Effects of thyroid hormone deficiency on electrocardiogram findings of congenitally hypothyroid neonates

Hypertrabecular aspect of left ventricular myocardium: a possible complication of congenital hypothyroidism in a preterm infant

We report a case of hypertrabeculated left ventricular myocardium associated with congenital hypothyroidism in a preterm infant. The myocardical anomalies and long QT interval, absent at birth, appeared simultaneously to abnormal thyroid hormones and progressively improved until complete recovery during Levo-Thyroxine treatment. We speculate that thyroid dysfunction could be the potential cause of transient hypertrabecular aspect of the left ventricle.

Drug-induced QT interval shortening: potential harbinger of proarrhythmia and regulatory perspectives

ATP-dependent potassium channel openers such as pinacidil and levcromakalim have long been known to shorten action potential duration and to be profibrillatory in non-clinical models, raising concerns on the clinical safety of drugs that shorten QT interval. Routine non-clinical evaluation of new drugs for their potential to affect cardiac repolarization has revealed that drugs may also shorten QT interval. The description of congenital short QT syndrome in 2000, together with the associated arrhythmias, suggests that drug-induced short QT interval may be proarrhythmic, and an uncanny parallel is evolving between our appreciation of the short and the long QT intervals. Epidemiological studies report an over-representation of short QT interval values in patients with idiopathic ventricular fibrillation. Therefore, as new compounds that shorten QT interval are progressed further into clinical development, questions will inevitably arise on their safety. Arising from the current risk-averse clinical and regulatory environment and concerns on proarrhythmic safety of drugs, together with our lack of a better understanding of the clinical significance of short QT interval, new drugs that substantially shorten QT interval will likely receive an unfavourable regulatory review unless these drugs fulfil an unmet clinical need. This review provides estimates of parameters of QT shortening that may be of potential clinical significance. Rufinamide, a recently approved anticonvulsant, illustrates the current regulatory approach to drugs that shorten QT interval. However, to further substantiate or confirm the safety of these drugs, their approval may well be conditional upon large-scale post-marketing studies with a focus on cardiac safety.

Fetal heart rate tracing patterns associated with congenital hypothyroidism

OBJECTIVE

This study was undertaken to determine fetal heart rate (FHR) tracing patterns associated with congenital hypothyroidism.

STUDY DESIGN

FHR patterns of 59 women whose babies were diagnosed with congenital hypothyroidism were retrospectively compared with tracings of 78 of their siblings. Tracings were interpreted during the first stage of labor. Multivariable analysis was used to control for confounders.

RESULTS

Neonates with congenital hypothyroidism had significantly higher rates of reduced variability in FHR tracing patterns as compared with those without congenital hypothyroidism (49.2% vs 3.8%; odds ratio, 24.1; 95% confidence interval, 6.8-85.3; P < .001). No significant differences were noted between the groups regarding decelerations or baseline abnormalities. The significant association between congenital hypothyroidism and reduced variability persisted after controlling for confounders such as treatment with pethidine, MgSO4, and gestational age (odds ratio, 14.1; 95% confidence interval, 1.1-190.7; P = .046).

CONCLUSION

Congenital hypothyroidism is significantly and independently associated with reduced variability in FHR tracing patterns.

Long-term cardiovascular effects of levothyroxine therapy in young adults with congenital hypothyroidism

CONTEXT

Congenital hypothyroidism (CH) is the most prevalent endocrine disorder in the newborn and is routinely treated with life-long levothyroxine replacement therapy. Although several studies have demonstrated that such therapy may impact on the cardiovascular system, little is known with regard to the effects of long-term levothyroxine administration in patients with CH.

OBJECTIVE

The aim of the current study was to evaluate whether long-term levothyroxine replacement therapy in young adults with CH is associated with cardiovascular abnormalities.

