Predictive Values of Different ECG Algorithms in
Differentiating Left Ventricular Outflow Tract
from Right Ventricular Outflow Tract Premature
Ventricular Beats Origin
Mostafa Abdelmonaem and Amira Nour*
Department of Cardiology, Ain Shams University Hospital, Egypt
Submission: November 08, 2019; Published: December 17, 2019
*Corresponding author: Amira Nour, Congenital and Structural Heart Disease Unit, Department of Cardiology, Ain Shams University Hospital,
Abbassya, Cairo, Egypt
How to cite this article:Mostafa Abdelmonaem, Amira Nour. Predictive Values of Different ECG Algorithms in Differentiating Left Ventricular Outflow Tract from
Right Ventricular Outflow Tract Premature Ventricular Beats Origin. J Cardiol & Cardiovasc Ther. 2019; 15(3): 555915. DOI: 10.19080/JOCCT.2019.15.555915
Background:Premature ventricular beats (PVBs) are early myocardial electrical oscillations, which are not life threatening in patients
with normal cardiac architecture, however causing annoying morbidity; radiofrequency catheter ablation became a curative tool for
elimination of this arrhythmia.
Methods: This study was held on 80 symptomatic patients with PVBs of same morphology provided being of significant burden,
these patients were eligible for PVB electrophysiological study and catheter ablation in EP unit, Ain Shams University. Detailed history,
comprehensive general and local examination was fulfilled. Trans-thoracic echocardiographic study and Holter ECG monitoring was offered
for the studied population. Different algorithms for PVB origin identification were utilized in all patients before electrophysiological
localization and radiofrequency ablation was done.
Results: mean age of studied population was 39.9±12.97 years, encompassing 44 (59.4%) males, admitted to our centre for EP study
and ablation. PVB origin was unleashed initially via various algorhythms, which matched precise intra-cardiac origin in 78 cases; patients
with PVBs originating from LVOT showed earlier transition, narrowed QRS complex, higher V2 transition ratio and R wave duration index as
compared to those with PVBs originating from RT side. With multivariate logistic regression, the only significant independent predictor for
RVOT origin was R wave duration index utilizing a cut off value of ˂ 0.3 (P=0.0057).
Conclusion:Accurate localization of PVB origin is feasible using surface ECG with positive impact on acute procedural success as well as
reducing procedural time.
Premature ventricular ectopic beats (PVBs) are early
ventricular depolarizations. Usually carrying benign course in
patients with structurally free heart. However, with frequent PVBs
many patients develop debilitating symptoms with impaired note
of life carrying a risk of cardiomyopathy, syncope and sudden
Routine 12 lead surface ECG identified ventricular ectopics in
1% of apparently healthy population, and this percentage jumped
to 40–75% after using extended ECG monitoring .
Ventricular outflow tracts are the most common site
of origin in normal heart. They could manifest as isolated,
clustered ectopics, or as sustained tachycardia. The main pathophysiological
cause is triggered activity; nevertheless, scar related
re-entry and abnormal automaticity were also accused. Medical
therapy encompassing Beta blocker activity or calcium channel
blockers usually show limited effectiveness in relieving patients’
complaints. Catheter ablation can be curative, unless limited by
tough and unpredictable induction [4,5].
We investigated and compared different algorithms to reach a
precise localization of PVB origin using surface ECG which is then
emphasized using intra-cardiac mapping.
Eighty patients with very frequent (>10% PVBs burden
documented on holter monitoring ) monomorphic PVBs,
regardless the presence of structural heart disease, who were
persistently symptomatic despite anti-arrhythmic medications
encompassing beta blockers, were studied. Patients with
atrial Tachy-arrhythmias, thyroid malfunction, hypertrophic
cardiomyopathy, non-revascularized myocardial ischemia, and
cardio-myopathic patients with worse NYHA class, were not
PVBs site of origin was identified using various formulas
as PVC transition in chest leads, lead V2 transition ratio (the
percentage R-wave in VT: (R/R+S) VT divided by the percentage
R-wave in sinus rhythm (SR): (R/R+S)SR), and R wave duration
index (dividing the QRS complex duration by the longer R wave
duration in lead V1 or V2). PVB duration, coupling interval and
inferior leads axis [7-9].
Patients received local anesthesia after holding medications
for at least 6 half-lives. Anti-coagulation was achieved by parentral
unfractionated heparin (bolus of 75 U/kg then 1000 U/ hour)
during the procedure.
