From the Guidelines
The primary cause of high output heart failure in hyperthyroidism is the excessive thyroid hormone-induced cardiovascular effects that lead to increased cardiac output, as noted in the 2016 American Heart Association scientific statement 1. In hyperthyroidism, elevated levels of thyroid hormones (T3 and T4) cause direct and indirect stimulation of the cardiovascular system. These hormones increase heart rate, contractility, and blood volume while decreasing peripheral vascular resistance. The heart must work harder to pump more blood at a faster rate, leading to increased cardiac output that can exceed the heart's capacity over time. Some key points to consider include:
- The increased cardiac contractile function in patients with hyperthyroidism can lead to the development of heart failure, which may be unexpected, raising the possibility of hyperthyroid cardiomyopathy 1.
- Abnormal left ventricular (LV) function may be observed during exercise in hyperthyroidism, suggesting a reversible functional cardiomyopathy, independent of β-adrenoceptor activation, that is presumably a direct effect of an excess in circulating thyroid hormones 1.
- The term "high-output failure" is not really appropriate in hyperthyroidism, because the ability of the heart to maintain increased cardiac output at rest and with exercise is preserved in most cases 1.
- Treatment focuses on controlling the underlying thyroid dysfunction with antithyroid medications, while beta-blockers can help manage the cardiac manifestations until euthyroidism is restored, as recommended in the 2016 American Heart Association scientific statement 1.
From the Research
High Output Heart Failure in Hyperthyroidism
The primary cause of high output heart failure in hyperthyroidism is due to the excessive levels of thyroid hormones in the body, which can lead to an increase in resting heart rate, blood volume, stroke volume, myocardial contractility, and ejection fraction 2. This can result in "tachycardia-mediated cardiomyopathy" and ultimately lead to high output heart failure.
Key Factors Contributing to High Output Heart Failure
- Increased cardiac output due to excessive thyroid hormones 2
- Reduced systemic vascular resistance due to peripheral vasodilatation 3
- Elevated heart rate and myocardial contractility 2
- Increased blood volume and stroke volume 2
Associated Conditions and Symptoms
- Chronic anaemia, systemic arterio-venous fistulae, sepsis, hypercapnia, and hyperthyroidism can all lead to high output heart failure 3
- Symptoms of high output heart failure include those of heart failure, such as shortness of breath, fatigue, and swelling, despite an elevated cardiac output 3
Treatment and Management
- Treatment of hyperthyroidism with antithyroid medications, radioactive iodine ablation, or surgery can help alleviate high output heart failure symptoms 4, 5
- Management of high output heart failure may involve dietary restriction of salt and water, judicious use of diuretics, and avoidance of vasodilators and beta-adrenoceptor positive inotropes 3