Left axis deviation. An electrocardiographic study with post-mortem correlation.

Left axis deviation: a reassessment.

“…32 If these observations are correct, then any leftward shift in the QRS axis with normal adult aging, including left anterior hemiblock, would represent part of a spectrum of unifascicular conduction delay.32 In the study of 8000 Japanese-American men referred to In discussing the sequence or coincidence of atherosclerotic coronary artery disease and left axis deviation, electrocardiographic-pathologic correlative studies have identified frequent myocardial fibrosis and infarction attributed to coronary artery disease. 14, 16,27,28,30 It is rational to infer, in this setting, that ischemic heart disease in its own right causes fibrosis that partially or completely interrupts conduction in one or more fascicles. This mechanism presupposes a decrease in flow via the coronary circulation to or relatively near specialized atrioventricular conduction pathways, especially the infranodal system.…”

“…An electrocardiographic-necropsy study also found that left axis deviation was more frequent with anterolateral infarction, but the incidence of inferior infarction was not low, although the majority of patients with inferior infarction had involvement of at least some portion of the anterior wall of the left ventricle. 30 Although dual primary blood supply to the left anterior fascicle sets the stage for potential left anterior hemiblock with either anterolateral or in-ferior infarction, the axis shifts in patients with inferior infarcts were originally attributed to loss of diaphragmatic electrical forces, leaving the superior and leftward forces unopposed.47 It has been reaffirmed that a large inferior infarction can cause a left and superior QRS axis of less than -30°in the absence of left anterior hemiblock.4" However, the electrocardiographic recognition of inferior infarction in the presence of left anterior hemiblock is difficult, and diagnostic accuracy benefits from vectorcardiographic analysis. 49 Is Left ventricular hypertrophy has long been considered an important cause of left axis deviation.…”

“…58 Focal anatomic lesions caused by several cardiac disorders can interrupt conduction in the left anterior fascicle. For example, this mechanism is believed to be the basis for left axis deviation in congestive cardiomyopathies (acute, chronic or healed) and restrictive cardiomyopathies (infiltrative diseases).28 30 Left axis deviation caused by left anterior hemiblock in certain neuromuscular disorders should be considered separately. In myotonic muscular dystrophy, for example, the most common infranodal electrocardiographic abnormality is defective conduction in the left bundle branch systemleft bundle branch block or left axis deviation"69 The dominant site of cardiac involvement appears to be the specialized conduction systemsinus node, atrioventricular node, infra-His and His-Purkinje system,60 analogous to disorders of impulse formation and conduction in much older subjects.6' Thus, the primary cardiac disturbancepremature degenerative disease of the cardiac fibroskeletonmay represent another of the non-myopathic manifestations of myotonic dystrophy, and may reveal itself in part as left anterior hemiblock.…”

“…28 Other investigators soon considered the gradual leftward migration of the frontal QRS axis, concluding that this electrocardiographic trend was a common sequel of aging, independent of the population prevalence of coronary atherosclerosis.29 Soon thereafter, a study of 353 necropsy patients ages 19-94 years indicated that the lesion causing left axis deviation in most cases involved the anterior-superior division of the left bundle branch. 30 In 1969 and 1970, the publications of Rosenbaum and colleagues stimulated interest in the three main fascicles of the intraventricular conduction systemthe right bundle branch and two divisions of the left.4-7 31 The concept of the hemiblocks was appealing, and the terms left anterior hemiblock, left posterior hemiblock, and trifascicular block were introduced and widely used. Different combinations and degrees of bifascicular and trifascicular block were formulated, and it was pointed out that each division of the left bundle branch could separately exhibit first-, second-, or third-degree block.…”

Significance of left anterior hemiblock.

“…Grant (1956) stressed the value of deviation of the mean manifest QRS axis in the frontal plane to the left beyond -30°as a sign of cardiac abnormality and postulated that left axis deviation signifies a conduction disturbance in the anterolateral wall of the left ventricle. On the basis of experimental evidence (Uhley and Rivkin, 1964;Watt et al, 1965;Rosenbaum et al, 1970), selected surgical experience (Samson and Bruce, 1962;Wigle et al, 1963;Kulbertus et al, 1969), electrocardiographicpathological-clinical correlative studies (Davies and Evans, 1960;Curd et al, 1961;Eliot et al, 1963;Banta et al, 1964;Come et al, 1965;Pryor and Blount, 1966;Bahl et al, 1969;Rosenbaum et al, 1970), and study of cases of intermittent left axis deviation (Rosenbaum et al, 1969), investigators concluded that left axis deviation was usually the 'This work was supported by the Great-West Life Assurance Company.…”