Abstract Body (Do not enter title and authors here): Introduction: Spontaneous coronary artery dissection (SCAD) is a significant cause of
acute coronary syndrome in young women. Fibromuscular dysplasia (FMD) is frequently
associated with SCAD, but its impact on clinical outcomes remains unclear.

Hypothesis: We hypothesized that SCAD patients with concurrent
FMD would have different clinical outcomes compared to those without FMD, potentially
reflecting distinct pathophysiological mechanisms.

Methods: Using the TriNetX Global Collaborative Network across 129 healthcare
organizations, we performed a retrospective propensity-matched cohort study. SCAD
patients (ICD-10: I25.42) with FMD (ICD-10: I77.3) were compared to those without
FMD. After 1:1 propensity matching based on demographics and comorbidities, 857
patients per group were analyzed. Primary outcome was all-cause mortality; secondary
outcomes included heart failure, cardiogenic shock, arrhythmias, and acute kidney
injury over five years. Analysis included risk ratios (RR), odds ratios, and hazard ratios
(HR) with 95% confidence intervals.

Results: SCAD patients with FMD had significantly lower all-cause mortality (1.3% vs
6.5%; RR 0.199, 95% CI 0.105-0.377; p<0.001), heart failure (4.7% vs 13.4%; RR
0.349, 95% CI 0.239-0.512; p<0.001), and acute kidney injury (1.2% vs 4.7%; RR
0.257, 95% CI 0.128-0.514; p<0.001). No significant differences were observed for
cardiogenic shock, ventricular tachycardia, or atrial fibrillation.

Conclusions: FMD is associated with markedly improved outcomes in SCAD patients,
suggesting it represents a distinct, more favorable pathophysiological subtype. These
findings support comprehensive FMD screening in SCAD patients for enhanced risk
stratification and personalized management strategies.