Abstract
Thrombectomy in coronary arteries and peripheral vasculature is a common procedure performed with electromechanical thrombectomy systems and basic syringe–catheter combinations. Electromechanical systems are associated with speed, power, high-cost, and complexity while basic syringe aspiration systems are associated with ease-of-use, lower cost, and less aspiration force. This report describes a novel mechanical thrombus aspiration system designed to improve aspiration speed and performance plus associated cases studies.
1
Introduction
Coronary thrombus aspiration can improve clinical outcomes and reperfusion when combined with angioplasty and stenting compared to angioplasty and stenting alone . Outside of the heart, successful thrombus aspiration has been reported in arterial–venous fistulas and grafts; deep veins in the legs; peripheral arteries; and other arteries and veins .
Thrombectomy is generally classified into two different platforms: electromechanical maceration/aspiration systems and manual thrombus aspiration devices. Typically, electromechanical systems ( Fig. 1 ) are configured with proprietary catheters, macerators, and/or pumps with integrated aspirant collection features. Manual thrombus aspiration devices include proprietary catheters with differentiated tip geometries and basic locking syringes ( Fig. 2 ). Manual aspiration may also be performed with basic syringes and standard catheters.
In general, electromechanical maceration–aspiration systems are used in older, and more organized, thrombus while manual thrombus aspiration devices are more commonly used in soft and fresh thrombus. In addition, electromechanical systems are characterized as more powerful, expensive, complex, and difficult to set-up/use than simple, and easy-to-use, syringe based systems. Accordingly, there is a performance, financial, and ease-of-use gap between electromechanical systems and basic syringe based thrombus aspiration devices.
Beyond the difference in technology platforms, numerous technical and pathological variables influence the quality of thrombus aspiration including the size (area) of the aspiration lumen, the length of the aspiration lumen, shape of the lumen, size of the aspirant, viscosity of the aspirant, the amount of proximal aspiration force, and other variables.
2
Existing technology
2.1
Aspiration force and catheter size
Loss of aspiration force can occur during manual thrombus aspiration with a basic syringe . And, despite industry attempts to differentiate basic aspiration devices based on proprietary catheter tip designs, catheter tip shape is not a major factor in effective thrombus aspiration . In addition, smaller bore (inner diameter) aspiration catheters require greater vacuum pressure compared to larger bore catheters .
Basic laws of physics and fluid dynamics provide additional foundation for these conclusions including Pascal’s Force = Pressure × Area and Poiseuille’s Rate of Flow Q = π × r 4 × (ΔP)/8 × n × L ( Q = Flow Rate, r = radius, p = pressure, n = viscosity, L = length).
As per Poiseuille Law, radius has the largest impact on the rate of flow of fluid through a tube. All other things being equal, a small increase in radius will dramatically improve the rate of flow. For example, a 10% increase in radius will result in a 47% + increase in the rate of flow. Reducing viscosity and shortening the length of the tube also increase the rate of flow. Increasing pressure differential between in-vivo pressure and the proximal catheter increases the rate of flow and force.
Clinicians and/or the clinical presentation influence some of these variables. For example, catheter inner diameters (ID), outer diameters (OD), and lengths may be dictated by access (sheath & guide cath) and target anatomy. Viscosity of the aspirant is dependent on thrombus size, location, and age plus any lytic and/or mechanical treatment. However, when using a basic syringe, a clinician does not have a way to modulate aspiration force and otherwise maintain, pulse, or increase aspiration during the procedure.
2.2
Loss of aspiration force with basic syringes
Loss of suction is problematic when trying to dislodge and aspirate blood clot . Typically, if there is no air in a barrel, connective tubing, or a catheter during preparation, insertion, and use, basic syringes used at sea level theoretically allow users to initially create maximum aspiration force when a plunger is first pulled back (− 1 ATM/− 14.7 psi/− 760 Torr (mmHg) at sea level).
However, air can enter the circuit-barrel through numerous sources including connectivity (Luer connection, leakage around y-adapter valves, etc.), catheter introduction, fluid degassing, cavitation, and other variables. Air is an elastic fluid and when it enters a barrel, aspiration force drops. The drop in aspiration force depends on how much air enters the barrel and barrel size.
Clinicians may purge air in the barrel of a basic syringe by repeatedly removing the syringe from the catheter, inverting the syringe, and expelling the air and/or aspirant, reconnecting the syringe, and reactivating aspiration. Alternatively, an electromechanical pump may be use to purge air, pulse aspiration, and/or maintain continuous aspiration (Bayer Medrad AngioJet and Penumbra).
