Effect of time since onset of risk factors on the occurrence of ischemic stroke.
OBJECTIVE
To determine the effect of time since onset of risk factors on the modeling of risk factors for ischemic stroke.


METHODS
The resources of the Rochester Epidemiology Project allowed identification of the 1,397 incident cases of ischemic stroke and age- and sex-matched control subjects from the population for 1970 through 1989. These cases and controls permitted the development of a multiple conditional logistic regression model to estimate the odds ratios of ischemic stroke for various risk factors. The time since onset variables for each risk factor were then added to the model to determine which were significant and to assess their impact on variables in the model.


RESULTS
The time since onset variables for congestive heart failure and TIA were the only variables of this type included in the resultant model. Each showed the highest risk for stroke soon after the onset of the risk factor. In addition, the influence of congestive heart failure was higher at younger ages. Hypertension (with or without left ventricular hypertrophy) increases the risk for stroke but has a diminishing influence with increasing age. In addition, persons with left ventricular hypertrophy are at a higher risk than those with hypertension alone, although this difference also decreases with age. The time since onset variables pertaining to systolic hypertension at 140 to 159 mm Hg, 160 to 179 mm Hg, and > or =180 mm Hg were not significant in any analysis.


CONCLUSIONS
TIA and congestive heart failure were the only risk factors for stroke for which time since onset was significant in the model for predicting ischemic stroke.
Whisnant
J P
JP
Department of Health Sciences Research, Mayo Clinic, Rochester, MN 55905, USA. whisnant.jack@mayo.edu
Wiebers
D O
DO
O'Fallon
W M
WM
Sicks
J D
JD
Frye
R L
RL
D006333:Heart Failure / Q000150:complications; D006801:Humans; D006973:Hypertension / Q000150:complications; D002546:Ischemic Attack, Transient / Q000150:complications; D016017:Odds Ratio; D012307:Risk Factors; D020521:Stroke / Q000209:etiology*; D013997:Time Factors