Atrial Septal Defect



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 left-to-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

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Table 1. Comparison of Device Characteristics.

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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 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. 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):1203-11.

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. 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 and can be reached at thomas.n.hoy@vanderbilt.edu

Problem Formulation

1. Build the Diagram

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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



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Table 4 a comparison of difference device costs and FDA approval status

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