Duration of the P Wave and P Wave Dispersion in Subclinical Hyperthyroidism

Objective: To determine whether the values for P wave dispersion (Pdis) and adjusted Pdis, which are simple noninvasive electrocardiographic markers to detect paroxysmal atrial fibrillation, differ in patients with endogenous subclinical hyperthyroidism in comparison with those in healthy control subjects.

Methods: We measured the maximal P wave duration and the difference between the maximal and the minimal P wave duration (Pdis) from the 12-lead surface electrocardiogram of 36 patients with endogenous subclinical hyperthyroidism and of 22 age- and sex-matched healthy control subjects. Adjusted Pdis (Pdis/square root of the number of measured electrocardiographic leads) was also calculated from each electrocardiogram.

Results: The minimal P wave duration was significantly shorter in patients with subclinical hyperthyroidism than in healthy control subjects (P<0.001). Pdis and adjusted Pdis were also significantly higher in the patient group than in the control subjects (P<0.05). By univariate analysis, only thyrotropin levels were found to be associated with adjusted Pdis (r = -0.28; P = 0.03).

Conclusion: Pdis and adjusted Pdis differed in patients with endogenous subclinical hyperthyroidism in comparison with those values in healthy control subjects. Thus, these simple electrocardiographic markers may be useful for identifying patients with endogenous subclinical hyperthyroidism who are at risk for paroxysmal atrial fibrillation.