Download Atrial Septal Defect - Research

Atrial Septal Defect
Closure
Thomas Hoy
Department of Biomedical Engineering
Vanderbilt University School of Engineering
April 27, 2004
Advisor: Dr. Thomas Doyle
Assistant Professor of Pediatrics, Vanderbilt University Medical School
Pediatric Cardiology, Vanderbilt University Children’s Hospital
Instructor: Dr. Paul King
Associate Professor of Biomedical Engineering
Vanderbilt University School of Engineering
I. Abstract
An Atrial Septal Defect (ASD) is a type of congenital heart disease (CHD) that
results in an abnormal opening in the atrial septum. The formation of the defect begins in
the early embryonic heart where the atria consist of a common chamber, later in
development the atria enlarge and fusion of the septum primum and septum secundum
interatrial wall occurs, an ASD forms when this fusion is absent or delinquent. Problems
arise when this type of defect is left until adulthood; the most common life threatening
problems associated with this disorder are congestive heart failure, pulmonary
hypertension, and atrial arrhythmias occurring mainly in adults.1 An ASD is present in 8
out of every 10,000 newborns giving rise to a significant patient base.2 There are two
approaches to treating this defect. The surgical approach and the transcatheter approach,
both with significant advantages and drawbacks. The goal of this design is to develop a
novel device that eliminates the problems associated with the existing transcatheter
models. Because every transcatheter device on the market today and many in
development consists of a wire framework for structural positioning and support this
model is designed to eliminate the wire-related problems arising from this framework and
opt for a more biocompatible device. Research and brainstorming of possible solutions to
this problem began in December of 2003 with the completion date of the model set for
April 27, 2004. The final design, a double balloon detachable device, uses a balloon with
a biocompatible support structure surrounding it to occlude the defect. Further progress
with this project would depend on finding or developing suitable materials for the
construction of a prototype.
II. Introduction
During embryonic heart formation the atria develop a wall or septum dividing a
single chamber into two separate partitions. An ASD occurs when this wall does not form
completely, resulting in a hole between the right and left atria. Since this defect occurs
during embryonic development, it is classified as a type of congenital heart disease that
mainly affects the right atrium, right ventricle, and pulmonary arteries.
With a hole between the interatrial septum, a heart with an ASD must work
overtime to pump the same amount of blood to the body. In a normally functioning heart
the changes in pressure throughout the four chambers allow the valves to open and close
with full compliance with each chamber pumping the same amount of blood. A heart
with an ASD allows for a pressure sink, called a shunt, across the septum, causing
oxygen-rich blood from the higher pressure left atrium to be transmitted to the lower
pressure right atrium and back into the lungs; thus, the right atrium is required to
continuously pump oxygen-rich blood.1
Overall an ASD occurs in 8 out of every 10,000 newborns and exist in an
estimated 4 in every 100,000 adults giving a significant patient base and recurring patient
base for the development of new devices.2 The majority of children are asymptomatic;
however fatigue and shortness of breath are the most common ailments. Because most
patients have no symptoms, an ASD is most often discovered during a routine medical
examination early in childhood, when a heart murmur heard and investigated.3 Twenty
percent of atrial septal defects close spontaneously within the first year of life. One
percent becomes symptomatic in the first year, with an associated 0.1% mortality. There
is a 25% lifetime risk of mortality in an unrepaired ASD.4 This is why known defects are
chosen to be close which has not closed spontaneously by school-age.
