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Skeletal Muscle
Skeletal Muscle NEWTECHNIQUES FOR TREATING HEARTFAILURE Alexis Koroteyev, MD; Alberto Pochettino; MD, Hiroshi Niinami, MD; Larry W. Stephenson, MD rreversible congestive heart failure remains one of the leading causes of death in the United States. Each year. thousands of patients die because their hearts are unable to pump enough blood to sustain life. During the last few years, significant advances have been made i n heart transplantation and artificial heart devices. Both still are far from optimal. Heart transplantation is associated with rejection and limited availability of donor hearts. About half of the patients who receive heart transplants die from rejection within five years of surgery. Drugs used to suppress rejection cause a number of complications. A significant donor shortage results in long waiting periods for desperately ill patients, and 10% to 25% die while on the waiting list.' Furthermore, many potential recipients have contraindications to heart transplantation.
Clinical use of artificial hearts is limited by the high rate of thromboembolic and infectious complications and by the necessity to use external power sources. At the present time, no totally implantable mechanical heart is available, and none is likely to be available for clinical use in the near future. All of these problems have prompted investigators to seek alternative methods of helping the failing heart. One such alternative is the use of skeletal muscle for cardiac assistance.
Alexis Koroteyev, MD, is an assistant pmfessos of susgery, diiv'sion of cardiothosacic susgesy, National Reseasch Centes of Sirsgesy for. the Soviet Union, M O S L Y ) MH~e . also is a visiting re se a sc h sc h o la I . , c.a sd i o t h o sa c ic s u 1.g e r y , Wayne State Uniiw.siiy, Detsoit. He easned his medical d e g s e e ,f'i-oni the M o s c o ~Medical > Institirte.
Hiroshi Niinami, MD, is a reseasch associate, dillision of cardiothosacic surgery, Wayne State Uniiwsiiy, Detroit, and cardiothoracic resident, Tokyo Women's Medical College, The Heart Institute of Japan. He earned his niedical degsee $-om Gunnia Uniivrsir[vSchool of Medicine, Tokyo.
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Alberto Pochettino, MD, is a sesearch associate, Wayne State Uniivssiiy, Detsoit, and susgery resident a t the State University of' NeM' Y o r k . Bsooklyn. He earxed his medic,al degsee at Nosthwestern Uniiwsity, Chicago.
Histoi-ical Background
T
he idea of using skeletal muscle for treating heart diseases is not new, and it seems quite reasonable because skeletal muscle can develop more power during a single contraction and more force per unit of cross-
Larry W . Stephenson, MD, is professor and chief of the diiision of casdiothosacic surgeiy, Wayne State Univessiiy; chiej of casrlrothosacic surgesy> Detsoit Medical Center; and chief of cardiothoracic surgery, Huspes Hospital: all in Detsoit. He eusned his medical degsee from Marquette Univessiiy, Milwaukee. 1005
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During the past 50 years, a number of investigators have tried to use skeletal muscle in cardiac surgery.
sectional area than cardiac muscle.2 During the past 50 years, a number of investigators have tried to use skeletal muscle in cardiac surgery. In 1931, a pectoralis muscle was used to treat a patient in Bolivia with a traumatic left ventricular injury.' Researchers in France and the United States wrapped skeletal muscle around the heart both in animals and humans in hopes of improving collateral blood upp ply.^ In 1959, a Soviet Union physician used diaphragmatic pedicle grafts to reinforce the heart in patients with left ventricular aneurysms.' He sutured the muscle grafts directly to the epicardial surface of the defect in the left ventricle under sufficient tension in an attempt to flatten out and obliterate the aneurysms. The grafts were well tolerated, b e c a m e firmly a d h e r e d to t h e myocardium, reinforced the scarred tissue, and may have improved the myocardial blood supply. About 30% of these patients were relieved from chest pain and dyspnea. The operative mortality was approximately 20%. In 1959, Adrian K a n t r o w i t z , M D , and William McKinnon, MD, State University of New York, D o w n s t a t e Medical C e n t e r , Maimonides Hospital, Brooklyn, performed a series of acute experiments. They wrapped pedicle grafts of the left canine hemidiaphragm around the heart and stimulated the muscle graft to contract in synchrony with the heart. They could not detect an improvement i n hemodynamics while the muscle was being stimulated. They also wrapped diaphragm muscle around the thoracic aorta and stimulated it via the phrenic nerve in synchrony with the heart. By stimulating the muscle graft, they increased both diastolic and mean aortic pressures. Unfortunately, because of m u s c l e fatigue, the increase in pressure lasted only 15 seconds.b Henry M. Spotnitz, MD, and colleagues from Columbia University, New York City, designed
a skeletal muscle pouch from canine rectus abdominis muscle that could develop pressures of up to 500 mm Hg, but it also fatigued rapidI Y . ~Although many others attempted to use skeletal muscle for cardiac assistance, the further development of this research was limited by t h e skeletal muscle's susceptibility to fatigue under conditions of intensive use. Useful work could be obtained, but only for short periods of time. Careful research in basic muscle physiology was needed to resolve the problem of early fatigue.
