Author + information
- Manoj N. Obeyesekere, MBBS⁎ ()
- ↵⁎Mildura Cardiology, 230 Thirteenth Street, Mildura, Victoria 3500, Australia
The interesting study by Gupta et al. (1) in a recent issue of iJACC assesses the feasibility of post-infarct scar identification by delayed-enhanced cardiac magnetic resonance (DE-CMR) imaging and intraprocedural real-time image registration with an electroanatomic mapping system (EAM) for ventricular tachycardia ablation. Scar area measured by DE-CMR was substantially lower when compared with scar area with EAM with a bipolar cutoff value of <1.5 mV (median 12 vs. 29.1 cm2), although DE-CMR scar area correlation was better at <1 mV compared with <1.5 mV (R = 0.82 vs. 0.62). No unipolar data were presented. The reason for better correlation requires careful thought in the context of the ability of DE-CMR and EAM (bipolar vs. unipolar) to assess scar. Even though >90% of the low voltage points were within 5 mm of DE-CMR defined scar (1), precise scar delineation is important for ablation, to target substrate that will yield better long-term patient outcomes (i.e., avoidance of healthy tissue and targeting border zones and critical isthmi).
An important potential reason for better correlation at <1 mV might be the directional dependence of bipolar amplitudes that over-estimates scar tissue (2) (i.e., a perpendicular wave front will have less bipolar amplitude than one that is parallel). Because unipolar recordings are not subject to directional dependence, sites with lower bipolar amplitude due to the direction of the wave front would have greater unipolar electrogram amplitudes. Similar to Gupta et al. (1), a prior report demonstrated that, when using a bipolar <1.5-mV cutoff, a mismatch of >20% in infarct surface measurement was observed in 33% (3). However, a <6.5-mV unipolar voltage best correlated with the presence of scar on CMR compared with bipolar <1.5 mV (R = 0.86 vs. 0.82) (3). A DE-CMR and EAM scar mismatch might also occur due to technical challenges in regions where lower EAM mapping density occurs due to poor catheter stability and/or wall contact. However, both unipolar (<5.5 mV or <5.8 mV) and bipolar (<1 mV or 1.3 mV) EAM have been demonstrated to correlate well with DE-CMR scar (4)—which included the scar border assessment (gray zone).
Thus, could the authors provide further insight into the scar area discrepancy observed between DE-CMR and EAM at bipolar <1.5 mV? Do the investigators have data on unipolar EAM in this population? Additionally, is the greater scar area on EAM at <1.5 mV due to the gray zone that was not accounted for on DE-CMR imaging? Does the inability of bipolar electrogram to predict epicardial scar promote the use of DE-CMR information and/or the need to use unipolar mapping more frequently, given that transmural/epicardial scar is observed not infrequently (3) and—as mentioned also in the accompanying editorial (5)—that endocardial bipolar EAM might be less sensitive to scar extending into the midwall and/or subepicardium?
- American College of Cardiology Foundation
- Gupta S.,
- Desjardins B.,
- Baman T.,
- et al.
- Codreanu A.,
- Odille F.,
- Aliot E.,
- et al.
- Bilchick K.C.