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A novel simplified approach to radiofrequency catheter ablation of idiopathic ventricular outflow tract premature ventricular contractions : from substrate analysis to results
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Summary: Premature ventricular contractions (PVCs) are a common finding in the general population. The
most common site of PVCs, in patients without structural heart disease, is the right ventricular
outflow tract (RVOT) and the left ventricular outflow tract (LVOT).
The prognosis associated with frequent PVCs depends on the presence of structural heart
disease, so that idiopathic PVCs have been considered benign. Recently however, evidence has
emerged that a small percentage of those patients may present with polymorphic ventricular
tachycardia or ventricular fibrillation or evolve to left ventricular dysfunction. Catheter ablation is
indicated for frequent symptomatic PVCs refractory to medical therapy or in case of patient’s
preference.
Currently, catheter ablation is based on activation mapping, confirmed by pace mapping match
of at least 11/12 ECG leads between the paced beat and the PVC morphology. The acute success
rate ranges from 78% to 100% according to the series, and to the location of the PVCs. Remote
magnetic navigation presents as a good option for PVC ablation offering a high success rate with
better safety profile.
Intraprocedural low PVC burden occurs in up to 30% to 48% of cases, resulting in either,
cancelation of the ablation procedure in up to 11% of patients, or reduction of the success rate
from 85% to 56% when ablation is attempted with pace mapping only.
Recently non-invasive mapping systems based on the electrocardiogram analysis (ECGI) have
been developed. These systems are capable of mapping an arrhythmia with just one beat, instead
of the usual point by point acquisition, being especially useful in the case of rare arrhythmias.
EGGI also constitutes a valuable noninvasive tool for studying the mechanisms of arrhythmias.
With this system we were able to demonstrate the presence of an electrophysiological substrate
in the RVOT of patients with PVCs and apparently normal hearts.
It has been accepted for many years that in patients with idiopathic PVCs from the outflow tracts,
the RVOT displays normal electroanatomical mapping features and electrophysiological
properties. However, we have demonstrated that there is a substrate for idiopathic PVCs in the
form of low voltage areas (LVAs) that are not detected by usual image methods including cardiac
magnetic resonance (CMR). We described for the first time, the association between the presence
of ST-segment elevation in V1-V2 at the 2nd intercostal space (ICS) with LVAs across the RVOT and
have proposed it as a non-invasive electrocardiographic marker of LVAs.
We also identified the presence of abnormal potentials in intracardiac electrograms at the
ablation site during diastole, after the T wave of the surface ECG that became presystolic during
the PVC and were called diastolic potentials (DPs).
In Chapter V we describe in detail the study that validated those findings and evaluated the
feasibility and efficacy of a proposed simplified substrate approach, for catheter ablation in patients with low intraprocedural PVC burden, defined as less than 2 PVCs/min in the first 5
minutes of the procedure.
It consists of fast mapping of the RVOT in sinus rhythm looking for LVAs and DPs, identifying the
area, and finally performing a restricted activation map of the PVCs at that area. Briefly, it was a
prospective single-arm clinical trial at two centers and three groups were studied: a) patients with
low intraprocedural PVC burden that underwent ablation with the novel simplified approach
method (study group); b) patients with low intraprocedural PVC burden that underwent ablation
using the standard activation mapping method between 2016 and 2018 (historical group); and c)
patients without PVCs, subjected to catheter ablation of supraventricular tachycardias that
agreed to have a voltage map of the RVOT in sinus rhythm performed (validation group).
The calculated sample size was 38 patients in each group. The exclusion criteria were as follows:
known structural heart disease, history of sustained ventricular arrhythmias, inability to perform
CMR, previous ablation and standard 12-Lead ECG with evidence of conduction or electrical
disease or abnormal QRS morphology were excluded.
Patients in the study and validation groups, had an ECG performed at the 2nd ICS and the RVOT
mapped in sinus rhythm to assess the presence of ST-segment elevation, and LVAS and DPs,
respectively. The results were compared between both groups.
The study group and the historical group were compared regarding the efficacy of the new
simplified ablation method in terms of abolishment of the PVCs and improvement of procedure
speed and success rate.
When available, ECGI was performed in the study group to evaluate the accuracy of the method
to identify the site of origin of the PVCs. The ECGI was performed with two systems, the Amycard
(EP Solutions SA, Switzerland) and the VIVO (Catheter Precision, NJ USA).
The prevalence of LVAs and DPs was significantly higher in the study group in comparison with
the validation group, respectively, 71% vs 11%, p<0.0001 and 87% vs 8%, p<0.0001. The ST-segment
elevation was a good predictor of LVAS with a sensitivity of 87%, specificity of 96%, positive
predictor value of 93% and negative predictor value of 91%.
The novel simplified approach abolished the PVCs in 90% of the patients as opposed to 47% of
patients in the historical group, p<0.0001. Only 74% patients underwent ablation in the historical
group versus 100% in the study group. In patients that underwent ablation, the procedure time
was significantly lower in the study group when comparing to the historical group, 130 (100-164)
vs 183 (160-203) min, p<0.0001 and the success rate was significantly higher, 90% vs 64%, p=0.013.
The recurrence rate in patients with a successful ablation after a median follow-up time of 1060
(574-1807) days, was not significantly different between both groups, Log-Rank=0.125 ECGI before ablation was performed in 17 patients in the study group. In 6 patients the ECGI was performed just with the Amycard system, in two just with the VIVO system and in 9 patients both
systems were used. We found a good agreement between the ECGI and the invasive mapping,
with the predicted site of origin being in the same or contiguous segment of the ablation site in
14/15 patients (93%) with the Amycard system and in 100% of patients with the VIVO system. When
both systems were used simultaneously, the agreement between them was 8/9 (90%).
So, in conclusion, the proposed approach partially based on substrate mapping including
searching for LVAs and DPs, proved to be feasible, faster, and more efficient than the previous
approach based exclusively on activation mapping. ST-segment elevation at the 2nd ICS proved
to be a good predictor of LVAs. ECGI was a valuable tool to noninvasively predict the site of origin
the arrhythmia.