Diagnostic Methods Body Surface Mapping

Body surface potential maps were recorded from 140 chest leads in 25 patients affected by the idiopathic long QT syndrome (LQTS) and in 25 healthy control subjects matched for age and sex. Potential time integrals of the QRST and ST-T intervals were calculated at each lead point and displayed as isointegral (ISOI) maps. The main abnormalities noted on the QRST and ST-T ISOI maps were one area of negative values larger than normal in the right anterior and inferior thorax and a complex multipeak distribution of the integral values. At least one abnormality was present in 19 (76%) of the patients with LQTS and four (16%) of the control subjects (p < .001). Each ISOI map was also represented as a weighted sum of nine fundamental components (eigenvectors) to detect and quantitate the nondipolar content. The percent contribution of the nondipolar eigenvectors (all eigenvectors beyond the third) was significantly higher in the LQTS group than in the control group (p < .005). Specifically, an abnormally high nondipolar content on the QRST ISOI maps was observed much more frequently for patients with LQTS than for control subjects (nine or 36% vs one or 4%), and this was also true on the ST-T ISOI maps (14 or 56% vs one or 4%). No correlation was found between the major abnormalities on body surface maps and syncopal episodes. However, the high prevalence (76%) of these alterations among the patients with LQTS and their infrequent occurrence in the control population strongly suggests that they may be useful markers for the diagnosis of atypical cases. The prominent electronegative area on the anterior thorax can be related to delayed repolarization of a portion of the anterior wall of the heart. This finding is in agreement with the hypothesis that lower than normal right cardiac sympathetic activity is the main pathogenetic mechanism of LQTS. Multipeak distribution and high nondipolar content suggest regional electrical disparities in the ventricular recovery process. This may in part account for the high susceptibility of patients with LQTS to malignant arrhythmias. Circulation 74, No. 6, 1334-1345, 1986 THE ELECTROPHYSIOLOGIC alterations underlying the idiopathic long QT syndrome (LQTS) are still unknown. Clinical and experimental observations'-3 support the hypothesis that the most likely pathogenetic mechanism of LQTS is an imbalance in the sympathetic innervation of the heart. Specifically, the basic defect might be lower than normal right cardiac sympathetic activity with reflexly high activity of the left cardiac sympathetic nerves. These concepts are reflected in the current therapy for LQTS.4 The recovery process of myocardial fibers is markedly influenced by sympathetic activity and regional From the Unita di Studio delle Aritmie, Centro di Fisiologia Clinica e Ipertensione, Clinica Medica Generale, and Istituto di Scienze Mediche, Universita di Milano, Milan, Italy. Address for correspondence: Peter J. Schwartz, M.D.. Associate Professor of Medicine, Clinica Med. Generale-Pad. Sacco, Via F. Sforza 35, 20123 Milan, Italy. Received March 10, 1986; revision accepted July 31, 1986. 1334 variations in sympathetic drive result in local changes in recovery times.' This may alter the sequence of ventricular repolarization and provoke greater disparities in electrical potential among myocardial areas. A more diverse pattern of repolarization may produce a more complex, perhaps multipolar potential distribution at the body surface that would not be revealed by the conventional 12-lead electrocardiogram (ECG), but only by potential mapping of the entire chest. In patients with LQTS the standard ECG shows various nonspecific abnormalities of the T wave in addition to QT prolongation; in some cases the ECG may even be normal.4 Body surface potential maps (BSPMs), which have been proven to provide diagnostic information undetectable by the conventional 12lead ECG,6 1 might be a suitable method for revealing even small abnormalities of ventricular recovery in patients with LQTS. CIRCULATION by gest on A ril 0, 2017 http://ciajournals.org/ D ow nladed from DIAGNOSTIC METHODS-BODY SURFACE MAPPING The aim of this study was to d4 istic features of BSPMs of patier establish whether BSPMs would that could be related to an altered lar recovery and to electrical d favor development of ventricul liminary data on this subject 1