Frequency of fragmented QRS on ECG and relationship with left ventricular dysfunction in patients with subclinical hypothyroidism.

Objective: Subclinical hypothyroidism (SH) is a biochemical definition that has been proven to be associated with cardiovascular diseases. Fragmented QRS (fQRS) is defined as an electrocardiographic (ECG) reflection of cardiac fibrosis. It is associated with increased cardiovascular mortality and morbidity. In this study, we aim to evaluate the presence and frequency of fQRS in SH patients and determine the relationship between fQRS presence and left ventricular dysfunction by using the myocardial performance index (MPI).

Patients And Methods: Our study included 50 newly diagnosed SH and 50 healthy participants with similar demographic characteristics. We compared demographic characteristics, laboratory findings, electrocardiographic and echocardiographic measurements of the study population. SH patients were evaluated as two groups in the subgroup analysis: [fQRS(+) SH] with fQRS and [fQRS(-) SH] without fQRS. We analyzed the correlation of thyroidstimulating hormone (TSH) levels with demographic characteristics, electrocardiographic and echocardiographic data. Independent predictors of fQRS presence were evaluated by logistic regression analysis.

Results: The mean age of SH patients was 44 ± 8 years, and 46% (n = 23) of the patients were women. In the control group, the mean age was 45 ± 11 years, and 52% (n = 26) of the participants were women. MPI was found to be significantly higher in the SH group compared to the control group (0.53 ± 0.07 vs. 0.41 ± 0.08, p< 0.001). fQRS was found to be significantly higher in the SH group compared to the control group (p= 0.004). In echocardiographic measurements, isovolumic relaxation time (IVRT) was found to be significantly longer in the fQRS(+) SH group (105.6 ± 21.8 ms vs. 91.1 ± 24.4 ms, p < 0.001), while isovolumic contraction time (IVCT) was not significantly different between the groups. Ejection time (ET) was significantly longer in the fQRS (-) SH group (286.9 ± 32.1 ms vs. 274.2 ± 30.6 ms; p = 0.011). MPI was 0.57 ± 0.12 in the fQRS (+) SH group and 0.48 ± 0.06 in the fQRS (-) SH group, which was significantly higher (p = 0.001). TSH was found to be 8.82 ± 4.58 in fQRS (+) SH group and 5.73 ± 3.10 in fQRS (-) SH group (p = 0.003). It was found that MPI (r = 0.302, p < 0.001) and fQRS (r = 0.321, p < 0.001) were significantly positively correlated with TSH. TSH levels [OR = 1,645, 95% CI = 1,322 to 2,067 (p = 0.001)], IVRT [OR = 1,502, 95% CI = 1,119 to 95% (p = 0.003)], and MPI [OR = 1,408, 95% CI = 0.989 - 1.806 (p = 0.001)] were found to be independent predictors of the presence of fQRS.

Conclusions: The frequency of fQRS in SH patients was found to be higher than in the healthy population. MPI values were higher in fQRS (+) SH patients compared to fQRS (-) SH patients, resulting indirectly having a higher risk of tendency to left ventricular systolic/diastolic dysfunction. MPI and fQRS had a significant positive correlation with TSH. TSH, IVRT, and MPI were found to be independent predictors of the presence of fQRS in SH patients.