While the traditional unsheathing technique for the deployment of stent retrievers has proved successful in clinical use, in their experience, Raul Gomes Nogueira (Emory University School of Medicine, Atlanta, USA) and colleagues have developed a new technique for the deployment of the Trevo ProVue stent retriever (Stryker Neurovascular) that they have found produces better results than the traditional technique. At the Society of NeuroInterventional Surgery 12th Annual Meeting (SNIS; 27–30 July, San Francisco, USA), Nogueira presented the Push & Fluff technique and he now speaks to NeuroNews about how it was developed and the results they have seen so far.
What is the traditional technique used for deployment of the Trevo stent retriever?
The standard technique for the deployment of the Trevo Retriever constitutes in positioning the device across the occluded segment, and unsheathing the device by retracting the delivery microcatheter while immobilising the device delivery microwire leading to a passive stent opening. The radial force of the stent retriever compresses the clot against the blood vessel wall with subsequent incorporation of the clot material through the stent struts.
How did the idea for the new technique come about?
When the Trevo device became radiopaque (ProVue version) we saw the opportunity to manipulate the device to achieve better expansion at the level of the thrombus. Previous experience with close-cell design stents, such as the Enterprise stent (Cordis), had demonstrated that simply unsheathing the device often results in suboptimal wall apposition and a combined pushing and unsheathing technique resulted in better perfomance. The “fluffing” manoeuvre was very commonly employed with the initial version of the Pipeline device (Covidien/Medtronic) to achieve better device expansion and wall apposition. Once the Trevo device became fully visible giving the operator real time feedback we decided to use a combination of manoeuvres to optimise its deployment. The Push & Fluff technique seemed to lead to the best results.
Can you describe the Push & Fluff technique?
The technique consists in positioning the stent retriever across the clot and unsheathing the distal end of the device until good wall apposition (anchoring) is achieved (brief unsheathing step). After this, forward force is applied into the device delivery wire, which generates spontaneous retraction of the microcatheter (pushing step). At the main targeted area (where clot is located), forward tension is applied to the microcatheter while the delivery wire continues to be pushed in order to maximise the device expansion (fluffing step). The radiopaque properties of the device allow real-time feedback of the amount of fluffing and wall apposition. In curves, the forward tension of the microcatheter may have to be progressively decreased if the device is seen to collapse / lose apposition to the inner wall. Proper planning for the distal landing zone is needed considering the expected foreshortening of the device that typically happens with the technique.
What advantages have you seen with the Push & Fluff technique?
The Push & Fluff technique leads to optimisation of the device wall apposition which improves the device-clot interaction as well as to larger cell size and improved cell configuration (from slit-like to squared geometry) which allows for better incorporation of the thrombotic material into the stent retriever interstices. In a fluoroscopic model study, we observed 75% larger diameter and 50% larger cell area size in relation to the traditional unsheathing technique. A review of our clinical experience comparing the Push & Fluff technique (n=70) with the traditional unsheathing technique (n=81) demonstrated that the Push & Fluff technique was associated with higher rates of first pass reperfusion (54% vs. 35%, p=0.03), lower number of passes (1.3±0.8 vs. 1.8±1.0, p<0.01), and higher rates of mTICI-3 reperfusion (58% vs. 40%, p=0.03).
What were the results of your study comparing the techniques with different types of clot?
We have performed an imaging model analysis to study the degree of incorporation of the clot with the Push & Fluff technique versus the traditional unsheathing technique and observed that most of the benefit occurs with clots of harder consistency. Softer clots tend to respond to both techniques while harder clots are a lot better incorporated by the stent retriever with the use of the Push & Fluff technique.
Do you think that this technique should now be the standard technique used with the Trevo device?
Our data support that the Push & Fluff technique should be considered as the first line method of deployment for the Trevo device but it will still require further validation by other operators and centres.
What about other stent retrievers?
We have not used this technique with other stent retrievers. We believe it would be difficult and potentially unsafe to try to manipulate non-radiopaque devices to the extent we would need to achieve the desired morphologic changes. More importantly, the technique may not be applicable to devices that have different designs (eg. are not close-cell stents).
Is there a learning curve associated with the Push & Fluff technique?
The technique is relatively easy to teach and we have seen it being successfully incorporated very rapidly by other colleagues.
I would like to acknowledge the contribution of my partner Diogo Haussen and our stroke research fellow Leticia Rebello who have helped me with the analysis of our clinical experience as well as our collaborators from the New England Center for Stroke Research at the University of Massachusetts led by Matthew Gounis who conducted our imaging model analysis.