Effect of cardiac resynchronization therapy on thyroid function

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.

Nonthyroidal illness and the cardiorenal syndrome

The cardiorenal syndrome represents a final common pathway for renal and congestive heart failure and heralds a poor prognosis. Factors that link the failing heart and the failing kidneys--the so-called cardiorenal connectors--are, therefore, of clinical and therapeutic interest. Alterations in the levels and function of thyroid hormones that fit the spectrum of nonthyroidal illnesses could be considered to be cardiorenal connectors as both renal failure and heart failure progress with the development of nonthyroidal illness. In addition, circumstantial evidence suggests that nonthyroidal illness can induce deterioration in the function of the heart and the kidneys via multiple pathways. As a consequence, these reciprocal associations could result in a vicious cycle of deterioration that likely contributes to increased mortality. In this Review, we describe the evidence for a pathophysiological role of nonthyroidal illness in the cardiorenal syndrome. We also discuss the available data from studies that have investigated the efficacy of thyroid hormone replacement therapy in patients with renal failure and the rationale for interventional trials to examine the effects of normalization of the thyroid hormone profile in patients with renal failure and congestive heart failure.

Subclinical thyroid dysfunction and the risk of heart failure in older persons at high cardiovascular risk

CONTEXT

Subclinical thyroid dysfunction is common in older people. However, its clinical importance is uncertain.

OBJECTIVE

Our objective was to determine the extent to which subclinical hyperthyroidism and hypothyroidism influence the risk of heart failure and cardiovascular diseases in older people.

SETTING AND DESIGN

The Prospective Study of Pravastatin in the Elderly at Risk (PROSPER) is an prospective cohort study.

PATIENTS

Patients included men and women aged 70-82 yr (n=5316) with known cardiovascular risk factors or previous cardiovascular disease.

MAIN OUTCOME MEASURES

Incidence rate of heart failure hospitalization, atrial fibrillation, and cardiovascular events and mortality according to baseline thyroid status were evaluated. Euthyroid participants (TSH=0.45-4.5 mIU/liter) were compared with those with subclinical hyperthyroidism (TSH<0.45 mIU/liter) and those with subclinical hypothyroidism (TSH≥4.5 mIU/liter, both with normal free T4).

RESULTS

Subclinical hyperthyroidism was present in 71 participants and subclinical hypothyroidism in 199 participants. Over 3.2 yr follow-up, the rate of heart failure was higher for subclinical hyperthyroidism compared with euthyroidism [age- and sex-adjusted hazard ratio (HR)=2.93, 95% confidence interval (CI)=1.37-6.24, P=0.005; multivariate-adjusted HR=3.27, 95% CI=1.52-7.02, P=0.002). Subclinical hypothyroidism (only at threshold>10 mIU/liter) was associated with heart failure (age- and sex-adjusted HR=3.01, 95% CI=1.12-8.11, P=0.029; multivariate HR=2.28, 95% CI=0.84-6.23). There were no strong evidence of an association between subclinical thyroid dysfunction and cardiovascular events or mortality, except in those with TSH below 0.1 or over 10 mIU/liter and not taking pravastatin.

CONCLUSION

Older people at high cardiovascular risk with low or very high TSH along with normal free T4 appear at increased risk of incident heart failure.