The Significance of Axis Deviation in the Human Electrocardiogram

Constructing Adult Zebrafish Einthoven’s Triangle to Define Electrical Heart Axes

“…In this study, we found the mean main axis of normal adult humans to be +51 • (Quadrant I, Figure 3D, left panel). Our finding is in good agreement with extensive literature reports of the mean human main axis value of +60 • within the vast normal range between −30 • and +105 • (Proger and Davis, 1930;Hiss et al, 1960;Simonson, 1972), which encompasses the entire Cabrera Quadrant I plus two adjacent wedges in Quadrants IV and II. This extensive normal range reflects, apart from biological variation across hearts, a counterclockwise shift on the Cabrera system in the same hearts with age such that the main axis orients more inferiorly (or rightward of +90 • ) in childhood/early adulthood and more superiorly (or leftward of 0 • ) in late adulthood (Figure 1C, left panel).…”

“…Thus, electrical axis in the frontal plane is the vector sum of at least two cardiac vector projections onto two Einthoven lead axes, which define the frontal plane (Dieuaide, 1921). The direction of electrical axis in the frontal plane is expressed in terms of an angle (angle α) that it makes with the horizontal, which is also lead-I axis or 0 • in the Cabrera system (Figure 1C; Dieuaide, 1921;Proger and Davis, 1930;Ferrer, 1972;Surawicz and Knilans, 2008).…”

“…First, as mentioned above, zebrafish cannot tolerate simultaneous ECG recording from three bipolar leads. Second, bipolar triple-lead ECG is unnecessary because construction of Einthoven's triangle and calculation of electrical heart axes in the frontal plane requires simultaneous recording from just two Einthoven leads (Proger and Davis, 1930;Ferrer, 1972;Surawicz and Knilans, 2008). Third, if needed for other purposes, advanced software allows robust derivation of simultaneous data from the third unrecorded Einthoven lead using simultaneous recordings from the other two Einthoven leads.…”

“…human main axis (i.e., QRS axis in the frontal plane), introduced by Einthoven as angle α, has had the highest pathophysiological relevance (Proger and Davis, 1930). Indeed, determination of human P-QRS-T frontal axes has become so entrenched in routine clinical practice that to date, twelve-lead ECG data acquisition software is readily equipped to calculate all three electrical axes automatically and precisely for each recording.…”

“…The diagnostic significance of frontal axis deviation from the normal range (Figure 1C, left panel) allows clinical recognition of intraventricular conduction defects, chamber enlargement/hypertrophy, certain congenital heart defects, and even acute or chronic lung disease in the proper clinical settings (Dieuaide, 1921;Proger and Davis, 1930;Ferrer, 1972;Surawicz and Knilans, 2008;Pérez-Riera et al, 2020). For example, left axis deviation (between −30 • and −90 • , i.e., most of Quadrant IV) may signal acquired or congenital cardiac structural abnormalities (such as left ventricular hypertrophy, inferior myocardial infarction, ostium primum atrial septal defect, or endocardial cushion defect) or cardiac conduction abnormalities (such as left anterior fascicular block or left bundle branch block).…”