Muscle Anatomy and Physiology 0th skeletal muscle and cardiac muscle are composed of the same contractile units called sarcomeres. The contractile proteins in both types of muscles are similar in structure and orientation. Cardiac muscle must contract relentlessly throughout a lifetime, and skeletal muscle generally is required to perform work for relatively short periods of time with intervening periods of rest. The difference in function predicts certain structural a n d metabolic differences. Mitochondria are the organelles in the cell responsible for energy conversion.The portion of mitochondria by volume in heart muscle is about 30%; in skeletal muscle it is not more than 5%. Thus, heart muscle has more energy available to perform continuous work. Cardiac muscle mainly uses aerobic metabolism, and skeletal muscle is more prone to use the less efficient anaerobic pathways for energy use. Furthermore, cardiac myosin, a contractile protein, uses energy more efficiently than skeletal muscle myosin does. Skeletal muscle is composed of two basic types of fibers.Type I contracts slowly, and, like the cardiac muscle fiber, is relatively resitant to fatigue, This type of fiber bas a well1007
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Researchers discovered that skeletal muscle fibers can alter their properties in response to changes in use. developed aerobic metabolism, has a large mitochondria1 volume, and uses “slow” isoforms of myosin. Muscles composed primarily of type I fibers are postural in function. Type I1 fibers (eg, those responsible for eye movement) contract more rapidly, obtain energy largely by anaerobic routes, and can develop large forces, but fatigue very rapidly. “Fast” fibers have a relatively small mitochondria1 volume and are made of fast isoforms of myosin. Muscles such as the latissimus dorsi, the pectoralis, the rectus abdominis, and the diaphragm are composed of both types of myofibrils. Australian researchers discovered that skeletal muscle fibers can alter their properties in response to changes in use. These physicians cross-anastomosed a motor nerve from a slow muscle with one going to a fast muscle. They found that under such conditions, fast muscle became slow and vice versa: thus the nerve influenced the properties of the muscle.8 Later, other researchers working in England, demonstrated that fast muscle could be transformed to slow, fatigue-resistant muscle by applying chronic electrical stimulation to the motor nerve.9 It seemed that it might be possible to exploit this phenomenon for skeletal muscle cardiac assist.” The process of chronic stimulation or training the skeletal muscle is called conditioning. Conditioning causes sequential changes in skeletal muscle. These include an increase in capillary density and mitochondria volume, an increase in oxidative enzymes, and a decrease in glycolytic enzymes. After six to eight weeks, a complete transformation of type I1 fibers to type I fibers occurs.” The conditioned muscle is more fatigue resistant, and it uses oxygen more efficiently than the unconditioned muscle.’* In cardiac muscle, when one cell is stimulated, the stimulus spreads rapidly from cell to 1008
cell causing the entire heart muscle to contract. In contrast, skeletal muscle cells are organized into groups called motor units, and each is activated by a separate nerve fiber. The entire muscle usually does not contract simultaneously. The strength of contraction depends on the quantity of fibers activated and the rate of fiber recruitment. A “burst” stimulus is a series of electrical impulses. When applied to a motor nerve, a burst stimulus can lead to mechanical summation of many motor units and generate a substantially greater force than a single electrical stimulus. A special burst pacemaker that is R-wave synchronous has been developed. It can stimulate skeletal muscle using a burst pattern and contract in synchrony with the heart. This pacemaker produces appropriately timed stimuli (ie, pulse trains) that cause skeletal muscle to generate cardiac-type work.”
Cardiac Assist
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urrently, two methods are used for skeletal muscle cardiac assist. Cardiomyoplasty involves wrapping muscle around the heart. The other method uses a separate muscle pumping chamber known as a skeletal muscle ventricle (SMV). The latissimus dorsi muscle is used in both methods. It also is used sometimes in plastic surgery to replace defects in the abdominal or the chest wall. The loss of the latissimus dorsi muscle causes relatively little physical impairment because other muscles compensate for its function. The latissimus dorsi also is easy to free from its natural position and can be moved near the heart. Another important surgical advantage is that this muscle has a single main blood supply and a single motor nerve, which makes it easy to work with. Other muscles including the pectoralis, psoas, rectus abdominis, and diaphragm
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cardiomyostimulator
Fig 1. Cardiomyoplasty. The latissimus dorsi muscle graft is wrapped around the heart.
have been used for cardiac assistance.