There are three types of atrial septal defects. The ostium primum type accounts
for 20%, the ostium secundum accounts for 70%, and the sinus venosus accounts for the
remaining 10%.1 Each is formed in the early embryonic heart as the atrium grows from
one shared chamber to two separate chambers. As the atrium enlarges the septum primum
forms and grows toward the developing atrioventricular (AV) canal area, which is later
divided by the atrial and ventricular endocardial cushions. These cushions combine
towards the atria, thereby approaching the septum primum, which is downwardly
growing. This process narrows the hole between the atria, called the ostium primum. An
ostium primum ASD occurs when there is a deficiency of the endocardial cushions and
the AV septum.5 This defect is almost always associated with a cleft in the anterior
leaflets of the mitral and tricuspid atrioventricular valves and can result in left-to-right
atrial shunting, mitral valve regurgitation, and AV shunting, each of which causes
congestion of the right, left, or both sides of the heart, respectively.6
In the ostium secundum ASD, the ostium primum closes completely but not
before a central hole appears in the septum primum; this allows for continuous blood
flow from the right atrium to the left atrium, which is essential in embryonic development
due to the lack of pulmonary circulation. This hole is the second opening in the septum
primum and is called the ostium secundum. As the atria expand to either side of the heart,
a fold is produced within the atria near the septum primum. This fold is the septum
secundum. The tip of the septum secundum is concave in shape and is called the foramen
ovale. It overlays the ostium secundum but does not interfere with blood flow from right
to left through the ostium secundum. After birth, as pulmonary circulation begins and the
left atrial pressure rises, the septum primum is pushed against the septum secundum,
closing the ostium secundum.5 An ostium secundum ASD occurs when the septum
secundum and foramen ovale do not fuse after birth. This defect is accompanied by a leftto-right shunt across the interatrial septum. This type of defect is more often excessively
large because of the increased resorption of tissue of the septum secundum that is to
cover the ostium secundum and can result in left-to-right atrial shunting, which causes
congestion to the right side of the heart.6
The sinus venosus type is the least prevalent major type of ASD whose
embryology is not fully understood. It is usually positioned nearest the top of the atrial
septum close to the entrance to the superior vena cava and is formed as a result of the
superior vena cava inserting abnormally and thus overriding the atrial septum.7 This
abnormality generally affects the pulmonary veins, whose purpose is to carry oxygenated
blood from the lungs to the left atrium, but with the sinus venosus ASD it causes blood to
drain into the right atrium instead. As a result this causes a left-to-right shunt across the
atria that result in the enlargement of the right side of the heart as well as the pulmonary
artery.6
IIa. Current Treatment Options
There are two methods used for treating atrial septal defects. The first method is a
surgical approach. Pioneered in the 1940’s this approach can be used in any situation
involving an ASD with treatment options that include direct suture repair, which is
reserved for small atrial septal defects, and the more common patch repair. The material
utilized for patch closure of ASD’s may be the patient’s own pericardium, commercially
available bovine pericardium, or synthetic material.3 This type of surgery is “minimally
invasive,” where the surgeon gains access to the heart through either the sternum (median
sternotomy), between the ribs (right thoracotomy), or under the breast tissue
(submammary).8 The main drawbacks of surgical closure are costs associated with the
procedure, the use of a cardiopulmonary bypass machine, the length of hospital stay, and
the overall recovery time of the patient. However, the results of surgical repair of atrial
septal defects are excellent. Surgical mortality is less than one percent, and average
hospital stay is four days.9 These results indicate that ASD’s of all types may be
effectively repaired in infants and children with very low mortality and morbidity.
A more popular method is the transcatheter approach which involves the
implantation of one of several devices, shown in Table 1, with basically single or double
wire frames covered by fabric, using cardiac catheterization, and without the need for
cardiopulmonary bypass. This method uses the same technique as a cardiac
catheterization with a catheter being introduced into the groin and advanced into the
heart. By using a balloon catheter the defect is then sized in comparison so that a device
of the appropriate diameter can be chosen. The device is then advanced into the heart,
across the ASD, and opened to occlude the defect. The limitations of transcatheter
closure include the size and location of the defect. Drawbacks of this procedure include
wire related problems such as perforations, wire failure, migration, and clot formation on
the device; all of which account for a complication rate of approximately 5% following
closure of the defect by a device.10 Other drawbacks include a large septal rim for the
device, difficult device retrieval, and problems centering the device. The major advantage
of this method is its relatively non-invasive approach. Patients are usually hospitalized
and monitored overnight, and many return to work or school within 1-2 days with the
ability to resume vigorous exercise within one week. Successful closure of these defects
using a device occurs in 80 to 95% of patients with no significant shunting through the
occluded defects.9 A comparison of the two methods using a small test group is shown
below in Table 2. As you can see the statistical difference between certain sections of the
procedure give rise to the advantages and disadvantages of each method. However,
certain types of ASD's (sinus venosus and certain primum) have no chance of
spontaneous closure, and patients with these types of ASD's are not candidates for
transcatheter closure because of the location of the ASD and therefore, open heart surgery
is the only alternative for defect closure.8
Table 1. Comparison of Device Characteristics.
Table 2. Comparison of Surgical results to that of a Transcatheter method.
IIb. Design Specificaitons
The objective goal of this design project was to design a device that would better
serve the patient and cardiologist. Dr. Doyle described it to me as “a better way of doing
the procedure.” Based off the considerations of the drawbacks of the surgical and
transcatheter methods it was shown that the development of a new type of transcatheter
device would serve the premise of the design project. Listening to the recommendations
and design ideas given from my advisor a number of device possibilities arose and
through further consultation and research the following parameters for a new device were
developed.
