56

For patients with scar-related ventricular tachycardia (VT), the identification of a critical isthmus that sustains reentry is the “holy grail” during mapping and ablation. More recently, extensive ablation strategies have been shown to decrease recurrence due to the presence of multiple VTs for a given scar substrate, where homogenization increases the probability of transecting components of a reentrant circuit.1–4 Identification of critical sites during sinus rhythm is advantageous, given that induction of VT is often associated with hemodynamic intolerance and often exacerbates underlying electrical instability. Currently, a voltage-based mapping strategy during sinus rhythm is the mainstay to guide linear, circumferential, or extensive lesions sets around and/or within scar.^5–7 Voltage mapping has inherent limitations due to catheter orientation relative to the wavefront of activation and far-field sensing.^8,9 Therefore, utilization of a functional mapping display that systematically depicts both late and slow propagation zones during sinus rhythm may be clinically helpful, if there is consistent mechanistic evidence that supports a correlation between reentry and specific regions within an isochronal late activation map.

Background

Accurate, high-density electroanatomic mapping (EAM) is essential for successful substrate-based ablation procedures for VT. Using a voltage cutoff of < 1.5 mV,¹⁰ EAM allows real-time assessment of scar location and heterogeneity and helps to localize arrhythmogenic substrate such as late potentials (LPs). At present, there are imperfect methods to identify surrogates for isthmus sites and the most functionally relevant abnormal electrograms during sinus rhythm. Pace mapping is an important tool to localize the exit-site morphology, and sites with stimulus delay possess greater specificity for isthmus sites.¹¹ Abnormal tissue signals such as local abnormal ventricular activities (LAVA) have been used to describe electrograms that record local uncoupling of near- and far-field activation, and the ablation aimed at eliminating these signals has been associated with decreased recurrence and improved survival.^3,12 Previously published studies have suggested that multipolar mapping achieves higher-density maps with increased detection of LPs/LAVAs in shorter periods of time.¹³

Complete elimination of LAVA and ablation within the entire region of low voltage or scar homogenization has been shown to decrease VT recurrence, and rehospitalization in both ischemic and nonischemic cardiomyopathy.^1,2 The ablation of “earlier” LPs has been shown to eliminate downstream activation within interconnected channels, and “dechanneling” has been associated with high rates of freedom from recurrent VT.^14,15 An improved understanding of the correlation of VT and LAVAs within channels has the potential to focus homogenization in higher yield areas. Since 2012, we began analyzing patterns of sinus rhythm scar propagation with functional EAM by creating isochronal late-activation map (ILAM) displays to investigate if there are propagation zones that mechanistically correlate with critical components for reentry.

ILAM is a functional method of EAM to prioritize uncoupled and delayed local potentials in the context of the entire window of sinus rhythm during intrinsic or paced rhythm.16 It allows for conduction velocity to be represented visually in order to identify deceleration zones or areas of slow conduction. Manual overreading of the annotation of local activation timing points in a given chamber and surface mapping are required. Automated methods to annotate this offset are currently being evaluated across various systems (“Last deflection”, Precision, St. Jude Medical). Each electrogram is timed at the offset of the last local bipolar electrogram deflection, which denotes the completion of local activation (Figure 56.1). The tagging of the most delayed component captures the entirety of late activation. Given intra-observer variability in determining the onset, maximum dV/dT, peak deflection, we found greater reproducibility with offset annotation. Electrogram deflections with an amplitude lower than the baseline noise and those that were not reproducibly seen on preceding beats were not annotated. In our experience, we have seen critical sites with amplitudes of 0.01 mV, so we do not use a low-voltage exclusion algorithm at any specified threshold.

Stay updated, free articles. Join our Telegram channel

Join