Electro-anatomical mapping was achieved using the CARTO
3 system (Biosense, Diamond Bar, CA, USA) or the EnsiteNavX®
system (St Jude Medical, Inc, St Paul, MN) referenced to doctor
wish and availability. Ablation catheters, (Thermocouple 4mm tip
7F for EnsiteNavX system and Thermocool 3.5mm 8F for CARTO
3 system) were utilized. plus a multi-electrode (quadripolar
or decapolar) catheter positioned in the RV (apex or RVOT) for
pacing and as a reference catheter if required.
Targeted activation map was created for the chamber of
interest; ventricular navigation was achieved using catheter
dragging technique over the endocardium. The earliest ventricular
activation (red isochrones in CARTO 3 or white isochrones in
NavX) with a local electrogram racing QRS onset by at least 30
msec was ablated. Voltage maps were created in patients with
suspected scar tissue (areas with local voltage <0.5 mv).
In cases of PVB paucity, pharmacological induction with
adrenaline (0.1mcg/kg/min) was used. If PVBs still very
infrequent, pace mapping protocol was done at suspected sites
within the ventricle of interest. Ablation was commenced at sites
with excellent score of 12/12 when compared to surface ECG
recording of clinical PVBs.
A written and informed consent was taken from all patients
and the study was guaranteed by the Research and Ethics
Committee of the cardiology department, Ain Shams University
Data were analyzed using SPSS version 21 for Windows
and graphics by MS Excel. Categorical data were expressed
as frequencies and percentages, while continuous data were
expressed as mean ± SD or median. Comparison between
categorical variables was done using Chi square or Fisher’s exact
test as appropriate. Comparison between continuous variables
was done using t-test or Mann-Whitney test according to normality
of distribution. Multivariate stepwise logistic regression analysis
was used to identify predictors of PVB origin. Receiver operating
characteristics (ROC) curve analysis was done to find the impact of
different ECG parameters on PVB localization. Cutoff values were
selected if area under the curve (AUC) was significantly different
from 0.5. P value was considered significant if <0.05.
80 cases with a mean age of 39.9±12.97 years, with male
predominance, and suffering from frequent monomorphic PVBs,
who were referred to the EP clinic at Ain Shams University
hospitals, were included in the current study.
Initial localization of ectopic beats was done utilizing various
algorithms. Based on surface ECG identification of origin matched
EP localization in 78 cases, apart from 2 patients in the LVOT
group who had initially inaccurate localization. Four cases had non
outflow origin of PVBs evidenced by superior axis in limb leads
(Table 1). Moreover, group of patients with LV origin had earlier
transition, shorter complex width, higher V2 transition ratio and
R wave duration index compared to RVOT group (Table 2).
A statistically powerful bond was noticed between PVB
transition and origin, (P value = 0.0001). From fourty patients in
the LV group, fourteen patients had PVB transition at V1, four at
V2 and twenty tow patients at lead V3.
In contrary, among patients in the RV group (n=36), nine had
transition in V3, twenty at V4, five lead V5 and tow patient at lead
PVB complex width was related to PVB origin, in which mean
width for RVOT PVBs was 148.23ms versus 134 ms in LVOT PVBs
with P value of 0.05, as shown in (Table 2), V2 transition ratio was
calculated for outflow tract PVBs and was statistically significant
with PVB origin, the mean ratio for RVOT origin was 0.41 while for
LVOT origin it was 1.7, with P value = 0.004 (Table 2 & Figure 1).
R wave duration index had statistically significant relation
with PVB origin, the mean index for RVOT origin was 0.25,
however in LVOT and supra-aortic group was 0.45, with P value of
0.0001, as shown in (Table 2 & Figure 2).
R/S ratio had statistically significant relation with PVB origin
with mean ratio of 0.14 for RVOT PVBs and 0.93 for LVOT PVBs,
with P value of 0.0001, as shown in (Table 2 & Figure 3).
Uni-variate analysis was done to verify the predictive value of
different maneuvers, V2 transition ratio ≤0.58 predicted RVOT PVB
origin reaching sensitivity of 88.24% and specificity of 87.50%, P
value of ˂ 0.0001, R/S ratio ˂0.28 denoted RVOT ectopics origin
with sensitivity of 64.71% and specificity of 94.12%, P value of
R wave duration index ˂0.3 predicted RV focus with sensitivity
of 82.35% and specificity of 76.47%, P value of ˂0.0001. Identifying
free wall from septal origin was done through calculating the ratio
of PVB duration to its preceding sinus beat, ratio ˃1.8 supported
free wall origin with sensitivity of 97.06% and specificity of
83.33%, P value of ˂0.0001 (Table 3 & Figure 4).
