sex (22.35% women), drugs with known risk of TdP according to the CredibleMeds website (Cred-drugsTdP) and serum thyroid-stimulating hormone (TSH) concentrations correlated with QTcF in univariate analysis at both T1 and T2. In multivariable analysis, all these covariates except age were significantly associated with QTcF at both T1 (women: standardized β=0.24±0.07, P=0.001; Cred-drugsTdP: β=0.19±0.07, P=0.007; TSH concentration: β=0.18±0.07, P=0.01) and T2 (women: β=0.25±0.08, P=0.002; Cred-drugsTdP: β=0.25±0.08, P=0.001; TSH concentration: β=0.19±0.08, P=0.01). Furthermore, variation in QTcF over the years was associated with variation in TSH concentration (r=0.24, P=0.007) and changes in use of Cred-drugsTdP (r=0.2, P=0.02).

CONCLUSIONS

Serum TSH concentration and its variation were associated with QTcF and its variation, even after correcting for the main determinants of QTcF. Interventional optimization of TSH concentration in T2DM warrants further investigation to establish its impact on the risk of TdP and sudden cardiac death.

Outcomes of Cardiac Resynchronization Therapy in Patients with Hypothyroidism and Heart Failure

Background

Hypothyroidism is known to be associated with adverse clinical outcomes in heart failure. The association between hypothyroidism and cardiac resynchronization therapy outcomes in patients with severe heart failure is not clear.

Methods

The study included 1316 patients who received cardiac resynchronization therapy between 2002 and 2015. Baseline demographics and cardiac resynchronization therapy outcomes, including left ventricular ejection fraction, New York Heart Association class, appropriate implantable cardioverter-defibrillator therapy, and all-cause mortality, were collected from the electronic health record.

Results

Of the study cohort, 350 patients (26.6%) were classified as the hypothyroidism group. The median duration of follow-up was 3.6 years (interquartile range, 1.7–6.2 years). Hypothyroidism was not associated with a higher risk of all-cause mortality in patients receiving CRT for heart failure. The risk of appropriate implantable cardioverter-defibrillator therapy significantly increased in association with increased baseline thyroid-stimulating hormone level in the entire cohort (hazard ratio, 1.23 per 5mIU/L increase; 95% CI, 1.01–1.5; P = 0.04) as well as in the hypothyroid group (hazard ratio, 1.44 per 5mIU/L increase; 95% CI, 1.13–1.84; P = 0.004).

Conclusions

CRT improves cardiac function in hypothyroid patients. The ventricular arrhythmic events requiring ICD therapies are associated with baseline TSH level, which might be considered as an important biomarker to stratify the risk of sudden death for patients with heart failure and hypothyroidism.

Ticagrelor-Induced Prolongation of the QTc Interval

Background

Ticagrelor has been accepted as a class I antiplatelet agent in patients undergoing percutaneous coronary angioplasty (PTCA). There have been cases reported on ticagrelor being associated with various cardiac conduction defects. But there is no evidence of QTc prolongation associated with the drug as of yet.

Case Presentation

A 64-year-old male who underwent PTCA was given ticagrelor. A baseline electrocardiogram (ECG) showed a QTc of 402 ms. He returned after 1.5 months with complaints of shortness of breath. An ECG revealed a prolonged QTc of 468 ms. Ticagrelor was discontinued in view of ticagrelor-induced dyspnea and the patient was started on clopidogrel. The other medications were kept unchanged. The patient returned after a month without any complaints. A follow-up ECG showed a reduced QTc of 425 ms.

Conclusion

We present a case of ticagrelor-induced QTc prolongation. To our knowledge, this is the first case to be reported on the same. The Naranjo algorithm for causality assessment gave a total score of 6 indicating that the adverse drug reaction falls under the probable category.

Thyroid dysfunction and electrocardiographic changes in subjects without arrhythmias: a cross-sectional study of primary healthcare subjects from Copenhagen

OBJECTIVE

The objective of the present study was to investigate associations of both overt and subclinical thyroid dysfunction with common ECG parameters in a large primary healthcare population.

DESIGN

Cross-sectional study.

SETTING AND PARTICIPANTS

The study population comprised of primary healthcare patients in Copenhagen, Denmark, who had a thyroid function test and an ECG recorded within 7 days of each other between 2001 and 2011.

DATA SOURCES

The Danish National Patient Registry was used to collect information regarding baseline characteristics and important comorbidities.

