Abstract
The procedure for epicardial mapping consists of three stages : [1] recording of epicardial and reference signals, [2] extracting of the time of epicardial excitation and the reference time, and computing of the time difference (transmission time) between them, [3] displaying of epicardial map. At present, these procedures are executed by manual operation, and the results obtained in the stages [2] and [3] are influenced by subjectivity. To remove these difficulties, we have developed a minicomputer-based system for automatic processing of the stages [2] and [3].
The epicardial map is generally displayed by equi-time lines on the plane which expresses heart surface. In our system, two types of shape are used to express the heart surface. One is the expression conventionally used in manual operation, and, the other is the polar coordinate expression which we have proposed. The equi-time lines are drawn as contours of a two-dimensional mathematical function that represents epicardial excitation pattern. This function is determined by the least mean square method from the extracted transmission time at the stage [2]. The extracted transmission time is considered to be accompanied with some errors, so it is reasonable to apply the least mean square method to determine the function.
Collecting the epicardial potential waves from 65 points on the heart surface of a dog, we extracted the excitation transmission time by both the manual operation and the computer calculation. The transmission time difference at one point between the two methods was within 3 msec on 56 of the 65 points. Maximum difference was 8 msec at two points. In spite of the existence of these differences, the obtained epicardial maps by both methods were similar, and showed the normal excitation pattern.
