Objective of the study: To examine risk factors for thyrotoxic cardiomyopathy (ThC).
Methods: In retrospective study (1975 to 2003) 272 patients aged 54 [43; 62] years with different forms of toxic goiter in combination with cardiac rhythm disturbances with or without heart failure (HF) were included. Atrial fibrillation (AF) and/or atrial flutter and/or ventricular premature beats accompanied with HF were diagnosed in 80.5% (219/272) patients (group 1), whereas 19.5% (53/272) patients had sinus tachycardia and/or atrial premature beats without HF (group 2).
Results: The prevalence of demographic and clinical characteristics of two groups was compared by use of χ2-test. The factors associated with ThC P<0.05 (age at onset of thyrotoxicosis, age at hospitalization, period from onset of thyrotoxicosis until first treatment, period from onset of thyrotoxicosis until hospitalization, ophthalmopathy, relapse of Graves disease, familial history of hypertension and coronary heart disease, such cardiovascular characteristics as previous history of rhythm disturbances, angina and HF) were retained as potential confounders. Then, binominal logistic regression was performed to identify those factors most associated with ThC using a probability value of P<0.05 and to calculate odds ratios (ORs) and 95% confidence intervals (CIs).
After adjustment for above-mentioned factors period over 1 year from onset of thyrotoxicosis until first treatment (OR=1.8, CI 95% 1.063.13; P=0.02) and age at hospitalization (OR per 1-year increment=1.1, CI 95% 1.021.15; P=0.01) remained independently associated with ThC. Weak positive interaction was observed between these two factors (r=0.16; P=0.007).
Conclusion: The data on natural history of patients with thyrotoxicosis and cardiovascular symptoms allowed us to identify risk factors for ThC. The frequency of ThC is increased in older patients with period from onset of thyrotoxicosis until first treatment over 1 year.