(15.08) Is complete heart block caused by isolated hypothyroidism always reversible?

Hypothyroidism causes global slowdown of various organ systems. Patients with hypothyroidism rarely display symptoms of dysfunction in cardiac conduction system, however, in a patient with complete heart block, hypothyroidism can be a potential etiology. There are only a few case reports, in which isolated hypothyroidism has been associated with complete AV blocks. By presenting one such rare case where hypothyroidism played a causal role in symptomatic AV nodal dysfunction requiring a permanent pacemaker, we hope to highlight the importance of thyroid function tests during workup for high degree AV blocks and to bring to attention the mechanistic relationship between the thyroid hormone and the cardiac conduction system.

Case(s) Description :

Patient data for this case report, including demographic details, medical history, physical exams, and test results, were collected by reviewing records. Details of interventions and follow-up procedures, along with a focus on patient confidentiality and ethical considerations, were outlined. Informed consent was obtained, and ethical approval was secured from the relevant committee. Relevant literature was reviewed to contextualize and support the reported case.


Discussion :

The prevalence of overt hypothyroidism in the general population varies, ranging from 0–3 percent to 3–7 percent in the United States. Thyroid hormone directly influences heart function, impacting inotropy, chronotropy, and dromotropy. The physiological chronotropic response relies on proper tri-iodothyronine expression in heart cells, affecting ion pumps in the endoplasmic reticulum. Profound hypothyroidism may worsen cardiac contractility, slow heart rate, and impede electrical conduction in the heart muscle, leading to ECG changes like bradycardia, low voltage complex, RBBB, QT prolongation, and T wave inversion. In our case study, a patient with 3rd degree AV block due to hypothyroidism, initially managed with oral thyroid supplementation, was readmitted with atrial fibrillation and persistent heart block. Despite improved thyroid function, the patient eventually received a permanent pacemaker. While some cases show resolution of AV block with thyroid hormone therapy, others may necessitate permanent pacemakers. The report underscores the importance of managing thyroid dysfunction, recognizing that successful normalization may not always prevent the need for a pacemaker.