Cardiomyoplasty
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ardiomyoplasty is the only method of skeletal muscle cardiac assist presently undergoing clinical trials.With this method, the surgeon frees the latissimus dorsi muscle except for its nerve and main blood supply. He or she moves it into the chest cavity and wraps it around the cardiac ventricles (Fig 1). The muscle graft is stimulated during systole with bursts of impulses delivered by a cardiomy ostimulator. 1010
In 1985, Alain Carpentier, MD, PhD, from Paris was the first to perform cardiomyoplasty on a patient. In treatment of a benign cardiac tumor, he successfully replaced a resected part of the cardiac wall with a pedicle graft of the latissimus dorsi m u ~ c 1 e . lThis ~ surgery usually is performed through two separate incisions-a lateral chest approach to dissect the left latissimus dorsi muscle graft and a subsequent midline sternotomy. Patients are positioned in a left thoracotomy position for dissection of the latissimus dorsi and in a supine position for the midline sternotomy incision. When patients are placed in the thoracotomy position for resection
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If a patient's pulmonary function is moderately to severely depressed, cardiomyoplasty will not be done. of the latissimus dorsi muscle, the perioperative nurses take usual precautions including placing padding under the right hip and the axilla. No special surgical instruments o r electrical devices are needed for this procedure other than the cardiomyostimulator and electrodes, which go to the heart and muscle flap, respectively. Frequently, a plastic surgeon will raise the latissimus dorsi muscle flap as he or she would when raising the flap for other uses. The surgeon dissects the latissimus dorsi muscle free from the iliac crest, the spine, the inferior scapular angle, and the ninth to 12th rib attachments. He or she removes a 6-cm segment of the anterior portion of the second rib to allow for transposition of the graft into the thorax. The surgeon places the muscle graft in the thorax by carefully pushing the muscle through the opening left where the rib had been resected. He or she gently works the muscle into the thorax to the point where the proximal tendon is left out, and sutures it to the first or third rib. Care is taken not to twist the neurovascular pedicle because the thoracodorsal artery, vein, and nerve are left intact. The surgeon also must be careful not to let the muscle compress the lung once the chest is opened and the latissimus is wrapped around the heart. Even when great care is taken, the lung can be partially compressed, causing a decrease in pulmonary function. For this reason, most surgeons who perform cardiomyoplasty determine preoperative pulmonary function. If a patient's pulmonary function is moderately to severely depressed, cardiomyoplasty will not be done. The surgeon implants two pacing electrodes in the proximal portion of the muscle for longterm stimulation. Depending on the cardiac disorder, cardiomyoplasty can be used as ventricular reinforcement (ie, to increase the contractility of the damaged myocardium), ventricular substitution (eg, in case of cardiac tumors or 1012
aneurysms), or as both reinforcement and sub~ t i t u t i o n . The ' ~ two latter procedures are performed with the patient on cardiopulmonary bypass. Cardiopulmonary bypass generally is not used for the reinforcement procedure (ie, wrapping the muscle around the ventricles), although the pump is always available in the room because these patients are quite ill and the heart could decompensate and require cardiopulmonary bypass at any time. When cardiopulmonary bypass is used, the ascending aorta is cannulated as with any other bypass procedure, and a single venous drainage cannula is placed through the right atrium. Cardiopulmonary bypass is always used if additional procedures are being performed during the cardiomyoplasty procedures, such as coronary artery bypass grafting, valve replacement, or left ventricular aneurysm resection. To synchronize the muscle contraction to the heart rate, the surgeon places two sensing leads on the heart and a cardiomyostimulator beneath the rectus abdominis muscle. If cardiomyoplasty is performed without additional cardiac procedures, the length of the operation usually is about four to six hours. During the early postoperative period, the care for these patients is similar to other patients undergoing cardiac surgery. The main difference is the patient has two wounds to deal with instead of one. Stimulation begins two weeks after the surgery, and the muscle graft is progressively put into use by slowly increasing the burst frequency pattern (ie, number of pulses and heart-muscle contraction ratio). After four months, the skeletal muscle can be stimulated at a synchronization ratio of 1:l or 1:2 with the heart.I6 Since 1985, more than 100 procedures of this type have been carried out in a number of centers around the world. The major indications for this procedure are diseases associated with
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cardiomyostimulator
Fig 2. Skeletal muscle ventricle used as an aortic diastolic counterpulsator. The SMV is on the outside of the chest wall. The limbs of the bifurcation graft have been divided, tailored, and rejoined to prevent kinking.
irreversible and extensive loss of cardiac muscle contractility, such as ischemic cardiomyo p a t h y , dilated c a r d i o m y o p a t h y , C h a g a s myocarditis, dysplastic myocardial disease (ie, Uhl’s anomaly), and myocardial tumors. In most patients, symptoms of heart failure have improved dramatically after the surgery and the muscle conditioning period. In some patients, surgery has increased the cardiac ejection fraction.” Although these improvements often are
small, patients feel much better when the muscle is stimulated. Some patients’ symptoms are worse when the stimulator is temporarily s w i t c h e d o f f . O n e can speculate that f o r patients with dilated hearts, even a small increase in ejection fraction may cause a comparatively significant increase in the cardiac output resulting in improvement of symptoms. T h u s f a r , the measured hemodynamic improvements following cardiomyoplasty have 1013
