Major findings
In clinical settings, to determine the origin of OTVAs, we might get
confused by different diagnostic criteria. This is the first
systemic
and comprehensive study that included 10 parameters to identify OTVA
origin between 2002 and 2020. The main findings of our study are
summarized as follows. (1)
Among
the seven parameters
without
restrictions in the transition lead, the
larger
ISA in leads V1 and V2 exhibited the best predictive value in
differentiating the VAs in the LVOT,
with
a cutoff value
of
57
ms
× mv, which was different from a previous study (cutoff value of 15 ms ×
mv)[10], and the V2S/V3R index exhibited the best predictive value
in differentiating the VAs in the RVOT, with a cutoff value of 1.5. (2)
The algorithm combining the larger ISA in V1 and V2 and the V2S/V3R
index has the best predictive value in determining the origin of OTVAs
without
restrictions in the transition lead. (3) Among the 10 parameters with
the transition lead in V3, the V3 R-wave deflection interval exhibited a
greater power to predict the origin of VAs than the other parameters. It
has an accuracy similar to the algorithm proposed by us. (4) In the
validation study, the algorithm exhibited optimal accuracy (95%). Taken
together, the findings suggest that the algorithm can reliably determine
the origin of the OTVA without restrictions in the transition lead.
Need forreviewing
and comparing the accuracy of different diagnostic criteria for
determining OTVA origin
The criteria proposed to differentiate OTVA origin spanned nearly two
decades, with
considerable
discrepancies among the studies. (1) Different cases were included in
the studies. The outflow tract was classified into six subdivisions: RV
septum, RV free wall, RV near the His-bundle region,
LV
endocardium, ASC, and
LV
epicardium remote from the LSV[15]. Ouyang et al.[3] and
Yoshida
et al.[5] just enrolled patients with VAs originating from the RVOT
and ASC. Di et al.[9] and Cheng et al.[6] did not enroll
patients with the OTVAs originating from the LV epicardium. However,
patients with OTVAs
originating
from all six subdivisions were enrolled in other studies. These
discrepancies in the included cases might inevitably lead to
different
diagnostic accuracies. (2) A considerable discrepancy was present in the
number of participants among the different studies. Ouyang et al.[3]
only enrolled 15 cases, whereas Xia et al.[11] enrolled 382 cases.
(3) Considerable differences in sample capacity might lead to different
diagnostic accuracies,
whether
or not accounting for sinus rhythm.
Betensky
et al.[4], Yoshida et al.[5], and Di et al.[9]
performed
QRS measurement during sinus rhythm. This measure
takes
into account variations in body habitus, cardiac rotation, respiration,
and ECG lead position. (4) Precordial transition lead. The criteria
established by Betensky et al.[4], Cheng et al.[6], and Di et
al.[9] just included OTVAs with the transition lead in V3. However,
other studies included OTVAs without
restrictions
in the precordial transition lead. Given the discrepancy among the
studies mentioned above, we need to comprehensively review and compare
these criteria. In our retrospective and validation study, 200 patients
with OTVAs originating from all six subdivisions were enrolled. The
precordial transition lead varied from V1 to V6. Given the anatomic
complexity of the ventricular outflow tract, it may be difficult to
differentiate the origin of PVCs using a single parameter. Therefore, it
is better to combine several simple and credible parameters to predict
OTVA origin.
Thelarger
ISA in leads V1 and V2 and theV2S/V3R
index have great power in predicting VA origin without restrictions in
the transition lead
The precordial V1–V3 leads are adjacent to the LVOT and RVOT and are
the best parameters to distinguish OTVA. As the focus moves far away
from the lead, R-wave amplitude increases, and S-wave amplitude
decreases. This results in a higher R-wave amplitude and lower S-wave
amplitude in the V1–V3 leads during OTVAs originating from the LVOT
than those originating from the RVOT. Therefore, VAs originating from
the LVOT would have a larger ISA and a smaller V2S/V3R index than those
originating from the RVOT.
The ablation targets of five patients who were misdiagnosed by the
algorithm were analyzed. In three patients, the VA was located in the
septum of the RVOT
(misdiagnosed
as in the LVOT), and in two, the VA was located in the LCC (misdiagnosed
as in the RVOT). Anatomically, the location of the RVOT is more anterior
and leftward of the LVOT, whereas that of the LVOT is more posterior and
rightward of the RVOT. The intimate nature of these two structures
explains why OTVAs from these two distinct locations can be
morphologically similar on surface ECG and result in successful ablation
in the RVOT with the origin in the LVOT, or vice versa[16, 17].