The relation of unipolar limb leads to precordial and esophageal leads

Abstract Multiple semidirect leads from the thorax and esophagus along with the augmented unipolar limb leads were obtained in normal subjects in the recumbent and erect postures during quiet breathing and sometimes during forced expiration and full inspiration as well. If a sufficient number of semidirect leads were taken, the counterpart of the QRS-T pattern of each of the unipolar limb leads could be demonstrated in a precordial or esophageal lead and a pathway along which the QRS-T complex maintained a fairly uniform configuration could be found bridging the gap between the extremity and the point on the thorax near the heart where the corresponding semidirect lead was obtained. From the anatomic position of the corresponding semidirect lead and of the pathway leading into the extremity, it was concluded that the potential variations of a given extremity are dominated by those of the epicardial surface which faces toward that extremity. The findings are presented graphically for five subjects, who were selected as collectively illustrative of the normal variations in QRS-T pattern in unipolar limb leads. The illustrations include the marked variations which may be produced by postural or respiratory shifts in cardiac position. The QRS-T pattern in each of the unipolar limb leads was classified in accordance with the corresponding semidirect lead. The findings in Lead aV L were classified into the five basic patterns: (1) QRS-T resembling that in semidirect leads over the anterolateral aspect of the left ventricle (Leads V 5 and V 6 ) and characterized by a prominent R with or without a small Q and/or S, preceded by an upright P and followed by an upright T; (2) QRS-T resembling that in semidirect leads over the anterior aspect of the right ventricle (Leads V 1 and V 2 ) and characterized by a small R 1 relatively deep S, and by a T wave which is usually upright, but occasionally flattened or shallowly inverted; (3) QRS-T resembling that in precordial leads at the transitional zone (generally Lead V 3 ) and characterized by a QRS of low voltage, consisting of two or more phases of approximately equal amplitude; (4) QRS-T resembling that in esophageal leads opposite the posterior aspect of the left ventricle and characterized by a relatively small Q and tall R preceded by an inverted P wave and followed by an upright, flattened, or inverted T; and (5) QRS-T resembling that in esophageal leads from behind or above the left atrium and characterized by a relatively deep and prolonged Q and small late R, preceded by an inverted P and followed by an inverted T. The findings in Lead aV F usually corresponded fairly closely with those in leads from the lower esophagus and stomach and were classifiable into four basic patterns: (a) QRS-T resembling that in precordial leads over the right ventricle (Leads V 1 and V 2 ) which was associated with Pattern 1 in aV L as a manifestation of counterclockwise rotation into a horizontal position; (b) QRS-T resembling that in leads at the transitional zone, which was also associated with Pattern 1 in aV L as a manifestation of less counterclockwise rotation into a semihorizontal position; (c) QRS-T resembling that in leads from the apical portion of the left ventricle (Leads V 5 and V 6 and lower esophageal leads) which might be found in association with any of the five patterns in Lead aV L , depending upon the degree of rotation on the anteroposterior, longitudinal, and transverse axes into an intermediate, semivertical, or vertical position; and (d) QRS-T resembling that in esophageal leads opposite the posterobasal aspect of the left ventricle, characterized by a distinct Q, tall R, isoelectric to slightly depressed RS-T, inverted, diphasic, or flattened T, and accompanied by Patterns 2 or 5 in Lead aV L , depending mainly upon the rotation on the longitudinal axis. While the pattern in Leads aV L and aV F is subject to marked variation due to the mobility of the ventricles in the left chest, the pattern in Lead aV R is more uniform due to the fixation of the base of the heart, which faces toward the right arm, by the attachments to the great vessels. The major deflection of ventricular origin in Lead aV R is derived from the potential variations of the endocardial surfaces and cavities of the two ventricles and consists of a downward QRS and inverted T wave. Minor variations may occur in Lead aV R , consisting of either or both of the following: (1) a minute initial R transmitted from the epicardial surface of the right ventricle across the anterior chest wall; or (2) a late R which tends to be transmitted from the posterobasal surface of the left ventricle across the posterior chest wall when the heart is rotated backward on a transverse axis. The standard limb leads have been analyzed in terms of unipolar limb leads. If unipolar limb leads and multiple precordial leads are available, standard leads are superfluous, since they contribute no information that cannot be derived more precisely from the unipolar limb leads, studied in conjunction with multiple precordial leads.