Endocrine Abstracts

Objective

Does subclinical hypothyroidism (SCH)cause increased cardiovascular risk and how does treatment affect cardiac and vascular function in patients with SCH?

Methods

Cardiac function and central arterial stiffness(CAS)were measured in 20 females (mean age 50.1 plus/minus 4.1 years)with SCH (mean free T4 12.2 plus/minus 0.2 picomol per litre [normal range 9.8-22.1],median TSH 8.8 milliunits per litre[normal range 0.35-5.5]) prior to and during incremental Synthroid therapy.Local ethical committee approval approval was granted.

Tissue doppler echocardiography (TDE) was performed at baseline and at 6 months allowing regional myocardial velocity to be measured from 6 basal segments of the left ventricle,a sensitive measurement of left ventricular function.Intravenous dobutamine (5-40 micrograms per kilogram per minute) quantified myocardial reserve function.

Pulse wave analysis via applanation tonometry at the radial artery at 0,6,12 and 24 weeks measured indices of CAS,augmentation gradient(AG),augmentation index(AI),and time of travel of the reflected wave(TR).

Results

After Synthroid therapy (mean daily dose 112.5 micrograms,mean FT4 18.6 plus/minus 2.5 picomol per litre, TSH 1.5 plus/minus 0.64 milliunits per litre)neither baseline heart rate (66.6[pre],68.1[post]per minute)or peak heart rate (134.6[pre],133.0[post]per minute) altered significantly.

Basal mean systolic velocities did not alter with treatment(6.4[pre]to 6.2[post]centimetres per second), nor after dobutamine (14.1[pre]to 14.1 [post] centimetres per second).

AG fell from 10.3 to 8.9 millimetres of mercury (p<0.03),AI fell from 28.2 to 22.4 percent(p<0.001) and TR increased from 134 to 144 milliseconds (p<0.05).

Conclusion

There is no change in left ventricular or myocardial reserve function following the treatment of SCH, however CAS reduces significantly with treatment.This may reflect peripheral arterial involvement in this condition prior to cardiac involvement.