OUTCOME MEASURE AND STUDY GROUPS

Common ECG parameters were determined using Marquette 12SL software and were compared between the study groups. The study population was divided into five groups based on their thyroid status. Euthyroid subjects served as the reference group in all analyses.

RESULTS

A total of 132 707 patients (age 52±17 years; 50% female) were included. Hyperthyroidism was significantly associated with higher heart rate and prolonged QTc interval with significant interaction with age (p<0.009) and sex (p<0.001). These associations were less pronounced for patients with higher age. Subclinical hyperthyroidism was associated with higher heart rate among females, and a similar trend was observed among males. Hypothyroidism was associated with slower heart rate and shorter QTc but only in women. Moreover, longer P-wave duration, longer PR interval and low voltage were observed in patients with both subclinical and overt hypothyroidism. However, the presence of low voltage was less pronounced with higher age (p=0.001).

CONCLUSION

Both overt and subclinical thyroid disorders were associated with significant changes in important ECG parameters. Age and gender have significant impact on the association of thyroid dysfunction particularly on heart rate and QTc interval.

The relationship between the TSH values and the Tpeak – Tend interval duration in hypothyroid patients receiving Levothyroxine treatment

Introduction . Changes in thyroid hormone level can affect the cardiovascular system. The aim of this study was to show how the Tpeak -Tend (Tpe) interval, which is a new marker of ventricular arrythmia, is affected in patients who have become euthyroid following Levothyroxine treatment for hypothyroidism, as this has not been examined previously in literature.

Materials and Methods . This, cross-sectional study included a total of 119 females aged 18-45 years, separated into 3 groups as hypothyroid, euthyroid and control groups. For evaluation of the QTc and Tpe intervals, examination on precordial V5 lead was made of all the ECGs taken routinely on presentation of the patients.

Results . The Tpe and QTc intervals of the hypothyroid group were determined to be significantly prolonged compared to those of the euthyroid and control groups (p < 0.001) and the values of the euthyroid and control groups were similar. A positive correlation was determined between TSH levels and Tpe and QTc intervals. Tpe interval AUC = 0.801 (%95 CI: 0.719 – 0.884) was higher than that of QTc AUC = 0.689 (%95 CI: 0.591 – 0.786).

Conclusions . The Tpe duration was evaluated in respect of the risk of arrythmia in hypothyroid patients. In patients who had become euthyroid, the Tpe interval was found to be similar to that of healthy individuals and was more predictive than QTc. In the light of these findings it can be recommended that measurement of the Tpe interval should be preferred to QTc as a marker of the arrythmogenic effect in hypothyroid patients.

Discriminant function analysis of the occurrence risk of abnormal electrocardiogram in thyroidectomized differentiated thyroid carcinoma patients with short-term overt hypothyroidism

OBJECTIVES

The common form and risk factors of electrocardiogram (ECG) abnormality in thyroidectomized differentiated thyroid carcinoma (DTC) patients with short-term overt hypothyroidism were investigated and some discriminant formulas for forecasting the occurrence of abnormal ECG in this specific population were deduced in this study.

METHODS

A total of 260 thyroidectomized DTC patients were retrospectively reviewed, 67 of whom had abnormal ECG and 193 normal ECG after short-term (3 weeks) levothyroxine (L-T4) withdrawal. One-way ANOVA, Spearman's rank correlation analysis and discriminant function analysis were performed using data from these DTC patients.

RESULTS

A flat or inverted T wave in inferior myocardial and left ventricular wall leads was the most common abnormal ECG finding in short-term overt hypothyroidism. Statistical analyses showed that age, interval, TSH-end (The serum hormothyrin level at the end of L-T4 withdrawal for 3 weeks), and TSH-vel (The average ascending velocity of serum hormothyrin level during L-T4 withdrawal for 3 weeks) were statistically significant and positively correlated with the occurrence of abnormal ECG. Meanwhile, TSH-vel showed the highest correlation coefficient (r = 0.358, p = 0.000). The formulas, especially deduced from age, interval and TSH-vel, could discriminate patients with abnormal ECG or not as high as 77.6 and 70.5%, respectively (resubstitution accuracy: 72.3%).

CONCLUSION

The thyroidectomized DTC patients undergoing short-term L-T4 withdrawal before their first radioiodine ablative therapy, who had one or more of the above-mentioned risk factors, are likely to show abnormal ECG findings. The formulas from discriminant function analysis may be helpful for predicting patients with abnormal ECG with short-term L-T4 withdrawal and allow appropriate medical intervention beforehand.

