Treatment of Slow‐Flow After Primary Percutaneous Coronary Intervention With Flow‐Mediated Hyperemia: The Randomized RAIN‐FLOW Study

BACKGROUND: ST‐segment–elevation myocardial infarction complicated with no reflow after primary percutaneous coronary intervention is associated with adverse outcomes. Although several hyperemic drugs have been shown to improve the Thrombolysis in Myocardial Infarction 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 versus flow‐mediated hyperemia in patients with ST‐segment–elevation myocardial infarction complicated with no reflow. METHODS AND RESULTS: In the RAIN‐FLOW (Treatment of Slow‐Flow After Primary Percutaneous Coronary Intervention With Flow‐Mediated Hyperemia) study, 67 patients with ST‐segment–elevation myocardial infarction and no reflow were randomized to receive either pharmacologic‐mediated hyperemia with intracoronary adenosine or nitroprusside (n=30) versus flow‐mediated hyperemia (n=37). The angiographic corrected Thrombolysis in Myocardial Infarction frame count and the minimal microcirculatory resistance, as assessed with intracoronary pressure‐thermistor wire, dedicated microcatheter, and thermodilution techniques, were compared after study interventions. Both Thrombolysis in Myocardial Infarction frame count(40.2±23.1 versus 39.2±20.7; P=0.858) and minimal microcirculatory resistance (753.6±661.5 versus 993.3±740.8 Wood units; P=0.174) were similar between groups. Thrombolysis in Myocardial Infarction 3 flow was observed in 26.7% versus 27.0% (P=0.899). Flow‐mediated hyperemia showed 2 different thermodilution patterns during saline infusion indicative of the severity of the no reflow phenomenon. In‐hospital death and nonfatal 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 patients with ST‐segment–elevation myocardial infarction. REGISTRATION: URL: https://www.clinicaltrials.gov; Unique identifier: NCT04685941.