Distinguishing epicardial fat from scar: analysis of electrograms using high-density electroanatomic mapping in a novel porcine infarct model.

<bold>Background: </bold>The presence of epicardial fat can confound the quantification of scar during transpericardial electroanatomic mapping. The electrogram (EGM) characteristics of epicardial fat have not been systematically compared with infarct scar using gross and histopathological analysis as a gold standard.<bold>Objective: </bold>The purpose of this study was to compare the EGM characteristics of epicardial fat with infarct scar.<bold>Methods: </bold>A closed-chest infarction was created in 40-50 kg pigs by occlusion of the circumflex artery for 150 minutes using an angioplasty balloon. This artery was chosen to minimize any potential overlap of epicardial fat with infarct and to spare any septal involvement. After 4-12 weeks of infarct healing, epicardial mapping was performed. EGMs in low-voltage regions (<1.5 mV) were analyzed, and bipolar amplitude, duration, number of deflections, and the presence of late potentials were recorded. Statistical analysis was performed using unpaired t-test and chi(2) analysis. Gross and histopathological examination was used to confirm areas of fat and infarct scar.<bold>Results: </bold>Seven porcine hearts were analyzed after high-density epicardial mapping (364 +/- 92 points) was performed 48 +/- 19 days after infarction. The mean bipolar EGM amplitude was similar in fat and scar (0.77 +/- 0.34 vs. 0.75 +/- 0.38 mV; P = not significant). The mean EGM duration was longer in scar than in fat (68.8 +/- 18.9 vs. 50.1 +/- 11.6 ms; P <.0001) and exhibited more fractionation (8.5 +/- 3.1 vs. 4.7 +/- 1.8 deflections; P <.0001). The presence of late potentials was 99% specific for scar. Further, areas of fat >4 mm in thickness registered low-voltage bipolar EGMs.<bold>Conclusion: </bold>Scar from healed myocardial infarction exhibits more fractionation and longer EGM duration when compared with fat. Late potentials are highly specific for locating infarct scars. [ABSTRACT FROM AUTHOR]