Three-dimensional electroanatomic voltage mapping technique is performed using the CARTO system (Biosense-Webster) [20-26]. In brief, the magnetic mapping system includes a magnetic sensor in the catheter tip that can be localized in 3D using ultralow magnetic field generators placed under the fluoro-scopic table. A 7F Navi-Star catheter, with a 4 mm distal tip electrode and a 2 mm ring electrode with an interelectrode distance of 1mm, is introduced into the RV under fluoroscopic guidance and used as the mapping/ablation catheter during sinus rhythm. The catheter is placed at multiple sites on the endo-cardial surface to record bipolar and/or unipolar electrograms from RV inflow, anterior free wall, apex and outflow tract. Bipolar electrogram signals are analyzed with regard to amplitude, duration, relation to the surface QRS, and presence of multiple components. Complete endocardial maps are obtained in all patients to ensure reconstruction of a 3-D geometry of the RV chamber and to identify regions of scar or abnormal myocardium. Regions showing low-amplitude electrograms are mapped with greater point density to delineate the extent and borders of "electroanatomic scar" areas. Bipolar voltage reference for normal and abnormal myocardium are based on data previously validated in both intraoperative and catheter mapping studies [18, 19, 24-28]. "Electroanatomic scar" area is defined as an area >1 cm2 including at least three adjacent points with bipolar signal amplitude <0.5 mV . The color display for depicting normal and abnormal voltage myocardium ranges from "red" representing "electroanatomic scar tissue" (amplitude <0.5 mV) to "purple" representing "electroanatomic normal tissue" (amplitude >1.5 mV). Intermediate colors represent the "elec-troanatomic border zone" (signal amplitudes between 0.5 and 1.5 mV) (Figs. 17.1-3).
Fig. 17.1 • Representative normal and abnormal 3-D electroanatomic voltage maps. Voltages were color coded according to corresponding color bars.Color range is identical for all subsequent figures: purple represents signal amplitudes >1.5 mV ("electroanatomic normal myocardium"); red <0.5 mV ("electroanatomic scar tissue"); and range between purple and red 0.5 to 1.5 mV ("electroanatomic border zone"). Top: Anteroposterior view of the RV bipolar voltage map from one control subject with normal bipolar voltages (a). Anteroposterior view of the RV bipolar voltage map from a patient with ARVC/D showing diffuse low-amplitude electrical activity involving anterior, lateral, infer-obasal, anteroapical and infundibular regions (b). Bottom: Right anterior oblique (c) and left anterior oblique (d) views of the RV bipolar voltage from a patient with ARVC/D showing low-voltage areas in the infundibular, inferobasal and anterior regions; the septum is characteristically spared
Fig. 17.2 • Examples of electrical signals sampled from a low-amplitude and normal RV areas in the same patient with ARVC/D. As indicated by the catheter tip, the low-voltage electrogram (0.26 mV) recorded from anterior region is fragmented with prolonged duration and late activation (a). By comparison, a normal voltage electrogram (6.59 mV) sampled from the lateral region is sharp with uniphasic deflection and shorter duration (b)
Voltage Mapping: Clinical Results in ARVC/D
A preliminary study by Boulos et al.  reported a series of seven patients with ARVC/D, in whom elec-troanatomic voltage mapping accurately identified RV "dysplastic" regions . The authors found a concordance between voltage mapping results and echocar-diographic or CMR findings in all studied patients.
Corrado et al.  tested the hypothesis that characterization of the RV wall by electroanatomic voltage mapping increases the accuracy for diagnosing ARVC/D. Thirty-one consecutive patients (22 males and nine females, aged 30.8±7 years) who fulfilled the criteria of the Task Force of the European Society of Cardiology and International Society and Federation of Cardiology (ESC/ISFC) for ARVC/D diagnosis after "noninvasive" clinical evaluation, underwent further "invasive" study including RV electroanatomic voltage mapping and EMB to validate the diagnosis. Multiple RV endocardial, bipolar electrograms (175±23) were sampled during sinus rhythm. Twenty patients (Group A, 65%) had an abnormal RV elec-troanatomic voltage mapping showing one or more areas (mean 2.25±0.7) with low-voltage values (bipolar electrogram amplitude <0.5 mV), surrounded by a border zone (0.5-1.5 mV) which transitioned into normal myocardium (>1.5 mV) (Fig. 17.1). Low-voltage electrograms appeared fractionated with significantly prolonged duration and delayed activation (Fig. 17.2). In eleven patients (Group B, 35%) elec-troanatomic voltage mapping was normal, with preserved electrogram voltage (4.4±0.7 mV) and duration (37.2±0.9 ms) throughout the RV. Low-voltage areas in patients form Group A corresponded to echocar-
diographic/angiographic RV wall motion abnormalities and were significantly associated with myocyte loss and fibrofatty replacement at EMB (p<0.0001) and familial ARVC/D (p<0.0001). Patients from Group B had a sporadic disease and histopathologic evidence of inflammatory cardiomyopathy (p<0.0001). During the time interval from onset of symptoms to the invasive study (mean 3.4 years), eleven patients (55%) with electroanatomic low-voltage regions received an ICD due to life-threatening ventricular arrhythmias, whereas all but one patient with normal voltage map remained stable on antiarrhythmic drug therapy (p=0.02). These results indicate that 3-D electroana-tomic voltage mapping may enhance accuracy for diagnosing ARVC/D by demonstrating low-voltage areas which are associated with fibrofatty myocardial replacement, and by identifying a subset of patients who fulfilled ESC/ISFC Task Force diagnostic criteria, but show a preserved electrogram voltage. This latter subset appears to have an inflammatory cardiomyopathy mimicking ARVC/D, and a better arrhythmic outcome.
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