3 3

33 Emerging Cardiac

Devices and Technologies

PAUL A. IAtZZO, PhD

CONTENTS

INTRODUCTION

RESUSCITATION SYSTEMS AND DEVICES IMPLANTABLE THERAPIES

CATHETER-DELIVERED DEVICES NOVEL A~ENTS TO COAT DEVICES IMPLANTABLE SENSORS

PROCEDURAL IMPROVEMENT TELEMEDICINE

TRAINING SYSTEMS SUMMARY

REFERENCES WEB RESOURCES

1. INTRODUCTION

In previous chapters, authors provided brief histories of car- diac device development and several fairly thorough discus- sions of currently employed devices or assessment technologies.

To gain insight into how rapidly innovations in the area of car- diac disease are progressing, a search of the US Patent and Trademark Office Website (www.uspto.gov) can simply be searched. Such a search produces an impressive number of companies or individuals attempting to secure intellectual prop- erty protection in this clinical category. More specifically, the following are the numbers of published patent applications, identified in November 2004, citing the following key words:

• cardiac (18,920 patent applications)

• cardiac surgery (1015 patent applications)

• cardiology (1480 patent applications)

• cardiac electrophysiology (79 patent applications)

• cardiovascular stents (52 patent applications)

• cardiac repair (32 patent applications)

From: Handbook of Cardiac Anatomy, Physiology, and Devices Edited by: P. A. Iaizzo © Humana Press Inc., Totowa, NJ

This does not include all issued patents to date, many of which detail prospective future products. For example, in searching the same database, the key word "cardiac" produces 37,410 issued patents to date since 1976. There are several other places to locate information on up-and-coming cardiac devices, such as the Food and Drug Administration Website (http://

www.fda.gov/) or websites listed at the end of this chapter.

It should be mentioned that many novel ideas that eventually lead to new products, therapies, or training first occur through basic cardiac research. For emerging technologies to continue to advance at a rapid rate, it is imperative that laboratories per- forming basic research in such technological areas continue to receive necessary support. Furthermore, prototype testing and clinical trials are essential to ensure that the best possible tech- nologies are both developed and eventually made available for general use. Yet, it is important to note that many lessons can be learned from trials that employed either misdirected devices or technologies.

The primary goals of this last chapter are to: (1) discuss, in more detail, some of the aforementioned technologies; (2) intro- duce several additional technological advances associated with

4 4 5

446 PART IV: DEVICES AND THERAPIES / IAIZZO

A B

Fig. 1. Various compression-decompression devices. (A) The LifeStick TM Resuscitator is an investigational, noninvasive, manually powered cardiopulmonary resuscitation (CPR) device, invented and designed by Datascope Corporation (Montvale, NJ), that is designed to enhance circulatory perfusion by facilitating sequential phased active compression and decompression of the chest and abdomen. (B) The AutoPulse Resuscitation System consists of a portable AutoPulse Platform, a single-patient use LifeBand TM, rechargeable batteries, battery charger, and carrying case (Revivant Corp., Sunnyvale, CA).

Fig. 2. Shown is the impedance threshold device ResQPod TM, distrib- uted by Zoll Medical (Chelmsford, MA). Used with permission from the ZOLL Medical Corporation Website. © 2004.

cardiovascular health care that have been recently introduced or are currently in clinical testing or soon to be released; and (3) discuss future opportunities in the cardiac device arena. It should be noted that other areas of importance in cardiac treat- ment, such as biological approaches to disease management (e.g., stem cell therapy), genomics (i.e., diagnostics and gene therapy), proteomics, and tissue engineering will also have a major impact on the future of cardiac clinical care; however, detailed discussions of these approaches are beyond the scope of this text. More specifically, this last chapter reviews several innovations in each of the following areas: (1) resuscitation systems and devices; (2) implantable therapies; (3) delivery systems; (4) invasive therapies; (5) procedural improvements;

(6) less-invasive surgical approaches; (7) postprocedural fol- low-ups; and (8) training tools.

2. R E S U S C I T A T I O N SYSTEMS A N D DEVICES Even before the cardiac patient enters the emergency or operating room, there are many new technologies being devel- oped to aid in the resuscitation of an individual who has suffered from cardiovascular failure. Such devices range from improve- ments of existing tools (e.g., the automated application of car- diopulmonary resuscitation or CPR) to novel mechanisms that accomplish improved outcomes (e.g., an impedance threshold valve). Furthermore, automated external defibrillators have become commonplace in the United States, with such units purchased for use in schools, health clubs, emergency vehicles, shopping malls, and even homes.

2.1. Active Cardiopulmonary Resuscitation Devices A number of active compression-decompression devices have been developed (Fig. 1), and numerous clinical trials have suggested improved short-term survival in patients with an out- of-hospital cardiac arrest (1-7). In addition, in one study it was reported that active compression-decompression CPR per- formed during advanced life support significantly improved long-term survival rates among patients who had cardiac arrest outside the hospital (6). Furthermore, when such active com- pression-decompression devices were used in combination with inspiratory impedance threshold devices (Fig. 2), there was an even greater positive outcome (8,9). More specifically, it was described that the use of an active compression-decom- pression device combined with an inspiratory impedance threshold device improved 1-h and 24-h survival in 103 patients who received that form of CPR vs 107 who received standard CPR (10).