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been variable and usually less than would have been expected from the improvements in the patients’ symptoms. This reflects uncertainties about the way the procedure works. These uncertainties remain because of the lack of a good experimental model for cardiomyoplasty. Most animal research has been performed on healthy animal hearts, and the effect of cardiomyoplasty on a healthy heart is likely to differ significantly from the effect on a dilated and failing heart. In trying to explain the clinical observations, some have suggested that an external wrap of skeletal muscle provides an accessory contractile layer that assists in the ejection of blood.’8 Others think that the stimulated latissimus dorsi muscle graft prevents the heart from further di1atati0n.I~An improvement in the blood supply to the heart via skeletal muscle graft collaterals also may play an important role. As the mechanisms of action of cardiomyoplasty are better understood, improved patient selection criteria will develop. Some predict that this procedure may become an alternative for patients with heart failure in whom cardiac transplantation is contraindicated.20
Skeletal Muscte Ventricles
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he second approach using skeletal muscle for heart assist is to construct separate skeletal muscle pumping chambers or SMVs. A number of investigators over the years have studied skeletal muscle pumps. Dr Spotnitz constructed an SMV from the canine rectus abdominis muscle and demonstrated that some characteristics were similar to those of the heart as described earlier. Unfortunately, all of these muscle pouches fatigued rapidly. After the demonstration that electrical preconditioning was able to transform skeletal muscle into fatigue-resistant muscle, a number of skeletal muscle ventricle systems were designed. In our laboratory, SMVs usually are constructed from the latissimus dorsi muscle. The surgeon completely mobilizes the muscle from its chest wall and back attachments, leaving the neurovascular bundle intact. After the mobilization, the surgeon wraps the muscle around a 1014
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Teflon stent, which is cylindrical or conical in shape. The shape of the mandrel will become the shape of the ventricular cavity. The surgeon places a pacing electrode around the proximal thoracodorsal nerve while implanting a sensing electrode into the left ventricular wall, Both electrodes are connected to an implantable Rwave-synchronous cardiomyostimulator.*’ It is important to understand that mobilizing the latissimus dorsi requires division of many chest wall blood vessels, which leads to ischemia of the distal half of the muscle graft. To allow for recovery of this initial ischemia, the muscle should be rested after the surgery, for a so-called “vascular delay period.” Usually, this takes three to four weeks.22The combination of a vascular delay period and electrical conditioning allows for the development of a fatigue-resistant SMV. In a second surgical procedure, the surgeon removes the Teflon mandrel and connects the SMV to the cardiovascular system. To test the ability of an SMV to function for long periods of time, a totally implantable “mock circulation system” was developed which allowed for control of both preload (ie, filling pressure) and afterload (ie, vascular resistance), and for measurement of SMV output in chronic experiment^.^^ Some SMVs pumped fluid in this mock circulation for as long as nine weeks. The S M V s were able to generate stroke work between that of the canine left and right ventricle^.^^ Much effort has been put forth to define the best stimulation patterns of electrical conditioning, the optimal length of vascular delay, and the best shape of an SMV. In a recent study, after SMV construction, experimental animals were placed in three groups to test different delay and conditioning protocols. The best results were obtained from the group that received the longest vascular delay period, demonstrating the importance of recovery of the blood ~ u p p l y . ~ ~ Oofn ethe ways in which SMVs can be used for cardiac assistance is as arterial diastolic counterpulsators. Michael A. Acker, MD, from our laboratory, constructed a tube-shaped SMV and connected it to the descending thoracic aorta.26By stimu-
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Carotid 200
Femoral 100 Pressure
(mmHg)
ECG
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25 Hz
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Fig 3. Arterial pressure and electrocardiogram traces taken at one year in one dog whose SMV had been pumping continuously for more than one year. Asterisks mark diastolic augmentation. The SMV contracts every other heartbeat. lating the muscle during diastole, the SMV produced arterial pressures similar to those produced by the intra-aortic balloon pump. During the assisted cardiac cycle, the SMV increased forward blood flow by up to 63%. The longest surviving animal lived 11 weeks. Since that first set of experiments, we have been connecting conical or cylindrical SMVs to the thoracic aorta via a bifurcated graft anastomosed to the neck of the SMV (Fig 2). In ongoing experiments, the aorta was ligated between the proximal and distal limbs of the bifurcated graft so there was obligatory blood flow through the SMV. This type of SMV-counterpulsator caused less thromboembolic complications than the first one tested.*’ One of the dogs with such a device is alive after more than a year, and the SMV continues to function effectively. There has been no evidence of throm1016
boembolism at the time of this writing (Fig 3). Charles R. Bridges, Jr, MD, ScD, also working in our laboratory, recently studied the possibility of using S M V s to completely bypass the right heart.28 He connected the S M V to the vena cava (inflow) and to the proximal pulmonary artery (outflow), so that the right heart was excluded from the circulation. For several hours, the SMVs performed the work of the right ventricle.
