Manitoba Follow-up Study Research Articles

The Effect of Age on Risk Factors for Ischemic Heart Disease: The Manitoba Follow-Up Study, 1948–1993

PURPOSE: The purpose of this paper is to determine the age-specific relationships between risk factors at age 40 through 75 years and ischemic heart disease (IHD), and to determine the effects of aging on these relationships in a cohort of 3983 Canadian males. METHODS: The Manitoba Follow-Up Study is the prospective investigation of cardiovascular disease as it develops in a cohort of 3983 young men. Over a period of 45 years, from 1948 to 1993, 1094 study members (27%) developed clinical evidence of IHD. Blood pressure, body weight, smoking, and presence of diabetes mellitus have been recorded at regular intervals throughout the follow-up period. Using measurements from examinations every 5 years between ages 40 and 75 years, age-specific Cox proportional hazard models were fit to relate these risk factors to IHD. RESULTS: The adjusted relative risk of IHD for systolic blood pressure, diastolic blood pressure and smoking were found to significantly ( p < 0.001) decline with advancing age. The adjusted relative risk for body mass index and presence of diabetes mellitus for ischemic heart disease did not vary with age ( p > 0.05). After age 65 years, these risk factors were of little value for the prediction of IHD. CONCLUSIONS: The relative risk and statistical significance of blood pressure and smoking, as risk factors for IHD, decline with age.

The natural history of atrial fibrillation: Incidence, risk factors, and prognosis in the manitoba follow-up study: A.D. Krahn, J. Manfreda, R.B. Tate, F.A.L Mathewson, T.E. Cuddy. Manitoba University Follow-Up Study, Winnipeg, Canada. Am J Med 1995;98:476-84.

The natural history of atrial fibrillation: Incidence, risk factors, and prognosis in the manitoba follow-up study: A.D. Krahn, J. Manfreda, R.B. Tate, F.A.L Mathewson, T.E. Cuddy. Manitoba University Follow-Up Study, Winnipeg, Canada. Am J Med 1995;98:476-84.

Tracking of Blood Pressure over a 40-Year Period in the University of Manitoba Follow-up Study, 1948–1988

High blood pressure is a well-recognized, modifiable, cardiovascular disease risk factor. Tracking of blood pressure was examined in the University of Manitoba Follow-up Study, a cohort of 3,983 men followed over a 40-year period, between 1948 and 1988. Blood pressure measurements recorded over time in these men, prior to the development of ischemic heart disease, were used in this analysis. Two approaches to tracking were used; correlation analysis and the quantification of the likelihood for a man whose blood pressure was in either the top or bottom quintile to remain in the extreme end of the distribution at later measurement. For ages 25-75 years and for intervals between blood pressure measurement ranging from 5 to 35 years, significant evidence for tracking was found. The strongest evidence for tracking was in middle age, 45-55 years. Strength of tracking decreased with increasing time between measurements. This analysis suggests that men at highest risk for hypertension can be identified at a young age. Hence, strategies for prevention of cardiovascular complications can be targeted in early adulthood.

The natural history of atrial fibrillation: Incidence, risk factors, and prognosis in the manitoba follow-up study

Atrial fibrillation is a common arrhythmia associated with increased cardiovascular morbidity and mortality. This study was undertaken to identify the natural history of this condition, including risk factors for its development, and outcome. The incidence of atrial fibrillation among 3,983 male air crew recruits observed continuously for 44 years was calculated based on person-years of observation. Age and 23 variables were examined to identify risk factors for atrial fibrillation. Controlling for age and 9 prognostic variables, the effect of atrial fibrillation on 8 outcomes was examined. Analysis of risk factors for atrial fibrillation and outcome after atrial fibrillation was based on a Cox proportional hazard model using time-dependent covariates. Of the 3,983 study members, 299 (7.5%) developed atrial fibrillation during 154,131 person-years of observation. The incidence rose with age from less than 0.5 per 1,000 person-years before age 50 to 9.7 per 1,000 person-years after age 70. Risk for atrial fibrillation was increased with myocardial infarction (relative risk [RR] 3.62), angina (RR 2.84), and ST-T wave abnormalities in the absence of ischemic heart disease (RR 2.21). The RR for atrial fibrillation was strongest at the onset of ischemic heart disease and diminished over time. The rate of atrial fibrillation was 1.42 times increased in men with a history of hypertension. Congestive heart failure, valvular heart disease, and cardiomyopathy were important but uncommon risk factors. Atrial fibrillation independently increased the risk for stroke (RR 2.07) and congestive heart failure (RR 2.98). Total mortality rate was increased 1.31 times; cardiovascular mortality including and excluding fatal stroke were also increased (RR 1.41 and 1.37, respectively). The incidence of atrial fibrillation in men increases with advancing age. Clinical cardiac abnormalities, particularly recent ischemic heart disease and hypertension, are strongly associated with increased risk for atrial fibrillation. Atrial fibrillation increases morbidity and mortality, but the magnitude of the increase may be less than previously reported.

