DISCUSSION
In the current study, we researched the significance of frontal QRS-T angle in recently diagnosed COPD patients. The primary finding of our study was that the patients with severe-very severe COPD had significantly higher frontal QRS-T angle than patients with mild-moderate COPD. To the best of our knowledge, ours is the first research study that demonstrated an association between frontal QRS-T angle and severe-very severe COPD.
COPD is a disease in which there is an irreversible limitation of airflow and an increased inflammatory response in the lungs. Hypoxia, which is the main finding of the disease, gets worse as the disease progresses 14. The hypoxia contributes to the deterioration of the quality of life, increased morbidity, disability, and mortality 15. Moreover, the pathologic changes in COPD can alter the cardiac repolarization and depolarization. Thus, the increased risk of mortality due to cardiovascular causes in the patients has been principally attributed to cardiac arrhythmias and SCD due to the altered cardiac repolarization and depolarization2-5, 16. Although the main mechanism of the altered cardiac repolarization and depolarization in the patients with COPD has not been clearly elucidated, it has been suggested that hypoxemia, autonomic dysfunction, and acid-base disturbances might be the potential causes 6, 8, 17.
Alteration in myocardial repolarization represents an increased risk for malign cardiac arrhythmia and SCD 7,8. Myocardial repolarization has been traditionally evaluated considering the QT interval on surface ECG 18. However, the calculation of QT interval is not easy and requires devices like ruler and magnifying glass, as well as sophisticated software programs. Besides, the reproducibility of QT interval measurements is low19. For this reason, most investigators have focused research studies on identifying the novel ECG parameters that can be easier to calculate using the surface ECG. Frontal QRS-T angle may be used as a basic marker that reflects the absolute difference between the repolarization and depolarization of the myocardium9,10. Investigations have shown that frontal QRS-T angle was less sensitive to sound than the measurements of QT interval13,20. Moreover, the calculation of the frontal QRS-T angle did not require any additional tools and was much easier than calculating the QT interval. Furthermore, it has been shown that the increase in the frontal QRS-T angle was an earlier event than the development of overt electrocardiographic changes 11. The axes of QRS and T are automatically reported by the vast majority of ECG devices; therefore, the calculation of the frontal QRS-T angle can be readily performed incorporating those measurements in the formula Frontal QRS-T angle = │QRS axis – T axis│.
The clinical importance of QT interval in the patients with COPD had been investigated in previous studies. It was found that the QTc interval and QT dispersion were significantly longer in COPD patients when compared to controls 8,21. Zulli et al. demonstrated that the increased QT dispersion was an important independent predictor of pulmonary and cardiovascular mortality in COPD patients 22. Moreover, it was reported that the increased QT dispersion could decrease after the partial correction of the hypoxemia by medical treatment. Those results suggested that the variations in blood gas levels might be critical for the increased QT interval in the patients with COPD 23. Although QT interval was comprehensively evaluated in COPD, there are no studies that investigated the importance of frontal QRS-T angle in the recently diagnosed COPD patients.
We studied for the first time that the patients with severe and very severe COPD had significantly increased frontal QRS-T angle compared to the patients with mild and moderate COPD. Additionally, significant reductions in the ratio of FEV1/FVC and the levels of MEF25-75 were detected in severe and very severe COPD patients. We observed that the predictive value of a frontal QRS-T angle≥ 30o for severe to very severe COPD had a sensitivity and a specificity of 73% and 67%, respectively, while the ratio of FEV1/FVC was found to be an independent predictor of the frontal QRS-T angle. Our findings suggest that the frontal QRS-T angle has a very important clinical role in patients with COPD. It can be concluded that the patients who have an increased frontal QRS-T angle on initial ECG will have worse pulmonary function test results than the patients who do not have.
Previous studies showed that the frontal QRS-T angle could be wider in the patients with various conditions like hypertension and diabetes mellitus 20,24,25. To exclude the possible effects of comorbid factors in elucidating the relationship between frontal QRS-T angle and COPD, we included only the COPD patients without any comorbidities. Therefore, the number of patients in our study remained relatively small, which could be considered as a limitation of the study. In addition, drugs that are used in the treatment of COPD may change the myocardial repolarization. So, to exclude the possible effect of COPD drugs on frontal QRS-T angle, we evaluated the patients recently diagnosed with COPD and who had not been started on a medication regimen yet. We consider that the choice of inclusion criteria had strengthened our study. Some other limitations of our study should also be acknowledged. As mentioned earlier, the small size of the study group had been further limited by the lack of a control group that did not permit us to investigate our results in a comparative way. Second, the patients were not followed up for any possible cardiovascular complications. It would be better to use a 24-hour Holter ECG for that purpose, and the associations among frontal QRS-T angle, arrhythmias, and SCD could be demonstrated more clearly.
In conclusion, based on the current study results that indicated a significant increase in the frontal QRS-T angle in severe to very severe COPD patients, we suggest that frontal QRS-T angle can be used as a novel electrocardiographic marker which can be readily calculated using the surface ECG. Nevertheless, further prospective studies with larger population sizes are needed to verify our results and to demonstrate the relationship between the frontal QRS-T angle and COPD.