IN DEFENCE OF THE INTRINSIC DEFLECTION

Abstract

The existence of a component of the epicardial electrocardiogram that can be properly called the intrinsic deflection, to use Lewis's term (Lewis and Rothschild, 1915), is a matter of both im-portance and dispute. Whether or not intrinsicoid deflections (MacLeod et al., 1930) occur in prncordial leads is of considerable interest to vectorcardiographers, most of whom base their work on the belief that events represented in the electrocardiogram find themselves, to a greater or lesser extent, represented in the corresponding vectorcardiogram. The significance of correlation between the ECG and the VCG has been pointed out by Duchosal and Sulzer (1949). The introduction of more advanced vectorcardiographic lead systems has improved such correlation (Sano et al., 1959) and certain cancellation experiments have indicated that on theoretical grounds, with accurate image space data for the individual examined, almost perfect correlation might be achieved (Frank, 1959). This view has not, however, been universally accepted; for example, McFee and Parungao (1959) have cast some doubt upon previous interpretations of cancellation experiments. Whether all significant electrocardiographic data provided by the standard 12-lead electrocardiogram were present in the X, Y, Z-orthocardiograms obtained from the SVEC III lead system (Schmitt and Simonson, 1955), was recently investigated in an interesting manner by Pipberger et al. (1961) who used a lead resolver to reconstruct the 12-lead electrocardiogram from the 3 X, Y, Z-orthocardio-grams and presented the standard 12-lead and the reconstructed 12-lead electrocardiograms for clinical interpretation. Differences were insignificant. This would suggest that the existence of an intrinsicoid deflection in prwcordial leads is unlikely. That the concept of the intrinsic deflection itself was also in error was given direct experimental support by Sano et al. (1956), who compared the intrinsic deflection in direct leads taken from the frog's heart with the upstroke of the transmembrane potential curve simultaneously obtained from an intracellular microelectrode, recording from the same point of the heart surface. These workers took the point of inflection of the upstroke of the monophasic curve obtained from an intracellular electrode to indicate activation of the area beneath a surrounding ring electrode that recorded the electrocardiogram containing the "intrinsic deflection". A complete lack of apparent correlation was found and this was taken to indicate that the concept ofintrinsic deflection as originally proposed by Lewis was spurious. Because it would seem unarguable that the transmembrane potential curve obtained from an intracellular microelectrode does in fact indicate activation of the cell penetrated, the method employed by Sano et al. (1956) to prove the intrinsic deflection appears unassailable. Furthermore, so important was their finding that it appeared worthy of confirmation