Functional pace-mapping responses for identification of targets for catheter ablation of scar-mediated ventricular tachycardia

Abstract

Background: Myocardial scars harbor areas of slow conduction and display abnormal electrograms. Pace-mapping at these sites can generate a 12-lead ECG morphological match to a targeted ventricular tachycardia (VT), and in some instances, multiple exit morphologies can result. At times, this can also result in the initiation of VT, termed pace-mapped induction (PMI). We hypothesized that in patients undergoing catheter ablation of VT, scar substrates with multiple exit sites (MES) identified during pace-mapping have improved freedom from recurrent VT, and PMI of VT predicts successful sites of termination during ablation.

Methods and results: High-density mapping was performed in all subjects to delineate scar (0.5-1.5 mV). Sites with abnormal electrograms were tagged, stimulated (bipolar 10 mA at 2 ms), and targeted for ablation. MES was defined as >1 QRS morphology from a single pacing site. PMI was defined as initiation of VT during pace-mapping (400-600 ms). In a 2-year period, 44 consecutive patients with scar-mediated VT underwent mapping and ablation. MES were observed during pace-mapping in 25 patients (57%). At 9 months, 74% of patients who exhibited MES during pace-mapping had no recurrence of VT compared with 42% of those without MES observed (P=0.024), with an overall freedom from VT of 61%. Thirteen patients (30%) demonstrated PMI, and termination of VT was seen in 95% (18/19) of sites where ablation was performed.

Conclusions: During pace-mapping, electrograms that exhibit MES and PMI may be specific for sites critical to reentry. These functional responses hold promise for identifying important sites for catheter ablation of VT.

FIGURE 1

Schematic of MES: Three exit morphologies from a single pacing site (center, marked +). Blue areas present scar, or replacement fibrosis.

FIGURE 2

Upper. Two morphologies with two different stimulus latencies seen during pace-mapping within dense scar. The second morphology matches the targeted VT. Lower. Three distinct morphologies with 2:1 exit block from a pace-map site with last beat matched for targeted VT.

FIGURE 3

Approach to mapping and ablation of VT. NIPS=noninvasive programmed stimulation , ICD=implantable cardioverter defibrillator, TCL=tachycardia cycle length, EGM=electrogram

FIGURE 4

Pace-mapping in patient with inferior infarction from an electrogram with LP results in 3:2 conduction out of scar. Two morphologies with different stimulus latencies are seen (red and black dashed boxes) and the first morphology is a good match for a targeted VT. Red circles represent ablation lesions within dense scar and pink circles are other sites where pace-mapping was performed. Note that this MES lies within a potential channel, flanked by two areas of dense scar (red). LP= late potential. Need time scale for rather upper panel

FIGURE 5a

Kaplan-Meier curves comparing VT recurrence in patients with MES and without MES seen during mapping and ablation.

FIGURE 5b

Kaplan-Meier curves comparing VT recurrence in patients with MES and without MES in ICM (above) and non-ICM groups (below).

FIGURE 6

Upper. Pace-mapped induction (solid red box) is a perfect match for the induced VT (dashed red box) at a site with LP. Lower. Concealed entrainment was demonstrated at this site prior to ablation.

FIGURE 7a

Two-exit site pace-mapped induction. Proof of both MES and PMI as isthmus surrogate. The first morphology (red solid box) is a closer match to the induced VT (red dashed box) than the second morphology (blue box). Ablation at this site (red asterisk), despite the absence of overt diastolic activity, resulted in prompt termination of VT.

FIGURE 7b

Construct of two exits on electroanatomic map during pacemapped induction (blue and red arrows) attached to the same reentrant VT circuit in the same patient with anteroseptal infarction. Voltage threshold displayed at 0.5-1.5mV.