e341 Correspondence To the Editor:

I read with interest the article by Fearon et al,1 which presents an important consecutive series correlating index of microcirculatory resistance (IMR) with prognosis after primary percutaneous coronary intervention. Their work raises a number of issues: No correlation between myocardial damage, enzymatic or func-tional, and IMR is made. A small myocardial infarct could have the same IMR as a large one because the index is a ratio, not an absolute measurement. The same error may occur with coronary flow reserve. The prognoses for single-vessel and multi-vessel disease are dif-ferent. The IMR in nonculprit vessels was not measured, making identification of single- or multivessel causes of heart failure or death difficult. It would be unusual for a single-vessel infarct associated with no viable distal myocardium to be associated with a 1-year mortality rate of 8.8 % or an 11.2 % chance of readmission for heart failure. The IMR of the culprit vessel in isolation does not delineat