Consecutive patients who underwent CA of VAs in our institution between May 2018 and December 2019 were included. In general, patients with SNH and idiopathic VAs, as well as patients with ventricular tachycardias (VT) resulting from SHD were included.
Indications to undergo CA were followed according to the published guidelines and consensus documents1. Included patients with SNH had an ECG documentation of ventricular ectopy, with an estimated daily ectopy burden of at least 10%, or tachycardia that were causing either severe symptoms unresponsive to anti-arrhythmic drugs (AADs), or presumed tachycardia-induced cardiomyopathy. All included patients with SHD had a documented sustained VA either with 12-lead ECG or a cardiac implantable electronic device (CIED).
Trans-thoracic echocardiogram was performed in all patients before the CA procedure. Pre-procedural computed tomography (CT) or magnetic resonance imaging (MRI) were accessible in most patients. All patients with a suspected SHD had pre-procedural assessment of coronary anatomy with invasive coronary angiography or CT angiography. Combined results of imaging studies were used to assess the presence of SHD. Basic laboratory blood tests, clinical examination and CIED interrogations were also performed in all patients.
Procedures were preferably performed in conscious sedation, except for patients undergoing epicardial approach in whom general anaesthesia was used. Femoral vein and artery punctures were performed to access the heart. A 3D EAM system (Carto®, Biosense Webster, Irvine, California, USA or NavX™ Precision™, Abbott, Abbott Park, Illinois, USA) and intra-cardiac echocardiography (ICE) (Acuson AcuNav™, Biosense Webster, Irvine, California, USA) were routinely used simultaneously. In patients with left-sided arrhythmias, we generally used the ante-grade trans-septal approach, except when mapping and ablation in the aortic root were needed in which case a retrograde trans-aortic approach was used. A steerable long sheath (Agilis™, LRG Curl, Abbott, Abbott Park, Illinois, USA) was used to improve catheter stability in trans-septal approach. Typically, uni-directional irrigated tip radio-frequency (RF) ablation catheters with (Thermocool Smarttouch® and Thermocool Smarttouch® SF, both Biosense Webster, Irvine, California, USA) and without (FlexAbility™, Abbott, Abbott Park, Illinois, USA) the ability of contact force sensing were utilised. In patients with SHD and suspected substantial arrhythmogenic substrate we used a multipolar catheter enabling high-density mapping (PentaRay®, Biosense Webster, Irvine, California, USA).
Once all catheters and the ICE probe were inserted, we followed two basic protocols depending on the type of arrhythmia.
- In patients with a SHD and a recorded VA, the first step was VT induction with programmed ventricular stimulation. The next step was substrate mapping with the ablation catheter and later detailed mapping with the multipolar mapping catheter. Anatomical and voltage maps of the chamber of interest were created with the 3D EAM system and all electrograms with characteristics of local abnormal ventricular activity (LAVA)22 and obvious late and diastolic electrical potentials (LP) were tagged23. Additionally, the areas of the substrate with suspected LAVA and without obvious LP were mapped during decremental RV pacing to reveal hidden slow conduction, which was also tagged24. Substrate mapping was combined with limited pace-mapping to reveal the exit point of the induced VT, with adjacent low voltage areas thoroughly mapped. Finally, all areas with late potentials and hidden slow conduction were extensively ablated using the described irrigated catheters with power-controlled settings of 30-45W for at least 40 seconds or until the disappearance or at least attenuation of the local electrocardiogram. A re-mapping of the ablated parts of the substrate and surrounding areas with the multipolar mapping catheter was routinely performed and additional ablations were done if needed to achieve complete substrate modification, i.e. absence of local electrical activity. Endpoints of the procedure were substrate modification and non-inducibility of VT with programmed ventricular stimulation with up to four delivered extrasystoles combined with isoproterenol infusion.