The active compression-decompression device used in the

previously described study (1 O) was handheld, with a suction cup

CHAPTER 33 / EMERGING TECHNOLOGIES 447

Fig. 3. A LIFEPAK 12 internal defibrillator (Medtronic, Inc., Minneapolis, MN) used externally (outside) on an overwlntering black bear. In this case, Dr. Tim Laske is using the system to monitor a 12-1ead electrocardiogram (ECG) via its connection to surface electrodes.

that attached to the chest and a gauge that helped evaluate the force needed for effective compression and decompression, thus creating a vacuum within the chest (Fig. 1A). It is considered that the vacuum draws more blood back into the heart, which then results in more blood flowing out during the subsequent com- pression. However, it is also considered that air drawn into the lungs during a decompression can in turn reduce the volume of blood that can be drawn into the heart. Therefore, employing an impedance threshold device can minimize this situation.

The impedance threshold device is a small, 35-mL device that fits on a face mask or an endotracheal tube (Fig. 2). Its pressure-sensitive valves limit the inflow of air during chest decompression, allowing more blood to come into the thorax area (10). Initially, in an animal study, Lurie et al. (11) showed an increase in blood flow to vital organs in animals eliciting 6 min of ventricular fibrillation and then 6 min of standard CPR plus the use of an impedance threshold device.

2.2. External Defibrillators

Today, most emergency medicine service units utilize a multitier response system, with emergency medical techni- cians (EMTs) providing basic life support services, backed up by paramedics if advanced life support is needed. All of these p e r s o n n e l are trained in the use of a u t o m a t e d external defibrillators. There are several companies that produce such devices, and their availability is no longer limited to hospital or emergency services settings.

Yet, such units may also have expanded features that not all individuals are sufficiently trained to utilize. For example, the LIFEPAK ® 12 defibrillator/monitor series, manufactured by Medtronic, Inc. (Minneapolis, MN), allows the recording of a standard 12-lead ECG even in remote locations (Fig. 3). Nev- ertheless, with the same equipment, various personnel with different levels of expertise and training can provide lifesaving support, for instance, some units have even incorporated push button turn controls with voice prompts.

To date, devices such as the LIFEPAK 12 defibrillator/moni- tor series give paramedics access to sophisticated diagnostics and treatment in the field. This single piece of equipment moni- tors the ECG continuously, measures the level of oxygen in the bloodstream, and if necessary, provides defibrillation or pacing to help maintain the heart's rhythm. Thus, it allows paramedics to perform computerized 12-lead ECGs before the patient reaches the hospital.

Such ECG data can be transmitted by cellular phone to the emergency room physician from the ambulance while en route.

With this information in hand, the team of doctors and nurses

can be ready and waiting for the patient's arrival; importantly,

they can administer treatment in as little as 15 min after the

patient enters the emergency room, compared to an hour or

more if the ECG is first done at the hospital. It is generally

considered that any shortening of the time to treatment can

significantly speed recovery and improve a patient's chances of

returning to a fully productive life.

448 PART IV: DEVICES AND THERAPIES / IAIZZO

Fig. 4. The Bio-Pump was originally developed for cardiopulmonary bypass, but it can be used for short periods of circulatory support (usually 5 or fewer days) beyond the surgical setting (Medtronic, Inc., Minneapolis, MN). The Bio-Pump has been used both in postcar- diotomy cardiogenic shock patients (those who have developed heart failure as a result of heart surgery) and as a bridge to transplantation for patients who cannot be weaned from the device. This short-term assist device can be implanted in a broad range of patients, from new- borns to adults, and can be used alone or with another Bio-Pump or other type of assist device if biventricular support is needed. The B io- Pump is an extracorporeal, centrifugal device that can provide sup- port for one or both ventricles. Two disposable models are available:

80-mL model for adults and 48-mL model for children. The transpar- ent pump housing is shaped like a cone. The pump consists of an acrylic pump head with inlet and outlet ports placed at right angles to each other. The impeller, which is a stack of parallel cones, is driven by an external motor and power console. Rotation of this impeller at high speeds creates a vortex, which drives blood flow in relation to rotational speed. Blood enters through an inlet at the top of the cone and exits via an outlet at the base. The adult model pump can rotate up to 5000 rpm and can provide flow rates of up to 10 L/rain.

The following scenario has been provided by Medtronic Physio-Control Corporation (Redmond, WA) to demonstrate the significance of such features:

By the time a given patient had arrived at the hospital, the symptoms had subsided, and the ECG in the hospital appeared normal, yet the attending doctors compared the ECG done in the ambulance with the one obtained from the patient's physical exam a month prior and then there was no question about the diagnosis, a progressing heart attack. With 12-lead ECGs on board, an ambu- lance becomes a mobile clinic and paramedics become the doctors' eyes and ears.

