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.