Summary
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resently, only cardiomyoplasty has been used clinically. This is not surprising because it is a relatively safe operation to perform, avoids problems of thrombosis, and is unlikely to do harm. Evidence is beginning to emerge that clinical improvement may be due
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to enhanced cardiac output and not simply to limiting ventricular distension or to a placebo effect. We consider skeletal muscle ventricles to be experimental; however, our experiment in which one dog continues to do well after one year demonstrates that long-term function is achievable. Many problems remain. Further refinement may enable SMVs to work at even lower filling pressures. Although the great majority of cardiac failure occurs in adults, a significant number of children are born with congenital cardiac deficiencies for whom skeletal muscle assist also may offer potential therapy. 0 Notes 1. J G Copeland et al, “The role of mechanical support and transplantation in treatment of patients with end-stage cardiomyopathy,” Circulation 72 (September 1985) I1 7-12. 2. S Salmons, J Jarvis, “Cardiomyoplasty: The basic issues,” Cardiac Chronicle 4 (February 1990) 1-7. 3. F R De Jesus, “Breve concideraciones sobre un case de herida penetrante del corazon,” Asociacion Medica De Puerto Rico Boletn 23 (August 1931) 380-382. 4. C S Beck, “A new blood supply to the heart by operation,” Surgery, Gynecology & Obstetrics 6 1 (September 1935) 407-410. 5. B V Petrovsky, “The use of the diaphragm grafts for plastic operations in thoracic surgery,” Journal of Thoracic and Cardiovascular Surgery 4 1 (March 1961) 348-355. 6. A Kantrowitz, W McKinnon, “The experimental use of the diaphragm as an auxiliary myocardium,” Surgical Forum 9 (1959) 266-268. 7. H M Spotnitz, C Merker, J R Malm, “Applied physiology of the canine rectus abdominis: Forcelength curves correlated with functional characteristics of a rectus powered ‘ventricle’: Potential for cardiac assistance,” Trans American Society of Artificial Internal Organs 20 (July 1974) 747-756. 8. J C Buller, J C Eccles, R M Eccles, “Interactions between motor neurons and muscles in respect of the characteristic speeds of their responses,” Journal of Physiology 150 (February 1960) 418439. 9. S Salmons, G Vrbova, “The influence of activity on some contractile characteristics of mammalian fast and slow muscles,” Journal of Physiology 210 (May 1969) 535-549. 10. F R Armenti et al, “Transformation of skeletal muscle for cardiac replacement,” Surgical Forum 35 1018
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(1984) 258-260; J A Macoviak et al, “Electrical conditioning of in situ skeletal muscle for replacement of myocardium,” Journal of Surgical Research 32 (May 1982) 429-439; J D Mannion, L W Stephenson, “Potential uses of skeletal muscle for myocardial assistance,” Surgical Clinics of North America 65 (June 1985) 679-687. 11. Armenti, “Transformation of skeletal muscle for cardiac replacement,” 258-260. 12. M A Acker et al, “Oxygen consumption of chronically stimulated skeletal muscle,” Journal of Thoracic and Cardiovascular Surgery 94 (November 1987) 702-709. 13. M A Acker et al, “An autologous biologic pump motor,” Journal of Thoracic and Cardiovascular Surgery,” 92 (October 1986) 733746; M A Acker et al, “Skeletal muscle as the potential power source for a cardiovascular pump: Assessment in vivo,” Science 236 (April 17, 1987) 324-327; M A Acker et al, “Skeletal muscle ventricles in circulation: One to eleven weeks’ experience,” Journal of Thoracic and Cardiovascular Surgery 94 (August 1987) 163-174; R C Chiu et al, “Implantable extra-aortic balloon assist powered by transformed fatigue-resistant skeletal muscle,” Journal of Thoracic and Cardiovascular Surgery 94 (November 1987) 694-701; M L Dewar et al, “Synchronously stimulated skeletal muscle graft for myocardial repair: An experimental study,” Journal of Thoracic and Cardiovascular Surgery 87 (March 1984) 325-331. 14. A Carpentier, J C Chachques, “Myocardial substitution with a stimulated skeletal muscle: First successful clinical case,” (Letter) The Lancet 1 (June 1, 1985) 1267. 15. J C Chachques, P A Grandjean, A Carpentier, “Latissirnus dorsi dynamic cardiornyoplasty,” Annals of Thoracic Surgery 47 (April 1989) 600604. 16. Ibid; Carpentier, Chachques, “Myocardial substitution with a stimulated skeletal muscle: First successful clinical case,” 1267; J C Chachques et al, “Dynamic cardiomyoplasty: A new approach to assist chronic myocardial failure,” Life Support System 5 (October/December 1987) 323-327; J C Chachques et al, “Effect of latissimus dorsi dynamic c ardi om y o p I a s t y on vent r i c u 1ar function, ” Circulation 78 supplement 111 (November 1988) 203-216; J C Chachques et al, “Dynamic aortomyoplasty to assist left ventricular failure,” Annals of Thoracic Surgery 49 (February 1990) 225-230. 17. A Carpentier, “In discussion of: R L Kao et al, ‘The importance of skeletal muscle fiber orientation for dynamic cardiomyoplasty,’ ” Journal of Thoracic and Cardiovascular Surgery 99 (January 1990) 134140. 18. S Salmons, J C Jarvis, “Cardiomyoplasty: The
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basic issues,” Cardiac Chronicle 4 no 2 (1990) 1-7. 19. Chachques, “Dynamic cardiomyoplasty: A new approach to assist chronic myocardial failure,” 323-327; Chachques, “Effect of latissimus dorsi dynamic cardiomyoplasty on ventricular function,” 203-216; Carpentier, “In discussion of: R L Kao et al, ‘The importance of skeletal muscle fiber orientation for dynamic cardiomyoplasty,’ ”134- 140. 20. Chachques, “Latissimus dorsi dynamic cardiomyoplasty,” 600-604. 21. Acker et al, “Skeletal muscle ventricles in circulation: One to eleven weeks’ experience,” 163174. 22. Chachques, “Latissimus dorsi dynamic cardiomyoplasty,” 600-604; J D Mannion, R Hammond, L W Stephenson, “Hydraulic pouches of canine latissimus dorsi: Potential for left ventricular assistance,” Journal of Thoracic and Cardiovascular Surgery 91 (April 1986) 534-544; J D Mannion et al, “Transmural blood flow of multi-layered latissimus dorsi skeletal muscle ventricles during circulatory assistance,” Trans American Society of Artificial Infernal Organs 32 (July/September 1986) 454-460;
J D Mannion et al, “Effects of collateral blood vessel ligation and electrical conditioning on blood flow in dog latissimus dorsi muscle,” Journal of Surgical Research 47 (October 1989) 332-340. 23. Buller, Eccles, Eccles, “Interactions between motor neurons and muscles in respect of the characteristic speeds of their responses,” 417-439. 24. Ihid; Salmons, Jarvis, “Cardiomyoplasty: The basic issues,” 1-7. 25. A Pochettino et al, “Skeletal muscle ventricles for total heart replacement,” Annals of Surgery 212 (September 1990) 345-352. 26. Acker et al, “Skeletal muscle ventricles in circulation: One to eleven weeks’ experience,” 153174. 27. C R Bridges, Jr et al, “Functional right-heart replacement with skeletal muscle ventricles,” Circulation 80 supplement I11 (November 1989) 183-191. 28. D R Anderson et al “Autogenously lined skeletal muscle ventricles: Up to nine months’ experience,” Journal of Thoracic and Cardiovascular Surgery (1991) in press.
