Determinants of chronic myocardial perfusion abnormalities in Takotsubo syndrome: focus on index of microvascular resistance (IMR) and mismatch patterns

Abstract Background/Introduction Takotsubo syndrome (TTS) is characterized by transient left ventricular dysfunction triggered by emotional or physical stress. Although left ventricular function may subsequently normalized, chronic myocardial perfusion abnormalities are frequently observed even after functional recovery. Microvascular dysfunction have been suggested to play a significant role in the pathophysiology of TTS, contributing to both acute myocardial stunning and chronic perfusion abnormalities. Mismatch patterns between 123 I-β-methyl-P-iodophenyl-pentadecanoic acid (BMIPP) and thallium (Tl) imaging reflect differences in myocardial metabolism and perfusion, potentially indicating underlying microvascular dysfunction. However, the determinants of chronic perfusion abnormalities in TTS patients have not been fully elucidated. Purpose This study aimed to investigate the relationship between Index of Microvascular Resistance (IMR) and chronic myocardial perfusion abnormalities in TTS patients. Methods We prospectively enrolled 21 TTS patients who underwent myocardial scintigraphy with BMIPP and Tl imaging in both acute (within 48 hours of onset) and chronic phases (1 month after onset). IMR was measured during the acute phase using a pressure wire. Patients were divided into two groups based on IMR values: high IMR ( 25, n=11) and low IMR (≤ 25, n=10). Mismatch patterns were classified into three types: B-type (BMIPP uptake is higher than Tl uptake; metabolism perfusion), T-type (BMIPP uptake is lower than Tl uptake; perfusion metabolism.), and E-type (BMIPP and Tl uptake are equal). We evaluated changes in each mismatch patterns from the acute to chronic phases. Results The overall frequency of mismatch patterns showed that T-type increased significantly in the high IMR group (8.3% to 20.0%, P = 0.04) compared to no significant change in the low IMR group (7.6% to 4.9%, P = 0.5) (Figure 1). A positive correlation was observed between IMR and T-type change (Pearson r = 0.64, p = 0.002) (Figure 2). B-type and E-type decreased in both groups, with no significant differences. Conclusion High IMR is associated with the chronic persistence of T-type (perfusion-dominant) patterns in TTS patients, suggesting that elevated IMR contributes to sustained perfusion abnormalities. These findings indicate that IMR 25 may serve as a predictive marker for chronic myocardial perfusion abnormalities. Identifying high-risk TTS patients with elevated IMR may help guide long-term monitoring and management strategies.T-type Change IMR 25 vs IMR ≦ 25 Correlation between IMR & T-type Change