Time elapsed after contrast injection is crucial to determine infarct transmurality and myocardial functional recovery after an acute myocardial infarction

Background: In acute myocardial infarction (MI), late Gadolinium enhancement (LGE) has been proposed to include the infarcted myocardium and area at risk. However, little information is available on the optimal timing after contrast injection to differentiate these 2 areas. Our aim was to determine in acute and chronic MI whether imaging time after contrast injection influences the LGE size that better predicts infarct size and functional recovery. Methods: Subjects were evaluated by cardiovascular magnetic resonance (CMR) the first week (n∈=∈60) and 3 months (n∈=∈47) after a percutaneously revascularized STEMI. Inversion-recovery single-shot (ss-IR) imaging was acquired at multiple time points following contrast administration and compared to segmented inversion-recovery (seg-IR) sequences. Inversion time was properly adjusted and images were blinded, randomized and measured for LGE volumes. Results: In acute MI, LGE volume decreased over several minutes (p∈=∈0.005) with the greatest volume occurring at 3 minutes and the smallest at 25 minutes post-contrast injection; however, LGE volume remained constant over time in chronic MI (p∈=∈0.886). Depending on the imaging time, in acute phase, a change in the transmurality index was also observed. A transmural infarction (>75%) at 25 minutes better predicted the absence of improvement in the wall motion score index (WMSI), a higher increase in left ventricular volumes and a lower ejection fraction compared to 10 minutes. Conclusions: A change was observed in LGE volume in the minutes following contrast administration in acute but not in chronic MI. Infarct transmurality 25 minutes post-contrast injection better predicted infarct size and functional recovery at follow-up.