COMPARISON OF MEASURED AND COMPUTED EPICARDIAL POTENTIALS FROM A PATIENT-SPECIFIC INVERSE MODEL

This study reports the first direct comparison of measured and compute d epicardial potentials in which the specific anatomy of a test subjec t has been used to calculate the inverse electrocardiographic model. I t is now feasible to obtain low-noise body surface potential maps and to incorporate accurate anatomic data into inverse procedures for the purpose of computing epicardial potential distributions. The direct ve rification of computed human epicardial distributions remains an impor tant goal. The experiment reported here obtained direct measurements f rom six transcutaneous pacing wires that were attached to points on th e epicardial surface of the human heart in an intact subject. From the same subject, a magnetic resonance scan was used to produce a specifi c thoracic model consisting of 5-mm cubes. The forward model uses the finite difference method to compute a forward transfer matrix that rel ates each of 26 epicardial regions to body surface measurements. The i nverse computation was performed by zero-order Tikhonov regularization . Body surface potentials were used in the inverse procedure to comput e epicardial potentials, which were then compared with direct epicardi al measurements. The computed epicardial potentials were compared to t he measured ones by correlation, which gave an amplitude-independent m easure of similarity. Amplitude differences and time delays in compute d potentials were observed, but the morphologic trend was generally we ll recovered. The results obtained indicate the sensitivity of the inv erse model to a number of factors. The robustness of computed epicardi al distributions to errors in assumed lung conductivity is shown. Resu lts from a nonpatient-specific, but realistic, torso model are present ed. The computed epicardial potentials are sensitive to the division o f the epicardium into source regions, and proposals are made concernin g the choice of these regions. This study demonstrates the use of dire ct epicardial measurements to assess the performance of patient-specif ic inverse models.