The device was to meet the following specifications: to be less costly and more
simplistic compared to existing devices, to be easily centered upon the ASD, to have easy
use in the medical environment, to be favorable for endotheliazation of the device, to
increase the possible success rate of implantation, and to easily conform to this differing
size and shapes of defects.
IIc. Timeline
The device design process began in December of 2003 with research and
brainstorming atrial septal defects and possible ways for them to be closed. With the
completion date set for April 27, 2004 the four months of time between these dates
ensured that a certain amount of work was completed in each month. The first two
months were used for research and brainstorming of the device as well as web site
development. The next months were used to develop the material and supportive data
needed to justify this new device and to design a visual theoretical model. The timeline
for the projects development is illustrated on the project website and shows the
developmental process throughout the semester.
III. Methods
With so many devices either in market or under development it was difficult to
present a novel idea as a solution for this problem. I determined that an improvement
upon an existing device would be more fruitful rather than introducing a new design
model to the mix. However, when I talked with Dr. Doyle he instructed me on the
problems he sees with such existing devices and purposed I try a novel approach that
would be more theoretical in nature to solve the problems of today’s devices.
Within the past few years research into novel ways of approach this problem has
increased. In the past various solutions have left more questions than answers with the
main challenges regarding the fixation of the device to the defect.10 Along the lines of
developing a novel solution to this problem design development began with an in depth
research into existing devices, patents, investigational devices, and a constant redefinition
of the design parameters.
After meeting with Dr. Doyle it was determined that the ideal device would relate
most closely with the surgical procedure of applying a pericardial patch. This device
would exist as a thin membrane-like structure separating the two atriums. Some of the
recommendations include the non-invasive suture of a patch and the occlusion by a
detachable balloon device. In the interests of simplicity and cost associated with the
device, the detachable balloon approach was chosen as the design option to pursue.
With the detachable balloon device selected as the design questions as to how the
balloon would be implanted across the defect needed to be answered. In a study
performed in 2001 a group implanted detachable balloons across an artificially made
ASD in a piglet. This study required that the balloons stay inflated inside the heart for an
unlimited amount of time.10 Although the successful in occluding the defect the balloon
can not remain inflated after the procedure is completed; therefore, to be practicable in a
human the procedure must require that the balloon is deflated during the procedure. This
gives rise to the second part of the research into the solution.
There are many ways to adhere one object to another; however, intravenously
those options are severely limited. The necessary constraints of the method of adhesion of
the balloon to the interatrial septum were that it must be biocompatible, deployable at the
will of the cardiologist, and must act as a unit. First, I looked into the possibility of a
heat-activated bioadhesive or glue that could be used on the surface of the balloon and
activated by heated water passing through the balloon. However, this option was not
possible due to the high activation temperatures, toxicity of adhesive, and the inability to
bond to both the balloon and the septum effectively. Further investigation revealed
another possibility; that of a biodegradable material which offers support to the deflated
balloon structure until endothelialization could take over as a support structure. This
material is used, like nitinol wire, in coronary stents to brace an ablated artery wall from
collapsing; therefore, it has been proven to be safe for use inside various structures of the
heart.11 Then the final option of using a nitinol wire framework for support of the device
was researched and found to be the most practicable solution to this problem being that
the material has already proven in the medical environment as a reliable method for
device structure.
IV. Results
Upon meeting with Dr. Doyle in early March a final design was chosen and the
remaining device constraints were set. The device was to consist of a detachable double
balloon catheter that, when advanced into position, would be deflated across the defect
and would remain permanently in place. Among the reasons for choosing this manner of
occlusion was that the existing and developmental models had either trouble centering
upon the defect or required a septal rim 1.5 to 2 times that of the defect 10, meaning that
they were elaborate and large devices. A study published in Catheterization and
Cardiovascular Interventions documented the benefits of such a device in piglets;
showing that the use of a balloon catheter to completely occlude a defect required a septal
rim only slightly larger than that of the defect as well as being totally devoid of any
metallic complications.10 This device would be ideal however it is not practicable in the
human body because the study require the balloon to remain inflated for an extended
period of time following the procedure. This would leave too many variables to account
for in the device and pose a significant risk to the patient. However, the results of the
experiment showed that implantation of the device was received by the heart tissue with
endothelializtion of the device occurring at three weeks after implantation, and with the
device being fully covered by tissue at four weeks.10
The benefits of using a balloon for occlusion are documented however in
searching for a solution to how to deflate the balloon across the septum so that a thin
membrane were to remain was more difficult. The pressure across the atria is constant
and considerable with 5L of blood being circulated throughout the body every minute a
considerable amount of pressure can be introduced across a defect in the atria. Therefore,
a significant support structure must be in place to prevent dislodging of the device.
