Systolic time intervals in the evaluation of thyroid dysfunction

Cardiac performance in hyperthyroidism assessed by systolic time intervals and radionuclide ventriculography

Systolic time intervals (STI) and radionuclide ventriculography (RNV) were used in the assessment of cardiac performance in 22 patients with hyperthyroidism before and after antithyroid treatment. STI as well as RNV showed enhanced myocardial contractility which was normalized after antithyroid treatment. Beta-blocker treatment did not influence the hypercontractility in hyperthyroidism. This implies that beta-blockers alone cannot be regarded as satisfactory long-term treatment and that mechanisms other than increased sympathoadrenal drive are involved in the hypercontractility in hyperthyroidism. RNV suggested valvular regurgitation, probably of the mitral valve, in 11 patients. Possible hemodynamic consequences are discussed.

Left atrial systolic time interval in hyperthyroidism

The author noninvasively examined effects of thyroid hormone on left atrial function by using the left atrial systolic time intervals (LASTI) with its parameters as left atrial ejection time (LAET), left atrial preejection period (LAPEP), and LAET/LAPEP, as measured by pulsed Doppler echocardiography. The hyperthyroid (HTH) and normal control (NC) groups consisted of 21 and 25 subjects, respectively. He also considered serum triiodothyronine (T3) concentrations, age, heart rate, systolic blood pressure, left ventricular preload, afterload, contractility, diastolic function, P wave duration, PR interval, and left ventricular preejection period (LVPEP) as factors that might influence LASTI. LAET, LAET/LAPEP, and LVPEP in the HTH group were significantly shorter than in the NC group. LAET showed no significance with serum T3 concentration, but did with LVPEP in partial correlation analysis. These results demonstrated that a short LAET in the hyperthyroid state is controlled by a rapid rise in the left ventricular pressure.

Left ventricular function at rest and during exercise in acute hypothyroidism

The effect of hypothyroidism on left ventricular function at rest and during exercise was studied in nine patients without demonstrable cardiovascular disease who had had total thyroidectomy and ablative radioiodine treatment for thyroid cancer. Radionuclide ventriculography and simultaneous right heart catheterisation were performed while the patients were hypothyroid two weeks after stopping triiodothyronine treatment (to permit routine screening for metastases) and while they were euthyroid on thyroxine replacement treatment. When the patients were hypothyroid, cardiac output, stroke volume, and end diastolic volume at rest were all lower and peripheral resistance was higher than when they were euthyroid. Pulmonary capillary wedge pressure, right atrial pressure, heart rate, left ventricular ejection fraction, and the systolic pressure:volume relation of the left ventricle, which was used as an estimate of the contractile state, were not significantly different when the patients were hypothyroid or euthyroid. During exercise, heart rate, cardiac output, end diastolic volume, and stroke volume were higher when the patients were euthyroid than when they were hypothyroid. Again, pulmonary capillary wedge pressure, ejection fraction, and the systolic pressure:volume relation were similar in both thyroid states. The data suggest that the alterations in cardiac performance seen in short term hypothyroidism are primarily related to changes in loading conditions and exercise heart rate; they do not suggest that acute thyroid hormone deficiency has a major effect on the contractile properties of the myocardium.

Hypothyroid cardiomyopathy: echocardiographic documentation of reversibility

The concept of hypothyroid heart disease remains controversial. Although hemodynamic abnormalities have been described, the presence of underlying abnormal cardiac structures has not been confirmed. The authors studied 20 hypothyroid patients using M-mode echocardiography before and after l-thyroxine therapy. Fifteen additional hypothyroid patients were studied using two-dimensional echocardiography to confirm the data of the first study. The findings were the same in both studies: during hypothyroidism, the interventricular septum is thickened, the ratio of septal thickness to left ventricular posterior wall thickening is increased, the right ventricular wall is thickened, regional wall motion of interventricular septum and right ventricular wall is decreased, and global function of the left ventricle is decreased. These findings are reversed with l-thyroxine therapy; they occur within 6 months of the development of hypothyroidism, but appear unrelated to elevated TSH levels. Whether the thickened interventricular septum and right ventricular wall represent true muscular hypertrophy requires further elucidation. Nevertheless, these data demonstrate the existence of a hypothyroid cardiomyopathy.

Systolic time intervals: a review of the method in the non-invasive investigation of cardiac function in health, disease and clinical pharmacology

Measurement of systolic time intervals is a valuable, non-invasive procedure to assess left ventricular performance, particularly when influenced by drugs. In this review, we discuss various factors affecting systolic time intervals, the therapeutic implications of the technique and its place among other non-invasive tests of cardiac function.