Background and objectives: The pathophysiology of coronary microvascular dysfunction is multifactorial and includes impaired vasomotor function, microvascular obstruction (MVO), microvascular injury (MVI), intramyocardial hemorrhage (IMH) and inflammation. It can be assessed with invasive and non-invasive methods. Index of microcirculatory resistance (IMR) and MVO are the most used indices. As a non-invasive modality cardiac magnet resonance imaging (MRI) is an accurate method to visualize MVO, the invasive modality to assess microvascular dysfunction is a pressure-wire-based and thermodilution-derived method. A novel method to capture IMR non-invasively is using the software package Medis Suite 2.1.12.2 from Medis Medical Imaging System (Leiden, Netherlands). Patients with a chronic total occlusion (CTO) of a coronary artery have microvascular dysfunction in the CTO supplied territory. Interestingly the microvascular dysfunction persists immediately after successful CTO recanalization. Data on recovery of microvascular function after successful CTO PCI are rare. The aim of this study was to study the effect of successful CTO PCI on the microvascular function of the CTO supplied territory directly after CTO PCI and at 6 months follow-up. 

Methods and results: Our analysis included 30 patients undergoing successful CTO recanalization at the University Medical Center of Mainz. The measurement to assess IMR was performed directly after successful CTO PCI and at 6 months follow-up. IMR was performed offline using a software package (Medis Suite 2.1.12.2, Medis Medical Imaging System, Leiden, the Netherlands). In the patient collective, 87.1 % were male with a median age of 61 years (45-80). The mean follow-up period was 183± 17.62 days. Median J-CTO Score was 2 (1-3), CTO was localized at the RCA in 61.3%,  at the LAD in 29.0% and at the RCX in 9.7% of the patients. All included patients had a good result after CTO PCI confirmed by Quantitative flow ratio (QFR) (0.97± 0.05) directly after CTO PCI. We found increased IMR values directly after CTO PCI with a significant decrease at 6 months follow-up (38.49± 12.96 vs. 30.98± 9.24¸p= 0.001). 

In our collective 24 of the enrolled patients reported an improvement in CCS class (p < 0.001) and 19 an improvement in NYHA class (p < 0.001). 

Conclusions: We found microvascular dysfunction in our collective of patients with CTO assessed non-invasively by IMR. At 6 months follow-up successful CTO PCI could decrease IMR value, accompanied with an improvement in patients-reported clinical symptoms.