One proposal for a support structure that meets the requirements for the device
constrictions was the use of a heat activated adhesive to be coated around the portion of
the balloon that will have direct contact with the heart. Since balloon catheters use water
to inflate, a heated die could be used to activate glue on the exterior of the device and
adhere to the desired structure. The use of non-activated glues would not be possible due
to the risk of adhering to other structures in the heart; usually a constant repositioning of
the device is required before getting it right across the defect. Heat activated glues were
ruled out however, due to the temperature required for heat activation and the toxicity of
those that could be applied.
What I propose is the use of a biocompatible wire framework, fixated to the
balloon, and expandable with the device. There are two methods that I researched
regarding this solution. The first method involved a biodegradable stent recently
pioneered and is currently under FDA investigation. So called poly-l-lactic
monopolymers are used to create coronary stents for the native vessels of the heart. An
advantage here is that this material is self-expandable 37oC and degrades completely
within six to twelve months into lactic acid, which can be naturally absorbed by the
body.11 However, the most feasible design for development would comprise a cork-screw
structure surrounding the balloon created from nitinol wire; a commonly used memory
metal for use in medical devices. This wire would be expandable, retrievable, and cost
effective, comparably. This device would require a larger septal rim for the support of the
device but it would be less expensive and more effective at occlusion.
IVa. Safety Analysis
The risks associated with the device are limited but severe. In the past such
devices have had a high success rate in occluding the ASD and subsequently integrating
into the heart tissue. A significant risk clearly associated with this device is that of
dislodging. If device or any part of it were to break free of the environment controlled by
the cardiologist there would be a significant risk of embolism within the cardiovascular
system and subsequently death. Therefore, when choosing a proper design to develop the
consideration as to which method would best fixate the device across the defect was give
careful decided. This catastrophic consequence would subsequently become negligible
within a few months as the device became fully integrated into the heart tissue.
Other risks include wire related problems associated with the support structure of
the device including wire perforation, wire migration, and recovery related problems.
However, these problems are rare and due to the simplicity of the design would not pose
a significant threat to the safety of the patient.
The risks that the cardiologist incurs are related to the operational time of the
device placement. If the device were to involve a complex procedure the general fatigue
of the operator would become a factor in procedural error and thus increase the risk to
both the patient and the doctor. Since this device uses a balloon for centering and nitinol
wire for support the overall time of the procedure should be minimal due to the ease of
application to the defect.
All the risk factors for the procedure of implanting this device and the risks
associated to the patient are compiled in the designsafe analysis in Appendix II. This
program shows that the majority of the risks associated with the device are fairly low and
as with any medical device, unpredictable.
IVb. Economic Analysis
With the design process in such a theoretical state a cost based analysis of the
device would be difficult. However, estimation as to the possible costs that could be
incurred at development can be constructed from the known portions of the device.
The final device would most likely require a special design of a detachable double
balloon catheter. With current balloon catheter probes having a price of approximately
$90, an estimation of a device that would be left in the body and would be deflatable
could be adjusted to three times that amount. Therefore, the estimated cost of the balloon
system would be $270.
The price of two feet of 0.010 diameter medical grade nitinol wire is estimated at
being $10.12 This practical solution to the
structure of the device could vary with the
length of wire necessary for the proper
control of the device in vitro; however, the
price would not be significant. Overall, the
total price of the device can be estimated at
being ~$300 and compared to existing
devices
this
amount
is
more
than
competitive.
The market for such a device is vast,
with about 1 out of every 1500 babies born
Table 4 a comparison of difference device costs
and FDA approval status
each year, and 1 out of every 25,000 adults, having this type of congenital heart defect
the patient base is continually growing.2 As of now there are only two FDA approved
devices used for human implantation. These devices share a marketplace of
approximately $2750 (device) * 8 (babies born with ASD/day) * 365 (days/year) + $2750
(device) * 40 (ASD/million people) * 300 (million people in US) = $41,030,000 possible
dollars a year in just the United States alone. A comparison of the costs associated with
some of the devices that are in market and under development is shown in Table 4.