Evidence that height is an independent risk factor for coronary artery disease (the Manitoba follow-up study)

In conclusion, height is a risk factor for CAD. A similar trend was noted for cardiovascular and total mortality. The mechanism underlying this association may involve both genetic and environmental factors.

The Natural History of Electrocardiographic Preexcitation in Men

To examine the natural history of preexcitation occurring on the routine electrocardiogram (ECG). A longitudinal cohort study of 3983 originally healthy men followed prospectively for 40 years. Free-living (community-dwelling) study members residing predominantly in Canada. Nineteen male study members with preexcitation occurring during routine examination in the 40-year follow-up of the Manitoba Follow-up Study. Routinely requested clinical examinations and ECGs, supplemented by information supplied by the study member or his physician. Ten study members were found to have preexcitation at enrollment, for a prevalence of 2.5 per 1000 (95% CI, 1.2 to 4.6). A delta wave was first detected during follow-up in an additional nine study members. Seventeen of 19 study members did not have the delta wave at some later time, and preexcitation was intermittently present in most of these members. Over time there was a loss of preexcitation, with 15 of 19 study members no longer exhibiting a delta wave by the end of follow-up. Five of 11 study members with symptoms had physician confirmation of an arrhythmia. Fourteen study members remain alive, and none of the five deaths was attributed to preexcitation. Preexcitation found on routine ECG in our originally healthy male study group did not confer excess morbidity or mortality, even in those study members who developed symptomatic arrhythmias. Most preexcitation was intermittent and disappeared over time.

Blood pressure and body mass index patterns—A longitudinal study

The patterns of longitudinal changes in systolic blood pressure (SBP), diastolic blood pressure (DBP) and body mass index ( BMI = weight height 2 ) are explored on 3054 male subjects who remained alive and free of ischemie heart disease and/or stroke after 27 yr of follow-up in the Manitoba Follow-up Study. BMI tends to increase during adulthood, maintains in middle ages, and drops in old ages. With moderate acceleration, SBP continues to rise with age. DBP tends to rise with age until mid-fifties and then levels off. The correlations of age with BMI changes over time from significant positive at entry to significant negative by the end of the study period. The correlation of age with SBP changes from non-significant to highly significant positive; and with DBP, the correlation is significant but increases only in the first 10 yr, after which it fluctuates and decreases. These findings have implications on the relative importance of BMI, SBP andd DBP as coronary risk factors in younger and older men. Despite the high variability of blood pressure and the regression toward the mean phenomenon, BMI, SBP and DBP tend to retain their relative positions in their own distributions even after 25 yr. The correlation between the initial and later readings decreases with time but remains highly significant. The correlation between two readings five years apart is stronger in older men than in younger men. The future levels of blood pressure are predictable not only by its own attained levels, but also by age and BMI. Inclusion of all three of these factors improves the prediction. The overall distribution of the linear rate of change in BMI is bimodal, whereas that of SBP and DBP is unimodal. The differences in age does not account for these distributions, because similar unimodalities are also observed in men of the same single age. The variations in the rate of rise for men of the same single age indicate that factors other than age are responsible. Strong positive association between age and the mean linear rate of rise also indicate that the responsible factors are acting more effectively in older men. On the rate of rise, analytical results support the importance of age, not the attained level of blood pressure. The attained level of BMI, though strongly associated with the levels of blood pressure, is not related to the rate of change in blood pressure. The change of BMI, however, is strongly associated with those of blood pressure. In young men, the change of BMI is similarly associated with those of SBP and DBP; in older men, it is more related to that of DBP. As a mean of controlling high blood pressure, early prevention of weight gain is suggested. Although SBP and DBP are highly correlated and their correlation improves with time, evidence shows that they do not have the same pattern of change: SBP follows a fluctuating upward trend while DBP follows a quadratic trend. These observations confirm the findings from cross-sectional studies. By using orthogonal transformation, the parameters of an orthogonal polynomial fitted exactly to each individual are analyzed. This method of analysis gives similar results as obtained by using other methods and is shown to be simple, informative and effective in describing individual patterns of change over time, suggesting evidence of etiological interest and establishing relationships between trends of change.