Recognition of Need
Over the past decade, developments made in minimally invasive surgical techniques have dramatically increased both the popularity and efficacy of these procedures [1]. Innovations in surgical instrumentation have allowed for increasingly smaller incision sizes while maintaining or lowering the mortality and perioperative morbidity rates of conventional open-heart surgery [1]. Additionally, minimally invasive surgeries have been associated with lowered infection rates, shortened hospitalization times, reduced cost, and lessened pain experienced by the patient [1].
Despite this surge in popularity, surgical defibrillation technology has failed to adapt to the new challenges presented by the minimal access approaches to cardiac surgery. Internal defibrillation paddles typically used in conventional open-heart surgery are too large and rigid to be used through the smaller incision sizes associated with minimally invasive surgery. Instead, surgeons must use external defibrillation paddles attached to the patient’s chest to defibrillate the patient during minimally invasive surgery. This practice raises a large number of problems and complications, as discussed below.
In order to deliver sufficient energy to the heart, external defibrillation passes a significant current through the patient’s body, which causes skeletal muscle contraction and a “convulsion” on the operating table. This dramatic, uncontrolled movement can be very dangerous during surgery, as the delicate equipment involved can be easily disturbed. For example, the patient is commonly defibrillated while still on bypass, and if the cannulae attached to the patient are dislodged, the patient could lose dangerous amounts of blood. Dr. Ralph Damiano, the chief of cardiac surgery at Barnes Jewish Hospital and our mentor for this project, indicated that this movement caused by external defibrillation is extremely dangerous to the patient [2].
Unlike the external paddles, internal paddles are in direct contact with the heart, and therefore work successfully with much lower discharge power levels. External defibrillator paddles typically deliver 200-400 J, while internal paddles work successfully with as little as 10 J [3]. For this reason, external defibrillator paddles take longer to charge and waste critical seconds between defibrillation attempts, potentially affecting the success of the operation. Additionally, the much higher power discharge of external paddles commonly causes contact burns on the patient’s skin [4]. While this damage is not life threatening, the burn marks can cause permanent scarring, mental distress, and unnecessary discomfort to the patient. Surgeons can avoid these complications with the use of internal paddles.
Furthermore, one paper reported that external defibrillation was unsuccessful even at high energy levels in 30% of patients during valve surgery. This failure was attributed to the patient’s lungs being deflated while on bypass, increasing the amount of insulated space between the chest wall and the heart and making defibrillation more difficult [3].
In conclusion, an improvement in defibrillation technology is needed for minimally invasive surgery, as the only available method demonstrates clear weaknesses. As one paper reports, defibrillation was necessary in almost 20% of the past 43 minimally invasive valve surgeries at that hospital, indicating that defibrillation is a critical part of cardiac surgery [3]. Therefore, improved defibrillation technology for minimally invasive surgery could potentially contribute to the safety and efficacy of these procedures, as well as further their widespread popularity as an alternative to conventional open-heart surgery.
1. Soltesz, Edward G., and Lawrence H. Cohn. "Minimally Invasive Valve Surgery." Cardiology in Review 15.3 (2007): 109-15. Print.
2. Damiano, Ralph, MD, and Lindsey Saint, MD. Personal Interview by Moor, Kelly, Browning, Stephen, and Kafka, Kathleen. 15 09 2011.
3. R.M. Bojar, D.D. Payne, H. Rastegar, J.T. Diehl, R.J. Cleveland. “Use of self-adhesive external defibrillator pads for complex cardiac surgical procedures.” Ann Thorac Surg. 46 (1988) (587 - 588)
Despite this surge in popularity, surgical defibrillation technology has failed to adapt to the new challenges presented by the minimal access approaches to cardiac surgery. Internal defibrillation paddles typically used in conventional open-heart surgery are too large and rigid to be used through the smaller incision sizes associated with minimally invasive surgery. Instead, surgeons must use external defibrillation paddles attached to the patient’s chest to defibrillate the patient during minimally invasive surgery. This practice raises a large number of problems and complications, as discussed below.
In order to deliver sufficient energy to the heart, external defibrillation passes a significant current through the patient’s body, which causes skeletal muscle contraction and a “convulsion” on the operating table. This dramatic, uncontrolled movement can be very dangerous during surgery, as the delicate equipment involved can be easily disturbed. For example, the patient is commonly defibrillated while still on bypass, and if the cannulae attached to the patient are dislodged, the patient could lose dangerous amounts of blood. Dr. Ralph Damiano, the chief of cardiac surgery at Barnes Jewish Hospital and our mentor for this project, indicated that this movement caused by external defibrillation is extremely dangerous to the patient [2].