However, some costs can not be accounted for at this point in time. Such as the
cost associated with taking a device to market and through FDA approval would be
immense but with a recurring patient base and the need for ASD closure in adults
throughout the world it would seem as if there would be financial motivation to pursue
such a device.
V. Conclusion
Because atrial septal defect closure is the most commonly occurring congenital
heart disease there were a vast number of solutions already present when the design
process began. The device proposed is a step in the right direction towards the creation of
a truly novel device. It merges what is known to work with what is ideal to have for the
procedure.
The main issues left to be resolved in designing the device is the proper
configuration of the delivery device and the final balloon design. Inherently, the solution
to the problem is simple, plug a hole, however, the scope of methods already patented
and under development also significantly limited the possible solutions to the device and
due to the complex nature of the design constraints further evolution of the project is
necessary before it is ready to be tested in vivo.
VI. Recommendations
This was an exploratory project used to look into the possibility that there is a
better way of performing the procedure of ASD closure. I believe that the complexity of
this project would require a multifaceted team to think outside of the box and look into
the possibility of creating a design prototype for in vivo testing of the various solutions to
this device. A further analysis of the design constraints and materials at the disposal of
the team would help in the building of a prototype. Once a prototype has been
constructed a more accurate representation of the pressures incurred upon the device
across the septum can be further realized to reevaluate and design a final model.
VII. References
1.
Topol E (ed.) Pediatric and Congenital Heart Disease (2000). In Topol E (ed.)
Cleveland Clinic Heart Book, (pp205-229). New York:
2.
Childrens Hospital of Boston.
http://web1.tch.harvard.edu/cfapps/A2ZtopicIndex.cfm#A-C
Last accessed on 4/20/04. last updated 4/27/2004.
3.
Hughes ML, Maskell G, Goh TH, Wilkinson JL. Prospective comparison of costs
and short term health outcomes of surgical versus device closure of atrial septal
defect in children. Heart 2002; 88:67-70.
4.
Wren C, Richmond S, Donaldson L. Temporal variability in birth prevalence of
cardiovascular malformations. Heart 2000;83:414-419
5.
Vick GW, Titus JL: Defects of the atrial septum, including the atrioventricular
canal. In: Garson A, Bricker JT, McNamara DG, eds. The Science and Practice of
Pediatric Cardiology. Vol 2. Malvern, Pa: Lea & Febiger; 1990: 1023-1054.
6.
Friedman, William F., and John S. Child. "Congenital Heart Disease in the Adult."
In Harrison's Principles of Internal Medicine, ed. Anthony S. Fauci, et al. New
York: McGraw Hill, 1997.
7.
Warnes CA, Fuster V, Driscoll DJ, McGoon DC: Atrial septal defect. In: Mayo
Clinic Practice of Cardiology, 3rd edition, E. R. Giuliani, B. J. Gersh, M.D.
McGoon, D. L. Hayes, H. V. Schaff (eds.), Mosby, St. Louis, 1996.
8.
Sideris EB, Sideris CE, Toumanides S, Moulopoulos SD. From disk devices to
transcatheter patches: the evolution of wireless heart defect occlusion.J Interv
Cardiol. 2001 Apr;14(2):211-4.
9.
Bettencourt N, Salome N, Carneiro F, Goncalves M, Ribeiro J, Braga JP, Fonseca
C, Correia DM, Vouga L, Ribeiro VG. Atrial septal closure in adults: surgery
versus amplatzer--comparison of results.Rev Port Cardiol. 2003 Oct;22(10):120311.
10.
Sideris EB, Kaneva A, Sideris SE, Moulopoulos SD. Transcatheter atrial septal
defect occlusion in piglets by balloon detachable devices. Catheter Cardiovasc
Interv. 2000 Dec;51(4):529-34.
11.
Tsuji T, Tamai H, Igaki K, Kyo E, Kosuga K, Hata T, Okada M, Nakamura T,
Komori H, Motohara S, Uehata H. Biodegradable Polymeric Stents.
Curr Interv Cardiol Rep. 2001 Feb;3(1):10-17.
12.
Images of SI, Inc. http://www.imagesco.com/catalog/nitinol/nitinol.html
Last accessed on 4/23/04. Last updated 12/11/2003.
Appendix
I. Innovation WorkBench
Ideation Process
Innovation Situation Questionnaire
1. Brief description of the problem
To design a device that closes a hole existing between the two atria of the heart which is less
costly and more effective than existing devices.
