ClinicalVentricular TachycardiaPostinfarct ventricular tachycardia substrate: Characterization and ablation of conduction channels using ripple mapping
Graphical abstract
Introduction
Patients with previous myocardial infarction are susceptible to reentrant ventricular tachycardia (VT) maintained by a diastolic isthmus within scar. Catheter ablation of the isthmus is effective at preventing recurrences but can be difficult when faced with hemodynamic instability, presence of multiple VT morphologies, or noninducibility.
Substrate mapping has been proposed as an alternative method to identify and modify critical sites for reentry during normal rhythms.1,2 Three-dimensional navigation systems initially were used to create bipolar voltage maps, denoting areas of low-amplitude signal as scar. Empiric ablation was delivered around scar borders, transecting scar.2 Ablations became increasingly extensive until the entire scar was “homogenized.”3,4 Sophisticated approaches attempted to identify channels of viable myocardium that also could act as diastolic pathways.5,6 Bipolar voltage mapping could differentiate channels with slightly higher voltage amplitude from the very-low-amplitude scar.6 However, differentiating the higher-channel signal amplitude from far-field signal can be difficult and did not always correlate with the isthmus.5 Therefore, extensive ablation of all late potentials has been advocated as an alternative.3,7
Recently, activation mapping has been used to locate the entrances to substrate channels, with attention to the timing of the electrogram signal rather than its amplitude. This was based on the concept that channels form an interconnected network, and ablating their entrance should lead to loss of the signals within the scar core.8, 9 This method of ablation, dechanneling, is an effective method for substrate modification.8,9 However, these techniques can be labor-intensive; there is a need to manually tag, allocate, and interpret signals of interest as well as to specifically position catheters in a position that allows suitable signals to be mapped.
Ripple mapping (RM) was designed to overcome pitfalls of 3-dimensional mapping and shown to improve atrial tachycardia ablation by differentiating low-voltage critical isthmuses from nonfunctional scar.10,11 It has been applied in ischemic VT to show co-location of conduction channels in scar with diastolic isthmuses; ablation of these channels can prevent VT recurrence.12,13 We tested the feasibility of using RM to identify and ablate early scar potentials (SPs) in order to eliminate late SPs.
Section snippets
Population
We recruited patients with postinfarct VT undergoing catheter ablation. The study protocol was developed adhering to guidelines established by the Helsinki Declaration 2013 and approved by the London Queens Square Health Research Authority Ethics Committee (19/LO/0637). Patients were recruited at Imperial College Healthcare NHS Trust.
Electroanatomic mapping and ablation protocol
Patients underwent a mapping protocol designed to locate ripple mapping conduction channels (RMCCs) as previously described.13 The protocol for mapping is given in
Demographics
Eleven male patients were recruited (mean age 68.6 ± 6.4 years; mean left ventricular ejection fraction 34.1% ± 7.8%). The indication for ablation was recurrent antitachycardia pacing in 2 (18%), single implantable cardioverter-defibrillator shock in 2 (18%), recurrent shocks in 4 (36%), and slow VT in 3 (27%). Full demographic details are given in Supplemental Table 1.
Electroanatomic mapping
Single transseptal access was acquired in all patients: double in 1 (9%) and retrograde in 7 (64%). The mapped rhythm was
Discussion
In this study, we showed that selective radiofrequency ablation of early SPs identified by RM eliminates the latest SPs at spatially remote sites, without direct catheter ablation. This endpoint was associated with good medium-term outcomes.
Following myocardial infarction, remodeling within ventricular scar results in slow conduction characterized by electrograms that are delayed, with split, fractionated, and isolated components reflecting abnormal local activation.14 We referred to these
Conclusion
In this study, we used RM to identify channels of activation within scar. Ablation at channel entrance sites was able to eliminate the latest SPs without direct ablation. These findings provide further evidence of interconnected channels within postinfarct scar as an effective target for substrate modification.
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Funding sources: This work was supported by a research IIS-516 conducted with financial support from the Investigator-Initiated Study Program of Biosense-Webster, and a Project Grant from St. Mary’s Coronary Flow Trust.
Disclosures: Imperial College holds Intellectual Property relating to ripple mapping on behalf of Drs Kanagaratnam and Linton, who have also received royalties from Biosense-Webster. Drs Kanagaratnam, Linton, Jamil-Copley, and Luther have received consulting fees with respect to ripple mapping from Biosense-Webster. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.