It is likely that more and more computerized data collection (e.g., pressures, flows, etc.) will be performed by paramedics or others prior to a patient entering the hospital setting, which

will then be seamlessly integrated with the hospital's elec- tronic database to create a complete picture of a patient' s medi- cal condition from initial contact all the way through hospital discharge. Many such developments are currently available, and the challenge for health care providers in the coming years will be to provide the best possible care in the most cost- effective way.

3. IMPLANTABI.E THERAPIES

Advances in microtechnologies have now made it possible to create implantable therapies that can be lifesaving, such as implantable defibrillators, which have detected and treated thousands of episodes of sudden cardiac fibrillation. As men- tioned, the potential for large numbers of such devices will likely increase at an exponential rate and will be directed spe- cifically to all types of cardiac complications.

3.1. l-eft Atrial Appendage/Atrial Fibrillation Therapy

There are growing numbers of treatments for the side effects of atrial fibrillation that, in some patients, lead to crippling strokes. The focus of these devices is to modify the role of the left atrial appendage in pathologies associated with atrial fibril- lation. More specifically, this tiny alcove of the heart, which has been described to serve as a "starter heart" for the human embryo, can be a site for blood to pool and subsequently form clots that can be expelled into the brain, causing strokes. Today, it is estimated that atrial fibrillation affects 5 million people worldwide and is thought to be responsible for up to 25% of all strokes.

At present, the most common treatment for atrial fibrillation is the administration of a strong anticoagulant drug called coumadin. From a device perspective, suggested approaches to treat this problem include tissue clamps, screens, and other methods to seal off the appendage. More specifically, one start- up company, Atritech Inc. (Plymouth, MN), has promoted a solution to implant a tiny filter into the appendage, letting blood pass through, but trapping clots inside the minichamber; after some time, the body would naturally seals the chamber.

3.2. Cardiac Remodeling

Chronic cardiac remodeling is a well-known response of dilated cardiomyopathy and is thought to play a central role in disease progression (12-14). Associated heart chamber dila- tion or wall thinning will elevate overall wall stress, which is considered to trigger the local release of neurohormones, which adversely affects myocardial molecular biology and physiol- ogy (15). Therapeutic approaches to treat heart failure have been described, primarily as a means to inhibit or even induce reverse remodeling (e.g., [3-adrenergic blockade).

Mechanical unloading using left ventricular assist devices (LVADs; see Chapter 30) or extracorporeal pumps (Fig. 4) have been employed as alternatives. Such interventions can profoundly unload a heart, leading to reverse remodeling and improved physiological performance (12).

Another approach for accomplishing this benefit is to

induce structural remodeling by imposing alteration on or

within the heart. For example, the CorCap

Cardiac Support

CHAPTER 33 / EMERGING TECHNOLOGIES 449

Device (Acorn Cardiovascular Inc. TM, St. Paul, MN) is a fab- ric mesh multifilament implant that is surgically positioned around the ventricles of the heart (Fig. 5). This product is designed to reduce ventricular wall stress by supporting the heart muscle. Preclinical studies have shown that supporting the heart in this manner stops deterioration and allows the muscle to heal or remodel (14). More specifically, the deploy- ment of this device is expected to improve the heart's ability to pump blood, provide relief of heart failure symptoms, improve quality of life, and ultimately extend survival for those who suffer from heart failure. Since April 1999, more than 270 implantations of the CorCap TM Cardiac Support Device have been performed worldwide; the devices are currently being evaluated through randomized clinical trials in North America and Europe.

4. CATHETER-DELIVERED DEVICES

The delivery of specialized devices that can be introduced intravascularly or intracardially has been on the rise. Such de- vices include stents, septal occluder devices, leads, and ablation tools (see also Chapters 6, 22, 23, and 29).

4.1. Stents

An intraluminal coronary artery stent is a small, self-expand- ing, wire mesh tube that is placed within a coronary artery to keep the vessel patent (open). Stents are commonly deployed:

(1) during coronary artery bypass graft surgery to keep the grafted vessel open; (2) after balloon angioplasty to prevent reclosure of the blood vessel; or (3) during other heart surgeries.

For delivery, a stent is collapsed to quite a small diameter and inserted over a balloon catheter. Typically with the guidance of fluoroscopy, the catheter and stent are moved into the area of the blockage. When the balloon on the delivery catheter is in- flated, the stent expands, locking it in place within the vessel, thus forming a scaffold that holds the artery open.

Stents are intended to stay in the vessel permanently, keep- ing it open to improve blood flow to the myocardium, thereby relieving symptoms (usually angina). Note that a stent may be used instead of angioplasty. The type of stent to be deployed depends on certain features of the artery blockage (i.e., size of the artery and where the blockage is specifically located).

