Infarct healing is a dynamic process following acute myocardial infarction

Abstract

Background: The role of infarct size on left ventricular (LV) remodeling in heart failure after an acute ST-segment elevation myocardial infarction (STEMI) is well recognized. Infarct size, as determined by cardiovascular magnetic resonance (CMR), decreases over time. The amount, rate, and duration of infarct healing are unknown.

Methods: A total of 66 patients were prospectively enrolled after reperfusion for an acute STEMI. Patients underwent a CMR evaluation within 1 week, 4 months, and 14 months after STEMI.

Results: Mean infarct sizes for the 66 patients at baseline (acute necrosis), early follow-up (early scar), and late follow-up (late scar) were 25 ± 17 g, 17 ± 12 g, and 15 ± 11 g, respectively. Patients were stratified in tertiles, based on infarct size, with the largest infarcts having the greatest absolute decrease in mass at early and late scar. The percent reduction of infarct mass was independent of initial infarct size. There was an 8 g or 32% decrease in infarct mass between acute necrosis and early scar (p < 0.01) with a 2 g or 12% additional decrease in infarct mass between early and late scar (p < 0.01).

Conclusions: Infarct healing is a continuous process after reperfusion for STEMI, with greatest reduction in infarct size in the first few months. The dynamic nature of infarct healing through the first year after STEMI indicates that decisions based on infarct size, and interventions to reduce infarct size, must take into consideration the time frame of measurement.

Figure 1

Changes over time in infarct mass. Scatter plot showing the changes in absolute infarct mass over time (A) and the changes in infarct size as a percent of left ventricular mass over time (B) for all patients.

Figure 2

Infarct healing over time. Bar graph showing infarct mass (A) and infarct size (as percent of left ventricular mass, B) at acute necrosis, early scar, and late scar in patients subgrouped into tertiles of initial infarct size. Data are mean ± SD. Asterisks indicate p < 0.002 by paired t-test compared to previous time point, which is statistically significant after Bonferroni correction for 22 comparisons.

Figure 3

Absolute versus relative changes in infarct size. Bar graphs showing absolute decrease in infarct mass (left) and relative decrease as percent of the initial infarct mass (right) at the 3 time points among patients subgrouped into tertiles of initial infarct size. One-way ANOVA analysis with post hoc Bonferroni correction reveal that patients with the largest infarct size had the largest absolute decrease in infarct size when compared to the other two tertiles. However, the relative change in infarct size was not different between the infarct tertile groups.