CARDIAC-PERFORMANCE AND THYROID-FUNCTION - THE CORRELATION BETWEEN SYSTOLIC-TIME INTERVALS, HEART-RATE AND THYROID-HORMONE LEVELS

In the search for a clinical correlate to thyroid function, correlatio ns were sought between the plasma level of thyroid hormones and the ca rdiac function, assessed by heart rate and the systolic time intervals . The present study is the first to 1) use a curvilinear correlation a nd 2) do so in the entire hormone range. A third degree Chebychew's re gression equation was used to enable curvilinear correlation. In a pop ulation of 10 hypothyroid, 14 euthyroid, and 25 hyperthyroid patients a statistically significant curvilinear correlation was found between the thyroid hormone levels and the systolic time intervals. The correl ation coefficients showed the heart rate equally correlated to the thy roid hormone levels as the best correlated of the systolic time interv als. The correlation between the heart rate and T3 was almost linear, with a heart rate increase of 4 beats/minute with each increase in pla sma T3 of 1 nmol/l. Conclusion: The thyroid function reflects in the c ardiac function in a curvilinear regression between T3 and systolic ti me intervals and in an almost linear regression between T3 and heart r ate. The variation, however, is too great and the slope too low, to su ggest the use of the heart rate as a clinical correlate to thyroid fun ction.