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.