Safety and tolerability profile of second-line anti-tuberculosis medications

Tuberculosis (TB) remains a major public health problem, representing the second leading cause of death from infectious diseases globally, despite being nearly 100 % curable. Multidrug-resistant (MDR)-TB, a form of TB resistant to isoniazid and rifampicin (rifampin), two of the key first-line TB drugs, is becoming increasingly common. MDR-TB is treated with a combination of drugs that are less effective but more toxic than isoniazid and rifampicin. These drugs include fluoroquinolones, aminoglycosides, ethionamide, cycloserine, aminosalicyclic acid, linezolid and clofazimine among others. Minor adverse effects are quite common and they can be easily managed with symptomatic treatment. However, some adverse effects can be life-threatening, e.g. nephrotoxicity due to aminoglycosides, cardiotoxicity due to fluoroquinolones, gastrointestinal toxicity due to ethionamide or para-aminosalicylic acid, central nervous system toxicity due to cycloserine, etc. Baseline evaluation may help to identify patients who are at increased risk for adverse effects. Regular clinical and laboratory evaluation during treatment is very important to prevent adverse effects from becoming serious. Timely and intensive monitoring for, and management of adverse effects caused by, second-line drugs are essential components of drug-resistant TB control programmes; poor management of adverse effects increases the risk of non-adherence or irregular adherence to treatment, and may result in death or permanent morbidity. Treating physicians should have a thorough knowledge of the adverse effects associated with the use of second-line anti-TB drugs, and routinely monitor the occurrence of adverse drug reactions. In this review, we have compiled safety and tolerability information regarding second-line anti-TB drugs in both adults and children.

Cardiac Function in Newborns with Congenital Hypothyroidism: Association with Thyroid-Stimulating Hormone Levels

OBJECTIVE

The aims of this study were to demonstrate ventricular function changes in patients with congenital hypothyroidism and to investigate whether there is an association between any such changes and thyroid-stimulating hormone (TSH) levels using M-mode and Doppler electrocardiography (ECG) and tissue Doppler imaging (TDI).

METHODS

Twenty-seven patients 5-30 days of age with congenital hypothyroidism who were scheduled to receive L-thyroxine treatment and 20 healthy newborns were included in this study. Twelve-lead ECG and M-mode TDI recordings of the patient and healthy groups were obtained. The patient group was divided into two subgroups according to TSH level (>100 uIU/mL or <100 uIU/mL), which were then compared on all parameters.

RESULTS

Decreases were observed in the ejection fraction (EF), shortening fraction (SF), and mitral lateral annulus, mitral septal annulus, and tricuspid lateral annulus systolic velocity (Sa) on TDI, whereas left ventricular end-systolic diameter (LVESd) and corrected QT interval (QTc) dispersion were significantly increased in the patient group compared with the control group. No significant differences between the groups were found in left ventricular end-diastolic diameter (LVEDd) or heart rate. When the two patient subgroups (TSH >100 uIU/mL and <100 uIU/mL) were compared, TDI septal annulus Sa wave length and heart rate were significantly lower in the TSH >100 group.

CONCLUSION

Impairment in left ventricular systolic function and increased risk of arrhythmia were observed in newborn infants with congenital hypothyroidism. TSH level was associated with heart rate and interventricular septum velocity.

Thyroid functional disease: an under-recognized cardiovascular risk factor in kidney disease patients

Thyroid functional disease, and in particular hypothyroidism, is highly prevalent among chronic kidney disease (CKD) and end-stage renal disease (ESRD) patients. In the general population, hypothyroidism is associated with impaired cardiac contractility, endothelial dysfunction, atherosclerosis and possibly higher cardiovascular mortality. It has been hypothesized that hypothyroidism is an under-recognized, modifiable risk factor for the enormous burden of cardiovascular disease and death in CKD and ESRD, but this has been difficult to test due to the challenge of accurate thyroid functional assessment in uremia. Low thyroid hormone levels (i.e. triiodothyronine) have been associated with adverse cardiovascular sequelae in CKD and ESRD patients, but these metrics are confounded by malnutrition, inflammation and comorbid states, and hence may signify nonthyroidal illness (i.e. thyroid functional test derangements associated with underlying ill health in the absence of thyroid pathology). Thyrotropin is considered a sensitive and specific thyroid function measure that may more accurately classify hypothyroidism, but few studies have examined the clinical significance of thyrotropin-defined hypothyroidism in CKD and ESRD. Of even greater uncertainty are the risks and benefits of thyroid hormone replacement, which bear a narrow therapeutic-to-toxic window and are frequently prescribed to CKD and ESRD patients. In this review, we discuss mechanisms by which hypothyroidism adversely affects cardiovascular health; examine the prognostic implications of hypothyroidism, thyroid hormone alterations and exogenous thyroid hormone replacement in CKD and ESRD; and identify areas of uncertainty related to the interplay between hypothyroidism, cardiovascular disease and kidney disease requiring further investigation.

