In our pilot trial, the administration of low-dose intracoronary streptokinase immediately after primary PCI improved myocardial reperfusion but not long-term left ventricular size or function. These findings require clarification in a larger trial. (ClinicalTrials.gov number, NCT00302419.)

Background: In acute myocardial infarction (AMI), increased neutrophil count has been associated with more severe coronary artery disease and larger infarct size. Increased mean platelet volume (MPV) is also associated with poor clinical outcome and impaired angiographic reperfusion in patients with AMI. However, the associations of neutrophil count and MPV with the indices of tissue level reperfusion were not fully elucidated. Aim: To elucidate the relationship between baseline neutrophil count and MPV on presentation and microvascular injury in patients with anterior AMI treated with primary percutaneous coronary intervention (pPCI). Methods: 41 patients with anterior wall AMI treated successfully with pPCI were included. The leucocyte count, neutrophil count and MPV were obtained on admission, and the percentage of neutrophils was calculated. After PCI thrombolysis in myocardial infarction, grade 3 flow was established in all patients. The coronary flow velocity pattern (diastolic deceleration time (DDT)) was examined with transthoracic echocardiography and measured intracoronary pressures with fibreoptic pressure-temperature sensortipped guidewire in the left anterior descending artery within 48 h after pPCI. Thermodilution-derived coronary flow reserve (CFR) was calculated. Index of microvascular resistance (IMR) was defined as simultaneously measured distal coronary pressure divided by the inverse of the thermodilution-derived hyperaemic mean transit time. Subsequently, a short compliant balloon was placed in the stented segment and inflated to measure coronary wedge pressure (CWP). Conclusion: Absolute and relative neutrophilia and higher MPV on admission were independently associated with impaired microvascular perfusion in patients with anterior AMI treated with pPCI. It is possible that neutrophilia and high MPV are simple surrogate markers of worse microvascular injury in patients with AMI.

Given its simplicity of measurement, independence from the presence of an epicardial stenosis, and good correlation with all measures of microvascular obstruction used in this study, IMR may prove to be a valuable modality for evaluating the microcirculation.

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The pressure-derived collateral flow index is a powerful independent predictor of 1-year left ventricular dilatation. Given its simplicity of measurement, and correlation with microvascular obstruction and left ventricular outcome at long term, the pressure-derived collateral flow index may provide useful and valuable estimates of clinical outcomes after acute myocardial infarction.