Chance favors the prepared mind

In 1894, during his inaugural lecture as the new Dean of University of Lille in Douai France, Louis Pasteur [1] commented; ‘‘Dans les champs de l’observation, le hazard ne favorise que les esprits préparés’’ (In the fields of observation, chance favors only prepared minds). Such is the case 100 years later when Dr. Juan Parodi began his meticulous observation of changes in transcranial Doppler flow patterns during different stages of carotid endarterectomy (CEA). It is likely many of us had seen these patterns before but after reflecting on the findings Dr. Parodi recognized some interesting subtle cerebral flow physiology signals. He was able to then amplify middle cerebral flow patterns during CEA with passive and active back bleeding of the internal carotid artery (ICA) in wake patients without causing symptoms. Through this work he then postulated that transcatheter carotid flow control and even reversal may be possible with a balloon tipped sheath in the common carotid artery (CCA). He also recognized the importance of collateral flow from the external carotid artery (ECA) and that persistent antegrade ICA flow via retrograde ECA collateralization could be expected during CCA occlusion and accordingly ECA occlusion would also be required to achieve protection. He believed occlusion of the ECA using a balloon on a wire navigated through the balloon tipped CCA sheath would solve the issue and the two components proximal carotid protection system reported herein was born. Interestingly, around the same time, a group of innovative well-known clinicians in Italy were also considering proximal protection alternatives to filters and their pioneering work gave rise to the single component proximal flow control system (Mo. Ma., Invatec, Roncadelle, Italy) While Dr. Parodi was solidifying his proximal protection vision our team was developing a distal filter protection system for carotid stenting. Based on our interpretation of past basic science embolization research and clinical analysis of the particle size threshold associated with documented neurologic events caused by particles from 10 to 50 microns, it seemed the filter pore size threshold should be well below 50 microns [2]. Unfortunately animal studies with sub-50 micron pore filter prototypes were disastrous as the flow resistance not only occluded the vessel but also caused a ‘‘sail’’ effect forcing the system forward with flow while also frequently causing the filter material to separate from the cage. Like many others, we began arbitrarily increasing pore size to solve the flow resistance issue. In the end, we found the ideal pore size needed to ensure normal end organ flow was best calculated by balancing the individual pore size and number of pores with the cone length to achieve the same final total pore cross-sectional area as the target vessel cross-sectional area (note: In carotids this turned out to be around 100 microns with our 25 mm cone length). Thus, the current filter pore size for available distal protection systems was selected based on the ability to maintain flow rather than objective data on particle size safety. Coincident with our work Dr. Takao Ohki [3] began studying filter embolic capture performance with a unique ex vitro model and found embolization (although minor) occurs during crossing with the wire and filter before protection can be initiated. Dr. Ohki’s work amplified our concerns about filters and it was at this time we were introduced to Dr. Parodi’s concept which seemed to solve some of the theoretical concerns related to filters. We then teamed up with Drs Parodi, Ohki, and Claudio Schonholz to move the proximal protection vision forward. The initial method of flow reversal with the Parodi system was passive back bleeding through the Touhy valve or via 10 cc syringe suction. During the first flow reversal animal studies in Charleston, we found there was significant blood loss and saturation of the operative field during passive back bleeding. Out of necessity, we worked on several remedies and found gradient