2. Information about the system
2.1 System name
Atrial Septal Defect Occluder
2.2 System structure
The system is to be a thin membrane like structure existing in the defect with a support
apparatus in place to ensure that the device does not dislodge. Also the device is to be
easily handled by the operator and deployable on command.
2.3 Functioning of the system
The functioning system would serve to prevent blood from flowing across the interatrial wall.
It would have to withstand the pressure drop across the septum as a rigid body and be able
to become part of the heart as time progressed (called endothelialization)
2.4 System environment
The system is placed in the heart in a hole between the two atria; therefore, it is in a viscous
environment of constant pressure changes with a naturally occuring growth that engulfs the
device after an allotted amount of time.
3. Information about the problem situation
3.1 Problem that should be resolved
To develop a device that is novel in nature to the other devices in market and under
development that completely occludes the atrial septal defect causing a left-to-right shunt
across the interatrial septum and thus reducing the complaince of the right side of the heart
and the pulmonary arteries.
3.2 Mechanism causing the problem
An ASD is known to be a congenital heart disease related to the early stages of heart
formation when the embryonic heart consists of a hollow tube. During further formation the
atrial share a common chamber due to the in utero state of the fetus the need for pulmonary
circulation is not yet apparent. Later on in heart development the septum primum and
septum secundum begin to form the interatrial wall dividing the common chamber. An ASD
forms when that wall does not completely form during this stage of development.
3.3 Undesired consequences of unresolved problem
With the on set of pulmonary circulation approximately 20% of ASD's close spontaneously
within the first year of life and generally children are asymptomatic. However, if left until
adulthood the risks of congestive heart failure as a result of pulmonary hypertension is a
increasing possibility depending on the size of the defect and its position in the interatrial
septum.
3.4 History of the problem
The problem is congenital with little relation to genetic disposition. Methods of closing this
defect include a surgical approach that involves the suture of a pericardial patch closing the
defect but requires open-heart surgery and the use of a cardiopulmonary bypass machine.
The transcatheter approach is a much more popular solution that consists of a occlusion
device that is advanced up the femoral artery to the site of the defect and then open to close
the defect intravenously.
3.5 Other systems in which a similar problem exists
The problem also exists in the ventricles as a ventricular septal defect as well as in other
structures of the heart such as the PFO, PDA, etc. All of the defects have solutions to their
closing.
3.6 Other problems to be solved
Other problems associated with ASD's that should be solved are the extreme disorders
involving either the mitral valve, known as a type of ostium primum defect, or sinus venosus
defects.
4. Ideal vision of solution
The ideal solution to this problem would be a non-invasive procedure that can be performed
through a catheter that would involve the direct application of a thin membrane to the defect,
without the use of metal or wire. Furthermore, the procedure would be inexpensive, quick, and
the endothelialization of the device would be encouraged by the device.
5. Available resources
Dr. Thomas Doyle, Pediatric Cardiology
Dr. Paul King, Biomedical Engineering
Cardiac Catheterization Laboratory
Biomedical Library
6. Allowable changes to the system
The system can not be manipulated in any way other than to close the defect. Since we are
dealing with the human heart each patient has a different problem of a similar scope, but the
area that is being occluded is sensitive to the overall function of the heart and therefore should
not be altered in any way.
7. Criteria for selecting solution concepts
The device should be inexpensive, novel, and serve the purpose of closing the device in the
most effective manner.
8. Company business environment
The device has significant competition in the marketplace. Having two FDA approved
transcatheter devices in market and five more going through FDA approval now the
competition is stiff but each design has drawbacks in the medical environment.
9. Project data
The project name is Atrial Septal Defect Closure Device Design. Its objective is to design a
device that more effectively occludes an ASD. The timeline is to take between December 2003
and April 2004. The project team consists of one undergraduate BME student: Thomas Hoy
and a pediatric cardiologist with VUMC: Dr. Thomas Doyle. The group website is
http://vubme.vuse.vanderbilt.edu/srdesign/2003/group22 and can be reached at
[email protected]
Problem Formulation
1. Build the Diagram
2. Directions for Innovation
4/26/2004 5:48:19 PM Diagram1
» 1. Find an alternative way to obtain [the] (Need for ASD occluder) that offers the following:
provides or enhances [the] (Design of new device to meet specific needs), eliminates, reduces,
or prevents [the] (Other devices), does not require [the] (Congenital Heart Disease - ASD).
2. Find a way to eliminate, reduce, or prevent [the] (Other devices).
3. Find an alternative way to obtain [the] (Congenital Heart Disease - ASD) that provides or
enhances [the] (Need for ASD occluder).