Stents are now considered to reduce the incidence of restenosis, which generally occurs within 4 - 6 months follow- ing an angioplasty procedure. Before stents, the incidence of restenosis was about 35-45%. Restenosis is a renarrowing of the treated coronary artery, which is largely related to the devel- opment of neointimal hyperplasia (that which occurs within an artery after it has been treated with a balloon or atherectomy device). In general, restenosis can be considered as scar tissue that forms in response to a previous mechanical insult. Hence, restenosis is somewhat different from atherosclerosis, which is related to calcium, fat, or cholesterol plaque buildup. Some individuals are considered genetically predisposed to develop restenosis.

To date, stents are the only widely employed devices that have been proven to reduce the incidence of restenosis (reduc- tion by approximately one-third). Stents alone are not consid- ered as "cures" for coronary artery disease, but their use will

Fig. 5. The CorCap

Cardiac Support Device (Acorn Cardiovascular IncJ M, St. Paul, MN) is a fabric mesh multifilament implant that is surgically positioned around the ventricles of the heart. Acorn devel- oped a new fabric made from implant-grade polyethylene terepthalate (PET polyester) fabricated into a proprietary mesh design. The CorCap

Cardiac Support Device fabric is composed of many interlinked filaments, each one-fifth the size of a human hair. The multifilament knit construction provides optimal support with conformability that evenly distributes support over the heart's sur- face. The proprietary processing of the device produces a highly biocompatible and durable material designed and tested for perma- nent implantation without adverse effects.

continue to have a major impact on decreasing the need for repeat procedures.

Nevertheless, one of the major goals for improving the out- come of stenting procedures is to minimize further the poten- tial for vessel restenosis. To accomplish this, several new types of stents, called drug-eluting stents, have been employed (Table 1). Such stents are coated with agents that are slowly released, further promoting the vessel from renarrowing and closing.

Yet, it should also be noted that, typically, patients who

have had a stent procedure must take one or more blood-thin-

ning agents such as aspirin, ticlopidine, or clopidogrel. Aspirin

is typically used indefinitely, and one of the other two drugs is

generally prescribed for 2 to 4 weeks. Therefore, goals for

future stent technologies will continue to include the develop-

ment of coatings that will minimize restenosis or the use of

anticoagulation therapy (Table 1).

450 PART IV: DEVICES AND THERAPIES / IAIZZO

A

Table 1

Currently Leading Stent Companies

Company Stent Stent coatings

Cook Cardiology Guidant/ACS

SCIMED/Boston Scientific Medtronic/AVE

Johnson & Johnson/Cordis

Gianturco-Roubin stents

Multilink/Duet/Tetra/Penta Stents Nir/Wall stents

GFX/S series stents Velocity stents

Pacltaxel (Taxol) Paclitaxel Sirolimus Company locations: Cook, Bloomington, IN; Guidant, Indianapolis, IN; Boston Scientific, Natick, MA; Medtronic, Minneapolis, MN; Johnson & Johnson, New Brunswick, NJ; AVE, Santa Rosa, CA; Cordis, Warren, NJ.

B

)

Fig. 6. (A) A steerable delivery catheter (Model 10600, Medtronic, Inc.) used to deploy a lead. (B) Image was obtained in our laboratory in an isolated swine heart (22).

Table 2

Types of Ablation Energy

• Radiofrequency (RF) energy • Direct current (DC) shock

• Laser energy energy

• Microwave energy • Cryoenergy

There are multiple methods of delivering energy during ablation;

radiofrequency delivery is the most common.

4.2. C a t h e t e r - D e l i v e r e d Leads

One of the continuing challenges in the area of intracardiac lead development is to downsize lead diameters and at the same time minimize the possibilities for fractures. Similarly, there is rapid development occurring in the placement of leads within the cardiac veins as well as in the development of tools for cannulation of the coronary sinus. For example, the Medtronic Attain TM Deflectable Catheter System features a percutaneous needle and syringe to access the venous insertion site, a guidewire to access the vein, an adjustable hemostasis valve to reduce blood loss during the implant procedure, a deflectable catheter to cannulate the coronary sinus and to deliver the pac- ing lead, and slitters to remove the deflectable catheter. In addition, the Attain Prevail TM, a steerable coronary sinus can- nulation tool is available from Medtronic, Inc. (Fig. 6). Such catheters need to be sterile and will likely be single use.

4.3. Endocardial Ablation Devices

Ablation is used to prevent tachyarrhythmias by modifying or destroying abnormal tissue. Clearly identifying the site of origin of the tachyarrhythmia (or tissue that is essential for maintaining reentrant activity) is important to the success of ablation (see Chapters 22 and 25); the goal of ablation is to create scar tissue in a critical myocardial area. Because scar tissue is electrically inert, it cannot originate or conduct electri- cal impulses. Scar tissue is created in the myocardium by either surgical incision or application of energy. Various forms of energy have been employed in the catheter-based approaches of ablation (Table 2). To date, surgical ablation is typically per- formed during an open chest procedure, but it is likely that with further enhancements of surgical methodologies, it could be performed using less-invasive approaches.