Thyroid hormones and electrocardiographic parameters: findings from the third national health and nutrition examination survey

Introduction

Altered thyroid status exerts a major effect on the heart. Individuals with hypo- or hyperthyroidism showed various changes in electrocardiograms. However, little is known about how variations in thyroid hormone levels within the normal range affect electrical activities of the heart in the general population.

Methods and Results

We conducted a cross-sectional analysis of 5,990 men and women from the Third National Health and Nutrition Examination Survey. Serum total T4 was measured by immunoassay and TSH was measured by chemiluminescent assay. We categorized T4 and TSH into 7 groups with cut-offs at the 5^th, 20^th, 40^th, 60^th, 80^th, and 95^th percentiles of the weighted population distribution. Electrocardiographic parameters were measured from the standard 12-lead electrocardiogram. We found a positive linear association between serum total T4 level and heart rate in men, and a U-shape association between T4 and PR interval in men and women. TSH level was positively associated with QRS interval in men, while a U-shape association between TSH and QRS was observed in women. No clear graded association between thyroid hormones and corrected QT or JT was found, except that men in the highest category of T4 levels appeared to have longer corrected QT and JT, and men in the lowest category of T4 appeared to have shorter corrected QT and JT.

Conclusions

Variation in thyroid hormone levels in the general population, even within the normal range, was associated with various ECG changes.

Thyroxine and cardiac electrophysiology-a forgotten physiological duo?

Thyroid hormone exerts numerous effects on the cardiovascular system. Hypothyroidism can lead to various electrocardiographic and mechanical changes in the heart and blood vessels.

The potential risk for sudden cardiac death in patients with hypothyroidism have never been properly explored. However, numerous reports of various electrocardiographic changes indicative of such a risk has been published.

In this case report the occurrence of ventricular late potentials in a case of overt hypothyroidism is described and furthermore, the disappearance of these potentials with T4 treatment alone is shown.

It is concluded that the concept that undiagnosed and/or untreated hypothyroidism poses a risk for sudden cardiac death is worth exploring.

Sibutramine-associated QT interval prolongation and cardiac arrest

OBJECTIVE

To report on a probable association between sibutramine and QT interval prolongation leading to ventricular fibrillation and cardiac arrest.

CASE SUMMARY

A previously well 51-year-old woman with obesity but no other relevant past medical history or cardiac risk factors was prescribed sibutramine (initial dose 10 mg daily, increased to 15 mg daily after 10 wk). Four months after initiation of therapy, the woman developed ventricular fibrillation and was successfully resuscitated. On admission, an electrocardiogram (ECG) demonstrated sinus tachycardia without any ischemic changes and a prolonged QTc interval (545 msec). A subsequent coronary angiogram revealed normal coronary arteries and no other abnormalities. Her QTc interval returned to normal (432 msec) by day 2 and remained within normal limits (<440 msec) thereafter. Due to a favorable neurologic recovery and the absence of any cardiac structural abnormality, the patient was readmitted for implantation of an automatic implantable cardioverter-defibrillator on day 35 and remained well from a cardiac and neurologic standpoint at a 2-year follow-up examination.

DISCUSSION

Sibutramine acts centrally to inhibit noradrenaline, dopamine, and serotonin reuptake, thereby sharing similar actions of other QT interval-prolonging drugs. Therefore, sibutramine might be anticipated to also share a tendency to QT interval prolongation. The current prescribing information for sibutramine does not specifically list any precautions or adverse reactions related to QT interval prolongation. QT interval prolongation associated with sibutramine in this case is considered probable based on the Naranjo probability scale.

CONCLUSIONS

Clinicians prescribing sibutramine should monitor their patients for ECG abnormalities and be cautious in coprescribing drugs known to prolong the QT interval.