Electrophysiologic Effects of Chronic Amiodarone Therapy and Hypothyroidism

ABSTRACT Amiodarone is a widely used antiarrhythmic drug, the mechanisms of action of which remain incompletely understood. Indirect evidence suggests that the class III properties of amiodarone may be mediated by cardiac antithyroid effects. We sought to determine whether the effects of chronic amiodarone on repolarization in guinea pig hearts can be attributed to an antithyroid action by studying the changes in dofetilide-sensitive rapid (I Kr ) and dofetilide-resistant slow (I Ks ) delayed rectifier currents, inward rectifier K ϩ current (I K1 ), and action potentials of ventricular myocytes from five groups of guinea pigs: control, hypothyroid, amiodarone-treated for 7 days, hypothyroid plus amiodarone, and vehicle (dimethyl sulfoxide) treated. I Ks was reduced by amiodarone (to 61% of control, P Ͻ .05, at 50 mV) but was more strongly reduced by hypothyroidism (to 35% of control, P Ͻ .01, 50 mV). Amiodarone significantly reduced I Kr and I K1 (by 55 and 64% at 10 mV and Ϫ50 mV, respectively), which were unaffected by hypothyroidism. Amiodarone alone and hypothyroidism alone had similar action potential-prolonging actions. Hypothyroid animals treated with amiodarone showed a combination of ionic effects (strong I Ks reduction, similar to hypothyroidism alone; reduced I Kr and I K1 , similar to amiodarone alone), along with action potential prolongation significantly greater than that caused by either intervention alone. We conclude that chronic amiodarone and hypothyroidism have different effects on ionic currents and that their combination prolongs action potential duration to a greater extent than either alone in guinea pig hearts, suggesting that the class III actions of amiodarone are not mediated by a cardiac hypothyroid state

Comparison of Newly Diagnosed Ocular Hypertension and Open-Angle Glaucoma: Ocular Variables, Risk Factors, and Disease Severity

Purpose. To describe the distribution of ocular variables, risk factors, and disease severity in newly diagnosed ocular hypertension (OH) or open-angle glaucoma (OAG). Methods. Eligible subjects underwent a complete history and examination. Adjusted odds ratios (ORs) and 95% confidence intervals (CIs) obtained from multiple logistic regression models were used to compare OAG to OH and advanced to early/moderate OAG. Results. 405 subjects were enrolled: 292 (72.1%) with OAG and 113 (27.9%) with OH. 51.7% had early, 27.1% moderate, and 20.9% advanced OAG. The OR for OAG versus OH was 8.19 (P < 0.0001) for disc notch, 5.36 (P < 0.0001) for abnormal visual field, 1.45 (P = 0.001) for worsening mean deviation, 1.91 (P < 0.0001) for increased cupping, 1.03 for increased age (P = 0.030), and 0.36 (P = 0.010) for smoking. Conclusions. Increased age was a risk for OAG, and smoking decreased the risk of OAG compared to OH. Almost half of the OAG subjects had moderate/advanced disease at diagnosis

A Canadian multi-centre, open-label long-term study of Pegvisomant treatment in refractory acromegaly

Purpose: Acromegaly is a rarely diagnosed condition with potentially serious complications including accelerated heart disease and reduced survival. After a mean interval of nearly 9 years from onset of disease, a significant proportion of patients are diagnosed with invasive adenomas precluding complete surgical resection. Furthermore, strict normalization of the growth hormone (GH) target insulin-like growth factor I (IGF-I) cannot always be achieved by adjunctive medical therapy with somatostatin analogues. Here we report the results of a Canadian multi-centre study open-label, dose-titrated long-term study examining safety and efficacy outcomes of a growth hormone receptor antagonist, pegvisomant in 19 patients with refractory acromegaly. Methods: Previously pegvisomant-treated and treatment-naïve refractory acromegalic patients at least 18 yr of age were eligible (n=19). Patients received open-label daily subcutaneous injections of pegvisomant adjusted according to IGF-I levels. Safety and IGF-I levels were assessed every 4 to 6 wk. Baseline and follow-up visits at 3-month intervals also included administration of the Signs and Symptoms of Acromegaly Questionnaire. This study is registered with ClinicalTrials.gov, NCT00151437. Results: We show that, in escalating doses, pegvisomant results in age-adjusted normalization of IGF-I in nearly all such patients. This IGF-I normalization occurred early on and was maintained throughout the study period of 27 months (IGF-I standard deviation score (SDS), mean ± SE: 1.66 ± 0.36, P=0.0003 vs baseline), with a nadir at 18 months (IGF-I SDS, mean ± SE: 1.50 ± 0.38, P=0.0010 vs baseline). IGF-I control was also accompanied by measurable improvements in disease-associated symptoms and without radiographic evidence of pituitary tumour progression. Overall, the safety profile of pegvisomant therapy in this patient population was found to be satisfactory and suitable for a long-term treatment. Conclusion: Our findings provide support for the long-term safety and efficacy of the GH receptor antagonist pegvisomant in achieving IGF-I control in patients with refractory acromegaly