Length of Lookback Period Important in Incident AMI Trends
(HealthDay News) — The length of the lookback period (LP) affects trends in incident acute myocardial infarction (AMI), with a greater effect in women, according to a study published online June 9 in Circulation: Cardiovascular Quality and Outcomes.
Gerhard Sulo, M.D., Ph.D., from the University of Bergen in Norway, and colleagues examined whether the length of the LP used to identify the first AMI affects trends in AMI incidence. Data were retrieved for all AMI events during 1994 to 2009. The authors compared the results obtained from analyses using the LP of 10 years versus shorter LPs (eight, seven, five, and three years).
The researchers found that for men there was a decrease in the incidence rates of AMIs from 2004 to 2009 (4.2 percent decrease; incidence rate ratio, 0.958; 95 percent confidence interval, 0.935 to 0.982). Similar results were obtained with use of other LPs, with no significant difference from the LP of 10 years. For women, the AMI incidence rates decreased by 7.3 percent with an LP of 10 years (incidence rate ratio, 0.927; 95 percent confidence interval, 0.901 to 0.955). A significantly smaller decline was seen for the LP of five years (6.2 versus 7.3 percent; P = 0.02) and for the LP of three years (5.9 versus 7.3 percent; P = 0.03).
"LPs of seven to 10 years are reliable for identifying the incident AMI in a given individual. Shorter LPs 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 authors write. "In the case of trends in survival after an incident AMI, the choice of the LP length does not seem to influence the results."