- In patients with presumably idiopathic VAs only very partial anatomical and voltage maps were created with the 3D EAM. Typically, our strategy relied on activation mapping of the present ventricular ectopy or VT. Pace-mapping was also used to complement activation mapping when needed. The mapped origin of the arrhythmia was ablated with similar settings and parameters as described in patients with SHD. The endpoint was termination of the ectopy or tachycardia. An additional endpoint was the absence and non-inducibility of VAs with fast and programmed ventricular stimulation, also after infusion of isoproterenol.
When epicardial mapping was needed a steerable long sheath (Agilis EPI™, Abbott, Abbott Park, Illinois, USA) was inserted over the J-tip guide-wire through surgically prepared sub-xiphoid epicardial approach.
Fluoroscopy minimising approach
Procedures were generally performed without any fluoroscopy and only with the use of the 3D EAM system and ICE. Fluoroscopy was only considered in two sets of cases: 1. In LV summit mapping for coronary angiography to avoid RF delivery in close vicinity of a coronary arteries. 2. In procedures where the epicardial approach for mapping and ablation was planned. Fluoroscopy time and dose area product (DAP) were measured and reported for each procedure.
The use of intra-cardiac echocardiography
ICE was used in conjunction with the 3D EAM system in all procedures. ICE had three basic roles:
- Providing guidance of guide-wire, long sheath, and trans-septal needle during trans-septal puncture (TSP) as previously described25.
- Providing additional imaging information about heart anatomy relevant for accurate and effective endocardial mapping and ablation. Examples include: achieving catheter stability at certain regions of the ventricles such as papillary muscles and moderator band; observing direction and position of the long sheath and catheter loops in cases of mapping and ablation at the base of the ventricles.
- Timely detection of possible complications such as sudden tissue whitening preceding “steam pops”, pericardial effusion, potential thrombotic masses in the heart cavities or on sheaths and catheters inserted into the heart, sudden deterioration of systolic function of the ventricles.
Definition of procedural parameters, procedural success, complications and follow-up
The procedural duration (total procedural time, TPT) was defined as the time interval from the placement of the venous and arterial sheaths to their removal at the end of the ablation procedure. In the case of a surgical sub-xiphoid epicardial approach time measurement was started with skin incision. Ablation time [time spent delivering radio-frequency (RF) energy to the tissue)] and the number of ablations were automatically recorded by the intra-cardiac electrogram registration and analysis system. Procedures were considered successful if predefined endpoints were reached. Overall procedural success rate (OSR) was defined as procedural success of combined first and repeat procedures for treated VA. Recurrence rate (RR) was defined as recurrence of the treated VA after the first procedure. Any early (during the same hospital stay) and late complications were reported as complication rate (CR), calculated as percentage of procedures. Major complications were all adverse events resulting in procedure termination, prolonged hospital stay, long-term disability, and any additional intervention and bleeding requiring transfusion.
Patients were followed clinically and with the 12-lead ECG recordings 3 months after the procedure and every 6 months thereafter. Patients with a CIED had its telemetry examined at every visit for possible episodes of VT, appropriate and inappropriate interventions, such as anti-tachycardia pacing (ATP), direct current cardioversions, and defibrillations. In patients treated for sustained VT, it's recording during the follow-up (ECG or CIED tracing) was regarded as a recurrence. In patients treated for ventricular ectopy, 24-hour holter recordings were typically used to assess the daily VAs burden at least one month after the ablation procedure. If the VAs burden was comparable to the one expected in the normal population, patients were considered to be cured and without recurrence. Procedures were considered successful if expected endpoints were reached. Any recurrences were used to calculate the recurrence rate (RR).
The statistical analyses were carried out using the IBM SPSS software version 24.0 for Windows (IBM Corporation, Armonk, NY, USA). Continuous variables were presented as mean ± standard deviation (SD) while categorical variables were presented as number and percentage. Differences between groups were analysed using unpaired Student’s t-test for numeric variables and Pearson Chi-square test and Fisher exact test for attributive variables. Multiple group comparisons were performed with one-way ANOVA. P value was considered significant when it was less than 0.05.