Currently, radiofrequency energy is used for almost all non-

operative ablation procedures (Fig. 7). In the past, DC (direct

current) shock energy was used for delivering energy to the

endocardium. A standard defibrillator was connected to the

ablation catheter to deliver the shock. The DC shock had the fol-

lowing undesirable effects that occurred at the catheter tip dur-

ing delivery of high energy: (1) excessive tip temperature and

(2) irregular-shape lesions that then could be proarrhythmic.

CHAPTER 33 / EMERGING TECHNOLOGIES 451

A

(On S~n)

RF ~enerator

B

/

Fig. 7. A typical radiofrequency (RF) catheter creates a lesion about 4 to 5 mm in diameter. The scar is large enough to ablate critical electrical circuits, yet small enough to pre- vent any significant damage to the heart. Typically, radiofrequency ablation heats tissue 1-2 mm deep. (A) The radiofrequency generator is able to instantaneously con- trol the amount of energy delivered. One type of generator circulates a cooling liquid around the tip of the catheter so that the temperature of the tip can be controlled; this gen- erator can minimize energy without causing fluid to boil.

(B) Deflectable tip catheters allow steering of the catheter tip to a position at the critical site to be ablated. Today, the majority of ablations are performed with typical electrode catheters. Usually, radiofrequency energy is delivered through the same electrode used for mapping.

Radiofrequency ablation catheters use energy similar to elec- trocautery. Radiofrequency energy heats the catheter tip-tissue interface, with resultant injury to the underlying tissue. Some advantages of radiofrequency ablation are: (1) small amounts of energy are required; (2) output power is easily controlled; (3) it creates small, homogeneous lesions; and/or (4) it does not cause dangerous/unpleasant stimulation or sensory effects. The amount of heating produced during radiofrequency ablation at the electrode tip can result in local blood boiling. To avoid this problem, one type of ablation catheter controls the temperature at the tip by using a cooling fluid.

There are numerous companies working on competing designs of such technologies. Thus, such cardiovascular device compa- nies continue to improve all design aspects of these catheter sys- tems (i.e., improving the ease of positioning of the distal electrode).

Other methods to focally destroy cells endocardially are also emerging: (1) laser energy has been used to destroy arrhyth- mogenic tissue via a cautery-type process; (2) microwave energy has been investigated as a possible energy source; and (3) cryoablation freezes tissue at the catheter tip to destroy muscle fibers without harming connective tissues (Table 2).

Visualization of the exact site where the lesion is to be created

remains an area of intense research; advanced echocardio- graphy systems as well as specialized catheters with built-in imaging possibilities are aggressively being pursued (16-18).

5. NOVEL AGENTS TO COAT DEVICES

As described in Section 4. l., drug-coated eluting stents have made a major impact on the field of interventional cardiology.

There is little doubt that such combined approaches that incor- porate pharmaceutics with implantable devices will continue to expand as a means to improve clinical management of the heart.

For example, steroid-eluting pacing leads have been on the market for years to manage acute inflammation associated with lead implantation (see Chapter 25).

Steroid-elution technology is considered to reduce inflam- mation; by eluting a steroid at the lead tip, leads are designed to reduce the typical tissue inflammation. Reduced inflammation allows lower pacing system energy requirements. For example, by reducing tissue inflammation, it has been described that such leads allow the use of lower electrical settings for low, stable, acute, and chronic energy outputs.

6. IMPLANTABLE SENSORS

Device and battery technologies both continue to decrease

in size and exhibit improved efficiencies. This in turn creates

452 PART IV: DEVICES A N D THERAPIES / IAIZZO

increasing possibilities for novel approaches for long-term assessment of various physiological parameters from unique aspects of the cardiovascular system.

One such device, the Medtronic Chronicle ®, is intended to sense and continuously collect unique and valuable informa- tion (e.g., intracardiac pressures, heart rate, and physical activ- ity) from a sensor placed directly in the heart's chamber. A patient can then periodically download this information to a home-based device that transmits this critical physiological data securely over the Internet to the Medtronic Patient Man- agement Network. Subsequently, physicians can access the network via a controlled Website at any time and review screens that present summaries from the latest downloads, trend infor- mation, or detailed records from specified times or problem episodes. The Chronicle Patient Management System is cur- rently undergoing investigational trials in the United States and Europe and is not yet approved for commercial sale.

Other types of implantable sensors that will likely be avail- able in the future include those for blood chemistries (respira- tory gases, pH, heparin, polyanions, etc.), flows, cardiac outputs, temperatures, glucose levels, drug levels, or other physiological data.

7. PROCEDURAL IMPROVEMENT

With pressures on the health care system to continually reduce treatment costs and document the outcome benefits of a given therapy, much effort will continue to be placed on procedural improvements for cardiac care.

