medicine&technology 01.2019

■ [ TECHNOLOGY ]
At 40,000 Revolutions per Minute,
Small Motor Clears Clot from Vessel
Small motors | At high speed, a drive is able to break up thrombi in the leg inside the
vessel and remove them. Very small, high-speed motors are used in such catheters
made by Straub Medical. That’s not all. This Swiss manufacturer is already working on
even smaller solutions for the treatment of heart attacks and strokes.
A metal spring in the catheter
rotates quickly to
break up and remove a
blood clot blocking a
vessel. In the catheter
head, chisel-like structures
can break up solid clots.
The fragments are transported
by a vortex current
into the catheter’s openings
and out of the body.
Photo: Straub Medical
A
thick clot, a thrombus of coagulated
blood, that gets stuck in the artery
from the knee into the thigh can practically
stop the flow of blood in the leg.
Smaller blood vessels are not able to compensate
fully for the blocked flow in the
artery, however. The outcome: Lack of
oxygen to the muscles makes walking
painful after a few steps. Patients are
forced to stand still, and in the city they
may inconspicuously browse the merchandise
in store windows. Peripheral artery
disease (PAD) has this behaviour to
thank for the colloquial name Germans
use: “shop-window disease.”
This type of blockage can be treated,
amongst other methods, with a medical
YOUR KEYWORDS
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Small motor
High speed
Contactless magnetic coupling
Protection of motor and vascular wall
Special vortex method
device that breaks up the clot and removes
it from the vessel. The Rotarex S
catheter, developed by Straub Medical in
Switzerland, features a head not much
bigger than that of a match. The doctor introduces
the catheter into the artery
through puncture and advances the device
to the occluded blood vessel. There,
the catheter head starts to rotate and suction
at the press of a button. A little while
later the thrombus is completely removed.
Chisel breaks up clot,
fragments removed by suction
To generate the rotational movement, a
motor outside of the body is connected to
the catheter through a contactless magnetic
coupling. The rotation generated by
the motor is transmitted to the head inside
the body by a high-strength steel spiral
(also called a helix) located inside the
catheter tube. The end of the catheter
head itself is slanted on both sides—like a
chisel. Once the head starts spinning,
these surfaces break up the solidified material
of the thrombus from inside out and
set the fragments spinning in a vortex that
cleans out the entire diameter of the
blood vessel.
The catheter head has two small side
openings where the helix is exposed. The
rotating helix suctions the free fragments
into the tube, based on the principle of
Archimedes’ screw. Inside the tube, the
fragments are broken down even further
by internal blades, making for smooth
passage to the retrieval bag outside of the
body.
“Removal of the occluded material
takes about three minutes on average,”
explains Dirk Dreyer, Director of Sales
and Marketing at Straub Medical. Known
from thrombolysis and other procedures,
effects like a stay on the intensive care
unit or damage to the vascular wall can be
avoided. For fresh thrombi, the Aspirex S
variant is used, which does not need the
rotating chisel of Rotarex S at its suction
head. The suction effect of the rotating
helix is enough to aspirate the clot
through the side openings and transport
it out of the body.
High, constant speed is needed so the
head of Rotarex S can break up the clot
50 medicine&technology 01/2019