Resistive reserve ratio (RRR) predicts myocardial metabolic recovery in the acute phase of takotsubo syndrome: a pilot study
Y Nishimura, J Komatsu, H Nakayama, M Nukariya, N Sasaoka, H Matsuda, H Sugane, Y Ikai, H Hosoda, R Imai, Y Nakaoka, S Mito, S Seki, K Kawai, Y DoiAbstract
Background
Takotsubo syndrome (TTS) presents as a cardiovascular emergency requiring rapid risk stratification. Microvascular dysfunction is central to its pathophysiology, yet no validated tool exists in the acute setting to predict myocardial recovery. Early identification of patients at risk for incomplete metabolic recovery could guide clinical decision-making and follow-up intensity.
Purpose
To determine whether acute-phase coronary microvascular indices — index of microvascular resistance (IMR) and Resistive Reserve Ratio (RRR) — predict subsequent resolution of BMIPP-Tl mismatch — defined as discordance between myocardial metabolism (¹²³I-BMIPP) and perfusion (²⁰¹Tl) scintigraphy — as a marker of myocardial metabolic recovery in TTS.
Methods
Among 21 consecutive TTS patients, 15 (mean age 78 ± 11 years; 67% female) who underwent invasive microvascular assessment (IMR and RRR) within 48 hours of onset and dual-isotope myocardial scintigraphy (BMIPP and Tl) at both acute and chronic phases (1 month) were prospectively enrolled. Patients were stratified by IMR (cut-off: 25) and RRR (cut-off: 2.1), and mismatch improvement rates were compared.
Results
Mean IMR and RRR were 28.3 ± 13.0 and 2.08 ± 1.14, respectively. IMR-based stratification showed no significant difference in mismatch improvement (high-IMR 60.5 ± 19.5% vs. low-IMR 28.6 ± 26.4%, p=0.35). In contrast, high acute-phase RRR was associated with significantly greater mismatch improvement (high-RRR 83.3 ± 40.8% vs. low-RRR 20.4 ± 63.9%, p=0.037) (FIGURE), suggesting that microvascular vasodilatory reserve — rather than resting resistance — drives metabolic recovery.
Conclusions
In this pilot study, acute-phase RRR emerged as a promising bedside predictor of myocardial metabolic recovery in TTS. These findings suggest RRR could serve as a novel risk stratification tool in the acute management of TTS, which should be validated in larger prospective cohorts.FIGURE