7.1. Cardiac Imaging

The ability to image internal and external features of the heart continues to improve at a rapid rate and, as indicated in Chapters 18 and 19 on echocardiography and magnetic reso- nance imaging, respectively, the sophistication of such systems can be quite extreme. Yet, as the cost of computer hardware continues to decrease while capabilities increase, opportunities to develop such technologies for widespread use become fea- sible.

Intracardiac echocardiography (ICE) has many possible applications, including guidance of radiofrequency ablation procedures and visualization of cardiac anatomy and physiol- ogy. Compared to standard 2D imaging, emerging 3D echocar- diography may provide additional clinical utility. To assess this, our laboratory compared real-time 3D ICE (RT3D ICE) images to capture real-time video images simultaneously in an isolated four-chamber working swine heart (19). The com- parative images obtained in this study verified the ability of RT3D ICE to provide appropriate anatomical identification that could be applied to clinical practice. Stationary anatomi- cal structures (i.e., coronary sinus ostium) are easily visual- ized with static 3D ICE images (Fig. 8). Moving structures (i.e., valves) were not easily distinguished on RT3D ICE when presented as still images; however, they were more easily identified during acquisition and full-speed playback.

7.2. Specialized Surgical Tools

Cardiovascular device companies typically work closely with clinicians to develop not only new technologies, but also

modifications of existing devices or enhanced means to deploy them with better precision. One example of such a collaboration is the recently marketed implant tool for the placement of epi- cardial leads during a less-invasive surgery. This malleable epicardial lead implant tool features a stainless steel shaft that can be shaped to maneuver and position a lead optimally on the posterior of the heart, either on the right or the left ventricle (Fig. 9).

Another example of an innovative device that has been developed to fit a unique need is the device designed to trap plaque that may dislodge during interventional procedures;

such plaque might otherwise migrate to smaller vessels, caus- ing serious endovascular deficits. The SPIDER

Embolic Protection Device (ev3 Inc., Plymouth, MN) is specially designed for capture and removal of dislodged embolic debris before it can harm the patient (Fig. 10). This device is consid- ered to provide protection while conforming to the require- ments of the primary intervention. The SPIDER

Embolic Protection Device has been recommended to provide distal embolization protection in patients during a general vascular procedure, including peripheral, coronary, and carotid inter- ventions.

7.3. Less-lnvasive Surgeries

In Chapter 28, the rapidly advancing field of less-invasive cardiac surgery and some initial uses of robotics to perform epicardial procedures (e.g., bypass grafting and lead implanta- tions) were described. Such approaches are becoming more practical because better tools to perform such procedures are continually refined. For example, the Octopus®3 Tissue Stabi- lizer (Medtronic, Inc.) is the pioneering and market-leading suction device featuring (1) malleable stabilizer pods that can be formed to the unique contours of the patient's anatomy and (2) a unique tissue-spreading mechanism that enhances stabili- zation of the anastomotic site and presentation of the coronary (Fig. 11). Similarly, the Starfish

Heart Positioner (Medtronic, Inc.) has been shown to simplify cardiac positioning and thus minimize associated hemodynamic deterioration (20).

As cardiovascular surgeries employ less-invasive tech- niques, more and more novel devices and tools will be needed.

For example, the HEARTSTRING

Proximal Seal System (Guidant, Indianapolis, IN) is a unique means to perform bypass procedures that meet the challenge of clampless hemostasis;

another example is the Symmetry Bypass System (St. Jude Medical, St. Paul, MN). Both of these devices allow the surgeon to complete coronary artery bypass successfully without cross- clamping or side biting (Fig. 12).

8. TELEMEDICINE

Telecommunication systems and devices, including the uti- lization of the Internet, have experienced unpredicted growth in the last decade. This explosion in technology has the potential to revolutionize the care of all types of cardiac patients.

8.1. Ambulatory Heart Monitors

Ambulatory heart monitors collect ECGs during daily patient

activity. Today, a Holter monitor typically collects up to 48 h of

continuous ECG data. The patient wears the monitor and notes

CHAPTER 33 / EMERGING TECHNOLOGIES 453

Fig. 8. Utilizing standard cardiac surgery procedures, the heart from a 70-kg swine was explanted to an isolated heart apparatus and reanimated.

This preparation utilized a clear, crystalloid perfusate that allowed intracardiac visualization. Following in vitro stabilization, the heart was instrumented with 6-mm videoscopes (Olympus Industrial, Tokyo, Japan) and a 12-French 3D intracardiac echocardiography (ICE) catheter (Duke University, Durham, NC) via access ports in the superior vena cava, left pulmonary vein, aorta, and right atrial appendage. Simultaneous ultrasound (Volumetrics Medical Imaging, Durham, NC) and intracardiac video images of the coronary sinus ostium and the tricuspid, mitral, and aortic valves were recorded to time-synchronized Beta video decks (Sony Beta SP, Tokyo, Japan). (A) Real-time 3D ICE (RT3D ICE) image; (B) intracardiac visualization. The inferior vena cava and coronary sinus ostium are very distinct in the 3D ICE image (19).

