Sitat:
The electrocardiogram reveals characteristic changes 5,7,10,15-19. The rate is slow and the voltage is low. The T waves are flattened or inverted. Axis deviation, an increased P-R interval, and widened QRS complexes and prolonged QT interval are seen, but these signs are not diagnostic of myxedema. The pattern reverts toward normal with treatment, but the final pattern depends on the presence or absence of intrinsic myocardial disease. The rare occurrence of complete heart block complicated by Adams-Stokes attacks, with reversion to sinus rhythm after treatment with thyroid hormone, has been reported as has ventricular tachycardia 18,19.
Changes resembling those of ischemic heart disease may be found during exercise: they may indicate an intrinsic anoxia rather than organic narrowing of the coronary vessels 5,7,10,17.
The ECG changes have usually been attributed to the histologic changes in the myocardium. However, removal of pericardial fluid may immediately reverse the pattern toward normal suggesting that the effusion may in part be responsible for the abnormalities.
The systolic time intervals are prolonged in hypothyroidism 5,7,10,20. They can be measured by several techniques and have been expressed as the ratio of the pre-jection period and the left ventricular ejection time or the interval between the onset of the QRS complex of the ECG and the onset of the Korotkoff sound 21,22. The most obvious effect of thyroid hormone deficiency on the heart is a lengthening of both systolic and early diastolic time characteristics. As evaluated by equilibrium radionuclide angiography, the time to peak emptying rate and the time to peak filling rate are longer in hypothyroid patients than in controls23; the time intervals are negatively related to serum FT4 in the hypothyroid patients. The subtle decrease in early active relaxation and prolongation of contraction without major changes in global systolic function of hypothyroid patients is reversible upon thyroid hormone replacement therapy24.
