Seasonal variation seen in myocardial infarct size


NEW YORK (Reuters Health) – Analysis of data from two large trials suggests that myocardial infarcts are smallest in size during the summer.

Dr. Robert A. Kloner, of Good Samaritan Hospital, Los Angeles, California, and colleagues retrospectively analyzed databases of the Multicenter Investigation of the Limitation of Infarct Size (MILIS) study, a prethrombolytic era study, and the Thrombolysis in Myocardial Infarction-4 (TIMI-4) study.

"Infarct size was determined for each patient," the team explains in the November 1st issue of The American Journal of Cardiology. The investigators observed no significant differences among demographics, "including coronary risk factors by season."

In the MILIS study, systolic blood pressure was slightly higher during the summer. However, they found no differences in percentage of Q-wave infarcts, location of infarcts, or history of infarcts by season. In the TIMI-4 study, the team observed no seasonal differences.

The mean MI size in the MILIS trial was 15.8 infarct size index units during winter and 16.7 during spring. "The lowest indexes were during the summer at 13.0 and autumn at 13.5 (p = 0.041 for summer versus the rest of the year; p = 0.009 for summer versus spring)," the researchers explain.

"In the TIMI-4 trial…the estimate of myocardial infarction size, determined by the CK-MB averaged over 14 time points, also revealed the smallest myocardial infarction size during the summer (101 CK-MB IU/L) versus winter (112 CK-MB IU/L), spring (138 CK-MB IU/L), or autumn (134 CK-MB IU/L) (p = 0.082 for summer versus the rest of the year; p = 0.055 for summer versus spring," Dr. Kloner and colleagues report.

They consider the possibility that an effect of temperature on vascular resistance may underlie the findings, but conclude that this seems unlikely and that the mechanism remains unknown.

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