Session S35.3

Estimating Salvaged Myocardium in Reperfused ST-Elevation Myocardial Infarction: An MRI Model

RAP Weir*, A Murphy, S Clements, E Dick, T Steedman,
S Polymeros, HJ Dargie, GS Wagner

Glasgow Western Infirmary
Glasgow, UK

There is an ECG method of estimating salvaged myocardium in ST-elevation myocardial infarction (STEMI), using the Aldrich and final QRS score. We developed a similar cardiac magnetic resonance imaging (CMR) model. Using 1st pass perfusion imaging, we can measure an initial “at risk” area that comprises the infarct and the peri-infarct zone. Delayed enhancement images allow measurement of the infarct size (IS); we can thus estimate the size of the peri-infarct zone, which may be a surrogate marker of salvaged myocardium. This study was performed to test the hypothesis that the ECG and CMR models will provide similar estimates of salvaged myocardium.
33 patients (mean age [SD] 60.8±11.7; 67% male) with STEMI treated with lytic therapy (19 anterior, 14 inferior) underwent CMR imaging at a mean of 3.2 days and again at 3 months post-MI. Manual planimetry was used to measure the first pass defect (acute scan) and IS (3 month scan). The acute ECG and a 3 month ECG were used to calculate Aldrich and QRS scores respectively.
Baseline Aldrich score was 22.9±8.1%, while QRS score at 3 months was 17.9±10.9%; there was a weak correlation (r=0.21, p=0.13). Mean 1st pass defect (49.7±18.2%) was greater than 3 month CMR IS (22.6±12.2%) but correlated closely: r=0.87, p=0.01. A Bland-Altman plot showed that, for small and medium-sized infarcts, the two models were similar, but for larger infarcts the CMR model overestimated salvaged myocardium, presumably related to the greater oedema surrounding such infarcts.
The first pass defect contains the infarct zone plus surrounding myocardium that may remain at risk, due to its vicinity to the acute changes within the infarct zone. We have suggested a CMR model that allows measurement of this peri-infarct “penumbra”, and have shown that, in small and medium-sized infarcts, it correlates with salvageable myocardium using a known ECG model. We suggest that the peri-infarct zone on first pass CMR may represent additional “at risk”, potentially salvageable myocardium.

(Abstract Control Number: 240)