PATIENTS AND METHODS

Thirty young adults with CH aged 18.1 +/- 0.2 yr and 30 age- and sex-matched controls underwent cardiac and carotid Doppler ultrasound and symptom-limited cardiopulmonary exercise testing. Hypothyroidism was diagnosed by neonatal screening, and levothyroxine treatment was initiated within the first month of life and carefully adjusted to maintain TSH levels in the normal range and free T(4) in the high-normal range.

RESULTS

Compared with controls, hypothyroid patients exhibited left ventricular diastolic dysfunction, impaired exercise capacity, and increased intima-media thickness. At multiple regression analysis, the number of episodes of plasma TSH levels less than 0.5 mU/liter and greater than 4.0 mU/liter from the age of 1 yr onward, and mean TSH plasma levels during puberty were independent predictors of diastolic filling and cardiopulmonary performance indexes (multiple r values: 0.61-0.75).

CONCLUSIONS

Long-term levothyroxine treatment in young adults with congenital hypothyroidism is associated with impaired diastolic function and exercise capacity and increased intima-media thickness.

Effects of levothyroxine therapy on left and right ventricular function in neonates with congenital hypothyroidism: a tissue Doppler echocardiography study

Cardiac function is impaired in adults or children with hypothyroidism and it can be reversed by levothyroxine (L-T(4)) substitution therapy. However, only a few studies are available on left and right ventricular function in neonates with congenital hypothyroidism (CH), most of which were performed with standard echocardiography. The aim of this study was to investigate the effects of L-T(4) substitution therapy on left and right ventricular function in neonates with CH, measured with tissue Doppler echocardiography (TDE) and conventional echocardiography. Fifty neonates (27 females and 23 males) with CH and 35 normal neonates (19 females and 16 males) underwent conventional echocardiography and TDE. On TDE, peak mitral and tricuspid annular systolic (Sa) velocity, peak early (Ea) and late (Aa) mitral and tricuspid annular diastolic velocity were measured, and the Ea/Aa ratio was calculated. All the biochemical tests and echocardiographic evaluations were reevaluated after 1 month of replacement therapy. In CH neonates, TDE showed that CH neonates had significantly lower Sa, Ea, and Ea/Aa of both left and right ventricles (P<0.001, respectively). However, Aa of left and right ventricles did not differ significantly. After 1 month of substitutive therapy, CH neonates showed a significant increase of Sa and Ea and a subsequent increase of the Ea/Aa ratio (P<0.001, respectively). Our findings suggest that neonates with CH suffer from right ventricular subclinical systolic and diastolic dysfunction in addition to left ventricular dysfunction. Early L-T(4) substitution therapy is able to reverse the impairment of cardiac function.

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

Hypothyroidism has various cardiovascular manifestation and exhibits electrocardiographic change. The QT dispersion on surface ECG reflects regional variations in myocardial repolarization. The effect of L-thyroxine treatment on ECG parameters, such as QT dispersion, in patients with primary hypothyroidism were investigated. This study involved 18 patients (3 men, 15 women, ages: 48+/-18 yr) with primary hypothyroidism. All patients were checked with a standard 12-lead ECG before and after L-thyroxine treatment. Various ECG parameters were then measured twice. The mean L-thyroxine treatment duration was 22+/-2.7 months. The mean thyroid-stimulating hormone levels of patients before and after therapy were 40.2+/-29.8 microU/mL, 3.6+/-4.6 microU/mL (p<0.001) and free-T4 levels were 0.44+/-0.38 ng/dL, 1.51+/-0.39 ng/dL (p<0.001). After L-thyroxine treatment, QT interval (395+/-42 vs. 380+/-24 msec, p<0.05), QTc interval (434+/-32 vs. 417+/-23 msec, p<0.05), QT dispersion (45+/-23 vs. 30+/-13 msec, p=0.008), QTc dispersion (49+/-23 vs. 32+/-14 msec, p=0.005) significantly decreased. There were no significant changes in the PR and RR intervals, as well as the QRS duration. Our findings suggest that the thyroid hormone affects ventricular inhomogenicity, and that L-thyroxine replacement therapy may reduce malignant ventricular arrhythmia and sudden cardiac death in primary hypothyroidism.