Quality Standards for Medical Gloves
Average Malpractice Award Increases
The US Food and Drug Administration (FDA) announced minimum quality levels and methods to test rubber and plastic gloves worn by health care workers. Manufacturers of medical gloves now conduct their own testing programs. The FDA action standardizes the testing and defines the maximum failure rate. Random samples of gloves will be inspected for tears, holes, and any foreign matter embedded in the gloves. The gloves also will be subjected to a water leak test. This test involves pouring 1L of water into the glove and checking for leaks. Gloves will not be sold for medical use if more than 25 per 1,000 surgeons’ gloves or 40 per 1,000 patient examination gloves are found to have leaks. The criteria are more stringent for surgeons’ gloves because they come in contact with internal areas of the body and may be exposed to bodily fluids for longer periods of time. The FDA regulations were published in the Dec 12, 1990, Federal Register.
It takes nearly five years to resolve a malpractice claim against an obstetrician/gynecologist. This is ajump from 3.5 years in 1987. These are results of a recent study of 2,200 physicians conducted by the American College of Obstetricians and Gynecologists, Washington, DC. The results were reported in the Nov 5 , 1990, issue of Hospitals. The results of the study also show that about 40% of all claims were dropped or settled without any payment on behalf of the physician. The average payment increased 33% to $21 1,320, according to the article. The most costly malpractice suits during 1987 and 1988 involved failure to diagnose a hemorrhage. The average award in those cases was $145,300. Other expensive malpractice settlements were failure to diagnose a bowel lesion, improper treatment related to birth, misdiagnosis of diabetes, and failure to detect a myocardial infarction.
1020
Clinical use of artificial hearts is limited by the high rate of thromboembolic and infectious complications and by the necessity to use external power sources. At the present time, no totally implantable mechanical heart is available, and none is likely to be available for clinical use in the near future. All of these problems have prompted investigators to seek alternative methods of helping the failing heart. One such alternative is the use of skeletal muscle for cardiac assistance.
Alexis Koroteyev, MD, is an assistant pmfessos of susgery, diiv'sion of cardiothosacic susgesy, National Reseasch Centes of Sirsgesy for. the Soviet Union, M O S L Y ) MH~e . also is a visiting re se a sc h sc h o la I . , c.a sd i o t h o sa c ic s u 1.g e r y , Wayne State Uniiw.siiy, Detsoit. He easned his medical d e g s e e ,f'i-oni the M o s c o ~Medical > Institirte.
Hiroshi Niinami, MD, is a reseasch associate, dillision of cardiothosacic surgery, Wayne State Uniiwsiiy, Detroit, and cardiothoracic resident, Tokyo Women's Medical College, The Heart Institute of Japan. He earned his niedical degsee $-om Gunnia Uniivrsir[vSchool of Medicine, Tokyo.
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Alberto Pochettino, MD, is a sesearch associate, Wayne State Uniivssiiy, Detsoit, and susgery resident a t the State University of' NeM' Y o r k . Bsooklyn. He earxed his medic,al degsee at Nosthwestern Uniiwsity, Chicago.
Histoi-ical Background
T
he idea of using skeletal muscle for treating heart diseases is not new, and it seems quite reasonable because skeletal muscle can develop more power during a single contraction and more force per unit of cross-
Larry W . Stephenson, MD, is professor and chief of the diiision of casdiothosacic surgeiy, Wayne State Univessiiy; chiej of casrlrothosacic surgesy> Detsoit Medical Center; and chief of cardiothoracic surgery, Huspes Hospital: all in Detsoit. He eusned his medical degsee from Marquette Univessiiy, Milwaukee. 1005
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During the past 50 years, a number of investigators have tried to use skeletal muscle in cardiac surgery.
