(HealthDay News) — The length of the lookback period affects trends in incident acute myocardial infarction (MI), with a greater effect in women, according to a study published in Circulation: Cardiovascular Quality and Outcomes.
Gerhard Sulo, MD, PhD, from the University of Bergen in Norway, and colleagues examined whether the length of the lookback period used to identify the first acute MI affects trends in acute MI incidence. Data were retrieved for all acute MI events during 1994 to 2009. The authors compared the results obtained from analyses using the lookback period of 10 years vs. shorter lookback periods (8, 7, 5 and 3 years).
For men, there was a decrease in the incidence rates of acute MIs from 2004 to 2009 (4.2% decrease; incidence rate ratio, 0.958; 95% CI, 0.935-0.982). Similar results were obtained with use of other lookback periods, with no significant difference from the lookback period of 10 years.
For women, the acute MI incidence rates decreased by 7.3% with a lookback period of 10 years (incidence rate ratio, 0.927; 95% CI, 0.901-0.955). A significantly smaller decline was seen for the lookback period of 5 years (6.2% vs. 7.3%; P=.02) and for the lookback period of 3 years (5.9% vs. 7.3%; P=.03).
“[Lookback periods] of 7 to 10 years are reliable for identifying the incident acute MI in a given individual. Shorter [lookback periods] may overestimate the true number (and hence rates) of incident events by creating a mixture of incident and recurrent cases and might also distort the real trends in the incidence, especially among elderly women,” the researchers wrote.
“In the case of trends in survival after an incident acute MI, the choice of the [lookback period] length does not seem to influence the results.”