B

IH:

Fig. 9. (A) The Model 5071 lead (Medtronic, Inc., Minneapolis, MN) is designed for ventricular pacing and sensing. (B) The Model 10626

(Medtronic, Inc.) is a single-use device indicated to facilitate placement of the Model 5071 pacing lead. The lead has application when

permanent ventricular dual-chamber pacing systems are indicated. Two leads may be used for bipolar pacing.

454 PART IV: DEVICES A N D THERAPIES / I A I Z Z O

Fig. 10. The SPIDER Embolic Protection Device (ev3 Inc.) provides distal embolization protection in patients during general vascular use, including peripheral, coronary, and carotid interventions. It can be delivered by any guidewire of choice to initially cross the lesion; it has a Nitinol filter design that is HEPROTEC

coated for patency up to 60 min. The radiopaque gold proximal loop is designed to provide visualization of filter-to-vessel apposition, and there are five filter sizes to match the vessel size appropriately. With permission from ev3 Inc., Plymouth, MN.

Fig. 1 l. Tools for less-invasive surgery, that is, an open chest proce- dure in which the heart is not stopped. The Octopus 3 Tissue Stabilizer (Medtronic, Inc., Minneapolis, MN) is a pioneering and market-lead- ing suction device, and the Starfish Heart Positioner (Medtronic, Inc.) has been shown to simplify cardiac positioning; both systems help minimize potential hemodynamic deterioration associated with less- invasive approaches.

the time and type of symptoms experienced, which are then later correlated with the ECG. In contrast, an external event recorder has a memory buffer that can store several weeks of symptom data. Instead of keeping a diary, the patient activates the recorder when symptoms occur; this latter approach is quite convenient for evaluating symptoms that occur infrequently.

A third type of device, an insertable loop recorder, is an implantable ECG recorder with a handheld, patient-controlled activator. The insertable loop recorder continuously r e c o r d s

ECGs. When symptoms occur, the patient activates the recorder, and the recorder stores the ECG for a preprogrammed period of time before and after activation. An insertable loop recorder is useful for patients with even more infrequent symptoms and who thus remain undiagnosed after an initial workup. Such an approach is also recommended to the patient for whom an external event recorder is impractical.

More specifically, the Reveal Plus (Medtronic, Inc.) is a second-generation insertable loop recorder; currently, it fea- tures autoactivation and is a high-yield, long-term, subcutane- ous, leadless ECG monitor that offers continuous 14-month monitoring (Fig. 13). Such systems provide new diagnostic approaches for patients with transient symptoms that may suggest cardiac arrhythmias, including: (1) unexplained syn- cope, (2) near syncope, (3) episodic dizziness, (4) unexplained recurrent palpitation, and/or (5) seizures and convulsions (21) (www. seizuresandfainting.com).

9. TRAINING SYSTEMS

As technologies have become more and more advanced, so has the need to teach students, residents, and physicians how to use them.

9.1. Simulator Mannequins

New products to enhance medical training are rapidly enter- ing the marketplace. The most impressive new systems incor- porate computerized mannequins, complex graphics, and sophisticated operator controls in state-of-the-art patient simu- lators. Students, residents, or physicians learn both medical con- cepts and manual procedures on life-size, interactive equipment that provides the benefits of anatomical correctness, unlimited repetition, scheduling convenience, and variable "health" con- ditions. One such system, the Human Patient Simulator, was developed by the University of Florida's College of Medicine to train anesthesiologists in routine and crisis situations. This interactive technology is considered to provide a realistic learn- ing experience adaptable for a wide range of health care prac- titioners, including medical students, residents, nurses, and biomedical engineers.

The simulator mannequin typically has palpable pulses, heart

and lung sounds, simulated muscle twitch responses to nerve

CHAPTER 33 / EMERGING TECHNOLOGIES 455

Fig. 12. HEARTSTRING Proximal Seal System (Guidant, Indianapolis, IN) is a surgically intuitive system that meets the challenge of clampless hemostasis with a design that is elegant in its simplicity and profound in its implications for a patient.

stimulation, and a body temperature. Thus, trainees can monitor its heart rate, cardiac rhythms, cardiac output, and blood pres- sure. C o m m o n l y equipped with interface software and an instructor's remote control, the simulator also gives accurate patient responses to over 60 different drugs, mechanical venti- lation, and other medical therapies and allows the instructor to introduce new conditions.

Another such device that is currently available is the ultra- sound training simulator, which allows students to perform sonographic examinations on a mannequin while viewing real- time sonographic images. The scanning motions and techniques that can be employed by the user realistically simulate the same skills necessary to examine a patient. It is considered that, by allowing trainees to practice on the simulator for as much time as needed to achieve initial competency, users should be able to perform more effectively in a shorter period of time in the actual clinical setting.

