The goal of this analysis was to determine the relation between
myocardial infarct size and left ventricular (LV) ejection fraction (EF) in patients with
ST-segment elevation myocardial infarction (
STEMI) after primary
percutaneous coronary intervention (pPCI) using cardiovascular magnetic resonance imaging (CMR). After
STEMI, LVEF and
infarct size correlate with prognosis, but the relation between
infarct size and LVEF is incompletely known. Consecutive subjects presenting to a single center with
STEMI treated with pPCI were enrolled, and cine functional and late
gadolinium enhancement CMR was performed 3 months after presentation. From cine images, LVEF was calculated using volumetric summation of disks method.
Infarct size was measured as percent LV myocardial volume with late
gadolinium enhancement. In the 78 patients enrolled (mean age 54.5 years, range 42 to 82), median LVEF was 56% (interquartile range 49 to 62) and median
infarct size was 11% (interquartile range 5 to 18). Of the 53 patients with
infarct size <15%, all had LVEF >40%, and there was no significant relation between
infarct size and LVEF (slope -0.43, R(2) = 0.045, p = 0.13). In patients with
infarct size > or =15%, there was a significant negative linear association between
infarct size and LVEF (slope -1.21, R(2) = 0.66, p <0.001), such that for every 5% increase in
infarct size, there was a 6.1% decrease in LVEF. In conclusion, there is a negative linear relation between
infarct size and LVEF for moderate to large
infarcts. For small
infarcts there is no significant relation between
infarct size and LVEF. Up to 15% of LV myocardial volume may be infarcted before there is any appreciable decrease in LVEF.