» 4. Find an alternative way to obtain [the] (Design of new device to meet specific needs) that
offers the following: provides or enhances [the] (Novel device), does not require [the] (Need for
ASD occluder).
» 5. Find an alternative way to obtain [the] (Novel device) that offers the following: provides or
enhances [the] (Brainstorming and Research), does not require [the] (Design of new device to
meet specific needs), is not influenced by [the] (Other devices).
» 6. Find an alternative way to obtain [the] (Brainstorming and Research) that offers the
following: provides or enhances [the] (Theoretical model), does not require [the] (Novel device)
and (Design Constraints).
» 7. Find a way to eliminate, reduce, or prevent [the] (Design Constraints) then think how to
provide [the] (Brainstorming and Research).
8. Try to resolve the following contradiction: The harmful factor [the] (Design Constraints)
should not exist in order to avoid harmful results and should be in place in order to provide or
enhance [the] (Brainstorming and Research).
» 9. Find an alternative way to obtain [the] (Theoretical model) that offers the following:
provides or enhances [the] (Testing), does not require [the] (Brainstorming and Research).
» 10. Find an alternative way to obtain [the] (Testing) that offers the following: provides or
enhances [the] (Solution), does not require [the] (Theoretical model).
» 11. Find an alternative way to obtain [the] (Solution) that does not require [the] (Testing).
» 12. Consider transitioning to the next generation of the system that will provide [the]
(Solution) in a more effective way and/or will be free of existing problems.
Prioritize Directions
1. Directions selected for further consideration
1. Find an alternative way to obtain [the] (Need for ASD occluder) that offers the following:
provides or enhances [the] (Design of new device to meet specific needs), eliminates,
reduces, or prevents [the] (Other devices), does not require [the] (Congenital Heart Disease ASD).
1.1. Improve the useful factor (Need for ASD occluder).
1.2. Obtain the useful result without the use of [the] (Need for ASD occluder).
1.3. Increase effectiveness of the useful action of [the] (Need for ASD occluder).
1.4. Synthesize the new system to provide [the] (Need for ASD occluder).
1.5. Apply universal Operators to provide the useful factor (Need for ASD occluder).
1.6. Consider resources to provide the useful factor (Need for ASD occluder).
4. Find an alternative way to obtain [the] (Design of new device to meet specific needs) that
offers the following: provides or enhances [the] (Novel device), does not require [the] (Need
for ASD occluder).
4.1. Improve the useful factor (Design of new device to meet specific needs).
4.2. Obtain the useful result without the use of [the] (Design of new device to meet specific
needs).
4.3. Increase effectiveness of the useful action of [the] (Design of new device to meet
specific needs).
4.4. Synthesize the new system to provide [the] (Design of new device to meet specific
needs).
4.5. Apply universal Operators to provide the useful factor (Design of new device to meet
specific needs).
4.6. Consider resources to provide the useful factor (Design of new device to meet specific
needs).
5. Find an alternative way to obtain [the] (Novel device) that offers the following: provides or
enhances [the] (Brainstorming and Research), does not require [the] (Design of new device
to meet specific needs), is not influenced by [the] (Other devices).
5.1. Improve the useful factor (Novel device).
5.2. Obtain the useful result without the use of [the] (Novel device).
5.3. Increase effectiveness of the useful action of [the] (Novel device).
5.4. Synthesize the new system to provide [the] (Novel device).
5.5. Protect [the] (Novel device) from the harmful influence of [the] (Other devices).
5.6. Apply universal Operators to provide the useful factor (Novel device).
5.7. Consider resources to provide the useful factor (Novel device).
6. Find an alternative way to obtain [the] (Brainstorming and Research) that offers the
following: provides or enhances [the] (Theoretical model), does not require [the] (Novel
device) and (Design Constraints).
6.1. Improve the useful factor (Brainstorming and Research).
6.2. Obtain the useful result without the use of [the] (Brainstorming and Research).
6.3. Increase effectiveness of the useful action of [the] (Brainstorming and Research).
6.4. Synthesize the new system to provide [the] (Brainstorming and Research).
6.5. Apply universal Operators to provide the useful factor (Brainstorming and Research).
6.6. Consider resources to provide the useful factor (Brainstorming and Research).
7. Find a way to eliminate, reduce, or prevent [the] (Design Constraints) then think how to
provide [the] (Brainstorming and Research).
