planning and is associated with radiation exposure. However, CT-derived coronary anatomy may also reduce the number of contrast injections before epicardial ablation and thus, reduce the radiation exposure during the procedure.
The relatively small number of mapping points, particularly in patients with idiopathic VA, may have limited the accuracy of the maps. The number of controls was small due to the fact that epicardial ablation is not required in the majority of patients with idiopathic VA. The number of NICM patients studied was also small because implanted devices fre- quently impeded CE-MRI acquisition. For patients in whom CE-MRI is not available during the procedure, we provide tools to distinguish scar from viable myocardium and fat.9
Clinical implications
Substrate mapping is of key importance during epicardial VT ablation since activation mapping cannot be performed in the majority of VTs. However, during epicardial EAM it may be difficult to distinguish scar from fat, as both are associated with attenuated bi- polar electrogram amplitudes. Moreover, even in the absence of epicardial fat, scars may be difficult to detect if located intramurally. The current study provides insight into the value of different epicardial EAM parameters for detection of scar in patients with NICM. Our findings have important implications when EAM is performed at areas covered by ≥2.8mm fat, such as the basal LV13 which is often affected in patients with NICM3,15. In addition, epicardial unipolar voltage mapping may be particularly useful for detection of intramural scars, which are common in patients with NICM1 and cannot reliably be detected based on bipolar voltage and electrogram characteristics alone.
Magnetic resonance imaging is limited by the presence of devices and even if safe, it is significantly hampered by artifacts.8 Computed tomography is however available in all patients and may be important not only to prove, but also to exclude the presence of epicardial fat. The combination of CT, unipolar voltage mapping and electrogram characteristics is likely to improve the accuracy of epicardial substrate mapping, which is important for successful catheter ablation of VT.
ConCLUSIon
Bipolar voltage ≤1.81mV and unipolar voltage ≤7.95mV are the optimal cutoff values to differentiate between scar and viable myocardium during epicardial EAM, but both are attenuated by epicardial fat. Specific electrogram morphologies are not affected by fat, but can identify only one quarter of all scar sites. The proposed easy-to-use algorithm al- lows more accurate differentiation between scar and viable myocardium during epicardial EAM. Unipolar voltage, but not bipolar voltage can be used to identify intramural scar.
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Supplemental Figure 1. histologic examination of scar architecture in biopsy specimens.
Endomyocardial biopsy specimens from the right ventricular septum (upper panels) and from the apicolat- eral left ventricle (lower panels) distant from areas with late enhancement on MRI. All reveal both compact and interstitial fibrosis.