The cause of low voltage QRS complex in primary hypothyroidism. Pericardial effusion or thyroid hormone deficiency?

In order to clarify the cause of low voltage QRS complex seen on ECG (low voltage), thyroid hormones, LDH isozyme and pericardial effusion (PE) were studied in 39 patients with primary hypothyroidism. Low voltage and PE were found in 12 of 39 (30.8%) and 12 of 27 (44.4%), respectively. Serum T4 in patients with low voltage (Group 1) was significantly lower than that in patients without low voltage (Group 2) (T4 1.4 +/- 1.7 vs 2.8 +/- 2.3 micrograms/dl, p less than 0.05). Group 1 had a higher incidence of large amounts of PE than Group 2 (6/8 vs 1/19, p less than 0.002). However, there was no significant difference in thyroid hormone levels between patients with and without PE. No significant difference in LDH isozyme pattern was found among the groups. Low voltage without PE was found in only one patient. Two patients with low voltage and PE demonstrated that in spite of the presence of large PE, low voltage improved after thyroid replacement therapy. By multi-variate analysis, low voltage was related to large PE, patient age and low T4 levels. From these results, it was suggested that in hypothyroidism low voltage was brought about by a combination of both severe thyroid hormone deficiency and large PE. In addition, elderly patients over 60 years had low voltage more frequently than did patients under 59 years.