Recovery of coronary artery distensibility after two and four years in vivo degradation of a resorbable magnesium-based scaffold

The elastic properties of coronary arteries are associated with different vascular conditions, in particular the degree of severity and pathology of coronary artery disease. In contrast to permanent stents, bioresorbable scaffolds provide temporary support to the treated lesion while allowing for restoration of the physiological vasomotion due to resorption within a certain period of time. Coronary artery distensibility may serve as a measure for vascular restoration after implantation and in vivo degradation of a bioresorbable scaffold. This study presents an investigation of the distensibility of porcine coronary arteries two and four years after implantation of a resorbable magnesium-based scaffold (RMS, Freesolve^TM scaffold prototype and Freesolve^TM scaffold, respectively, Teleflex) based on measurements of the pressure-dependent luminal area using an ex vivo test setup including intravascular optical coherence tomography. In case of a normotensive pressure regime, mean distensibility values were found to be 1.45 ± 0.47 × 10^-3 mmHg^-1 for the untreated artery regions and 1.03 × 10^-3 mmHg^-1 for the RMS region after two years in vivo degradation (71% distensibility recovery) as well as 1.40 ± 0.01 × 10^-3 mmHg^-1 after four years in vivo degradation (97% distensibility recovery), respectively. Reference measurements of a permanent drug eluting stent region revealed a distensibility of 0.80 × 10^-3 mmHg^-1. The findings of this study support the hypothesis that the radial elastic properties of the coronary artery can be regained following the in vivo degradation of a magnesium-based scaffold. STATEMENT OF SIGNIFICANCE: The elastic properties of coronary arteries are associated with the pathology of coronary artery disease. Measurement of coronary artery distensibility can be used to quantitatively assess passive radial elasticity of the arterial wall. Within the current study, two porcine hearts two years and four years after implantation of a resorbable magnesium-based scaffold were investigated regarding their coronary artery distensibility. Using an ex vivo test setup based on intravascular optical coherence tomography overcomes many limitations of in vivo investigations. The results show an increasing distensibility recovery over degradation time. For the first time, the hypothesis that the elastic properties of the coronary arteries can be restored following the in vivo degradation of a magnesium-based scaffold could be verified by quantitative measurements of distensibility.