Unlike the external paddles, internal paddles are in direct contact with the heart, and therefore work successfully with much lower discharge power levels. External defibrillator paddles typically deliver 200-400 J, while internal paddles work successfully with as little as 10 J [3]. For this reason, external defibrillator paddles take longer to charge and waste critical seconds between defibrillation attempts, potentially affecting the success of the operation. Additionally, the much higher power discharge of external paddles commonly causes contact burns on the patient’s skin [4]. While this damage is not life threatening, the burn marks can cause permanent scarring, mental distress, and unnecessary discomfort to the patient. Surgeons can avoid these complications with the use of internal paddles.
Furthermore, one paper reported that external defibrillation was unsuccessful even at high energy levels in 30% of patients during valve surgery. This failure was attributed to the patient’s lungs being deflated while on bypass, increasing the amount of insulated space between the chest wall and the heart and making defibrillation more difficult [3].
In conclusion, an improvement in defibrillation technology is needed for minimally invasive surgery, as the only available method demonstrates clear weaknesses. As one paper reports, defibrillation was necessary in almost 20% of the past 43 minimally invasive valve surgeries at that hospital, indicating that defibrillation is a critical part of cardiac surgery [3]. Therefore, improved defibrillation technology for minimally invasive surgery could potentially contribute to the safety and efficacy of these procedures, as well as further their widespread popularity as an alternative to conventional open-heart surgery.
1. Soltesz, Edward G., and Lawrence H. Cohn. "Minimally Invasive Valve Surgery." Cardiology in Review 15.3 (2007): 109-15. Print.
2. Damiano, Ralph, MD, and Lindsey Saint, MD. Personal Interview by Moor, Kelly, Browning, Stephen, and Kafka, Kathleen. 15 09 2011.
3. R.M. Bojar, D.D. Payne, H. Rastegar, J.T. Diehl, R.J. Cleveland. “Use of self-adhesive external defibrillator pads for complex cardiac surgical procedures.” Ann Thorac Surg. 46 (1988) (587 - 588)
Design Requirements
This section lists the device specifications which are defined in more detail in our Progress Report [5].
● Minimize Defibrillation Energy: We observed that 20 J applied to the heart using internal defibrillation paddles did not cause the myocardium or surrounding skeletal muscles to contract enough to disrupt the procedure or endanger the patient. Therefore, we have concluded that a device with a DFT of 20 J or below is ideal.
● Physical Attributes: The portions of the device that need to enter the thoracic cavity must be able to fit through an approximately circular incision with a diameter of four centimeters [6,7]. The wires connecting the electrodes to the defibrillator unit will measure 2.5-3 meters in length to ensure that the gap between the defibrillator unit’s position in the operating room and the patient can be spanned. Any electrical connections running from the device positioned inside the patient to the defibrillator unit will be flexible enough that they can be re-positioned to any point in the incision in order to minimize obstruction to the surgeon’s view.
● Time Until Stimulus Delivery:A maximum of 20 seconds should pass between the start of ventricular fibrillation and the stimulus delivery. This does not account for failed shocks, which may or may not occur depending on the energy and timing of the stimulus delivery, as decided by the person operating the device. However, this requirement is not necessary if the defibrillator is being used while taking the patient off of bypass, which is when defibrillation is often used.
● Compatibility with LIFEPAK 20e: The device must be compatible with the LIFEPAK 20e made by PhysioControl. Compatible is to be defined as achieving all desired device defibrillation characteristics while using all of the signal generation and transmission modalities of the LIFEPAK 20e unit. These signals range in energy from 2-360 Joules with a number of intermediate selectable energy levels.
● Safety: The device must be safe to the patient, the surgeon, and the other people present in the operating room. As long as the device is not being misused, it should cause no harm to the surgeon and others in the operating room. Device placementshould cause no unintended damage to the myocardium - including puncturing, cutting, scraping, or irritating the myocardium and surrounding tissues. Intended damage includes sutures used to secure the device or latching mechanisms like those used on ICD electrodes. These injuries will be limited to those that can be repaired (using sutures or clotting agents) once the device is removed. The severity of burns, post-shock arrhythmias, and temporary arrhythmias caused by the defibrillating shock will be minimized by reducing the dosage of voltage, current, and energy.
● Additional Procedure Time for Device Implantation and Removal: The total implantation and removal time will need to be minimized. According to our mentors, a few minutes would be ideal [6]. It would also be preferable if the device could be implanted and removed while the patient is not on bypass, in order to minimize the amount of time that the patient is on bypass.
● Hypoallergenic: It is important that the materials used in the device are unlikely to cause the patient to have an allergic reaction. Since it is hard to quantify the likelihood of an allergic reaction, the safest way to choose a “hypoallergenic” material is to use materials that are currently being used in commercial surgical devices and to avoid the use of common irritants, such as latex or nickel.
