Saturday, October 10, 2020

JAHA: Another Study Linking ILI To Increased Risk Of Heart Attack & Stroke


Ask just about anyone in emergency medicine and they will tell you that the incidence of heart attacks and strokes goes up in the winter months. More than twenty years ago, a study looked at the rate of heart attacks in the United States, and found that Acute Myocardial Infarctions (AMIs) run as much 53% higher during the winter months than than during the summer.
Seasonal distribution of acute myocardial infarction in the second National Registry of Myocardial Infarction.

Spencer FA, Goldberg RJ, Becker RC, Gore JM
While cold weather combined with strenuous physical activity (like clearing snow from sidewalks) has often been blamed for this spike, even in balmy Southern California, studies have shown a 33% increase in heart attacks over the holidays (see below).
When Throughout the Year Is Coronary Death Most Likely to Occur?

A 12-Year Population-Based Analysis of More Than 220 000 Cases

Robert A. Kloner, MD, PhD; W. Kenneth Poole, PhD; Rebecca L. Perritt, MS
Non-climate related factors – like over indulgence in food and alcohol, diminished activity levels, forgetting to take prescription medicines, and combined holiday stressors like shopping, running up debt, traveling, meal preparation, and the angst that comes from dysfunctional family gatherings are all likely contributors to this yearly spike.

But over the past decade we've seen mounting evidence linking ILIs (Influenza-like-illnesses) to an increased risk of heart attack or stroke.  A few relatively recent studies include:

To this growing list of studies we can add a new statistical analysis published in JAHA - the Journal of the American Heart Association - that finds that heart attacks and strokes rise (with differing lag periods) during times of elevated ILI activity.   

Of note: This study found the same 7-day window for heart attacks, and 28 window for strokes, as have previous studies.

Due to the length and complexity of the analysis, we'll begin by drawing some basic information from an AHA press release.

Published: October 8, 2020

Heart attack risk increases quickly after a flu-like illness, while stroke risk rises slower, according to new research.

The study, published Thursday in the Journal of the American Heart Association, examined the relationship between the flu, heart attacks and strokes, which all occur more frequently during winter months.

Researchers looked at New York state public health data from 2004 to 2015 and focused on adults who were hospitalized or came to the emergency department for stroke, heart attack or "flu-like illnesses." Study author Amelia Boehme said pinpointing people with the flu from administrative records is difficult. Instead, her study relied on an algorithm developed by the Centers for Disease Control and Prevention to identify influenza and influenza-like symptoms through billing codes.

The study found that strokes and heart attacks increase during times of high flu-like illness rates, with a "time lag" occurring only for strokes.

"We found that if someone's going to have a heart attack, it's going to occur within seven days of the flu-like illness, during the acute phase,
" said Boehme, assistant professor of epidemiology in the department of neurology at Columbia University in New York City. "With stroke, we see an increased risk seven to 15 days after, similar to heart attacks. But with stroke, there is an additional higher-risk period after 30 days."
The researchers didn't have information on whether people included in the study had received a flu vaccine. But they did find that "in the years where the vaccine effectiveness was higher, overall, the number of people who had influenza-like illness and the number of people who subsequently had strokes and heart attacks after influenza-like illness was lower."

Past studies have shown that those who skip a flu shot are six times more likely to experience a heart attack.

It should be noted that while `Influenza-like-illness' encompasses influenza A & B, it also includes non-influenza respiratory infections like rhinovirus, coronavirus, adenovirus, and parainfluenza which are not covered by the influenza vaccine - and when combined - generally exceed the number of flu infections. 

The full open-access study is available at the link below. I'll have a postscript when you return.
Seasonality of Influenza‐Like‐Illness and Acute Cardiovascular Events Are Related Regardless of Vaccine Effectiveness 
Erin R. Kulick, Michelle Canning, Neal S. Parikh, Mitchell S. V. Elkind, and Amelia K. Boehme
Originally published8 Oct 2020
Journal of the American Heart Association.  


Influenza has been identified as a trigger for stroke and myocardial infarction (MI) with prior studies demonstrating that influenza vaccination may decrease risk of stroke and MI.



We identified that seasonality of cardiovascular events may be associated with seasonality in ILI, though VE did not modify this relationship

          (Continue . . . )

The design of this study, and the lack of vaccination data for patients, makes it impossible to link receipt of the  flu vaccine with a lowered risk of stroke of heart attack, even though those rates did decline slightly during years with a high VE (Vaccine Effectiveness)

In the discussion section, the authors wrote:

In years with increased VE we did see overall reductions in the absolute risk of ILI, and small decreases in subsequent stroke and MI, but the overall association between ILI and stroke or MI was not significantly influenced by VE
Future work incorporating vaccination information is needed to elucidate the role of the influenza vaccine in reducing stroke or MI risk.

But we do have other, recent studies that suggest flu vaccines appear reduce the risk having a heart attack or stroke, and may even reduce the risk of dementia. 

While the current flu vaccine is nowhere near as effective as we'd like it to be, and the promise of a universal flu vaccine remains elusive (see  J.I.D.: NIAID's Strategic Plan To Develop A Universal Flu Vaccine), there is evidence to suggest the benefits of vaccination may extend beyond preventing influenza infection. 

I view getting a yearly flu shot like always wearing a seat belt in an automobile. It doesn't guarantee a good outcome in a wreck, but it sure increases your odds of walking away. 

And for me - now that I've entered that dreaded `elderly' demographic - that is an extra bit of insurance worth having.