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There may be a problem with the way myocardial salvage index (MSI) has been calculated in clinical research on cardioprotective therapies after ST-segment elevation MI (STEMI), researchers said.

Patients randomized to cardioprotective therapy at the time of percutaneous coronary intervention had smaller infarct sizes compared to controls, but these individuals also had reduced edema-based area at risk (AAR) by cardiovascular MRI, Derek Hausenloy, MD, PhD, of Duke-National University of Singapore Graduate Medical School in Singapore, and colleagues found from a meta-analysis.

Edema-based AAR stayed the same, however, in other trials suggesting that recipients of this therapy had no smaller infarcts, Hausenloy's group reported in the June 19 issue of the .

Ultimately, they questioned the suitability of the edema-based AAR as a basis for deriving MSI (which can currently be calculated as the difference between AAR and final infarct size).

"We found that in RCTs [randomized controlled trials] in which the cardioprotective therapy was potent enough to reduce MI size there was also a reduction in the edema-based AAR. This is probably not so surprising, given that a cardioprotective therapy capable of reducing MI size would also be expected to limit the severity of myocardial edema, as the latter is the direct result of acute myocardial ischemia and reperfusion injury," the authors said.

"Therefore, when the is quantified, the extent of the AAR would also be affected when the T2 intensity falls below the detection threshold."

It would be better not to use edema-based AAR to derive MSI in future studies of cardioprotective therapy in STEMI patients, the authors concluded.

The meta-analysis included 22 randomized trials, of which 14 were neutral for MI size and MSI. Five showed a reduction in MI size and an increase in MSI; another three showed an increase in MSI without a shrinking of MI.

Patient-level data was not available for full statistical adjustment, Hausenloy's group acknowledged.

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