The relationship of marked left axis deviation to the risk of ischemic heart disease

The purpose of this study was to examine the value of marked left axis deviation in men without apparent heart disease in the assessment of ischemic heart disease risk. In the Manitoba Study, a cohort of 3983 men who were predominantly between 25 to 34 yr of age at entry in 1948, 247 cases of marked left axis deviation (mean frontal plane QRS vector of -45 degrees to -90 degrees) were identified at a mean age of 46.1 +/- 0.7 (+/- 1 SEM) yr with a mean follow-up of 12.1 +/- 0.6 yr. The results were that the development of left axis deviation in men 40 to 59 yr of age, independent of blood pressure is a significant predictor of ischemic heart disease events that are usually manifest 5 to 10 yr after the onset of this electrocardiographic abnormality. Subsets of QRS variables examined to identify cases with different degrees of ischemic heart disease risk revealed that neither Q waves in leads I or aVL, or QRS duration or actual frontal plane QRS vector identified groups with different ischemic heart disease risk. However, subsets of age (less than 40 and 60 yr or greater) perhaps reflecting different etiologies of marked left axis deviation and previous electrocardiographic findings (S1S2S3 pattern) identify a low risk group.