Effect of intravascular cooling on microvascular obstruction (MVO) in conscious patients with ST-elevation myocardial infarction undergoing primary PCI: Results from the COOL AMI EU pilot study

Objective: COOL AMI EU pilot was a multi-center, randomized controlled trial to assess feasibility and safety of rapid intravascular therapeutic hypothermia (TH) in conscious patients with anterior ST-elevation myocardial infarction (STEMI) undergoing primary PCI (PPCI). We report the effect of hypothermia upon microvascular obstruction (MVO). Methods: Conscious patients with anterior STEMI and symptom duration <6 h were recruited and randomized to PPCI + TH or PPCI alone. TH was induced using the ZOLL® Proteus™ intravascular temperature management system and rapid infusion of 1 L of cold normal saline, with a target temperature of 32 °C. MVO was measured by cardiac magnetic resonance (CMR) at 4 to 6 days post-MI. MVO larger than 3.9% of LV was considered as extensive MVO. Results: 50 patients were randomized; mean age was 58 years, and 86% were men. At reperfusion, mean intravascular temperature for the TH group was 33.6 ± 1 °C. The presence of MVO was high and not different in both groups (74% vs. 77%, p = 0.79). The proportion of patients with extensive MVO was 11% in the TH group and 23% in the control group (OR 0.4 95%CI 0.07–2.35, p = 0.30). Patients with extensive MVO showed reduced EF at 4–6 days (34% versus 43%, p = 0.01). The percentage of patients with EF <35% at 30 days was 6% in the TH group versus 24% in the control group (p = 0.19). Conclusion: In the COOL-AMI Pilot Trial, the presence of MVO in both test groups was high and extensive MVO was related with reduced LVEF. The efficacy of therapeutic hypothermia (TH) in MVO reduction should be tested in a pivotal trial.