Cardiac function, physical exercise capacity, and quality of life during long-term thyrotropin-suppressive therapy with levothyroxine: Effect of individual dose tailoring

As recently claimed, TSH-suppressive therapy with L-T-4 may have adverse ef fects on the heart, but these results have not been consistently confirmed. We assessed cardiac function by clinical, echocardiographic, and ergometab olic criteria in 19 patients (16 women and 3 men) receiving long term L-T-4 at a fixed daily dose ranging from 1.8-4.0 mu g/kg. The results showed sig nificant alterations in several cardiac parameters suggestive of subclinica l hyperthyroidism. In particular, intraventricular septum thickness (10.0 /- 1.4 us. 8.1 +/- 1.1 mm), left ventricular posterior wall thickness (9.4 +/- 1.5 vs. 8.1 +/- 1.1 mm), end-diastolic dimension (47 +/- 4 vs. 44 +/- 3 mm), and left ventricular mass index (102 +/- 15 vs. 75 +/- 15 g/m(2)) wer e significantly increased compared to values in age- and sex-matched euthyr oid controls. Exercise tolerance (expressed as maximal tolerated workload; 102 +/- 14 us. 117 +/- 12 watts), maximal (V) over dot O-2 achieved at peak exercise (maximum (V) over dot O-2, 17.3 +/- 3.3 us. 21.9 +/- 2.5 mL/min.k g), and anaerobic threshold (expressed as a percentage of (V) over dot O(2) max, 46.5 +/- 8.4 us. 56.2 +/- 6.6) were significantly reduced in L-T-4 tre ated patients. The L-T-4 dose was then reduced to the minimal amount able t o keep the serum TSH concentration at 0.1 mU/L or less in 7 patients who we re reevaluated 6 months after the initial study. This individual tailoring of the TSH-suppressive L-T-4 dose was in all cases associated with normaliz ation of all echocardiographic and ergometabolic parameters. In conclusion, our findings show that abnormalities of heart morphology associated with i mpaired exercise performance occur as a consequence of long term therapy wi th fixed TSH-suppressive doses of L-T-4, but that these abnormalities impro ve or disappear after careful tailoring of TSH-suppressive therapy.