9.2. Endovascular Implant Simulators

A new generation of implant simulators that employs both visual and tactile feedback for practicing either right or left heart catheter-based procedures is currently available (e.g., AccuTouch ® Endovascular Simulator, Immersion Medical, San Jose, CA, http://www.immersion.com/medical/products/

endovascular/). In addition, such devices can be used to simu- late the placement of coronary stents (Procedicus VIST TM, Mentice AB, G6teborg, Sweden, http:/]www.mentice.com/).

More specifically, the VIST system allows highly realistic simu- lation-based training of angiography, angioplasty, and coro- nary stenting using realistic 3D patient anatomies, real nested tools, tactile feedback, as well as different cases/scenarios and complications.

Such systems consist of an interface device, a computer, and one or more displays (e.g., one for the simulated fluoroscopic image and another for the instructional system). The interface device is a virtual patient with an introducer in place; such systems will become more and more realistic in the future.

Through this, the different real-life tools and devices can be introduced, and actual tools are used (and reused). All tools are

~atient

Patient Fig. 13. Reveal Plus is the second-generation Reveal ILR (Medtronic, Inc., Minneapolis, MN). Now with auto-activation, the Reveal Plus ILR is a high-yield, long-term, subcutaneous, and leadless electrocar- diogram (ECG) monitor that offers continuous 14-month monitoring.

IR, insertable loop recorder.

active and can be manipulated at any time in the procedure. In

the VIST system, the interface and the tools (catheters, bal-

loons, guidewires, etc.) interact with the simulation through a

software package that generates the fluoroscopic display, the

forces that are reflected in the tools (for tactile feedback), the

456 PART IV: DEVICES AND THERAPIES / IAIZZO

contrast flow, h e m o d y n a m i c s , and the results o f the s i m u l a t e d i n t e r v e n t i o n ; a W e b - b a s e d u s e r i n t e r f a c e g u i d e s the u s e r through the p r o c e d u r e and facilitates self-learning.

M a n y training centers around the world, in both a c a d e m i c and corporate settings, have been created, and they utilize vari- ous types o f simulators; for instance, the K a r o l i n s k a ' s training center uses a n u m b e r o f such devices (http://utbildning.ks.se/).

1 0 . S U M M A R Y

In this book, and m o r e s p e c i f i c a l l y in this chapter, numerous areas o f c a r d i o l o g y and cardiac surgery in which the d e v e l o p - m e n t o f innovative t e c h n o l o g i e s continues to mature at a rapid rate have been reviewed. These areas include: (1) resuscitation systems and devices; (2) i m p l a n t a b l e therapies (e.g., p a c e m a k - ers, i m p l a n t a b l e c a r d i o v e r t e r d e f i b r i l l a t o r s , stents, s e p t a l occluders, valves, annular rings, fibrin patches, etc.); (3) deliv- ery s y s t e m s / i n v a s i v e t h e r a p i e s (e.g., a n g i o p l a s t y , ablations, catheters, etc.); (4) p r o c e d u r a l i m p r o v e m e n t s (e.g., m a p p i n g systems, 3D e c h o c a r d i o g r a p h y , m a g n e t i c resonance imaging, training simulators, etc.); (5) l e s s - i n v a s i v e surgical approaches (i.e., off-pump, robotics, etc.); (6) p o s t p r o c e d u r a l f o l l o w - u p / t e l e m e d i c i n e (e.g., electrical, functional, adverse events, etc.);

and (7) training tools. There is no doubt that continued i m p r o v e - m e n t o f all such technologies as well as advances in rehabilita- tion and other support services (e.g., patient education, training, h o m e monitoring, etc.) will extend or save lives and enhance the overall quality o f life for such patients.

Finally, it should be m e n t i o n e d that much w o r k has been done on the i m p l a n t a b l e r e p l a c e m e n t heart, but such prosthetic systems have yet to be used successfully (e.g., the A b i o C o r

I m p l a n t a b l e R e p l a c e m e n t Heart; A b i o m e d , D a n v e r s , M A ) . H o w e v e r , w h e n a g i v e n p a t i e n t is at i m m i n e n t risk o f death, the i m p l a n t o f an artificial heart is d e s i g n e d both to e x t e n d life and to p r o v i d e a r e a s o n a b l e q u a l i t y o f life. A f t e r i m p l a n t a t i o n , the d e v i c e d o e s not r e q u i r e any tubes or wires to pass t h r o u g h the skin; p o w e r to d r i v e the p r o s t h e t i c heart is t r a n s m i t t e d across the intact skin, a v o i d i n g skin p e n e t r a t i o n that m a y pro- v i d e o p p o r t u n i t i e s for infection. Just like the natural heart, the r e p l a c e m e n t heart consists o f two b l o o d - p u m p i n g c h a m b e r s c a p a b l e o f d e l i v e r i n g m o r e than 8 L o f b l o o d e v e r y minute.

In conclusion, it is exciting to think about the technologies that have been e m p l o y e d thus far as well as those that are being d e v e l o p e d that will p o s i t i v e l y affect the overall health care o f the cardiac patient. It is an exhilarating time to be w o r k i n g in the field o f c a r d i o v a s c u l a r sciences.

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