Relative timing of near-field and far-field electrograms can determine the tachyarrhythmia site of origin

Close-coupled pacing to identify the "functional" substrate of ventricular tachycardia: Long-term outcomes of the paced electrogram feature analysis technique

BACKGROUND

The conduction delay and block that compose the critical isthmus of macroreentrant ventricular tachycardia (VT) is partly "functional" in that they only occur at faster cycle lengths. Close-coupled pacing stresses the myocardium's conduction capacity and may reveal late potentials (LPs) and fractionation. Interest has emerged in targeting this functional substrate.

OBJECTIVE

The purpose of this study was to assess the feasibility and efficacy of a functional substrate VT ablation strategy.

METHODS

Patients with scar-related VT undergoing their first ablation were recruited. A closely coupled extrastimulus (ventricular effective refractory period + 30 ms) was delivered at the right ventricular apex while mapping with a high-density catheter. Sites of functional impaired conduction exhibited increased electrogram duration due to LPs/fractionation. The time to last deflection was annotated on an electroanatomic map, readily identifying ablation targets.

RESULTS

A total of 40 patients were recruited (34 [85%] ischemic). Median procedure duration was 330 minutes (interquartile range [IQR] 300-369), and ablation time was 49.4 minutes (IQR 33.8-48.3). Median functional substrate area was 41.9 cm² (IQR 22.1-73.9). It was similarly distributed across bipolar voltage zones. Noninducibility was achieved in 34 of 40 patients (85%). Median follow-up was 711 days (IQR 255.5-972.8), during which 35 of 39 patients (89.7%) did not have VT recurrence, and 3 of 39 (7.5%) died. Antiarrhythmic drugs were continued in 53.8% (21/39).

CONCLUSION

Functional substrate ablation resulted in high rates of noninducibility and freedom from VT. Mapping times were increased considerably. Our findings add to the encouraging trend reported by related techniques. Randomized multicenter trials are warranted to assess this next phase of VT ablation.

Tachyarrhythmia discriminator for implantable cardioverter-defibrillators in bundle branch block

BACKGROUND

Inaccurate arrhythmia classification by implantable cardioverter-defibrillators (ICDs) contributes to inappropriate shocks and increased health care utilization.

OBJECTIVE

The purpose of this study was to evaluate the ability of a novel discriminator using far-field (FF) and near-field (NF) right ventricular lead electrograms (EGMs) to differentiate ventricular tachycardia (VT) from supraventricular tachycardia (SVT) in patients with underlying conducted narrow QRS, right bundle branch block (RBBB), and left bundle branch block (LBBB).

METHODS

ICD interrogations were reviewed, identifying subjects with tachycardia events at least 5 beats in duration with stable morphology and cycle length. FF to NF (FF-NF) EGM intervals during tachycardia and baseline conducted rhythm were measured using digital calipers. Events with uncertain tachycardia rhythm mechanism were excluded.

RESULTS

Ninety-five subjects were included. Mean FF-NF interval during tachycardia was significantly lower during SVT than VT (25.8 ± 12.0 ms vs 91.0 ± 37.2 ms; P <.001). Participants with LBBB (n = 22) and RBBB (n = 21) had significantly lower mean FF-NF intervals during SVT compared with VT (LBBB 25.6 ± 7.26 ms vs 93.1 ± 41.5 ms; P <.001; RBBB 30.0 ± 16.6 ms vs 101.7 ± 34.3 ms; P <.001). In this cohort, FF-NF interval cutoff of 100 ms was 100% specific for VT discrimination regardless of underlying QRS morphology, with sensitivity of 46%, 50%, and 38% for LBBB, RBBB, and narrow QRS, respectively.

CONCLUSION

Prolonged FF-NF interval on intracardiac EGM during tachycardia is a highly specific discriminator for VT, regardless of baseline QRS morphology.