Material and Methods
Study population and laboratory analysis : This study was approved by the institutional review committee and ethics review board of our hospitals. From 2014 to 2019, 22 consecutive intolerably symptomatic patients with drug (including beta-blockers, calcium-channel blockers, and class I agents of the Vaughan Williams classification) refractory MA-PVCs visited our hospitals to undergo RFCA. All patients had their history recorded, and underwent a physical examination, laboratory analysis, 12-lead electrocardiography (12-ECG), 24-h Holter monitoring, and echocardiography, on admission or within at least 1 month before admission, and 6-months after the successful RFCA. The LV end-diastolic (LVDd) and systolic (LVDs) internal dimensions, right ventricle (RV) internal dimension (RVD), degree of mitral regurgitation (MR), and LV ejection fraction (LVEF) measured by the Teichholz method, were measured. All the echocardiography values were recorded during sinus rhythm, but not during PVC beats, nor post-PVC beats. The serum brain natriuretic peptide (BNP) concentration and New York Heart Association (NYHA) functional class using a specific activity scale were evaluated on admission and 6-months after the successful RFCA.
Definition of MA-PVC: Mitral annulus-PVCs were defined as having a characteristic electrocardiographic appearance of a right bundle branch block (RBBB) contour in V1 and positive concordant R waves in the precordial leads including V1~6 (Figure 1A). Ventricular tachycardia (VT) was defined with standard electrocardiographic criteria including at least 3 consecutive PVCs at a rate of > 120 beats per minute. Patients with ventricular tachycardia and atrial tachyarrhythmias including atrial fibrillation, atrial flutter, atrial tachycardia, and paroxysmal supraventricular tachycardia were excluded from this study because they may cause tachycardia-induced LV dilation4. The patients who received hemodialysis during this study were also excluded from this study.
Mapping and catheter ablation procedure: All procedures were performed after written informed consent was obtained. Anti-arrhythmic drugs were withdrawn in all patients at least five half-lives before the procedure. The anti-hypertensive and –hypercholesterolemic agents and/or others were continued in patients with hypertension and dyslipidemia before and after the RFCA. The anti-diabetic agents in patients with diabetes mellitus were continued before and after the RFCA but not on the procedural day. The QRS duration and peak deflection index (PDI)5 were measured before the RFCA. RFCA was performed under local anesthesia. After a 50 unit per kilogram administration of heparin was administered, 4 or 5-mm-tip electrode catheters (St. Jude Medical, St. Paul, MN, USA) were introduced percutaneously into the right ventricle (RV) and coronary sinus, respectively. A 100 unit per kilogram administration of heparin was administered following the trans-interatrial septal puncture, and heparinized saline was additionally infused to maintain the activated clotting time at 300–350 seconds. After left atrio- and ventriculography, electro-anatomical mapping during the PVCs was performed in the coronary sinus and around the MA, left atrium (LA), and LV near the MA in detail utilizing a 3D mapping system (EnSite NavX / VelocityTM Cardiac Mapping System, St. Jude Medical, St. Paul, MN, USA) by a circular mapping catheter (InquiryTM AFocusIITM Double Loop Catheter, St. Jude Medical, St. Paul, MN, USA) or high density mapping catheter (AdvisorTM HD Grid catheter, Abbott, Plymouth, Minn, USA) during culprit PVCs. If the culprit PVC was not found during the procedure, an isoproterenol administration and/or programmed electrical stimulation with a digital stimulator (Cardiac Stimulator, Nihon Kohden Co., Tokyo, Japan) was performed to induce the culprit PVC. Then, an open irrigated 3.5-mm-tip ablation catheter (FlexAbilityTM, St. Jude Medical, St. Paul, MN, USA) through a steerable introducer (AgilisTM NxT, Abbott, Plymouth, Minn, USA) was positioned at the MA. An optimal pace map was defined as a match of all 12 surface leads by comparing the R/S ratio and subtle notching in the QRS complex during pacing. An identical match was necessary in at least 11 of 12 leads. Further, based on the findings of the electro-anatomical mapping and an optimal pace map, radiofrequency energy was delivered at the site of the unipolar potentials from the ablation catheter demonstrating a QS pattern and bipolar potentials from the tip of the ablation catheter preceding the QRS in the 12-ECG by at least 20 -30 milliseconds during the PVC with a preset temperature of 43 to 50°C and power limit of 30-35 W. Further, when the radiofrequency energy was delivered from the coronary sinus, in order to avoid any complications, (1) heparinized saline was additionally infused to maintain the activated clotting time at more than 300 s, (2) a maximum power setting of 20 W for the radiofrequency energy was chosen, and (3) careful attention to and observation of the patient was paid during the radiofrequency energy delivery as we previously reported6. The radiofrequency energy application was terminated when an abnormal impedance rise (> 30 Ω) was observed. A successful ablation was defined as no recurrence and non-inducibility of the culprit PVC with and without an isoproterenol administration and/or programmed electrical stimulation for at least 30 minutes after the ablation. Procedural success was defined as no recurrence of the culprit PVC within 24 hours after the procedure under electrocardiogram monitoring. If the recurrence of the culprit PVC was observed, a repeat RFCA was performed.
Statistical Analysis: The numerical results are expressed in the text as the mean ± standard deviation. Paired data was compared by a Fisher’s exact test and Student t tests. The differences between the continuous variables before and 6 months after the RFCA in each group, or between the lower and upper groups in each period, were compared by using a repeated measures analysis of variance followed by a Bonferroni’s test for multiple comparisons. The correlation between the two parameters was determined by a simple linear regression analysis. All analyses were performed with SAS version 9.2 software (SAS Institute, Cary, NC). A p of < 0.05 was considered to indicate statistical significance.