Multivariate logistic regression was done to predict RVOT
focus using surface ECG through various algorithms, encountering
PVB transition, R wave duration index, and R/S ratio, revealed
that R wave duration index was the sole significant independent
predictor of RVOT ectopics, with cut off value of ˂ 3 (P=0.0057).
The most frequent non sustained arrhythmia seen by
cardiologists is isolated ventricular ectopics. A big proportion
of patients with frequent ectopic beats is suffering and often
requires long-term anti-arrhythmic therapy. Unfortunately,
pharmacological tools are rarely useful, and may be hazardous,
to the extent of increasing mortality, mostly owing to their proarrhythmic
nature. There is a high variability in the incidence of
PVBs among different observational studies, ranging from 4.6%
in healthy participants and up to 62% in patients with structural
heart disease. Outflow tracts are the commonest origin, either
beneath or just above the semi-lunar valves. Prognostic value of
ectopics differs according to patient’s age, presence of structural
heart disease and co-morbidities. Radio-frequency ablation is an
accepted therapeutic tool to alleviate patient’s morbidity despite
receiving pharmacological therapy including beta-blockers or
asymptomatic patients with either high burden of ectopics or PVB
induced cardiomyopathy. [10-13].
This study encountered 80 patients with monomorphic
ventricular ectopics refractory to medical therapy including betablockers,
calcium channel blockers, and class III anti-arrhythmics.
The studied cohort went through initial noninvasive work-up
including 12 lead surface ECG, trans-thoracic echocardiogram,
lab profile and scarce use of CMR in patients with heart muscle
disease, and then they underwent EP study with RF catheter
ablation after precise ECG and electrophysiological localization.
Pre-procedural identification of origin was fulfilled using
surface ECG. PVB transition in chest leads was very helpful, as V1,
V2 transition was associated absolutely with LV ectopics, the same
for V4-V6 transition which predicted RV origin, thirty one patients
transition at lead V3, 22 of them were mapped in LVOT and aortic
sinuses. Inferior axis denoted exclusively outflow tract ectopics
(n= 76), while superior axis was encountered in the remaining
four cases with non outflow origin.
RR’ notching in lead AVL which was noticed in a single case,
denoted Para-hissian origin, matching what stated by Zhang
et al.  that RSR’ or RR’ pattern in lead AVL predicts ectopics
originating from the His bundle region with 94.87% and 100%
positive predictive value respectively .
One of the different algorithms for ectopic localization is the
V2 transition ratio. In the current study, the mean transition ratio
for RVOT ectopics was 0.41 and 1.7 for LVOT PVBs with cut off
value of ≤0.58 to predict RVOT PVB origin reaching a sensitivity
of 88.24% and specificity of 87.50%. In the study conducted by
Betensky et al.  on 40 patients with outflow tract PVBs, the V2
transition ratio was higher for LVOT PVBs (1.27 ± 0.60 vs. 0.23
±0.16) and a V2 transition ratio ≥0.60 was used as a cut of value of
LVOT origin with 95% sensitivity and 100% specificity .
R wave duration index ˂0.3 supported RVOT origin with
sensitivity of 82.35% and specificity of 76.47%, and R/S ratio with
cut off value of ˂0.28 predicted RVOT PVB origin with sensitivity
of 64.71% and specificity of 94.12%. which is supported by Zhang
et al.  in his study on 39 patients with outflow tract ectopics, R
wave duration index of less than 0.5 and the R/S wave amplitude
index of less than 0.3 predicted RVOT PVBs with 94.87 sensitivity
and 100% positive predictive value .
With the aid of multivariate stepwise logistic regression,
we concluded that R wave duration index < 0.3 was the only
significant independent predictor of RVOT origin (P=0.0057).
Differentiating septal from free wall origin of PVB was
predicted using the ratio of PVB duration to preceding sinus
beat duration, ratio ˃1.8 predicted free wall origin of PVB
with sensitivity of 97.06% and specificity of 83.33%, which is
comparable to Zhang et al.  finding, that a PVB-QRS width/
the preceding sinus beat width ≥1.9 denoted PVBs originating
from the free wall with 94.44% sensitivity and 77.27% positive
predictive value .
Radiofrequency ablation is an effective and practical tool to
eradicate outflow tract ventricular ectopics regardless their origin
and the presence or absence of structural heart disease. Accurate
localization of PVB origin is feasible using surface ECG with
positive impact on acute procedural success as well as reducing