The present study is a rare report in the current
literature to highlight the importance of the
fQRS-T angle, which is an ECG sign of myocardial
repolarization and depolarization heterogeneity, and also affects adverse cardiovascular outcomes
and overall fatality rates in CTEPH patients. Our
study showed that the fQRS-T angle was negatively
associated with the TAPSE and TAPSE/sPAP ratio,
while it was positively correlated with RV Tei index
and RAA in CTEPH patients. Among hemodynamic
data, sPAP, mPAP, and PVR correlated positively with
the fQRS-T angle, while CI was negatively correlated
with the fQRS-T angle. However, there was no
significant association between the fQRS-T angle and
clinical and laboratory characteristics in patients with
CTEPH.
Under normal circumstances, the left ventricular
(LV) mass is higher than the RV mass, and RV
electrical activity is concealed by LV.[10] Pulmonary
hypertension results in RV pressure overload and RV
hypertrophy. As RV mass increases, RV contributes to
ventricular depolarization and QRS axis changes. The
course of the T-axis becomes divergent to QRS-axis
and the spatial QRS-T (sQRS-T) angle increase with
elevated PH.[11] It was previously shown that, even in
the very early phases of PH, the sQRS-T angle was
elevated in rats.[10] Henkens et al.[12] also demonstrated
that the sQRS-T angle was greater in patients with
chronically elevated RV pressure compared with
controls.
In the current study, we investigated the clinical,
echocardiographic, and invasive hemodynamic
correlates of fQRS-T angle CTEPH patients. We
were unable to demonstrate a correlation between
clinical variables and fQRS-T angle in patients
with CTEPH. The inadequate significance can be
attributed to the small sample size used in our
study. However, we were able to find significant
associations between echocardiographic variables
including TAPSE, TAPSE/sPAP ratio, RV Tei index,
and RAA and fQRS-T angle. Previously, similar to
our findings, the QRS-T angle was demonstrated to
be linked to echocardiographic variables such as SPAP,
dimension of RA and RV, and RV systolic dysfunction
and impaired diastolic function in patients with
CTEPH.[7] We showed that the fQRS-T angle was
negatively associated with TAPSE and TAPSE/sPAP
ratio. As TAPSE estimates RV contractile function,
an increase in fQRS-T angle CTEPH patients may
correspond to RV systolic dysfunction. Recently, a
new prognostic parameter was included in the current
PH guidelines. The TAPSE/sPAP ratio, which is a
surrogate non-invasive marker of RV-PA coupling and
provides information about RV diastolic function, was demonstrated to be a significant prognostic variable in
PH patients.[13,14] An increase in the fQRS-T angle was
also found to be linked to a reduction in TAPSE/sPAP
ratio in our study. Therefore, we can speculate that an
increase in fQRS-T angle in patients with CTEPH
may correspond to impaired both RV diastolic and
systolic function. Another parameter that reflects
the overall function of the RV is the RV Tei index.
The RV Tei index has been shown to be increased in
patients with connective tissue-associated-PAH due
to RV diastolic dysfunction and decreased myocardial
contractility of RV.[15] Similarly, we showed that the
RV Tei index was elevated in CTEPH patients and
an elevation in the fQRS-T angle corresponded to
an increase in RV Tei index of CTEPH patients.
Additionally, RAA has been shown to be a valuable
prognostic factor in PH patients. The mortality of PH
patients increases in patients with elevated values of
RAA.[4] In the current study, an increase in fQRS-T
angle was linked to an increase in RAA. Our results
are consistent with the findings of Sakhnova et al.[7]
showing that the QRS-T angle is related to elevated
RA size.
In this study, we also examined the correlations
between the fQRS-T angle and invasive hemodynamic
data in CTEPH patients. The sPAP, mPAP, and
PVR correlated positively, whereas CI was negatively
correlated with the fQRS-T angle. The positive
correlation between sPAP, mPAP, and PVR and
fQRS-T angle is comprehensible as an increase in
PA pressures and PVR results in an increase in RV
mass and a change in QRS and T-axis, resulting in
an increased QRS-T angle.[11] Chronic pressure and
volume overload on RV in patients with PH modify
the geometry of RV. As a result, RV occupies more
space in the pericardium and causes paradoxical
interventricular septum movement, thereby leading
to a decrease in LV volume at end-diastole.[16] The
decrease in LV diastolic volume at end-diastole results
in altered LV stroke volume as explained by the Frank-
Starling mechanism.[17] This may explain the negative
correlation between CI and fQRS-T angle.
Nonetheless, this study has several limitations.
First, our study has a single-center, retrospective
design. Second, since CTEPH is a rare condition, the
number of patients is limited. Although multi-center
studies involving more patients on this subject are
needed, we believe that our study may be a pioneer for
further studies on this subject. In addition, although
we have long-term follow-up data, the impact of the fQRS-T angle on prognosis in CTEPH patients is
unclear due to the small number of subjects. Another
limitation of our study was the utilization of an
fQRS-T angle instead of an sQRS-T angle. However,
the fQRS-T angle has been used instead of the sQRS-T
angle in studies on cardiovascular diseases. The main
reason for this is that sQRS-T angle measurement is
complicated and necessitates sophisticated computer
programs. On the contrary, the fQRS-T angle can be
simply calculated from the automatic description of the
ECG machine.
In conclusion, ECG seems to be a tool that should
not be ignored in the evaluation of CTEPH patients.
In these patients, the fQRS-T angle, which can be
computed simply by ECG, is negatively correlated
with TAPSE, TAPSE/sPAP ratio, and CI, while it is
positively correlated with RV Tei index, RAA, sPAP,
mPAP, and PVR, which are important prognostic
factors in patients with PH.
Ethics Committee Approval: The study protocol was
approved by the Dokuz Eylül University Faculty of Medicine
Ethics Committee (date: 29.03.2023, no: 2023/10-14). The
study was conducted in accordance with the principles of the
Declaration of Helsinki.
Patient Consent for Publication: A written informed
consent was obtained from each patient.
Data Sharing Statement: The data that support the
findings of this study are available from the corresponding
author upon reasonable request.
Author Contributions: Idea/concept, writing the article:
A.Ç., M.K.; Design: M.K., B.A.; Control/supervision: B.A.;
Data collection and/or processing: Z.K., D.S.; Analysis
and/or interpretation, materials: A.Ç., Z.K.; Critical review:
B.A., B.Ş.; References and fundings: A.Ç., B.Ş.
Conflict of Interest: The authors declared no conflicts
of interest with respect to the authorship and/or publication
of this article.
Funding: The authors received no financial support for
the research and/or authorship of this article.