The effect of thyrotoxicosis on the electrocardiogram.

The effect of thyrotoxicosis on the electrocardiogram of the patient, in whom there is no clinical evidence of other types of heart disease and no cardiac arrhythmia, has been a subject of considerable controversy. Joll (1932) maintained that electrocardiographic changes are produced that are pathognomonic of thyrotoxicosis, while other authorities have denied this and have stated that no specific changes occur (McGavack, 1951; White, 1951). A difference of opinion also exists about the occurrence of cardiac hypertrophy in uncomplicated thyrotoxicosis, that is, with no cardiac arrhythmia, congestive failure, or any associated cardiac abnormality, such as coronary artery disease, hypertension, or rheumatic heart disease. Early observers failed to find cardiac enlargement (Lahey, 1930; Hurxthal, 1928), but later reports indicated that clinical evidence of cardiac hypertrophy might be present (Parkinson and Cookson, 1931; Lerman and Means, 1932; Friedberg, 1950). The aims of the present study are, therefore, to determine whether any specific electrocardiographic abnormalities are produced by thyrotoxicosis, and to investigate the occurrence of left ventricular hypertrophy, assessed on electrocardiographic criteria in uncomplicated cases of hyperthyroidism.