Abstract 4358155: Coronary Microvascular Dysfunction Related to Disease Severity in Patients with Transthyretin Amyloid Cardiomyopathy

Background: The importance of coronary microvascular dysfunction in heart failure and cardiomyopathies is attracting attention. However, the significance of coronary microvascular dysfunction in transthyretin amyloid cardiomyopathy (ATTR-CM) is unclear. The prevalence and pathophysiology of coronary microvascular dysfunction in ATTR-CM was evaluated in this study. Methods: We prospectively studied patients with ATTR-CM diagnosed between January 2023 and March 2025 at Kochi Medical School Hospital. Coronary microvascular dysfunction was assessed using a pressure wire during catheterization and was defined as Coronary Flow Reserve (CFR) < 2.0, Index of Microcirculatory Resistance (IMR) ≥ 25, or both. Results: Coronary microcirculation was evaluated in 12 patients with ATTR-CM. The median age was 79 years [IQR 77-81 years], 7 (58%) were male. IMR and CFR were positive in seven patients (58%) and five patients (42%), respectively. All CFR positive patients were also IMR positive. Patients with positive IMR had more atrial fibrillation (5 vs. 0, p=0.028) and higher relative wall thickness (median 0.72 vs. 0.58, p=0.048). Patients with positive CFR were older at diagnosis of ATTR-CM (median 82 vs. 77 years, p=0.030), had more atrial fibrillation (5 vs. 0, p=0.001), and had thicker ventricular septal wall thickness (median 17mm vs. 14mm, p=0.048) and left ventricular posterior wall thickness (median 14mm vs. 12mm, p=0.030). There was a significant negative correlation between CFR value and ventricular septal wall thickness (r=-0.734, p=0.007). Chest pain was present in two patients in the coronary microvascular dysfunction positive group and absent in the coronary microvascular dysfunction negative group. Conclusion: Approximately 60% of patients with ATTR-CM had coronary microvascular dysfunction. Patients with ATTR-CM complicated by coronary microvascular dysfunction had thicker left ventricular wall thickness and a higher frequency of atrial fibrillation. The presence of coronary microvascular dysfunction may be associated with the progression of the pathogenesis of ATTR-CM.