Myocardial tissue characterisation and functional assessment by magnetic resonance imaging in ST elevation myocardial infarction

Objectives:-
To evaluate myocardial tissue characterisation by cardiovascular magnetic resonance (CMR) to predict functional recovery in reperfused acute myocardial infarction (AMI).
Background:-
Prognosis following AMI is closely related to recovery of myocardial contractile function. Accurate early prediction of functional recovery may allow for additional therapies in high risk patients, and avoid over-treatment of lower risk patients. Clinical prognostication commonly relies on echocardiographic evaluation of function, which may be misleading acutely. CMR offers a number of ways to refine prediction of functional recovery by characterising myocardial tissue, but these have not been extensively evaluated.
Methods:-
Patients following reperfusion for first-presentation ST-elevation AMI were scanned by CMR acutely, subacutely and in convalescence. Tissue pathologies visible on acute CMR were evaluated for their ability to predict recovery of contractile function. Oedema in the peri-infarct zone, microvascular obstruction (MO) and intramyocardial haemorrhage (IMH) in the infarct zone, and extracellular volume (ECV) of the infarct zone were evaluated. In addition, susceptibility-weighted MR imaging (SW-MRI) was evaluated against the reference standards of T2-weighted and T2* imaging to detect the known prognostic marker of IMH.
Results:-
Acutely oedematous myocardium demonstrated recovery of function over time (p<0.05), whereas non-oedematous peri-infarct myocardium did not (p>0.05). Recovery of function closely mirrored resolution of oedema. Infarct contractile recovery was attenuated in infarcts that demonstrated MO acutely as compared to those without (p<0.01), and attenuated further in those that demonstrated IMH acutely (p<0.01). SW-MRI had sensitivity 93% and specificity 86% as compared to T2-weighted imaging, with excellent inter-observer reliability and shorter breath-hold times (4 seconds vs. 16 seconds). Infarct ECV had higher accuracy to predict improved wall motion than late gadolinium enhancement imaging (c-statistic 0.80 vs. 0.70, p=0.04).
Conclusion:-
Tissue characterisation by CMR offers a variety of ways to predict functional outcome following AMI, using both established and novel imaging techniques.