People no longer being treated for irregular pulse 'may still have stroke risk'

Friday May 11 2018

"More than 1.5 million heart flutter patients should be on blood-thinning drugs to prevent stroke, study says," reports The Telegraph. The paper is referring to a condition called atrial fibrillation (AF), which affects around 1 million people in the UK.

AF is where the upper chambers of the heart (atria) pulsate in an erratic way, causing an irregular heartbeat. It's a known risk factor for stroke, as well as transient ischaemic attacks (TIA) or "mini strokes".

The irregular heartbeat increases the chances of blood clots forming, and these can travel around the circulatory system and lodge in an artery supplying the brain, reducing the blood supply and triggering a stroke or TIA.

In this study, the researchers were interested in the long-term health outcomes of people who had AF that had resolved and, as such, were believed to no longer require medication, like anti-clotting drugs (anticoagulants) such as warfarin. The researchers compared outcomes for thousands of UK adults with resolved AF to those who had existing AF, as well as to adults with no history of AF.

They found, perhaps unsurprisingly, that people with resolved AF had a lower risk of stroke or death than people with existing AF but a higher risk than people who had never had AF.

But just because people with resolved AF had a higher risk of stroke than people who had never had AF, this does not mean they would necessarily benefit from continuing anti-clotting medicines. Anti-clotting drugs are not risk-free, as they can cause excessive bleeding.

If you have AF that has resolved, the doctor responsible for your care will discuss with you the potential benefits and risk of continuing anti-clotting treatment.

Where did the story come from?

The study was conducted by researchers from the University of Birmingham and funded by the National Institute of Health Research. It was published in the peer-reviewed British Medical Journal and is free to read online.

The reports from The Telegraph and Mail Online that "millions should be on blood-thinning medications" could cause unnecessary public concern.

While the study did find a statistically significant increase in stroke risk for people with resolved AF, it's a considerable oversimplification to say that everyone who has ever had AF should continue anti-clotting medicines for the rest of their life. The risks would need to be carefully weighed up on an individual basis.

What kind of research was this?

This was a cohort study using general practice database records to compare death rates and rates of stroke or TIA in people with and without AF to those with resolved AF.

This type of study has the advantage of involving thousands of people, but it cannot attribute an outcome to a specific cause because multiple lifestyle and health factors are likely to affect the risk of stroke.

What did the research involve?

The study used The Health Improvement Network (THIN) database, which contains data for around 14 million patients registered with more than 640 general practices across the UK. It includes data on patient characteristics, investigations, diagnoses and prescriptions.

The researchers searched from the year 2000 to 2016 for people with a diagnosis of "atrial fibrillation resolved", and for a randomly selected group of age- and gender-matched people with AF and for a group of controls without AF. They excluded anyone with a prior history of stroke or TIA.

The participants were followed for around 3 years to check if they had a stroke or TIA, or died from any cause.

Analysis took account of confounders, including:

  • age
  • gender
  • body-mass index (BMI)
  • socioeconomic status
  • smoking
  • alcohol consumption
  • presence of associated illnesses such as heart disease, heart failure or high blood pressure
  • whether they were taking anti-clotting medication or statins

What were the basic results?

The analysis included a total of 11,159 adults with resolved AF, 15,059 adults with existing AF and 22,266 controls with no history of AF. The rates of stroke or TIA were:

  • 7.4 per 1,000 per year in people without AF
  • 12.1 per 1,000 per year in people with resolved AF
  • 16.7 per 1,000 per year in people with current AF

After adjusting for confounders, people with resolved AF had a:

  • 24% reduced risk of stroke or TIA compared with people with current AF (rate ratio [RR] 0 .76, 95% confidence interval [CI] 0.67 to 0.85)
  • 63% increased risk compared with controls without AF (RR 1.63, 95% CI 1.46 to 1.83)

Death rates from any cause were:

  • 24.4 per 1,000 per year in people without AF
  • 30.0 per 1,000 per year in people with resolved AF
  • 60.3 per 1,000 per year in people with current AF

Therefore, people with resolved AF had a:

  • 40% reduced risk compared with people with AF (RR 0.60, 95% CI 0.56 to 0.65)
  • 13% increased risk compared with controls without AF (RR 1.13, 95% CI 1.06 to 1.21)

When looking at the subgroup of people with resolved AF who were still taking an anti-clotting drug, their stroke rate was 11.4 per 1,000 per year, compared with 12.1 per 1,000 for those not taking medication. However, because this analysis involved a smaller number of people, this difference was not statistically significant.

How did the researchers interpret the results?

The researchers concluded that people with resolved AF have a higher stroke risk than people without AF and suggested "guidelines should be updated to advocate continued use of anticoagulants in patients with resolved atrial fibrillation".

Conclusion

This study shows that while people with resolved AF do have a lower stroke and mortality risk than those with current AF, they still have a higher risk than those with no history of AF.

The problem with this study is that it assumed that the simple solution to reduce this risk would be to prescribe anti-clotting medication on a long-term basis. But AF can have various underlying causes, such as heart disease and high blood pressure, and can still reoccur once resolved.

The study also cannot identify the exact cause of the increased risk in any of these individuals. For example, the increased risk of stroke and death in people with resolved AF may be due to a combination of underlying illness and lifestyle factors, not just because they were not taking anticoagulants.

In fact, as the study showed, people who had resolved AF but were still on anticoagulants showed little difference in risk in comparison with those not on anticoagulants, so the answer is likely not that simple. Doctors need to consider each person on an individual basis and manage their underlying illnesses and risk factors.

The findings are undoubtedly something for doctors to be aware of and may be considered in future guideline updates – but for now, people should not be overly concerned and should continue to follow their doctor's advice.

AF is not the only risk factor for stroke: you can reduce your risk of stroke by not smoking, and by maintaining a healthy weight through a balanced diet and regular exercise.

Analysis by Bazian
Edited by NHS Choices