Dec 15, 2004
London, UK - Acute infections are associated with a transient increase in vascular events such as myocardial infarction and stroke, according to a large new British study.[ 1 ]
Dr Liam Smeeth (London School of Hygiene and Tropical Medicine, UK) and colleagues found that the rate of MI was almost five times higher and that of stroke three times higher in the three days following diagnosis of systemic respiratory-tract infection. They report their findings in the December 16, 2004 issue of the New England Journal of Medicine this week.
"These findings, based on a very large set of data, support the link between acute infection and the risk of a vascular event, identify the magnitude of the association and its resolution over time, and offer insight into the factors that may determine the timing of acute vascular events," the researchers say.
Dr J Brent Muhlestein (University of Utah and LDS Hospital, Salt Lake City) told heart wire that "this massively large study using the UK database confirms previous findings."
Smeeth et al used the UK General Practice Research Database to perform within-person comparisons using the case-series method. They examined the risks of MI and stroke after common vaccinations and naturally occurring infections.
There was no increase in the risk of MI or stroke in the period after influenza, tetanus, or pneumococcal vaccination. But the risks of both events were substantially higher after a diagnosis of systemic respiratory-tract infection and were highest during the first three days. The risks then gradually fell during the following weeks. Risks for recurrent MIs and recurrent strokes were slightly lower than those for first events. The risks were also raised significantly but to a lesser degree after a diagnosis of urinary-tract infection.
Age-adjusted incidence ratio of a first MI in risk periods after exposure to infection
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Age-adjusted incidence ratio of a first stroke in risk periods after exposure to infection
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"This study shows that acute lower respiratory-tract infections and urinary-tract infections are associated with a transient increase in the risk of a vascular event," say Smeeth and colleagues. "The effect is seen for a first or a subsequent MI or stroke and is most marked in the few days after infection."
This indicates that the risk of a cardiovascular event fluctuates, the researchers say, and is "highly suggestive of a causal role for acute infections in triggering cardiovascular events."
They say that the fact that they also found an association between urinary-tract infection and events is important, "because it suggests that the effect of infections on cardiovascular risk may be generic and is not linked to specific types of infection." This "lends strong support to the concept that systemic inflammation itself alters the probability of the occurrence of a vascular event."
Smeeth told heart wire that the clinical implications of these findings "are relatively small" but "it's of great scientific interest." If further work can help establish the mechanisms involved, then this will have implications for prevention, he says.
[The research] provides better correlation than I've seen in other studies about the timing of this.
Another researcher with interest in this field, Dr Chris Cannon (Brigham and Women's Hospital, Boston, MA), said he believes that much of what is seen relates to the increased adrenergic surge during an infection, which in turn is a trigger for MI or stroke.
"When patients are admitted with an acute infection, they generally will have higher heart rate (from fever) and likely higher adrenergic status, and these I would think would be the 'cause' of the increased risk of MI and stroke. The fact that the increased risk is generally two to three days fits this idea," he commented to heart wire .
Muhlestein said, "This study suggests that on top of preexisting atherosclerosis, acute infection triggers an acute inflammatory response that leads to a vascular event." The research also "provides better correlation than I've seen in other studies about the timing of this," he adds.
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Medscape Medical News © 2004 Medscape
Cite this: Risk of MI and stroke raised after acute infection - Medscape - Dec 15, 2004.
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