346 HANDBOOK OF PHYSIOLOGY -^ CIRCULATION I 



leads \'i to Vj and by local leads \'ery near to the 

 heart. 



SPECIAL LEADS. LEADS FROM THE SURFACE AND THE 



INTERIOR OF THE HEART. Because of the difficulties in 

 getting "locar" recordings, many attempts have been 

 made to bring electrodes as near as possible to the 

 heart. One of the earliest attempts of this kind has been 

 the esophageal lead (96). A small electrode is swal- 

 lowed by the patient and, by virtue of the calibrated 

 length of the attached wire, its position relative to the 

 heart is well known. The second electrode is usually 

 a CT. The results have been reviewed by various 

 authors and are of more clinical than theoretical 

 interest (10, 61, 91, 289). The EGG has also been 

 recorded from the stomach (244, 274). The lead 

 fields of the esophageal electrodes have been in- 

 vestigated, so that an explanation of the curves can 

 be given (131, 352). This explanation is more or less 

 identical with that of the other leads near the heart 

 and shall be given in connection with them. 



The intrapulmonary leads, introduced into the 

 lung by a bronchial catheter (216, 402), show results 

 similar to those from the esophagus. If the electrode 

 positions are mapped in the fashion of figure 13, the 

 intrathoracic derivations fit perfectly well into the 

 picture, their lead lines (electrode to heart center) 

 being drawn and compared with the records of the 

 neighboring lead lines from the chest surface (367). 

 The onl\- ad\antage of electrodes like these is the 

 high atrial potential, so that both from intrapul- 

 monary and esophageal leads abnormalities in the 

 atrial rhythm are optimally recorded (515). 



The theory of such leads can be developed most 

 clearly using the patterns of direct surface electrodes 

 of the heart. Many electrophysiologists have experi- 

 mented with such electrodes on animals. In the last 

 few vears, surface electrodes have been used even in 

 man, during open-chest operations (30, 67, 95, 278, 

 279). The procedure of putting electrodes on the 

 heart's surface in animals has been commonly done 

 by electrophysiologists for a long time. The inter- 

 pretation of such curves is much more complicated 

 than most of these authors apparently realize. We 

 therefore discuss their theory in common with the 

 theory of all leads deriving potentials in direct contact 

 with mvocardial fiijers. 



7. LEADS IN DIRECT CONTACT WITH THE MYOCARDIUM 



Whenever one or two of the exploring eleclrodes 

 touch the surface of the heart or penetrate into its 



FIG. 28. Action potential from the surface of a dog's ventricle 

 with close bipolar microelectrodes of a distance of 0.2 mm. The 

 left record (R wave) is taken with low sensiti\ity (gauge to the 

 left) and high speed, the right with high sensitivity and lower 

 speed, to show the T wave. The QRS in the right record 

 consists of some short but low extrinsic potentials, too small to 

 be seen in the left record. The areas of R and T are nearly 

 equal (qo and 85 microvoltsec); T is discordant. R (left record) 

 is recorded as inverted, for technical experimental reasons. 

 [From Haas el al. (234).] 



muscular wall, a maximum of "proximity"' potentials 

 is recorded. The theory of such direct leads is of 

 importance because records from such leads have 

 loeen used to determine the spread of the excitation 

 process. 



First we shall consider the case of a bipolar elec- 

 trode system with a rather narrow distance. Such a 

 pair of electrodes records the potential gradient of the 

 resultant electrical field at its site. The resultant field 

 is preferably composed of flow lines stemming from 

 the very nearest myocardial fibers; but flow lines 

 from inore remote fibers do interfere in a confusing 

 manner and can never be completely eliminated. If 

 the electrode distance is very short (less than i mm) 

 and the contact to the myocardium very close, the 

 amount of potential arriving from remote fibers is 

 quite small. This can be demonstrated by the poten- 

 tial pattern. Figure 28 shows a record taken by such 

 electrodes. The total duration of the R wave is nearly 

 identical with the duration of the upstroke in mono- 

 phasic action potentials recorded by intracellular 

 electrodes (412). If the fibers were isolated in the air, 

 the bipolar derivation would yield the first derivative 

 of the monophasic action potential. But even if the 

 electrodes are put directly on the epicardium, the 

 distance to the next fiber is of the order of magnitude 

 of 50H, and the potential recorded is distorted by the 

 flow lines of the developed electrical field. As figure 

 29 shows, the arrangement of fibers near the surface 

 is strongly asymmetrical. If a pair of electrodes is 

 put on the surface, the recorded potential will be 

 triphasic, a first deflection downward indicating that 

 the dipole is approaching the electrodes, a second 

 main and upward deflection indicating the passage 



