Study population
This study retrospectively reviewed the records of 360 patients with AP-SVT who had detectable AP potentials in 1545 patients undergoing catheter ablation from 1/1/2015 to 12/31/2019,In the 360 patients, ablation within the endocardium was applied in 330 and CS ablation in 30 patients. In CS, 15 cases were ablated via TCC successfully, and 15 cases were performed with ITC after TCC ablation failure. Essential information included patient characteristics, ECG and electrophysiological findings were collected. Those with structural heart disease were excluded based on echocardiography, cardiac magnetic resonance imaging, or coronary angiography findings.
The study was conducted in accordance with the declaration of Helsinki and the International Conference on Harmonization Good Clinical Practice Guidelines (ICHGCP). The ethical review board of Hospital approved the study protocol. All patients were given written informed consent.
Electrophysiological study
All procedures were performed under local anesthesia. Two quadripolar catheters were then placed into each patient: one in the right atrium and another in the right ventricle. In addition, one decapolar catheter was positioned in the CS through a femoral approach. An electrode in the inferior vena cava (25 cm from the tip of a right atrial catheter) was used as the reference electrode for unipolar recordings (Ablation electrode is the positive pole; inferior vena cava electrode is the negative pole; and filter settings of 1 to 500 Hz reduce baseline drift during respiration), and recorded with a digital electrophysiological register system (EP-Work Mate / Work Mate Claris, St.Jude Medical, St.Paul, MN, USA). Programmed electrical stimulation was used to evaluate the atrium, ventricle, AV node, and AP conduction, and induce tachycardia. Tachycardia can also be induced by intravenous isoproterenol (1–4 mg/min), if needed.
Mapping and recording of accessory pathway potential
Endocardial and CS mapping were performed to identify optimal target sites for ablation. A 7Fr quadripolar TCC with a 4-mm tip(Cordis Webster Inc., Baldwin Park, CA, USA)was inserted through the right femoral vein and positioned in the tricuspid annulus, or in the mitral annulus via trans-septal puncture, or in CS to map and record AP.
The tricuspid/mitral annulus was mapped via the right femoral vein during tachycardia, as well as fixed ventricular pacing. Ideal ablation targets were those with AP potential or the earliest excited V wave or reverse A wave. If there were no ideal targets after endocardium mapping, or always a distance between A-V/V-A, or the bypass cannot be blocked by ablating at the earliest excited point of V-wave or A-wave. Then the ablation catheter was inserted into the CS or its branch for further mapping. If an ideal target can be found in CS, try to ablate by TCC for 10 seconds, and ITC is performed when the TCC ablation fails.
Electrophysiological register system recorded a sharp potential between A wave and P wave. When pacing the atria with a fixed-frequency (S1S1), and then stimulating the right ventricle (S1S2) in advance, as S2 gradually advanced, a sharp potential has nothing to do with A wave, V wave, which is termed as AP potential.
Endocardial and CS Ablation
Ablation was performed with 4-mm TCC (Cordis Webster Inc., Baldwin Park, CA, USA) or irrigated 4-mm catheter (Thermocool SF, Biosense Webster, Diamond Bar, CA, USA). During endocardium ablation, we used temperature-controlled ablation catheters (40–50 ℃, 30–40 W). In CS ablation, a radiofrequency application was set with target temperatures of 40–50℃ and maximum power outputs of 20–30 W for the non-irrigated catheter and (43℃, 15–25 W) for the irrigated catheter, respectively. Prior to ablation, a weight-adjusted bolus of unfractioned heparin was administered intravenously. And meanwhile, coronary angiography was performed to prevent injury to the coronary artery. Effective ablation will be achieved with a consolidation discharge lasting 60–90 seconds. Ablation success criteria were the disappearance of the delta wave on the surface ECG and elimination of antegrade and retrograde conduction over the AP in the postablation electrophysiological study with an isoproterenol infusion. If the antegrade and retrograde blocks were achieved, wait 30 minutes to evaluate whether the operation was successful.
Blood sample collection and cTnI assay
Cardiac troponin I (cTnI) levels were measured in all patients 24 hours before and 6 hours after ablation. Plasma was collected after centrifugation, stored at − 80 °C. The amplitudes of the AP potentials were measured using the digital electrophysiological register system. Following surgery, all patients underwent ECG monitoring for at least 24 hours.
Patient follow-up
After surgery, patients received antithrombotic therapy with aspirin for 1 month. After discharge from the hospital, patients were examined at our arrhythmia clinic or by their referring cardiologists every 3 to 6 months for the first year and annually thereafter.
Statistics
Continuous variables are presented as the median with the interquartile range. Continuous variables of independent groups were compared using the Mann-Whitney U test, and comparisons of paired groups were analyzed using the Wilcoxon Signed-Rank test. To assess the predictive performance of the AP potential with respect to catheter selection, a receiver operating characteristics (ROC) curve was plotted. Subsequently, cut-off values of the AP potential were determined based on the Youden index from the ROC curve. A P value less than 0.05 was considered statistically significant. All statistical analyses were performed using SPSS22 (SPSS Inc., Chicago, IL, USA).