7.1. Isolate the system or its part from the harmful effect of [the] (Design Constraints).
7.2. Counteract the harmful effect of [the] (Design Constraints).
7.3. Impact on the harmful action of [the] (Design Constraints).
7.4. Reduce sensitivity of the system or its part to the harmful effect of [the] (Design
Constraints).
7.5. Eliminate the cause of the undesired action of [the] (Design Constraints).
7.6. Reduce the harmful results produced by [the] (Design Constraints).
7.7. Apply universal Operators to reduce the undesired factor (Design Constraints).
7.8. Consider resources to reduce the undesired factor (Design Constraints).
7.9. Try to benefit from the undesired factor (Design Constraints).
9. Find an alternative way to obtain [the] (Theoretical model) that offers the following:
provides or enhances [the] (Testing), does not require [the] (Brainstorming and Research).
9.1. Improve the useful factor (Theoretical model).
9.2. Obtain the useful result without the use of [the] (Theoretical model).
9.3. Increase effectiveness of the useful action of [the] (Theoretical model).
9.4. Synthesize the new system to provide [the] (Theoretical model).
9.5. Apply universal Operators to provide the useful factor (Theoretical model).
9.6. Consider resources to provide the useful factor (Theoretical model).
10. Find an alternative way to obtain [the] (Testing) that offers the following: provides or
enhances [the] (Solution), does not require [the] (Theoretical model).
10.1. Improve the useful factor (Testing).
10.2. Obtain the useful result without the use of [the] (Testing).
10.3. Increase effectiveness of the useful action of [the] (Testing).
10.4. Synthesize the new system to provide [the] (Testing).
10.5. Apply universal Operators to provide the useful factor (Testing).
10.6. Consider resources to provide the useful factor (Testing).
11. Find an alternative way to obtain [the] (Solution) that does not require [the] (Testing).
11.1. Improve the useful factor (Solution).
11.2. Obtain the useful result without the use of [the] (Solution).
11.3. Increase effectiveness of the useful action of [the] (Solution).
11.4. Synthesize the new system to provide [the] (Solution).
11.5. Apply universal Operators to provide the useful factor (Solution).
11.6. Consider resources to provide the useful factor (Solution).
12. Consider transitioning to the next generation of the system that will provide [the]
(Solution) in a more effective way and/or will be free of existing problems.
12.1. Improve Ideality of your system that provides [the] (Solution).
12.2. Consider the possibility to transform the existing system that provides [the] (Solution)
into bi- or poly-system.
12.3. Consider segmentation of the existing system that provides [the] (Solution).
12.4. Consider restructuring the existing system that provides [the] (Solution).
12.5. Increase dynamism of the existing system that provides [the] (Solution).
12.6. Increase controllability of the existing system that provides [the] (Solution).
12.7. Make the existing system that provides [the] (Solution) and/or its elements more
universal.
2. List and categorize all preliminary ideas
The most effective method found was the combination of a detachable double balloon
catheter and Nitinol wire. While the elimination of the Nitinol from the design could be a long
term goal, it is currently not feasible given the status adhesive technology. A balloon shaped
device gives the advantages of centering and small septal rim, while the nitinol wire provides
the support until endothelialization can take over.
Develop Concepts
1. Combine ideas into Concepts
The Nitinol wire will be used as a backbone for the device. Both materials are biocompatible,
thus eliminating any concerns of rejection from the body. The nitinol wire will be coiled around
the device serving to support the deflated balloon structue
2. Apply Lines of Evolution to further improve Concepts
This product is an evolution from current market devices which currently use Nitinol wire to
serve as both structural and functional support. Current technology is also much more rigid
and less forgiving in its placement.
Evaluate Results
1. Meet criteria for evaluating Concepts
This device, as designed, currently meets a majority of the given criteria.
2. Reveal and prevent potential failures
One possible mode of failure could be a structural support failure, where the device would slip
through the defect. This is unlikely given the nature of the design, however. Another greater
possibility for problems could come from the clotting of platelets around the outside of the
device and potentially detaching and causing an embolism somewhere in the cardiovascular
system.
3. Plan the implementation
Get prototype developed.
Test prototype for ability to withstand pressure differential in a simulated in-vivo environment.
Patent idea.
Plan animal trials for device.
Begin FDA approval process.
Questions:
Is this device safe?
Is it more effective than current technologies?
Is it cost effective?
Will it provide a better outcome for patients?
What are the long term effects of its use in patients?
II. Design Safe Analysis
Attainable on Website
http://vubme.vuse.vanderbilt.edu/srdesign/2003/group22/