19. Rabkin, S.W., Mathewson, F.A.L., Tate, R.B.: Natural history of marked left axis deviation (left anterior hemi-block): Am J Cardiol 43: 605-611, 1979.
The purpose of this study was to examine several electrocardiographic variables that may be associated with the development of marked left axis deviation (AQRS-45 degrees to -90 degrees) in men free of ischemic heart disease and to determine whether left axis deviation is associated with an increased probability of developing other conduction disturbances. During the 28 year observation period in the Manitoba Study cohort of 3,983 men, 222 new cases of marked left axis deviation were noted in the absence of heart disease. The majority, 81.5 percent (181 men), had the same Q waves or absence of Q waves in leads 1 or aVL, or both, before and on detection of left axis deviation, 10.4 percent (23 men) had new Q waves or increased width of previous Q waves, and 8.1 percent (18 men) had Q waves that disappeared or became smaller. Not all cases of left axis deviation resulted from a superior and leftward movement of AQRS; 10.4 percent (23 men) had an indeterminate AQRS on entry due to an S1S2S3 pattern. Left axis deviation developed in a significantly (P<0.01) larger proportion of men with S1S2S3 on entry (44 percent, 23 of 52 men) than of those without S1S2S3 on entry (5.1 percent, 199 of 3,906 men).
Of the 247 cases of left axis deviation, 25 were detected on and 222 after entry into the study. Complete right bundle branch block developed in 2.4 percent of these men (6 of 247), a larger proportion than those without left axis deviation. In the absence of development of intercurrent ischemic heart disease, complete left bundle branch block developed in 0.8 percent (two men), and none had complete atrioventricular block. Men with an S1S2S3 pattern on entry or with left axis deviation before age 40 years comprised a subgroup that did not develop other conduction disturbances. The presence or absence of Q waves in lead I or aVL, or both, did not influence the association between left axis deviation and right bundle branch block. Therefore (1) the development of left axis deviation was not associated with a significant change in Q waves in leads 1 or aVL, or both; (2) an indeterminate AQRS from an S1S2S3 pattern is significantly associated with the subsequent development of left axis deviation; and (3) in the absence of clinically apparent heart disease, the likelihood of the development of complete right bundle branch block is increased slightly in men with marked left axis deviation.