Diagnostic Methods - Body Surface Mapping

Low-level activity at the end of the QRS complex was analyzed from 63 thoracic leads in 15 normal subjects and in 21 patients with ventricular tachycardia (VT). The latter had old myocardial infarction and no conduction disturbances and had not been receiving antiarrhythmic drugs. In both normal subjects and patients with VT, isopotential maps of the time-averaged and filtered (25 Hz highpass) electrocardiograms during the terminal portion of the QRS were dipolar, i.e., they showed single positive and negative regions. For patients with VT, the extrema were either distant, with one over the precordial area and the other over the back, or close together in the precordial region. In 10 patients, maps recorded after administration of antiarrhythmic drugs remained the same while QRS duration was prolonged. In six patients, maps recorded before antiarrhythmic surgery showed distant extrema for septal or posterobasal VT sites of origin and close extrema for anterior or posteroapical sites. Generally, QRS duration was reduced and maps were modified after surgery. Late potentials can be well detected with only three orthogonal leads because their distributions are dipolar, but maps provide additional information about their distribution, which may be related to conduction delay sites and possibly to VT sites of origin. Sources near the torso surface would produce close extrema, whereas deeper sources would produce distant extrema. Circulation 74, No. 6, 1323-1333, 1986 HIGH-RESOLUTION signal-averaged electrocardiograms have shown the presence of low-level, highfrequency potentials immediately after the QRS complex in patients withcoronary heart disease and ventricular tachycardia (VT) during normal sinus rhythm. It has been suggested that these late ventricular potentials reflect the presence of areas of delayed conduction where reentry can easily occur" 2 and that they can be used as a sensitive marker for the identification of subjects prone to sustained VT.31-2 These features have also been previously described in cases of right ventricular arrhythmogenic dysplasial3 and more recently in cases of nonischemic congestive cardiomyopathy with cardiomegaly and VT. 14 15 In this study, we have characterized the spatial distribution of the late potentials by analyzing 63 simultaFrom the Centre de recherche de l'H6pital du Sacr6-Coeur and Institut de genie biomedical, Universit6 de Montreal, Montreal, Quebec, Canada. Supported by the Medical Research Council of Canada and the Quebec Heart Foundation. Address for correspondence: Pierre Savard, Ph.D., H6pital du SacreCoeur, 5400 Gouin ouest, Montreal, H4J 1C5, Canada. Received April 15, 1986; revision accepted July 31, 1986. Vol. 74, No. 6, December 1986 neously recorded leads in normal subjects and in patients with old myocardial infarction and documented VT. Previously, late potentials had been recorded with only three or four bipolar leads,3-12 which did not supply information about the location and extent of these potentials on the torso surface. The analysis of these 63 time-averaged and filtered electrocardiograms can provide (1) information about the number and location of leads required to record late potentials, (2) a more detailed description of the late potentials and of the modifications caused by antiarrhythmic drugs or surgery than the one provided by three orthogonal leads, and (3) information about the location of the late potentials on the torso surface, which could be compared with the location of the arrhythmogenic site.