Noninvasive localization of ectopic ventricular activity using BSPM and different patient torso models

The possibility of noninvasive localization of the focus of ectopic ventricular activity and dependence of its accuracy on the used heart and torso model were examined. Body surface potentials were measured in 62 leads in two patients with idiopathic extrasystoles having the focus in different ventricular regions assessed by intracardiac electrophysiological study. Integral maps over the initial period of the premature ventricular activation and inhomogeneous torso model were used as input for an inverse solution to find noninvasively the focus of the premature activation represented by a single dipole. Three torso models representing the individual patient torso with different fidelity were attempted. The best agreement between the focus positions obtained from the inverse solution and from the electrophysiological study was achieved when the torso and heart model based on whole-torso CT was used. The use of an individually adjusted general torso model and properly positioned heart model obtained from CT gave less accurate but still acceptable location of the ectopic focus. If the same adjusted general torso model was used with simplified geometric heart model, the fidelity of its shape and position significantly influenced the inverse solution and the results varied from acceptable focus locations to locations scattered in a wide range of the ventricular volume. From the obtained results it can be presumed that by inverse solution based on dipolar cardiac generator model, measured body surface potential maps and CT-based torso model the initial location of the ectopic premature activity can be obtained. In addition, if the whole-torso CT is not available a model with a general torso shape adjusted to patient chest dimensions and with properly positioned heart model based on CT-scan of the heart area can still give acceptable location of the ectopic activity.