title: The influence of fat thickness on the human epicardial bipolar electrogram characteristics: measurements on patients undergoing open-heart surgery.
abstract: OBJECTIVE
  Reference values exist for endocardial but not for epicardial (EPI) substrate mapping in cases of cardiomyopathy-associated ventricular tachycardia. We sought to establish such values for EPI electrogram voltage, including areas with overlying fat.
  
  
  RESULTS
  Ten patients (six males) undergoing cardiac surgery were studied. After opening the pericardium, the distal bipole of an electrophysiology catheter was placed tangential to the EPI surface to obtain an electrogram recording. The bipole was tangentially rotated 90 degrees and the higher of the two amplitudes (mV) was taken as the local amplitude. Recordings were taken from normal left and right ventricular myocardium (n = 26 data points each), over thick (> or = 0.5 cm) fat at both ventricular bases (n = 16) and thin (<0.5 cm) fat at the mid-ventricular level (n = 32). A total of 100 recordings (mean 10/patient) were analysed. Four patients underwent valvular surgery, three bypass surgery, and three combined procedures. Mean age was 61.7 +/- 10.4 years and mean left ventricular ejection fraction was 46 +/- 12%. Electrogram amplitude was inversely related to EPI fat thickness. Over thick fat, 31% of recordings were <0.5 mV.
  
  
  CONCLUSIONS
  Human EPI electrogram amplitude varies by ventricular chamber and significantly by EPI fat thickness. A cut-off of 0.5 mV to define 'scar' will include normal areas with thick overlying fat. EPI substrate maps should include data on EPI fat thickness for higher specificity.
authors: Department of Medicine, University of Maryland, Cardiac Electrophysiology Service, 22 South Greene Street, Room N3W77, Baltimore, MD 21201, USA. msaba@medicine.umaryland.edu
authors: Magdi M
authors: MM
authors: Saba
authors: Jagan
authors: J
authors: Akella
authors: James
authors: J
authors: Gammie
authors: Robert
authors: R
authors: Poston
authors: Anthony
authors: A
authors: Johnson
authors: Robert E
authors: RE
authors: Hood
authors: Timm-Michael
authors: TM
authors: Dickfeld
authors: Stephen R
authors: SR
authors: Shorofsky
mesh_terms: D000273:Adipose Tissue / Q000503:physiopathology*; D018780:Body Surface Potential Mapping / Q000379:methods*; D006348:Cardiac Surgical Procedures / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods; D010496:Pericardium / Q000503:physiopathology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D017180:Tachycardia, Ventricular / Q000175:diagnosis* / Q000503:physiopathology*