28 August 2020

Assessing Ischemic Stroke Risk

Welcome back. Years ago, I blogged how grateful I was that, when I had trouble deciding whether to leave academia for government, I had help from above. Oh, not that above, just the ionosphere and a roving car radio station (see Decision-Making Time).

I thought of that moment when I was trying to decide between two possible topics for this week’s blog post. Soliciting Vicki’s opinion, I was interrupted by her smartphone buzzing with a first responder call. (She’s been sitting out these calls during the pandemic.) After I laid out the two topics, she glanced at her phone and learned the rescue involved an ischemic stroke…thus resolving my dilemma.

So, why should you continue reading about ischemic strokes? As a reward, I’ll tell you how to calculate and reduce your risk of having one.

Ischemic Stroke and Metabolic Syndrome
There are two types of strokes, ischemic and hemorrhagic, and both are medical emergencies. About 87% of strokes are ischemic. They’re usually caused by a blood clot blocking a blood vessel in the brain, though they might be due to atherosclerosis, in which plaque builds up inside arteries. Hemorrhagic strokes occur when a blood vessel ruptures and bleeds into the brain. 

Ischemic and hemorrhagic strokes (from www.strokeinfo.org/stroke-facts-statistics/).

A transient ischemic attack, often called a ministroke, is a brief interruption of blood flow to part of the brain, spinal cord or retina. It may cause temporary stroke-like symptoms but no brain cell damage or permanent disability. Having one is a warning sign. About 1 in 3 people experience a subsequent stroke.

Before moving on, I need to introduce metabolic syndrome, a group of five risk factors associated with blood vessel and heart disease: high blood pressure, high blood sugar, high triglycerides, low good cholesterol (HDL) and abdominal fat. These factors can lead to heart attacks and strokes as well as diabetes. While any one increases the risk of disease, metabolic syndrome is diagnosed if a person has at least three.

Metabolic syndrome risk factors (from

Metabolic Syndrome Severity Calculator
Researchers affiliated with Virginia and Florida universities developed an online scoring tool to assess metabolic syndrome severity. The tool, “Mets Calc,” uses values of an individual’s five factors to calculate the statistical standard score, commonly referred to as a z-score.

The z-score places the individual relative to others in the U.S. population. It’s the number of standard deviations by which an individual is higher or lower than the mean of the population. A z-score of 0, for example, indicates the individual’s metabolic syndrome severity is equal to the mean of the population. A z-score of plus or minus 2 indicates the value is 2 standard deviations above or below the mean.

The corresponding percentiles are informative. A z = 0 is equivalent to the 50th percentile; 50% of the population has a lower metabolic syndrome severity than the individual. A z = +2 is equivalent to the 97.7th percentile, indicating only about 2% of the population has a lower metabolic syndrome severity.

Data required to calculate metabolic syndrome severity with MetS Calc (from metscalc.org/).

Here’s the frosting. Your metabolic syndrome severity is going to determine your ischemic stroke risk.

Relating Z-Score to Ischemic Stoke
Collaborating with other researchers from the University of Florida and University of Mississippi Medical Center, the Mets Calc developers used the scoring tool to assess the association between metabolic syndrome severity and the risk of ischemic stroke.

The team evaluated 13,141 participants and their stroke outcomes from two prior studies (Atherosclerosis Risk in Communities Study and Jackson Heart Study). The participants were free from diabetes, coronary heart disease or stroke at baseline. Over a mean period of 18.6 years, there were 709 ischemic strokes.

The analysis found the risk of ischemic stroke increased consistently over the spectrum of metabolic syndrome severity. As metabolic syndrome severity increased, stroke risk increased. Race and gender did not seem to make a major difference, though the highest association was for white women, which could be the result of chance.

Wrap Up
The relationship between metabolic syndrome severity and ischemic stroke risk is terrific news. We can reduce the risk of stroke by reducing metabolic syndrome severity, and that can be done with lifestyle changes--lose weight, exercise more, healthier foods--all those New Year’s resolutions we let slide.

Thanks for stopping by.

Ischemic stroke:
Transient ischemic stroke: www.mayoclinic.org/diseases-conditions/transient-ischemic-attack/expert-answers/mini-stroke/faq-20058390
Metabolic syndrome:
MetS Calc, the metabolic syndrome severity calculator: metscalc.org/
I tried it and suggest you visit the site and “Check It Out.” There’s no cost. MetS Calc calculates your metabolic syndrome severity score based on a small set of data you know or got at your last physical. It’s all done online in real-time; no information is sent to a server.

The z-score was formulated by sex and race/ethnicity to avoid bias. Unlike traditional definitions of the underlying five factors, where you either have or don’t have metabolic syndrome, the z-score allows you and your doctor to monitor improvements over time.

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