2.3
Lack of speed, efficiency and control with basic syringe aspiration
Most manual aspiration systems are powered by one 30 ml-locking syringe and a stopcock
The above sequence is time consuming, messy, and may invite contamination, staff exposure to biohazard, and other complications. In addition, basic syringes do not allow users to increase, pulse, and maintain continuous aspiration force as the stopcock only allows clinicians to start and stop aspiration force.
Clinicians and certain manufacturers attempt to minimize the above sequence by including a basic 60 ml-locking syringe. A larger syringe barrel may generate more aspiration force but is physically more difficult to actuate and still does not solve the need to purge air in the barrel to maintain aspiration force.
By comparison, some electromechanical systems (AngioJet and Penumbra) are closed aspiration circuits with integrated collection/drainage that do not require multiple catheter–syringe connection, disconnection, and reconnection. Some electromechanical systems allow users to pulse and maintain continuous aspiration force.
2
Existing technology
2.1
Aspiration force and catheter size
Loss of aspiration force can occur during manual thrombus aspiration with a basic syringe . And, despite industry attempts to differentiate basic aspiration devices based on proprietary catheter tip designs, catheter tip shape is not a major factor in effective thrombus aspiration . In addition, smaller bore (inner diameter) aspiration catheters require greater vacuum pressure compared to larger bore catheters .
Basic laws of physics and fluid dynamics provide additional foundation for these conclusions including Pascal’s Force = Pressure × Area and Poiseuille’s Rate of Flow Q = π × r 4 × (ΔP)/8 × n × L ( Q = Flow Rate, r = radius, p = pressure, n = viscosity, L = length).
As per Poiseuille Law, radius has the largest impact on the rate of flow of fluid through a tube. All other things being equal, a small increase in radius will dramatically improve the rate of flow. For example, a 10% increase in radius will result in a 47% + increase in the rate of flow. Reducing viscosity and shortening the length of the tube also increase the rate of flow. Increasing pressure differential between in-vivo pressure and the proximal catheter increases the rate of flow and force.
Clinicians and/or the clinical presentation influence some of these variables. For example, catheter inner diameters (ID), outer diameters (OD), and lengths may be dictated by access (sheath & guide cath) and target anatomy. Viscosity of the aspirant is dependent on thrombus size, location, and age plus any lytic and/or mechanical treatment. However, when using a basic syringe, a clinician does not have a way to modulate aspiration force and otherwise maintain, pulse, or increase aspiration during the procedure.
2.2
Loss of aspiration force with basic syringes
Loss of suction is problematic when trying to dislodge and aspirate blood clot . Typically, if there is no air in a barrel, connective tubing, or a catheter during preparation, insertion, and use, basic syringes used at sea level theoretically allow users to initially create maximum aspiration force when a plunger is first pulled back (− 1 ATM/− 14.7 psi/− 760 Torr (mmHg) at sea level).
However, air can enter the circuit-barrel through numerous sources including connectivity (Luer connection, leakage around y-adapter valves, etc.), catheter introduction, fluid degassing, cavitation, and other variables. Air is an elastic fluid and when it enters a barrel, aspiration force drops. The drop in aspiration force depends on how much air enters the barrel and barrel size.
Clinicians may purge air in the barrel of a basic syringe by repeatedly removing the syringe from the catheter, inverting the syringe, and expelling the air and/or aspirant, reconnecting the syringe, and reactivating aspiration. Alternatively, an electromechanical pump may be use to purge air, pulse aspiration, and/or maintain continuous aspiration (Bayer Medrad AngioJet and Penumbra).
2.3
Lack of speed, efficiency and control with basic syringe aspiration
Most manual aspiration systems are powered by one 30 ml-locking syringe and a stopcock
The above sequence is time consuming, messy, and may invite contamination, staff exposure to biohazard, and other complications. In addition, basic syringes do not allow users to increase, pulse, and maintain continuous aspiration force as the stopcock only allows clinicians to start and stop aspiration force.
Clinicians and certain manufacturers attempt to minimize the above sequence by including a basic 60 ml-locking syringe. A larger syringe barrel may generate more aspiration force but is physically more difficult to actuate and still does not solve the need to purge air in the barrel to maintain aspiration force.
By comparison, some electromechanical systems (AngioJet and Penumbra) are closed aspiration circuits with integrated collection/drainage that do not require multiple catheter–syringe connection, disconnection, and reconnection. Some electromechanical systems allow users to pulse and maintain continuous aspiration force.
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