Miscellaneous
The influence of fat thickness on the human epicardial bipolar electrogram characteristics: measurements on patients undergoing open-heart surgery
1 Department of Medicine, University of Maryland, Cardiac Electrophysiology Service, 22 South Greene Street, Room N3W77, Baltimore, MD 21201, USA; 2 Department of Surgery, University of Maryland, Baltimore, MD, USA
Aims: 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.
Methods and 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° 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 (
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.
Conclusion: 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.
Key Words: Epicardial, Electrogram amplitude, Ventricular tachycardia, Epicardial fat, Ablation
* Corresponding author. Tel: +1 410 328 6056, Fax: +1 410 328 2062, Email: msaba{at}medicine.umaryland.edu
Manuscript submitted 22 January 2009. Accepted after revision 22 May 2009.