In vivo feasibility study of ultrasound potentiated collagenase therapy of chronic total occlusions.

Arterial chronic total occlusions (CTOs) pose considerable challenges for percutaneous interventions, due primarily to the presence of stiff proximal fibrous caps (PFCs) which act as a barrier to the penetration of guide wires. A new approach under development for improving the success rate of guide wire crossing in CTOs is to employ collagenase to degrade the mechanical integrity of the PFCs. This has been shown to be feasible in preclinical work and in a Phase 1 clinical trial. In a recent study we demonstrated using ex vivo experimental CTO specimens that ultrasound-stimulated microbubbles (USMBs) could potentiate the effects of collagenase and result in increased mechanical degradation of the PFCs of CTOs. Here we report the results of the first in vivo study examining the feasibility of this approach, which demonstrates that the force required to puncture through the PFCs of CTOs is reduced with combined USMB+collagenase treatments relative to collagenase only treatments. This approach has the potential to further improve the efficacy of the emerging technique of collagenase facilitation of percutaneous interventions for CTO.

The use of ultrasound-stimulated contrast agents as an adjuvant for collagenase therapy in chronic total occlusions.

AIMS: To investigate the effectiveness of combining collagenase and ultrasound-stimulated microbubble (USMB) treatments in reducing the mechanical force required for crossing a guidewire through CTOs. METHODS AND RESULTS: Experiments were conducted on ex vivo specimens of a rabbit femoral artery CTO model (n=45 total samples). Four primary groups were employed: control (n=6), collagenase only (n=15), USMB only (1 MHz frequency) (n=5), and collagenase+USMB (n=19). In one set of experiments the force required to puncture through CTO samples was measured and it was found that the puncture force was 2.31-fold lower for the combined treatment group relative to the comparable collagenase-only group (p<0.05). In a second set of experiments, the total protein and hydroxyproline content of the supernatant solution adjacent to the CTO was analysed. Significantly higher hydroxyproline levels were measured in collagenase+USMB treated CTOs (0.065 g/mL) compared to collagenase (0.030 g/mL), USMB (0.003 g/mL) and control (0.004 g/mL) (p<0.05), indicating that the combined treatment augmented collagenase degradation. CONCLUSIONS: Ultrasound-stimulated microbubbles improved the effectiveness of collagenase in reducing the force required to cross experimental CTOs. This new approach may have the potential to reduce treatment times and improve the success rates of emerging collagenase-based treatments of CTO.

A novel method for the measurement of proximal fibrous cap puncture force in chronic total occlusions: the effect of increasing age.

AIMS: The composition of CTO lesions changes significantly as they age. These changes may adversely affect PCI outcome. We present a robust ex vivo technique to measure the force required to puncture the proximal cap of CTOs, and to determine whether the puncture force differs according occlusion age to examine the effects of compositional changes over time on lesion stiffness. METHODS AND RESULTS: Occlusions were created in 44 rabbit femoral arteries by thrombin injection. Between two and 15 weeks following induction, vessels were harvested and tested in a custom setup to determine the force required to puncture the proximal cap. The puncture force mean values at 2, 6, 12, and 15 weeks were 0.61N, 0.78N, 1.21N and 1.52N, respectively. The puncture force required in occlusions of ≤6 weeks was significantly lower those≥12 weeks (0.72±0.10N versus 1.45±0.13N, p<0.01). Using a cutoff point of 1N, 86% of lesions≤6 weeks of age required<1N compared to 30% of those≥12 weeks. CONCLUSIONS: We have shown an objective and reproducible testing system for measuring CTO puncture force. Puncture force is correlated with occlusion age. This technique would be useful to evaluate therapies that alter CTO composition/compliance, as well as guidewire testing.