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).