Effect of Subclinical Thyroid Disease on Cardiac Function in Patients on Thyroid Replacement Therapy as Assessed by Radionuclide Ventriculography

Document Type : Original Paper, Cardiology

Author

Nuclear Medicine Unit, Faculty of Medicine, Cairo University,Cairo, Egypt.

Abstract

Objective: The evidence indicates that the
cardiovascular system responds to the
minimal but persistent changes in
circulating thyroid hormone levels, which
is typical of individuals with subclinical
thyroid dysfunction. However, there is no
study to compare between control or
euthyroid and subclinical thyroid cases
with tong-term L-thyroxine therapy
regarding cardiac function of the heart
using radionuclide ventriculography. The
objective of our study is to assess and
compare the left ventricular function
through the evaluation of the radionuclide
systolic parameters, diastolic parameters
and heart rate for these conditions.
Methods: Ten healthy controls and 32
patients with surgically treated
differentiated thyroid carcinoma followed
by radioactive iodine ablation and
receiving suppressive L-thyroxine were
evaluated by gated radionuclide
ventriculography. The patients were
divided into 3 groups according to their
thyroid hormone profile. These groups
were: euthyroid, subclinical hypothyroid,
subclinical hyperthyroid groups. Results:
Long-term L-thyroxine therapy
significantly affected the left ventricular
systolic function in patients with
subclinical thyroid dysfunction. It
prolonged TPER and TPFR in patients with
subclinical hypothyroid dysfunction while
it decreased TPER and TPFR in patients
with subclinical hyperthyroid dysfunction.
However, there was no effect on the
euthyroid group. Conclusions: These
abnormalities in cardiac function in
subclinical hypo- or hyperthyroidism may
lead to long-term effect on patient's lives.
Early effective and accurate treatment for
these patients is important to avoid the
consequences of long term exposure of the
cardiovascular system to small increases or
decrease of thyroid hormone.


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