Electrocardiographic Textbooks Based on Template Hearts Warped Using Ultrasonic Images

Advances in technology make the application of sophisticated approaches to assessing electrical condition of the heart practical. Estimates of cardiac electrical features inferred from body-surface electrocardiographic (ECG) maps are now routinely found in a clinical setting, but errors in those inverse solutions are especially sensitive to the accuracy of heart model geometry and placement within the torso. The use of a template heart model allows for accurate generation of individualized heart models and also permits effective comparison of inferred electrical features among multiple subjects. A collection of features mapped onto a common template forms a textbook of anatomically specific ECG variability. Our template warping process to individualize heart models based on a template heart uses ultrasonic images of the heart from a conventional, phased-array system. We chose ultrasound because it is nonionizing, less expensive, and more convenient than MR or CT imaging. To find the orientation and position in the torso model of each image, we calibrated the ultrasound probe by imaging a custom phantom consisting of multiple N-fiducials and computing a transformation between ultrasound coordinates and measurements of the torso surface. The template heart was warped using a mapping of corresponding landmarks identified on both the template and the ultrasonic images. Accuracy of the method is limited by patient movement, tracking error, and image analysis. We tested our approach on one normal control and one obese diabetic patient using the mixed-boundary-value inverse method and compared results from both on the template heart. We believe that our novel textbook approach using anatomically specific heart and torso models will facilitate the identification of electrophysiological biomarkers of cardiac dysfunction. Because the necessary data can be acquired and analyzed within about 30 min, this framework has the potential for becoming a routine clinical procedure.