2.1 Patients
Our retrospective and comparative analysis included 584 consecutive patients who had an inducible and ablated SVT, including atrioventricular nodal reentrant tachycardia (AVNRT), atrioventricular reentrant tachycardia (AVRT), and atrial tachycardia (AT) between December 2014 and May 2019. Patients with a visible ventricular preexcitation and an ablation of the accessory pathway (AP) were also included regardless of tachycardia induction. Patients with atrial fibrillation and/or atrial flutter were excluded. Two groups of patients were analysed and the outcomes compared: the CF group, where X-ray fluoroscopy was used during CA procedures and the ZF group, where CA procedures were performed without the use of X-ray fluoroscopy. The ZF group was further divided into a ZF subgroup for adult patients and a ZF subgroup for paediatric patients. Paediatric patients aged ≤ 18 years were referred to ZF CA as a default. Adult patients were referred to either ZF or CF CA at the referring physician’s discretion. Patient characteristics, procedural information, and follow-up data were collected and analysed. Written informed consent to undergo the CA was obtained from all patients, their parents, or legal guardians before the procedure. The ZF CA procedure protocol was approved by the national medical ethics committee. All patients underwent a pre-procedural clinical examination, routine blood biochemistry laboratory analysis, and AAD therapy was discontinued for a minimum of five half-lives of the active agent prior to the procedure. The discontinuation of amiodarone was left to the physician’s discretion.
2.2 Electrophysiological study
Patients over 14 years of age had procedures performed in conscious sedation, with the rest under general anaesthesia. Local anaesthesia was used for femoral vein access in all patients, which was obtained under ultrasound guidance at the operator’s discretion. In the CF group, guidance and placement of the catheters was performed using fluoroscopic guidance. In addition, the 3D EAM system (Carto 3, Biosense Webster, Diamond Bar, CA, USA) and intracardiac echocardiography (ICE, AcuNav, Siemens Healthineers AG, Erlangen, GER) were used at the operator’s discretion in the CF group. In the ZF group, only the 3D EAM system (Carto 3, Biosense Webster, Diamond Bar, CA, USA; EnSite NavX, Ensite Velocity, Ensite Precision, Abbott, St. Paul, MN, USA) was used for the guidance of catheters in right-sided SVTs. For left-sided SVTs, in addition to the 3D EAM, intracardiac echocardiography (ICE) (AcuNav, Siemens Healthineers AG, Erlangen, GER) was used for transseptal punctures in both groups, and was further used for navigation of the catheters at the operator’s discretion.
After femoral vein access was obtained, a ten-polar steerable diagnostic catheter (Polaris X, Boston Scientific, Marlborough, MA, USA; ViaCath, Biotronik, Berlin, GER) was advanced from the femoral vein into the heart and inserted into the coronary sinus (CS). Next, a four-polar diagnostic catheter (MultiCath, Biotronik, Berlin, GER) was inserted into the heart and placed on the basal section of the right side of the interventricular septum. In the ZF group, the ten-polar diagnostic catheter was used to mark the location of His potential on the 3D EAM map and to construct a partial 3D model of the right atrium. In the CF group, an additional diagnostic catheter (MultiCath, Biotronik, Berlin, GER) was placed at the location of the His potential. Figures illustrating positioning of the catheters are available in the supplemental data in the Figures chapter.
Atrio-ventricular (AV) and ventriculo-atrial (VA) conduction testing followed. Atrial pacing was performed with the ten-polar diagnostic catheter in the CS and ventricular stimulation with the four-polar catheter at the basal interventricular septum. Atrial programmed stimulation and fast atrial stimulation were performed with the aim of tachycardia induction. If induction of tachycardia was not achieved or conduction over the AP was not detected, the protocol was repeated with an isoprenaline challenge. In cases of clear ventricular preexcitation, the induction of tachycardia was left to the physician’s discretion. Standard diagnostic maneuvers were employed as needed to determine the type of induced tachycardia.
2.3 Cryoablation of AVNRT
Cryoablation was used in the ZF group in AVNRT cases at the physician’s discretion. A 4-mm or 6-mm tip cryocatheter (Freezor and Freezor Xtra, Medtronic, Minneapolis, MN, USA) was used. Cryomapping (-30 ºC) was first performed during ongoing tachycardia or during programmed atrial stimulation with manifest conduction over the slow pathway. If the tachycardia terminated during cryomapping or the conduction over the slow pathway was terminated, the cryomapping was then switched to cryoablation (-80 ºC), usually for 240 seconds. An additional lesion was applied in close proximity to the successful one. If the tachycardia or slow pathway conduction were terminated mechanically during cryoablation, the location was tagged on the 3D EAM system and additional lesions were applied at the spot of mechanical termination when possible.