● Sterile: The device should be able to withstand one or more of the most commonly used sterilization techniques: steam autoclave, ethylene oxide, Sterrad, Steris System 1, or gamma sterilization. Barnes Jewish Hospital uses ethylene oxide for sterilization. [6] Therefore, if the device is reusable, it would be ideal if it could be sterilized by that method.
4. Richards, K. "Skin Reactions Following Defibrillation or Cardioversion." Physio-control.com. Physio-Control Corporation, 1995. Web.
5. Browning, Steven, Kafka, Kathleen, and Kelly Moor. “Defibrillator for Use in Minimally Invasive Surgery: Progress Report.”
6. Robertson, Jason, MD, and Shoichi Okada, MD. Personal Interview by Moor, Kelly, Browning, Stephen, and Kafka, Kathleen. 06 10 2011.
7. Gillinov, A. Retracted Incision Site During Minithoracotomy. Digital image. Cleveland Clinic. 6 Mar. 2010. Web.
● Minimize Defibrillation Energy: We observed that 20 J applied to the heart using internal defibrillation paddles did not cause the myocardium or surrounding skeletal muscles to contract enough to disrupt the procedure or endanger the patient. Therefore, we have concluded that a device with a DFT of 20 J or below is ideal.
● Physical Attributes: The portions of the device that need to enter the thoracic cavity must be able to fit through an approximately circular incision with a diameter of four centimeters [6,7]. The wires connecting the electrodes to the defibrillator unit will measure 2.5-3 meters in length to ensure that the gap between the defibrillator unit’s position in the operating room and the patient can be spanned. Any electrical connections running from the device positioned inside the patient to the defibrillator unit will be flexible enough that they can be re-positioned to any point in the incision in order to minimize obstruction to the surgeon’s view.
● Time Until Stimulus Delivery:A maximum of 20 seconds should pass between the start of ventricular fibrillation and the stimulus delivery. This does not account for failed shocks, which may or may not occur depending on the energy and timing of the stimulus delivery, as decided by the person operating the device. However, this requirement is not necessary if the defibrillator is being used while taking the patient off of bypass, which is when defibrillation is often used.
● Compatibility with LIFEPAK 20e: The device must be compatible with the LIFEPAK 20e made by PhysioControl. Compatible is to be defined as achieving all desired device defibrillation characteristics while using all of the signal generation and transmission modalities of the LIFEPAK 20e unit. These signals range in energy from 2-360 Joules with a number of intermediate selectable energy levels.
● Safety: The device must be safe to the patient, the surgeon, and the other people present in the operating room. As long as the device is not being misused, it should cause no harm to the surgeon and others in the operating room. Device placementshould cause no unintended damage to the myocardium - including puncturing, cutting, scraping, or irritating the myocardium and surrounding tissues. Intended damage includes sutures used to secure the device or latching mechanisms like those used on ICD electrodes. These injuries will be limited to those that can be repaired (using sutures or clotting agents) once the device is removed. The severity of burns, post-shock arrhythmias, and temporary arrhythmias caused by the defibrillating shock will be minimized by reducing the dosage of voltage, current, and energy.
● Additional Procedure Time for Device Implantation and Removal: The total implantation and removal time will need to be minimized. According to our mentors, a few minutes would be ideal [6]. It would also be preferable if the device could be implanted and removed while the patient is not on bypass, in order to minimize the amount of time that the patient is on bypass.
● Hypoallergenic: It is important that the materials used in the device are unlikely to cause the patient to have an allergic reaction. Since it is hard to quantify the likelihood of an allergic reaction, the safest way to choose a “hypoallergenic” material is to use materials that are currently being used in commercial surgical devices and to avoid the use of common irritants, such as latex or nickel.
● Sterile: The device should be able to withstand one or more of the most commonly used sterilization techniques: steam autoclave, ethylene oxide, Sterrad, Steris System 1, or gamma sterilization. Barnes Jewish Hospital uses ethylene oxide for sterilization. [6] Therefore, if the device is reusable, it would be ideal if it could be sterilized by that method.
4. Richards, K. "Skin Reactions Following Defibrillation or Cardioversion." Physio-control.com. Physio-Control Corporation, 1995. Web.
5. Browning, Steven, Kafka, Kathleen, and Kelly Moor. “Defibrillator for Use in Minimally Invasive Surgery: Progress Report.”
6. Robertson, Jason, MD, and Shoichi Okada, MD. Personal Interview by Moor, Kelly, Browning, Stephen, and Kafka, Kathleen. 06 10 2011.
7. Gillinov, A. Retracted Incision Site During Minithoracotomy. Digital image. Cleveland Clinic. 6 Mar. 2010. Web.