Study participants
Among 437 consecutive patients who presented with VAs for RFCA, including idiopathic VT and PVC, between July 2010 and August 2018, 26 (5.9%) patients were found to have an acute successful RFCA site at the AP-MA during the index procedure. None of these patients exhibited significant coronary artery disease by coronary angiography or CT coronary angiography and any structural heart disease. They failed beta-blocker or at least one anti-arrhythmic drug therapy. Monomorphic non-sustained VT (defined as three or more consecutive PVCs, was present in 3 patients, and monomorphic PVCs were seen in the remaining 23 patients. All patients were in normal sinus rhythm (SR) before RFCA. Twelve-lead ECG and 24-h ambulatory Holter were carried out at least once before RFCA. The demographic and clinical data, including patient age, sex, height, weight, biochemical blood examination results, echocardiographic parameters and clinical arrhythmias, were collected prior to the index procedure.
ECG analysis
Twelve-lead ECGs were recorded utilizing the Libang Electrical system (Libang ECG recording, Libang Medical, Shenzhen, China). The ECGs were analyzed at a paper speed of 25 mm/s, and the signals were amplified at 10 mm/mV. VAs were analyzed for the following parameters: (1) The QRS amplitude in the inferior leads; (2) The QRS width; (3) The maximum deflection index (MDI), defined as the duration from the earliest activation to the peak of the largest amplitude deflection divided by the total QRS duration, measured in the precordial leads; (4) The peak deflection index (PDI), defined as the duration from the earliest activation to the peak of the largest amplitude deflection divided by the total QRS duration, measured in the inferior leads; (5) The S-wave in lead V6; and (6) Inferior lead notching. All parameters were measured with electronic calipers by 3 experienced investigators blinded to the site of origin. We adopted the mean values of these measurements as the data. If the interobserver difference was more than 5 ms, the final decision was made by a joint meeting of the observers.
Preparation before RFCA
All antiarrhythmic drugs were discontinued at least 5 half-lives before the electrophysiological (EP) study. Intracardiac tracings were recorded utilizing a Prucka CardioLabTM electrophysiology system (General Electric Health Care System, Inc, Milwaukee, WI, USA). If the clinical VAs did not occur spontaneously and were not induced at baseline, intravenous isoproterenol (0.5 to 2.0 g/min) was administered to induce the clinical VAs. A 7.5-French, 3.5-mm-tip, irrigated ablation catheter (NaviStar ThermoCool, Biosense Webster, Diamond Bar, CA, USA) was then introduced into the left ventricle (LV) using a transaortic or transseptal approach, and intravenous heparin was administered to maintain an activated clotting time of 250 - 300 seconds.
Electrogram (EGM) collection and analysis
During an episode of clinical VA, activation mapping was performed. A minimum of three arrhythmic beats were recorded at the mapping site. The unipolar EGM was recorded from the distal (D) electrode of the mapping catheter and filtered at 0.5-100 Hz. The bipolar EGM was recorded from the distal (D-2) electrode pairs of the mapping catheter and filtered at 30-500 Hz. All EGM and twelve-lead ECG data were stored on the multichannel mapping system for offline analysis with a paper speed of 100 mm/s [5]. As shown in Figure 1, the morphological features can be used to determine the R-ratio, which is derived from the unipolar EGM as the amplitude of the first positive peak relative to that of the nadir (R-ratio). If no positive peak is present, then the R-ratio is 0. The QRS - Uni interval was calculated from the QRS onset to the maximum descending slope (D-Max) in the unipolar EGM. The V-QRS interval was calculated from the start of the bipolar ventricular EGM to the QRS onset. All parameters were measured with electronic calipers by 3 experienced investigators blinded to the site of origin. We adopted the mean values of these measurements as the data. If the interobserver difference was more than 5 ms, the final decision was made by a joint meeting of the observers.
Pace mapping
Pace mapping was also performed at the earliest activation site using the distal bipolar electrodes at a coupling interval of the VA interval and a stimulus amplitude 1 mA greater than the late diastolic threshold (up to a maximum output of 10 mA and pulse width of 2.0 ms). If present, a perfect pace-mapping match (12/12 leads) was defined as indicating the site of origin; otherwise, the activation mapping result was only used for guiding RFCA.
RFCA
RFCA were applied at the site where the earliest V-QRS, shortest QRS - Uni interval, or perfect pace-mapping match on ECG were recorded. RFCA was delivered using the power-control mode at a maximum power of 35 to 40 W and temperature of 43°C with irrigation mode at a flow rate of 17 mL/min. If the VAs were not eliminated within 30 seconds after energy delivery, the energy application was terminated, and the RFCA site was tagged as an unsuccessful site on the map. If the VAs were abolished within 30 seconds, the energy application was continued for a total of 300 - 500 seconds, and the site was tagged as a successful site on the map.
Definition of acute successful RFCA
Acute successful RFCA was defined according to the following criteria: absence of spontaneous or induced clinical VAs, both in the absence and presence of isoproterenol infusion after RFCA with observation lasting 0.5 to 1 hour.
Definition of AP-MA origin
We defined an AP-MA location as follows: 1) the catheter tip demonstrated that the characteristic AP-MA location and motion when viewed on the left and right anterior oblique fluoroscopic views at the successful RFCA site; 2) the catheter tip could be curved and decurved freely on the left anterior oblique fluoroscopic view; 3) the ratio of atrial /ventricular EGMs at the RFCA site was <1, and the amplitudes of the atrial / ventricular EGMs were > 0.08 / 0.5 mV at the RFCA site during sinus beat, respectively [3]; 4) the catheter tip was on the left side of the AMC based on the CARTO3 map; 5) acute successful VAs elimination were achieved by RFCA energy delivery at the site; 6) the ECG showed a monophasic R-wave and no S-wave in the inferior leads during VA.
Observation after RFCA and at the one-year follow up
The patients were monitored for at least 3 days in the hospital after RFCA, and twelve-lead ECG and 24-hour ambulatory Holter monitoring were carried out at least once. The patients were followed in our outpatient arrhythmia clinic for one year after RFCA, and twelve-lead ECG and 24-hour ambulatory Holter monitoring were carried out at least once every three months. In addition, all patients were contacted by telephone at the time of manuscript preparation. Clinical success was defined as free of clinical VAs (symptomatic or asymptomatic) that were targeted during RFCA at the follow-up visit, and at least 80% reduction of VAs burden documented on post-RFCA 24-hour Holter recording as compared to pre-RFCA VAs burden.
Statistical analysis
Continuous data are given as the mean ± SD. Noncontinuous data are given as the interquartile range and median in parentheses. A p value <0.05 was considered to indicate statistical significance.