2.3 ECG analysis of the PVC morphology and definition of the ECG
criteria
With standard 12-lead ECG electrode placement, sinus rhythm (SR) and PVC
ECG morphologies were measured on the BARD recording system before
ablation, with the recordings displayed at 100 mm/s. PVC morphology was
defined as right bundle branch block pattern (RBBB) if QRS was positive
in lead V1 or left bundle branch block pattern (LBBB) for negative QRS
in V1. The following measurements were also assessed manually of the
first beat of PVC on the surface ECG by two independent observers: (1)
coupling interval (CI); (2) QRS duration (QRSd); (3) intrinsicoid
deflection time (IDT); (4) Pseudo-delta wave (PdW); (5) maximum
deflection index (MDI); (6) Q-wave ratio in leads aVL and aVR18.
CI
The CI was measured from the beginning of an SR QRS complex to the
beginning of the PVC.
PVC QRSd
The PVC QRS duration (ms) was defined as the interval measured from the
earliest ventricular activation to offset the QRS complex in the
precordial leads.
IDT
IDT was defined as the interval measured from the earliest ventricular
activation to the peak of the R wave in V2 19.
PdW
The PdW was defined as the interval from the earliest ventricular
activation to the onset of the earliest fast deflection in any
precordial lead 19.
MDI
MDI was defined as the interval measured from the earliest ventricular
activation to the peak of the largest amplitude deflection in each
precordial lead (taking the lead with the shortest time) divided by the
QRSd 20.
Electrophysiology study, mapping, and ablation
The details of the procedure protocol have been described in our
previous study 21. All VAs originated from the LVS by
the definition that the earliest activation site within the LVS (great
cardiac vein/anterior interventricular vein [GCV/AIV] or epicardium)
based on fluoroscopy and electroanatomic mapping. The absolute earliest
activation time discrepancy (AEAD) was defined as the absolute value of
the difference in the earliest activation times (EAT) preceding the VA
which was obtained from the epicardial (epicardium or GCV/AIV) and
endocardial LVS (AEAD [ms]
=∣EATepi-EATendo∣) 22.
Example cases of VAs from LVS with the AEAD measurement was shown inFigure 1 .
For sustained VTs, acute procedural success was defined as
noninducibility of clinical sustained VT after ablation. For patients
who underwent nonsustained VT/PVC ablation, acute procedural success was
defined as complete elimination, and noninducibility of frequent PVCs
previously observed during the procedure 21.
Follow up
The absence of VA recurrences was assessed by 24-hour Holter monitoring
and surface ECG during follow-up. VT recurrences were defined by the
presence of sustained VTs, nonsustained VTs using 24- hour Holter
monitoring and surface ECG and PVCs > 1000/day assessed by
24-hour Holter monitoring 21. In addition, the
assessment of the LVEF by echocardiography was repeated 3 to 6 months
after ablation. LV systolic function recovery after ablation was defined
as LVEF < 50% before ablation and normalization of LVEF or
LVEF improved at least 15% after ablation12, 23.
Statistical analysis
Data are expressed as the mean ± standard deviation for normally
distributed continuous variables and proportions for categorical
variables. The continuous variables were analyzed using a two-tailed t
test. Discrete variables were compared using a χ2 test or Fisher’s exact
test The association between the selected parameters and PVC-induced
cardiomyopathy was studied by a univariate logistic regression analysis.
The variables selected for testing in the multivariate analysis for a
logistic regression model were those with a P value < 0.05 in
the univariate models. The differences in the LVEF before and after the
ablation were compared by Student’s t test. The worst LVEF before
ablation was compared to those after ablation. All statistical
significances were set at a P value < 0.05, and all
statistical analyses were carried out using SPSS 22.0 software (IBM
Corporation, Armonk, NY).