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.