RECONSTRUCTION OF ENDOCARDIAL POTENTIALS AND ACTIVATION SEQUENCES FROM INTRACAVITARY PROBE MEASUREMENTS - LOCALIZATION OF PACING SITES AND EFFECTS OF MYOCARDIAL STRUCTURE

Background Mapping of endocardial activation is an important procedure for diagnosing cardiac arrhythmias and locating the arrhythmogenic si te before treatment. The objective of the present study was to develop and test a mathematical method to reconstruct the endocardial potenti als and activation sequences (isochrones) from potential data measured with a noncontact, intracavitary multielectrode probe (the ''inverse problem''). Methods and Results A boundary element based mathematical method, combined with a numeric regularization technique, was develope d for computing the inverse solution. Endocardial potentials were comp uted from intracavitary potentials measured with a multielectrode prob e placed in the cavity of an isolated, perfused canine left ventricle. Data were acquired during rhythms induced by electrical stimuli appli ed at different locations and varying depths within the myocardium. En docardial potentials were measured using intramural needles to evaluat e the accuracy of the inverse solutions by direct comparison. Inversel y computed endocardial potentials, from measured probe potentials, rec onstruct with good accuracy the major features (potential maxima and m inima, regions of negative and positive potentials) compared with the measured endocardial potentials. During early activation, the computed endocardial potentials exhibit a potential minimum in close proximity to the pacing site, determining the location of the stimulus with goo d accuracy (within 10-mm error). Multiple stimuli, as close as 10 to 2 0 mm to each other, can be distinguished and localized to their sites of origin by the inverse reconstruction. Similar to the measured endoc ardial potentials, the spatial distribution of the computed endocardia l potentials reflects the underlying cardiac fiber direction, and dyna mic changes of the computed endocardial potentials reflect the rotatio n of fibers with intramural depth. Maps of isochrones show good corres pondence between the isochrones determined from the computed endocardi al potentials and those determined directly from the measured endocard ial potentials. Conclusions Compared with actual, measured endocardial potentials and activation sequences, endocardial potential patterns a nd activation sequences can be reconstructed on a beat-by-beat basis f rom cavitary potentials measured with a multielectrode, noncontact pro be. The approach presented here is shown to reconstruct, with 10-mm ac curacy and resolution of 10 to 20 mm, local events of cardiac excitati on (eg, pacing sites). In addition, the reconstructed endocardial pote ntials correctly reflect the underlying fibrous structure of the myoca rdium. These results demonstrate the feasibility of the approach. In t he experiments, the probe position and endocardial geometry were deter mined invasively. To be clinically applicable, the reconstruction meth od should be combined with a noninvasive method for determining the pr obe-cavity geometry in the catheterization laboratory. It could then b e developed into a catheter-based technique for locating arrhythmogeni c sites and for studying and diagnosing conduction abnormalities, reen trant activity, and the effects of drugs and other interventions on ca rdiac activation and arrhythmias.