Clinical Needs Assessment at Strong Memorial Hospital

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1 Clinical Needs Assessment at Strong Memorial Hospital Endoleaks in Endovascular Repair Endoleaks are a common problem during endovascular aortic repair and occur in 29% of all TEVAR (Thoracic Endovascular Aortic Repair) procedures. This can lead to an increase in the size of the aneurysm and risk of rupture. Develop better aortic fixation (Type I endoleaks 40%). The proximal end of the endograph is a metal scaffold with pins for attachment to the arterial wall. The blood sometimes flows around the graph entrance, known as a Type I endoleak. Develop better monitoring of aneurysm sac (Type II endoleaks 35%). These leaks occur due to lumbar (collateral) vessels feeding into the aneurysm sac. These cases are common and little can be done to combat this except close monitoring of the sac size. This is not a huge problem because for every vessel feeding into the sac, there are usually a significant number of vessels exiting blood as well. Develop better connections between graft components (Type III endoleaks 20%). Procedure is to balloon the same type of graft component into an already deployed endovascular graft. This may cause puncturing due to the pins on the proximal end leading to leakage. A locking mechanism may be advantageous to prevent these types of endoleaks. There are roughly 200,000 abdominal aortic aneurysms and thoracic aortic aneurysms every year that can potentially be treated with endovascular approaches.

2 Ventricular Assist Devices Transcutaneous power cables are responsible for most problems with VADs (infection, cable fraying, limiting device lifetime). Assist devices require energy to pump a 10 watt motor and power a motor control unit. The most reliable method of power transfer is a cable going through the skin attached to a motor control unit and two batteries. Stronger and more flexible cable (higher fatigue life). The wires in the cable can fray due to fatigue failure of the metal. This occurs in more active patients who tug and bend the cable. In addition, accidents can occur (dog biting on cable) such that the device fails. Reduce infection at the transcutaneous interface (tissue integration). The wire is covered with a velour fabric to incorporate the cable into the tissue better. This configuration allows for bacterial infection and inflammation when the cable is jarred loose. Patients must be monitored regularly after surgery. Installation surgery is in need of more customized tools to help implant the VAD. A VAD replacement requires the removal of the old motor unit leaving the ventricular port and aortic graft in place. The VAD is unscrewed using tiny clamps which need longer handles. Locating the left ventricle is sometimes difficult for the surgeon. The method is to find the apex and use a punch just to the left of this. The inflow conduit is inserted here, but there could be an incidence of improper placement. There are few good options for a right heart assist devices. After an LVAD surgery, the patient is more susceptible to right hear failure which is induced by negative suction in the left ventricle, transmitted to the right ventricle. A VAD with less negative inflow could decrease right heart complications. Loss of pulsatile flow causes the interface between the oxygenated and deoxygenated capillaries to break down. A motor that mimics this pulsatile environment could help reduce this risk in patients with very low natural cardiac output. There are roughly 25,000 VADs implanted a year with only 2,000 heart transplants. The assist device is a bride to transplant procedure and not intended for long term use, but many patients are stuck with them because of the lack of transplant donors.

3 Bypass machines The heart lung machines haven t changed much over the past 50 years. They are basically a system of tubes that are set up by an operator who monitors the flow of blood through the machine. Debake rollers push blood through the heparinized tubes with minimal cell damage. The operator occludes flow through a tube by clamping hemostats over it. Line pressure is monitored on a display panel and blood is run for diagnostic tests regularly).

4 Reduce the risk of microemboli developing in the bypass circuit. Reduce the volume of the bypass circuit (minimize the amount of blood bypassed) to increase hematocrit. Line pressure warning signals would be useful. One case involved the aortic bypass cannula being flipped around and occluded. Line pressure was above normal and not noticed by the operator. Basically the blood flow from the bypass machine was significantly reduced for about 5 minutes before this was noticed.

5 TAVI Transcatheter aortic valve implantation (TAVI) involves treatment of inadequate mitral valve performance due to calcification of the leaflets. Patients are normally treated in cardiac surgery where the old valve is removed and a new one sewn in place. For high risk patients who cannot undergo open heart surgery, the valve stenosis is addressed endoscopically. A pig valve is crimped onto an expandable balloon in an endoscopic catheter. The valve is inserted transfemorally and run up to the heart where it is expanded into the calcified valve. One problem is perivalvular leakage of blood flowing around the valve and causing aortic regurgitation. The severity of calcification has been linked to the degree of paravalvular aortic regurgitation. Better adhesion for valve stenting to calcified leaflets. The metal stenting cannot adhere well to the walls of the calcified valve and complete seal is difficult to obtain. Better devices/techniques to reduce the need for balloon redilation or second valve implantation. If there is leakage after an angiogram the balloon is expanded inside the valve again to remold it to the valve. If this doesn t work, then a second valve can be implanted inside of the first one. 45,000 TAVI procedures done worldwide since start, of which 12-20% develops postprocedural PVL (severe aortic regurgitation is rare).

