Background No reflow phenomenon is described in up to 65% of patients undergoing primary percutaneous coronary intervention for ST elevation myocardial infarction (STEMI). It is known to be associated with worse outcomes but predictors of no reflow are not clearly described.

Objectives A single centre case-control observational study of patients presenting with acute myocardial infarction appropriate for PPCI comparing baseline clinical, biochemical and angiographic characteristics between patients with no reflow phenomenon and those without. Aiming to establish incidence for the UK population.

Secondary outcomes will be to gain further insight into those presenting with STEMI for PPCI and develop a risk model to guide management and clinical outcomes of patients to 30days.

Methods This study will prospectively recruit all consecutive patients attending a single centre for primary percutaneous coronary intervention for STEMI. Angiographic assessment of the recanalised epicardial vessel will be used to diagnose no reflow (reduced TIMI flow or blush grade). Baseline demographic, angiographic and biochemical characteristics and outcomes at 30days for reflow and no reflow cohorts will be statistically assessed and compared with logistic regression.

Inclusion Criteria:

• Age ≥ 18 years
• Presenting with ST elevation myocardial infarction
• Appropriate for Primary Percutaneous Coronary Intervention

Exclusion Criteria:

• Primary Percutaneous Coronary Intervention not performed eg due to non- flow- limiting coronary artery disease
• Unsuccessful PCI
• Thrombolysis
• Patients who do not survive the procedure to leave the catheterisation laboratory

The cohort is defined as all patients attending with ST elevation myocardial infarction undergoing primary percutaneous coronary intervention. Cases are those subjects who suffered no reflow phenomenon, with control comparators those that had TIMI III flow and grade III myocardial blush post procedure.