Medical TextilesATI Special Report Cardiac Support
Acorn knits polyester medical device to improve the quality of life for heart-failure
patients. What will they think of next Knitted and woven textiles have been showing up in
innovative medical devices that are correcting life-threatening conditions of the heart and
vascular system. Implantation of the new devices requires less invasive surgical procedures and
involves less risk than traditional procedures, while also causing fewer complications and
necessitating shorter hospital stays and recoveries.
In the knitted category, Acorn Cardiovascular Inc. (acorn), St. Paul, Minn., has developed a
new textile device that will potentially help more than 23 million people worldwide fight the
progressive effects of heart failure.Heart failure is a chronic syndrome caused by a number of
conditions that, in the end, impair the ability of the heart to move the correct amount of blood
through the body. To compensate, the heart enlarges (dilates), stressing the heart muscle. Other
changes due to dilation, such as the initial valve leakage, cause additional stress. Unfortunately,
50 percent of those diagnosed with heart failure pass away within five years.According to the
American Heart Association, 550,000 new cases of heart failure are diagnosed in the United States
every year. Most treatments for the condition, including extensive drug therapies and surgical
correction of the underlying causes, relieve symptoms or temporarily improve the patients
condition, but they are not effective long-term cures. Only a heart transplant will prevent
progression of the condition and eventual death due to heart failure, but unfortunately, many
heart-failure patients will not qualify for a heart transplant. In addition, the number of hearts
available for transplant is quite limited. acorn has developed the Cardiac Support Device (CSD),
which is intended to halt the progression of heart failure. The CSD FabricExtensive research
was conducted by acorn to determine the best material, yarn configuration, knit pattern and
processing to use in producing the CSD fabric. The mesh-like, warp-knitted proprietary fabric is
made using machinery manufactured by Germany-based Karl Mayer Textilmaschinenfabrik GmbH. Michael
J. Girard, director of product development, describes the device: The acorn Cardiac Support Device
(CSD) is a warp-knitted textile substrate. The fabric is fabricated from multifilament textured
polyethylene terephthalate (commonly known as polyester) yarns. Polyester was the material of
choice due to its biological tissue response and compatibility with the epicardial surface of the
heart.The polyester yarns are warp knitted into a mesh configuration using a variation of an atlas
stitch. After knitting, the fabric is conditioned to ease its handling during the processing to
manufacture the CSD.Manufacture of the CSD includes cutting the fabric to pattern, sewing, scouring
and heat-forming. The result of these proprietary processes is a device with specific mechanical
characteristics and a shape that closely resembles a diseased heart.Key mechanical characteristics
of the CSD design and manufacturing include a device that gently conforms to the surface of the
heart and provides mechanical support by uniformly distributing stresses. To accommodate a wide
range of diseased heart sizes and shapes, the CSD is manufactured and offered in multiple clinical
sizes. How The CSD WorksThe CSD has been designed to conform to the heart, while at the same
time providing strength, compliance to varying degrees, tear-resistance and compatibility with
heart tissue. The device is slipped easily over the heart, adjusted to provide proper support and
stitched into place. It is less compliant in its circumference and more so in its vertical
direction, thus facilitating reshaping of the heart from the sphere-like shape associated with
heart failure into the more ellipsoidal shape of a healthy heart.By conforming to the shape of the
heart and supporting it, the CSD resists further dilation, while the devices compliance allows the
heart to maintain a normal beat. It is thought that the support given by the CSD may also prevent
further stretching of the mature muscle cells and allow relaxation and recovery of the affected
cells. Advantages Over Other DevicesThe procedure used to implant the CSD is considerably less
complicated than other cardiothoracic surgical procedures for heart failure. Furthermore, it is
anticipated that the implantation will require a shorter hospital stay than other procedures. Other
advantages include: compatibility with other cardiovascular surgeries and minimally invasive
surgical techniques; a minimal potential for complications, such as blood clots, that are
associated with vascular devices; and lower cost to the patient than other heart-failure
devices.The CSD has been evaluated in a clinical safety study conducted in Germany, and in
extensive pre-clinical studies, with promising results. The new device has received CE (European
Conformity) mark approval in Europe, and acorn recently earned ISO 9001/EN46001 certification as
well.The CSD is now classified as an investigational device. A randomized clinical trial underway
in the United States eventually will involve up to 170 patients in approximately 15 centers, and
studies are also being conducted in Germany and Australia.The CSD is acorns first product developed
to improve the quality of life for heart-failure patients. The company is investigating other
possible textile applications for future products.
As heart failure progresses, the shape of the heart changesfrom its normal ellipsoidal shape
to a sphere-like shape.
Editor In Chief James M. Borneman and Assistant Editor Janet Bealer Rodie contributed to this
article.
February 2001