6 Maze Procedure The cardiac muscle tissue is signaled to contract by nervous tissue located at nodes in the heart. The sino-atrial node conducts a signal to the atrio-ventricular node but can spread due to conduction issues in the cardiac tissue. This causes unwanted depolarization and unusual heart rhythm known as atrial fibrillation. This affects roughly 2.5 million people in the US and is treated with drugs and a procedure known as a MAZE. This involves ablation of the cardiac tissue in a path from the SA to the AV node. Basically if you kill a path of cells then the signal cannot spread and the fibrillation is treated. MAZE procedures can be time consuming due to non-transmural (not completely through the cardiac tissue) ablation and variations in the heart s nervous structure. The procedure involves laproscopic or open chest ablation of the cardiac tissue using unipolar or bipolar ablation devices. The conduction is tested using a device that measures the electrical impulses on the heart to see if the signal is getting through. If it is, the entire ablation procedure must be redone to make sure no signal is escaping. Improve the percentage of ablations that are transmural. The unipolar ablation tools are basically an ablator tip attached to a rod which doesn t allow for optimal control. If the tip could be removed and attached to a finger of the surgeon, then they could hold the heart in place and make an ablation where they can feel the amount of pressure being applied. Develop techniques to design individualized maze pathways

7 IVC Filters Inferior Vena Cava filters are implanted in the vena cava which feeds blood into the lungs. If a deep vein thrombosis occurs, there is a risk of pulmonary embolism (basically a clot from the legs blocking off bloodflow in the lungs). These filters trap emboli and can be intended for permanent or temporary use. Needs Successful removal of these filters can be difficult for inexperienced surgeons (can be as rare as 3.7% retrieval rate of temporary filters). Develop technique/device to make removal of IVC filters easier for the surgeon (better proximal-distal control). One concern of the surgeons is a clot trapped on the filter that could break off and go downstream. Better proximal and distal control would mean less worry about pulmonary embolism. Develop a new IVC filter that can be removed easily. Ideas such as a bioresorbable filter could offer a unique solution to the problem of temporary filter removal. About 200,000 IVC filters implanted per year in US (use of IVC filters has increased over the last 3 years)

8 Pacemaker and ICD Leads Pacemakers and Implanted Cardioverter Defibrillators (ICDs) need to be replaced sometimes due to problems with the leads. The attachment sites to the heart may break due to fatigue failure and the cable my fray. Develop leads that are more resistant to cable fraying. The cyclic environment of the heart leads to fatigue failure of the metal wires. Develop better lead attachment to the heart as to minimize risk of detachment due to fatigue of the wire corkscrew or tissue failure.

9 Contrast Fluid Radio-opaque contrast fluid is used in diagnostic angiograms to visualize the blood flow using x-ray imaging. This fluid is typically an iodine or barium compound and is toxic to the kidneys. The amount of this fluid is monitored closely and is variable due to age and weight (younger and heavier can take greater amounts). Develop a technique or method to reduce the amount of contrast fluid needed. This could be done through changing the delivery method to maximize the area the fluid will cover while minimizing the amount of contrast agent needed. Develop a method of contrast agent filtering as to reduce the concentration going to the kidneys. Radiation Exposure Use of CT or x-ray imaging is done wearing lead vests to protect the body from harmful rays. The patient is the only person who does not get protection, but the exposure is not very harmful for the short period of time they are exposed. Surgeons and nurses on the other hand are exposed regularly and need protection in the form of lead vests. Lead vests can be bulky and limiting to the range of motion of a surgeon (they can also get pretty hot too). Develop lead vests that are lighter and more flexible. Develop an ulterior method other than vests to block x-ray exposure to the clinicians. Could be something like lead scrubs.

10 Miscellaneous Guidewire for vessel catheterization untangles when not in use by surgeon but needed for later part of procedure. Need: develop a system to store these wires when not in use so that they do not untangle for the surgical technician. Radial entry into the arterial/venous system is becoming more common due to easier entry and closure techniques (less risk of bleeding, radial arm cuff TR band). Need: the catheters used are not specifically designed for radial entry (IFU is for femoral) so there is a need to design better shaped catheters for this purpose. Closure of the sternum after an open chest procedure is done with metal wires that are permanent until the next procedure. Need: develop a sternal closure system that allows for these wires to be absorbable.