Improving the accuracy of forward computations: Different methods to implement the propagation of the depolarization wave front

This study addresses the problem of discontinuities in the body surface potentials (BSPs) introduced by the discrete nature of a cardiac surface source model. These physiologically unrealistic discontinuities result from the switching on of the elementary surface source elements based on the timing of activation assigned to their nodes. Two new methods for avoiding such discontinuities are introduced and their effectiveness is analyzed. In the first method only the contributions of the activated parts of the source elements are evaluated. This results in a more physiologically realistic description of cardiac source activity and is referred to as the gold standard. In addition, a faster, approximate method was developed, in which the contribution of any source element at a particular time is weighted with the activated fraction of its surface. Both methods prevent the discontinuities; the fast method provides a useful approximation and yields a fast implementation as required in interactive forward simulations and is useful in inverse modeling.