sectional area than cardiac muscle.2 During the past 50 years, a number of investigators have tried to use skeletal muscle in cardiac surgery. In 1931, a pectoralis muscle was used to treat a patient in Bolivia with a traumatic left ventricular injury.' Researchers in France and the United States wrapped skeletal muscle around the heart both in animals and humans in hopes of improving collateral blood upp ply.^ In 1959, a Soviet Union physician used diaphragmatic pedicle grafts to reinforce the heart in patients with left ventricular aneurysms.' He sutured the muscle grafts directly to the epicardial surface of the defect in the left ventricle under sufficient tension in an attempt to flatten out and obliterate the aneurysms. The grafts were well tolerated, b e c a m e firmly a d h e r e d to t h e myocardium, reinforced the scarred tissue, and may have improved the myocardial blood supply. About 30% of these patients were relieved from chest pain and dyspnea. The operative mortality was approximately 20%. In 1959, Adrian K a n t r o w i t z , M D , and William McKinnon, MD, State University of New York, D o w n s t a t e Medical C e n t e r , Maimonides Hospital, Brooklyn, performed a series of acute experiments. They wrapped pedicle grafts of the left canine hemidiaphragm around the heart and stimulated the muscle graft to contract in synchrony with the heart. They could not detect an improvement i n hemodynamics while the muscle was being stimulated. They also wrapped diaphragm muscle around the thoracic aorta and stimulated it via the phrenic nerve in synchrony with the heart. By stimulating the muscle graft, they increased both diastolic and mean aortic pressures. Unfortunately, because of m u s c l e fatigue, the increase in pressure lasted only 15 seconds.b Henry M. Spotnitz, MD, and colleagues from Columbia University, New York City, designed
a skeletal muscle pouch from canine rectus abdominis muscle that could develop pressures of up to 500 mm Hg, but it also fatigued rapidI Y . ~Although many others attempted to use skeletal muscle for cardiac assistance, the further development of this research was limited by t h e skeletal muscle's susceptibility to fatigue under conditions of intensive use. Useful work could be obtained, but only for short periods of time. Careful research in basic muscle physiology was needed to resolve the problem of early fatigue.
Muscle Anatomy and Physiology 0th skeletal muscle and cardiac muscle are composed of the same contractile units called sarcomeres. The contractile proteins in both types of muscles are similar in structure and orientation. Cardiac muscle must contract relentlessly throughout a lifetime, and skeletal muscle generally is required to perform work for relatively short periods of time with intervening periods of rest. The difference in function predicts certain structural a n d metabolic differences. Mitochondria are the organelles in the cell responsible for energy conversion.The portion of mitochondria by volume in heart muscle is about 30%; in skeletal muscle it is not more than 5%. Thus, heart muscle has more energy available to perform continuous work. Cardiac muscle mainly uses aerobic metabolism, and skeletal muscle is more prone to use the less efficient anaerobic pathways for energy use. Furthermore, cardiac myosin, a contractile protein, uses energy more efficiently than skeletal muscle myosin does. Skeletal muscle is composed of two basic types of fibers.Type I contracts slowly, and, like the cardiac muscle fiber, is relatively resitant to fatigue, This type of fiber bas a well1007
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Researchers discovered that skeletal muscle fibers can alter their properties in response to changes in use. developed aerobic metabolism, has a large mitochondria1 volume, and uses “slow” isoforms of myosin. Muscles composed primarily of type I fibers are postural in function. Type I1 fibers (eg, those responsible for eye movement) contract more rapidly, obtain energy largely by anaerobic routes, and can develop large forces, but fatigue very rapidly. “Fast” fibers have a relatively small mitochondria1 volume and are made of fast isoforms of myosin. Muscles such as the latissimus dorsi, the pectoralis, the rectus abdominis, and the diaphragm are composed of both types of myofibrils. Australian researchers discovered that skeletal muscle fibers can alter their properties in response to changes in use. These physicians cross-anastomosed a motor nerve from a slow muscle with one going to a fast muscle. They found that under such conditions, fast muscle became slow and vice versa: thus the nerve influenced the properties of the muscle.8 Later, other researchers working in England, demonstrated that fast muscle could be transformed to slow, fatigue-resistant muscle by applying chronic electrical stimulation to the motor nerve.9 It seemed that it might be possible to exploit this phenomenon for skeletal muscle cardiac assist.” The process of chronic stimulation or training the skeletal muscle is called conditioning. Conditioning causes sequential changes in skeletal muscle. These include an increase in capillary density and mitochondria volume, an increase in oxidative enzymes, and a decrease in glycolytic enzymes. After six to eight weeks, a complete transformation of type I1 fibers to type I fibers occurs.” The conditioned muscle is more fatigue resistant, and it uses oxygen more efficiently than the unconditioned muscle.’* In cardiac muscle, when one cell is stimulated, the stimulus spreads rapidly from cell to 1008
cell causing the entire heart muscle to contract. In contrast, skeletal muscle cells are organized into groups called motor units, and each is activated by a separate nerve fiber. The entire muscle usually does not contract simultaneously. The strength of contraction depends on the quantity of fibers activated and the rate of fiber recruitment. A “burst” stimulus is a series of electrical impulses. When applied to a motor nerve, a burst stimulus can lead to mechanical summation of many motor units and generate a substantially greater force than a single electrical stimulus. A special burst pacemaker that is R-wave synchronous has been developed. It can stimulate skeletal muscle using a burst pattern and contract in synchrony with the heart. This pacemaker produces appropriately timed stimuli (ie, pulse trains) that cause skeletal muscle to generate cardiac-type work.”
