Introduction
Hyperthyroidism is defined as a clinical condition resulted from
abnormal high serum thyroid hormones levels
(1). Any increase in the level of thyroid
hormone leads to change in many systems of human body including
cardiovascular system, because Thyroid hormone acts through genomic and
non-genomic mechanisms to regulate cardiac
function.(2) Cardiomyocytes have thyroid
hormone nuclear receptors that when bound alter gene transcription, can
regulate intracellular calcium metabolism and myofilaments. Nongenomic
effects on cardiomyocytes include altering ion channel permeability and
then leading to tachycardia. (3)
Hemodynamic effects of hyperthyroidism increased heart rate (HR);
reduced peripheral vascular resistance; and increased preload, stroke
volume, and consequently cardiac output.
(4). Thus cardiovascular manifestation are
common among the patients and hyperthyroid patients may clinically
develop some symptoms like exertional dyspnea, palpitation, orthopnea,
paroxysmal nocturnal dyspnea and peripheral
edema.(1, 2)
More common cardiac manifestations of hyperthyroidism that was
documented in various studies are systolic hypertension, left
ventricular(LV) hypertrophy, increased LV mass, heart failure, and
cardiac arrhythmia including atrial fibrillation
(1, 2,
5, 6);
however, evaluation of left ventricular diastolic function in
hyperthyroidism showed conflicting results in different
studies.(7-11) accordingly, in some of
them, diastolic dysfunction was supposed as a cause of heart failure
symptoms in the patients with preserved EF
(7, 12),
while in others, the enhanced diastolic function was
observed.(10) Considering that
frequently, symptom of diastolic dysfunction only occurs during
exercise, as LV filling pressure is normal at rest, but it is increased
with exercise.(13) So, exercise stress
echocardiography is a useful modality to detect diastolic capacity
reserve by providing insight to cardiovascular hemodynamic. In this
study, we tried to assess diastolic function in the hyperthyroid
patients using the latest guideline of American society of
echocardiography (ASE) (14) and also
evaluation of diastolic function in response to exercise during stress
echocardiography to see whether it cause exertional dyspnea or not.