How Control of Hypertension Affects Stroke Risk
The risk of suffering stroke, stratified by patient age and health status, has been well defined for decades. Look back at the Framington study data from the 1990s for example. The bottom line is that the odds average about 0.5%/year in your 50s through to 2.5%/year in your 80s, but whether or not you are in good shape matters a great deal when it comes to where you sit in relation to the average. Hypertension, raised blood pressure, is important in determining stroke risk for the obvious reasons: greater blood pressure means a greater chance of rupturing weakened blood vessels or atherosclerotic plaque. The reason why control of blood pressure can increase life expectancy is by reducing the risk of this and other forms of pressure damage throughout the body.
Data from the Framingham Study suggests that hypertension doubles the risk of stroke in older adults age 65-94, with a relative risk of 1.9 in men and 2.3 in women. While hypertension treatment has been shown to reduce stroke risk, it is less clear when stroke reduction occurs. In contrast, the harms of hypertension treatment, which include orthostatic hypotension, syncope, falls, and electrolyte abnormalities, appear to occur soon after treatment initiation. For example, the risk of falls and fractures was found to be increased in the first 7 to 45 days after the initiation of antihypertensive medications. Thus, while hypertension treatment decreases stroke risk over time, it can also lead to an increased risk for adverse effects.
To help clinicians identify, which patients are most likely to benefit from hypertension treatment (and which patients are more likely to be harmed), our objective was to determine the TTB of hypertension treatment for the primary prevention of stroke. We conducted a survival meta-analysis of major randomized clinical trials to determine the time to benefit (TTB) for various stroke absolute risk reduction (ARR) thresholds.
We determined that 200 adults aged ≥65 years would need to be treated for 1.7 years to avoid 1 stroke (ARR = 0.005). Since the overwhelming majority of older adults have a life expectancy of more than 1.7 years, these results suggest that almost all older adults with hypertension would benefit from treatment. We found substantial heterogeneity across studies suggesting that for older adults with poorly controlled hypertension, systolic blood pressure (SPB) higher than 190 mmHg, the TTB to prevent 1 stroke for 200 persons treated is likely substantially shorter than 1.7 years. Conversely, for older adults with relatively well-controlled hypertension (i.e., SBP less than 150 mmHg), the TTB to prevent 1 stroke for 200 persons treated is likely substantially longer than 1.7 years.