PMC4778089_01
A: A 12-lead electrocardiogram showing sinus rhythm. The electrocardiogram in sinus rhythm demonstrates epsilon waves in V1-V5 (red arrow), and low voltage, given epicardial-to-endocardial fibrofatty infiltration. B: Ventricular tachycardia morphology observed during electrophysiological study is consistent with a right ventricular outflow tract origin. C: Comparison of ex vivo cardiac magnetic resonance image (left upper panel) and gross pathologic section (left lower panel). Thick diffuse fatty tissue around the right ventricle and left ventricle was observed. There is evidence of fibrofatty infiltration in both ventricles, including in the interventricular septum (IVS) (blue square). D: Fatty infiltration in the IVS on the gross (left panel) and histopathologic (right panel) sections demonstrates an area with surviving myocardium surrounded by fibrofatty infiltration. (Asterisk, arrow, and arrowhead point to similar regions between the gross and histopathologic sections.)
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The pathological findings correlated well with cardiac MRI results, but MRI could not distinguish between epicardial fat and fibrofatty replacement of the LV (Figure 1).
Correlation of electroanatomic mapping with gross pathology A: A gross section of the left ventricle (LV) demonstrates surviving myocardium in the LV anteroapex (upper panel) and apex covered with fibrofatty tissue (lower panel). B: Superimposed right ventricular (RV) endocardial and epicardial electroanatomic mappings (EAMs). The electrograms (EGMs) from corresponding sites in panel A are shown. A fractionated EGM with evidence of a late potential is observed in the border-zone region between surviving myocardium and fat. The surviving myocardium shows normal voltage, while fat demonstrates very low-voltage EGMs. C: Histopathologic findings from the gross section shown in panel A and the corresponding sites on EAMs and EGMs from panel B are shown: (1) Significant fibrofatty infiltration with surviving myocardium (FFSM) was seen in an area of fractionated EGM with late potentials; (2) predominantly viable myocardium with some interstitial fibrosis was seen in an area of normal voltage; and (3) epicardial fat was seen in an area of low-voltage, short-duration EGM.
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EGMs from multiple regions with very low voltage (<0.5 mV) and border zones (0.5 to 1.5 mV), as well as viable myocardium on EAM were analyzed and the histologic findings at these sites evaluated (Figure 2, Figure 3).
Correlation of electroanatomic mapping with histopathologic findings in the right ventricular outflow tract (RVOT). A: Electrograms (EGMs) from an area of low voltage below the pulmonic valve and 2 sites on the epicardium (Epi) and endocardium (Endo) prior to ablation are shown. B: Gross section (upper panel) and corresponding histopathologic findings (lower panel) of an ablated region in the RVOT. The red arrow points to the ablation site, and the black arrows demonstrate corresponding sites between gross and histologic sections. The corresponding EGMs in panel A from both epicardium and endocardium (red arrow) prior to ablation demonstrate fractionation and late potentials. After ablation, this site shows a transmural fibrotic lesion. The asterisk demonstrates fat below the pulmonic valve on histologic findings (region 1). C: Analysis of a total of 100 EGMs (25 from each region) of corresponding sites on histologic findings and electroanatomic mappings (EAMs). Pure fatty or fibrofatty replacement had low-voltage, short-duration EGMs. Sites near areas of normal voltage consisting of surviving myocardium surrounded by fibrofatty infiltrations exhibited low-voltage but long-duration EGMs. Areas with border-zone EGMs (voltage between 0.5 and 1.5 mV) often also contained fatty or fibrofatty infiltration with surviving islands of myocardium and exhibited EGMs of long duration. FFSM = fibrofatty infiltration admixed with surviving myocardium; BZ = border zones; FAT = fatty tissue without surviving myocytes; viable = areas of normal myocardium.
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EGMs from multiple regions with very low voltage (<0.5 mV) and border zones (0.5 to 1.5 mV), as well as viable myocardium on EAM were analyzed and the histologic findings at these sites evaluated (Figure 2, Figure 3).