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.