Tuesday, May 16, 2017

Int. Med. J.: Triggering Of Acute M.I. By Respiratory Infection


Last November, in UK ONS: 2014-15 Excess Winter Mortality Highest Since 1999, we looked at an all too familiar statistic that showed the number of deaths rises during the winter, and that number is usually highest during years when influenza is more prevalent.

Almost 2 decades 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 numerous theories have been offered (holiday stress, cold weather, over-indulgence during the holidays, etc.), a growing number of studies have suggested that Influenza - and other acute respiratory infections - can act as a trigger for heart attacks (see Study: Influenza And Heart Attacks).

Not quite two years ago, in UNSW: Flu Vaccine Provides Significant Protection Against Heart Attacks, we saw a study that found that if you are over 50 - getting the flu vaccine can cut your risk of a heart attack by up to 45%.

We've another study from down under this morning that links an increased risk of heart attack to not just influenza, but any respiratory infection.
And not by just a little. They report `The relative risk (RR) for MI occurring within 1–7 days after respiratory infection symptoms was 17.0'.  A 17-fold increase.
First the Abstract from the Internal Medicine Journal, followed by excerpts from a University of Sydney new report.  Then I'll return with a brief postscript.

Triggering of acute myocardial infarction by respiratory infection
 Lorcan Ruane, Thomas Buckley, Soon Y. S. Hoo, Peter S. Hansen, Catherine McCormack, Elizabeth Shaw, Judith Fethney and Geoffrey H. Tofler
14 MAY 2017 | DOI: 10.1111/imj.13377


Respiratory infection has been associated with an increased short-term risk of myocardial infarction (MI). However, previous studies have predominantly been conducted without angiographic confirmation of MI. The possibility can therefore not be excluded that raised troponin levels or electrocardiogram abnormalities that may be seen with respiratory infections are due to non-ischaemic causes.

To investigate the association between respiratory infection and angiographically confirmed MI.

Interviews were conducted within 4 days of hospitalisation in 578 patients with angiographically confirmed MI, to assess for recent exposure to respiratory infection symptoms and the usual annual frequency of these symptoms. Using case-crossover methodology, exposure to respiratory infection prior to the onset of MI was compared against the usual frequency of exposure in the past year.

Symptoms of respiratory infection were reported by 100 (17%) and 123 (21%) within 7 and 35 days, respectively, prior to MI. The relative risk (RR) for MI occurring within 1–7 days after respiratory infection symptoms was 17.0 (95% confidence interval (CI) 13.2–21.8), and declined with subsequent time periods. In a subgroup analysis, the RR tended to be lower in groups taking regular cardiac medications. For those who reported milder, upper respiratory tract infection symptoms, the RR for the 1–7-day time period was 13.5 (95% CI 10.2–17.7).

These findings confirm that respiratory infection can trigger MI. Further study is indicated to identify treatment strategies to decrease this risk, particularly in individuals who may have increased susceptibility.

Respiratory infections can trigger a heart attack

16 May 2017

Warning for flu season
New research from University of Sydney finds the risk of a heart attack is increased 17-fold in the week following a respiratory infection such as influenza or pneumonia.

The risk of having a heart attack is 17 times higher in the seven days following a respiratory infection, University of Sydney research has found.

Published today in Internal Medicine Journal, this is the first study to report an association between respiratory infections such as pneumonia, influenza and bronchitis and increased risk of heart attack in patients confirmed by coronary angiography (a special X-Ray to detect heart artery blockages).

“Our findings confirm what has been suggested in prior studies that a respiratory infection can act as a trigger for a heart attack," said senior author Professor Geoffrey Tofler, cardiologist from University of Sydney, Royal North Shore Hospital and Heart Research Australia.
“The data showed that the increased risk of a heart attack isn't necessarily just at the beginning of respiratory symptoms, it peaks in the first 7 days and gradually reduces but remains elevated for one month.”
The study was an investigation of 578 consecutive patients with heart attack due to a coronary artery blockage, who provided information on recent and usual occurrence of symptoms of respiratory infection.
Seventeen per cent of patients reported symptoms of respiratory infection within 7 days of the heart attack, and 21 per cent within 31 days.
Patients were interviewed about their activities before the onset of their heart attack, including if they experienced a recent “flu-like illness with fever and sore throat”. They were considered affected if they reported sore throat, cough, fever, sinus pain, flu-like symptoms, or if they reported a diagnosis of pneumonia or bronchitis.

A second analysis was among those with symptoms restricted to the upper respiratory tract, which included the common cold, pharyngitis, rhinitis and sinusitis.

Lead author Dr Lorcan Ruane, who conducted the work at University of Sydney said: “For those participants who reported milder upper respiratory tract infection symptoms the risk increase was less, but was still elevated by 13 fold.”

(Continue . . . )

Although the `street creds’ of the flu vaccine took a major hit in 2014 after the late arrival of a `mismatched’ H3N2 virus (see CDC: Updated Estimated Seasonal Flu Vaccine Effectiveness), most years the flu vaccine provides a `moderate’ level of protection.

Anywhere from 30%-70%, depending upon the strain and the age and immune response of the recipient. 
While influenza isn't the only respiratory infection that might trigger cardiac events, it imposes a heavy disease burden most years, and likely contributes heavily to the excess winter mortality rate.
While the vaccine can’t promise 100% protection, it – along with practicing good flu hygiene (washing hands, covering coughs, & staying home if sick) – remains your best strategy for avoiding the flu and staying healthy this winter.

And maybe, just maybe . . .  for those of us of a certain age . . .  avoiding a heart attack as well.

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