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Rautaharju et al's method of obviating the need for the central terminal by using lead I and lead II alone to derive the configuration of the other limb leads may, hopefully, finally determine whether the artifact produced by this central terminal is of practical importance or not. Louis A. Soloff, M.D. Temple University Health Sciences Center Philadelphia, PA 19140

REFERENCE 1. SOLOFF,L A: The relationship of lead II to lead I in posterior infarction and its bearing on the configuration of lead aVF. Am Heart J 40:839, 1950

The Effect of Ventricular Interpolation on Subsequent Atrioventricular Conduction I read with interest the study published in a recent issue of the J o u r n a l of Electrocardiology by J. P. Camous on the effect of ventricular interpolation on subsequent a t r i o v e n t r i c u l a r conduction. 1 We are pleased t h a t this study confirmed our previous observation of a reduction in the m i n i m u m H 1 - H 2 i n t e r v a l a c h i e v e d by t h i s method when compared with introduction of premature atrial contractions alone. 2 I agree with the authors t h a t this is an apparent facilitation since it has been said t h a t atrioventricular conduction cannot be more rapid t h a n normal; however, the expected degree of conduction delay m a y not occur. 3 The reduction in the m i n i m u m H1-H2 interval is due to a reduced A2-H2 delay when compared with A1-H1 following an interpolated ventricular beat. A2-H2 m a y be increased when compared with control beats, but the expected degree of A-V nodal delay does not occur although the effective refractory period of the A-V node m a y be prolonged as the authors have reported. The A2-H2 response using the extrastimulus technique m a y reflect the fact t h a t the effects of concealed conduction are transient so t h a t significant depression of A-V nodal conduction is observed in only the post-extrasystolic beat. Alternately, the relatively small A2-H2 change m a y be due to a form of facilitation as reported by Moore et al., who demonstrated t h a t concealed conduction of a ventricular depolarization m a y completely block A1 but allow conduction of a previously blocked A2. 3 Additional information might be obtained by J. ELECTROCARDIOLOGY, VOL. 14, NO. 3, 1981

comparing the effects of v e n t r i c u l a r and supraventricular interpolation using an interpolated atrial depolarization to prolong AV nodal delay of the subsequent atrial depolarization A1. If the m i n i m u m H1-H2 interval was reduced with vent r i c u l a r as opposed to a t r i a l interpolation, it would appear t h a t some form of facilitation had occurred. If the H1-H2 interval was similar using both methods, the opposite conclusion would be suggested. Joe K. Bissett, M.D., F.A.C.C. Professor of Medicine Chief, Cardiology Section University Hospital Little Rock, Arkansas 72205 REFERENCES 1. CAMOUS,J P, BAUDOUY,M, GUARINO,L, GIBELIN,P, PATOURAUX,G AND GUIRAN,J P: Effects of an interpolated premature ventricular contraction on the AV conduction of the subsequent premature atrial depolarization. An apparent facilitation. J Electrocardiol 13:353, 1980 2. BISSETT,J K, KANE,J J, DE SOYZA,N, MCCONNELL, J AND SCHMITT, N: Dual effects of concealed A-V nodal conduction in man. J Electrocardiol 10:5, 1977 3. MOORE,E N AND SPEAR, J F: Experimental studies on the facilitation of AV conduction by ectopic beats in dogs and rabbits. Circ Res 29:29, 1971

Spatial Cardiac Summary Vectors At the 30th a n n u a l scientific session of the American CoIlege of Cardiology last March in San Francisco, we presented a scientific exhibit entitled ' T o u r Spatial Cardiac S u m m a r y Vectors. ''1 Under the common denomination of spatial cardiac s u m m a r y vectors we presented Wilson's ventricular gradient, 2,3 Burger's polar vector, 4 and Zao's ventricular vector and polar gradient 5 in 3-D models determined with the F r a n k lead system from normal subjects and various cardiac patients. One of the important differences among these vectors is t h a t the ventricular gradient and the ventricular vector are both dependent on the time course of the ventricular electrical activities, whereas the polar vector and the polar gradient are independent of it. In the course of our investigation we observed the following regular occurrances which m a y ultimately be found useful in clinical medicine. The sensitivity of each s u m m a r y vector, measured by the degree of deviation of its spatial direction, or a change in its spatial magnitude, or both, is

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to an i d e n t i c a l change of the ventricular electrical activities. Among the anatomical, physiological and pathophysiological origins of such changes, the effects of clinical stress tests, stresses in aero-space medicine, and results after corrective surgery in congenital heart diseases, are to be emphasized for practical importance. We believe that determination of all s u m m a r y vectors (possibly included in computerized ECG & VCG analyses) m a y be likely to enhance diagnostic accuracy and prognostic value in individual cases. Wolfgang S. Zao, B.A., Research Fellow Peter Z. R. Zao, B.A., Research Fellow Research in Electrocardiology, Inc. P.O. Box 923-B San Diego, Calif. 92109

9 different

REFERENCES 1. ZAo, P Z R ANDZAO,W S: Four spatial cardiac summary vectors. A scientific exhibit. Prog 30th Ann Scient Session, Am Coll Cardiol 1981, p 119 2. WILSON, F N, MACLEOD, A G, BARKER, P S AND JOHNSTON, F D: The determination and the significance of the areas of the ventricular deflections of the electrocardiogram. Am Heart J 10:46, 1934 3. PLONSEY,R A: A contemporary view of the ventricular gradient of Wilson. J Electrocardiol 12:337, 1979 4. BURGER,H C AND VAANE,G P: A criterion characterizing the orientation of a vectorcardiogram in space. Am Heart J 56:29, 1958 5. ZAO,Z Z: The ventricular vector and the polar gradient. Cardiovasc Res 1:167, 1967

Body Surface Potential Mapping We observe closely the recent progress in body surface potential mapping. An article appearing in the current issue on this subject with the color prints 1 reminds me of a paper of similar nature published m a n y years ago. In 1951 we performed a study at the University of Paris, France 2 showing that the isopotential lines on the h u m a n face were created by the appearance of an intracranial bio-electrical dipole due to ocular movement (with its negative retinal charges) as a consequence of closing, opening or blinking the eyes. We also used color to portray the facial electrical field. An intense red spot represented the positive pole, dark blue the negative pole. As the potential gradually diminished with distance, the color of the red and blue areas between the isopotential lines slowly faded. Technology was of course more limited at that time. Except for a multi-channel EEG recorder, everything was done by hand, including the interpolation. Nevertheless, our study was an early day body surface potential mapping. Zang Z. Zao, M.D., F.A.C.C. San Diego, Calif. 92109 REFERENCES 1. LIEBMAN,J, THOMAS, C W, RUDY,Y ANDPLONSEY,R: Electrocardiographic Body Surface Potential Maps of the QRS of Normal Children. J Electrocardiol 14:249, 1981 2. ZAO,Z Z, GELBIN,R ANDRI~MONO,A: Le champ ~lectrique de l'oeil. Semaine des Hopitaux de Paris 28:1506, 1952

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