Systolic Time Interval (STI) in hypothyroid patients receiving high dose L-thyroxine

• Main Authors: Zakaria, Nurul Aulia, Pasi, Hafizah, Shahar, Mohammad Arif
• Format: Conference or Workshop Item
• Language: English; English
• Published: 2019
• Subjects: RC648 Specialties of Internal Medicine-Diseases of The Endocrine Glands. Clinical Endocrinology; RC667 Specialties of Internal Medicine-Diseases of Circulatory (Cardiovascular) System
• Online Access: http://irep.iium.edu.my/81835/1/MRS_STI.pdf; http://irep.iium.edu.my/81835/7/MRS%202019%20Abstract%20Book.pdf; http://irep.iium.edu.my/81835/

INTRODUCTION: Systolic Time Interval (STI) is a simple,noninvasive and precise technique to assess left ventricular (LV) function. It measures aortic Pre-Ejection Period (PEP) over Left Ventricular Ejection Time (LVET) from echocardiogram. Thyrotoxicosis will enhance LV function and cause reduction of STI. OBJECTIVES : This study was perform to measure the changes of STI after administration of high dose L-thyroxine and to determine the correlation between high dose L-thyroxine administration and STI METHOD : A Total of 22 patients were screened. Those with cardiac diseases and high Framingham risk score were excluded. Nine patients were started on high dose L-thyroxine (7x their usual dose) once a week during the month of Ramadan. Thyroid hormones ( T3,T4,TSH) and STI (PEP/LVET) were measured at baseline and within 24 hrs after high dose of L-thyroxine ingestion. RESULTS : All patients have normal thyroid hormones level and normal cardiac function at baseline. The median dose (mcg) of L-thyroxine was 600 (437.5,700) while the median level of fT4 level was 17.43(12.38,20.8). Despite the significant increment of fT4 after L-Thyroxine ingestion [baseline 13.21(8.19,14.63) vs high dose 17.43(12.38,22.55) p= 0.011] there was no significant change in STI [baseline 0.3(0.2,0.4) vs high dose 0.28(0.26,0.45) p; 0.513]. There was no correlation found between the dose of L-thyroxine and STI (r=0.244 , p;0.526). CONCLUSION : Administration of high dose L-thyroxine did not significantly alter STI, unlike the naturally occurring thyrotoxicosis.Therefore ‘exogenous’ administration of high dose L-thyroxine is cardiac safe.