Discussion
Cardiovascular symptom such as exertional dyspnea and impaired exercise tolerance are common in the hyperthyroid patients. (1, 15). In our study, 19.2% of the patients had a history of exertional dyspnea. Probable explanations for exertional symptoms include ineffective oxygen utilization, respiratory muscle weakness and increased ventilator drive to breath, increased airway resistance, diminished lung compliance, and heart failure. (15) In Raphael’s study (2), heart failure with the reduced EF was seen in 6% and heart failure with the preserved EF was seen in 10% of the patients. Yue et al. also reported heart failure presentation in 5.8% of the hyperthyroid patients that only in 50% of them, there was reduced EF (16), and they proposed that, diastolic dysfunction is the reason of HF symptoms in others.
We found that, no hyperthyroid patient had diastolic dysfunction that was in contrast with many previous studies, because Diastolic dysfunction specially impaired relaxation (grade 1) was frequently reported in many previous studies evaluated the hyperthyroid patients(1, 2, 4, 7, 17) . The most important explanation for this discrepancy was that, we used newer guideline criteria for defining diastolic dysfunction compared to previous studies that were based on the conventional indices, and also we excluded the patients with comorbidities that may affect diastolic function such as those with diabetes, hypertension, and Coronary artery disease. We included newly diagnosed hyperthyroid patients who received no medication and this point was another difference between our study and previous studies that were done on the patients consuming anti-thyroid medications, and suggested that, maybe initiation of drugs induced diastolic change that need to be assessed in future studies.
By comparing diastolic parameters between the two groups, IVRT was the only index that significantly differed and other indices including E/e’, LAVI, TR velocity, septal, and lateral e’ were comparable. Enhanced diastolic function was also reported in Mintz G’s study (10), and their results about IVRT was similar to us, however their study was done only at rest. Shorter IVRT in hyperthyroidism is due to lusitropic effect of thyroxin (18) through positively regulated sarcoplasmic Ca-ATPase because Reuptake of calcium into the sarcoplasmic reticulum early in diastole can determine the rate of the left ventricle relaxation (isovolumic relaxation time).
In our study, diastolic function reserve was also assessed by exercise stress echocardiography using ASE guideline criteria. Accordingly, this evaluation was not performed in previous studies, and interestingly, we found that no one in hyperthyroid group had developed diastolic dysfunction criteria.
Conclusion : our finding did not support Hyperthyroidism associated diastolic dysfunction as a cause of exertional intolerance and dyspnea in the patients with preserved EF and normal PAP.