Treatment of Slow‐Flow after Primary Percutaneous Coronary Intervention with Flow‐Mediated Hyperemia: the Randomized RAIN‐FLOW Study

Background: ST-segment Elevation Myocardial Infarction (STEMI) complicated with no reflow after primary percutaneous coronary intervention is associated with adverse outcomes. Although several hyperemic drugs have shown to improve the Thrombolysis In Myocardial Infarction (TIMI) flow, optimal treatment of no reflow remains unsettled. Saline infusion at 20 ml/min via a dedicated microcatheter causes (flow-mediated) hyperemia. The objective is to compare the efficacy of pharmacologic vs. flow-mediated hyperemia in STEMI patients complicated with no reflow. Methods: STEMI patients with no reflow were randomized to receive either adenosine or nitroprusside vs. flow-mediated hyperemia. The angiographic corrected TIMI Frame Count (cTFC) and the Minimal Microcirculatory Resistance (MMR), as assessed with intracoronary pressure-thermistor wire, dedicated microcatheter and thermodilution techniques, were compared after study interventions. Results: Sixty-seven were included (30 allocated to pharmacologic and 37 to flow-mediated hyperemia). After study interventions, cTFC (40.2{+/-}23.1 vs. 39.2{+/-} 20.7; p=0.858) and MMR (753.6{+/-}661.5 vs. 993.3{+/-}740.8 Wood units; p=0.174) were similar between groups. TIMI 3 flow was observed in 26.7% vs. 27.0% (p=0.899). Flow-mediated hyperemia showed two different thermodilution patterns during saline infusion indicative of the severity of the no reflow phenomenon. In-hospital death and non-fatal heart failure were observed in 10.4% and 26.9%, respectively. Conclusions: Both treatments showed similar (and limited) efficacy restoring coronary flow. Flow-mediated hyperemia with thermodilution pattern assessment allowed the simultaneous characterization of the no reflow degree and response to hyperemia. No reflow was associated with a high rate of adverse outcomes. Further research is warranted to prevent and to treat no reflow in STEMI patients (NCT04685941).