RESULTS
A total of 104 COPD patients without any significant comorbidities were included in this study. Mild and moderate COPD (group I) was detected in 35 patients, whereas severe and very severe COPD (group II) was detected in 69 patients according to the COPD GOLD stage. Comparison of baseline characteristics and laboratory parameters between two groups are listed in Table 1. No significant difference was found between two groups.
Spirometry and pulmonary function tests are demonstrated in Table 2. Patients in group II had significantly lower FVC (2.9 [2.0-3.6] vs. 1.8 [1.4-2.2], P < 0.001), FEV1 (1.9 [1.3-2.3] vs. 1.0 [0.7-1.3], P < 0.001], FEV1/FVC (67.0 [62.0-69.0] vs. 55.0 [49.5-64.0], P < 0.001), MEF25-75 (1.1 [0.8-1.4] vs. 0.6 [0.4-0.9], P < 0.001) and TLC (5.6 [4.3-6.2] vs. 4.7 [3.7-5.2], P = 0.003) values compared to patients in group I.
Comparison of frontal QRS-T angle between two groups is shown in Figure 2. Frontal QRS-T angle was significantly higher in group II patients than in group I patients (43.0 [25.5-60.0] vs. 20.0 [12.0-32.0], P < 0.001). ROC curve analysis was performed to determine the best cutoff value of frontal QRS-T angle for predicting severe-very severe COPD (Figure 3). Frontal QRS-T angle ≥ 34.5° predicted severe-very severe COPD with a sensitivity of 63.8% and specificity of 89.2% (AUC: 0.752, P < 0.001, 95% CI: 0.657-0.848).
Correlation analysis of frontal QRS-T angle with other variables is shown in Figure 4. Frontal QRS-T angle was negatively correlated with FEV1/FVC (r = –0.524, P < 0.001) and MEF 25-75 (r = –0.453, P < 0.001).
Multivariable logistic regression analysis demonstrated that frontal QRS-T angle was the independent predictor of severe-very severe COPD (odds ratio: 1.051, 95% confidence interval: 1.024-1.079, P < 0.001) (Table 3). Linear regression analysis was used to determine the independent predictors of frontal QRS-T angle. It was found that MEF25-75 (β: –0.593, P = 0.006) was the only independent predictor of the frontal QRS-T angle (Table 4).