Journal of Electrocardiology Vol. 32 Supplement 1999 Are Additional Right Precordial and Left Posterior ECG Leads Useful for the Diagnosis of Right Ventricular Infarct and Posterior Infarct? Also a Plea for the Revival of Vectorcardiography Gerard van Herpen, MD, PhD, Jan A. Kors, PhD, and Bob J.A. Schijvenaars, MSc It seems that over the last 2 decades, roughly, some of the luster of electrocardiography has faded, that some disenchantment has crept into the minds and hearts of the flock of the electrocardiographic faithful. "What's wrong with electrocardiography?" is the self-conscious question asked by Mirvis (1), and a defiant bugle call to "concerted action for change" in dealing with electrocardiography is sounded by Selvester (2). There have been "actions for change." Heart rate variability and time-averaged signals were once embraced but have dropped in public favor and have not acquired a place in routine electrocardi- ography. As to QT dispersion, it seems to us a crowded dead-end from which one should back out as soon as possible (3,4). The use of extra right and left posterior chest leads to improve the diagnosis of right ventricular and true posterior infarction (5-7) or of coronary heart disease in general (8) seems to be the next action for change. The idea is old, but of late has again found convinced proponents and fits in with the thinking underlying body surface potential mapping (BSPM)--still another infant fathered by From the Institute of Medical Informatics, Faculty of Medicine and Health Sciences, Erasmus University, Rotterdam, The Netherlands. Reprint requests: Gerard van Herpen, MD, PhD, Institute of Medical Informatics, Faculty of Medicine and Health Sciences, Erasmus University, P.O. Box 1738, 3000 DR Rotterdam, The Netherlands. Copyright © 1999 by Churchill Livingstone ® 0022-0736/99/320S-0011 $10.00/0 the desire to expand the limits of electrocardiogra- phy. This hope is not without justification. BSPMs contain all the external information one could possibly collect about the electrical activity of the heart. The standard so-called 12-lead electrocardio- gram (ECG) offers only a limited sample of that information. Minimum Electrode Set The question is how many and which elec- trodes-or, vicariously, leads--are necessary and sufficient (ie, collect all information desired for a specific purpose without undue redundancy). The problem can be phrased as follows: Find the limited set K of leads Lk(t ) from which every other body surface lead Sj(t) can be estimated to within an error at noise level, using linear transformations with coefficients ajk, If the set has to satisfy any arbitrary person p in a population, the transforma- tion appears in its general form as: Spj(t) = ~ajkLkp(t) k-I where the closeness of the approximation can be expressed by a resynthesis index (R) (9): RMS(S - S) R=I RMS(S) 51