Cardiac Assist
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urrently, two methods are used for skeletal muscle cardiac assist. Cardiomyoplasty involves wrapping muscle around the heart. The other method uses a separate muscle pumping chamber known as a skeletal muscle ventricle (SMV). The latissimus dorsi muscle is used in both methods. It also is used sometimes in plastic surgery to replace defects in the abdominal or the chest wall. The loss of the latissimus dorsi muscle causes relatively little physical impairment because other muscles compensate for its function. The latissimus dorsi also is easy to free from its natural position and can be moved near the heart. Another important surgical advantage is that this muscle has a single main blood supply and a single motor nerve, which makes it easy to work with. Other muscles including the pectoralis, psoas, rectus abdominis, and diaphragm
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cardiomyostimulator
Fig 1. Cardiomyoplasty. The latissimus dorsi muscle graft is wrapped around the heart.
have been used for cardiac assistance.
Cardiomyoplasty
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ardiomyoplasty is the only method of skeletal muscle cardiac assist presently undergoing clinical trials.With this method, the surgeon frees the latissimus dorsi muscle except for its nerve and main blood supply. He or she moves it into the chest cavity and wraps it around the cardiac ventricles (Fig 1). The muscle graft is stimulated during systole with bursts of impulses delivered by a cardiomy ostimulator. 1010
In 1985, Alain Carpentier, MD, PhD, from Paris was the first to perform cardiomyoplasty on a patient. In treatment of a benign cardiac tumor, he successfully replaced a resected part of the cardiac wall with a pedicle graft of the latissimus dorsi m u ~ c 1 e . lThis ~ surgery usually is performed through two separate incisions-a lateral chest approach to dissect the left latissimus dorsi muscle graft and a subsequent midline sternotomy. Patients are positioned in a left thoracotomy position for dissection of the latissimus dorsi and in a supine position for the midline sternotomy incision. When patients are placed in the thoracotomy position for resection
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If a patient's pulmonary function is moderately to severely depressed, cardiomyoplasty will not be done. of the latissimus dorsi muscle, the perioperative nurses take usual precautions including placing padding under the right hip and the axilla. No special surgical instruments o r electrical devices are needed for this procedure other than the cardiomyostimulator and electrodes, which go to the heart and muscle flap, respectively. Frequently, a plastic surgeon will raise the latissimus dorsi muscle flap as he or she would when raising the flap for other uses. The surgeon dissects the latissimus dorsi muscle free from the iliac crest, the spine, the inferior scapular angle, and the ninth to 12th rib attachments. He or she removes a 6-cm segment of the anterior portion of the second rib to allow for transposition of the graft into the thorax. The surgeon places the muscle graft in the thorax by carefully pushing the muscle through the opening left where the rib had been resected. He or she gently works the muscle into the thorax to the point where the proximal tendon is left out, and sutures it to the first or third rib. Care is taken not to twist the neurovascular pedicle because the thoracodorsal artery, vein, and nerve are left intact. The surgeon also must be careful not to let the muscle compress the lung once the chest is opened and the latissimus is wrapped around the heart. Even when great care is taken, the lung can be partially compressed, causing a decrease in pulmonary function. For this reason, most surgeons who perform cardiomyoplasty determine preoperative pulmonary function. If a patient's pulmonary function is moderately to severely depressed, cardiomyoplasty will not be done. The surgeon implants two pacing electrodes in the proximal portion of the muscle for longterm stimulation. Depending on the cardiac disorder, cardiomyoplasty can be used as ventricular reinforcement (ie, to increase the contractility of the damaged myocardium), ventricular substitution (eg, in case of cardiac tumors or 1012
aneurysms), or as both reinforcement and sub~ t i t u t i o n . The ' ~ two latter procedures are performed with the patient on cardiopulmonary bypass. Cardiopulmonary bypass generally is not used for the reinforcement procedure (ie, wrapping the muscle around the ventricles), although the pump is always available in the room because these patients are quite ill and the heart could decompensate and require cardiopulmonary bypass at any time. When cardiopulmonary bypass is used, the ascending aorta is cannulated as with any other bypass procedure, and a single venous drainage cannula is placed through the right atrium. Cardiopulmonary bypass is always used if additional procedures are being performed during the cardiomyoplasty procedures, such as coronary artery bypass grafting, valve replacement, or left ventricular aneurysm resection. To synchronize the muscle contraction to the heart rate, the surgeon places two sensing leads on the heart and a cardiomyostimulator beneath the rectus abdominis muscle. If cardiomyoplasty is performed without additional cardiac procedures, the length of the operation usually is about four to six hours. During the early postoperative period, the care for these patients is similar to other patients undergoing cardiac surgery. The main difference is the patient has two wounds to deal with instead of one. Stimulation begins two weeks after the surgery, and the muscle graft is progressively put into use by slowly increasing the burst frequency pattern (ie, number of pulses and heart-muscle contraction ratio). After four months, the skeletal muscle can be stimulated at a synchronization ratio of 1:l or 1:2 with the heart.I6 Since 1985, more than 100 procedures of this type have been carried out in a number of centers around the world. The major indications for this procedure are diseases associated with
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Fig 2. Skeletal muscle ventricle used as an aortic diastolic counterpulsator. The SMV is on the outside of the chest wall. The limbs of the bifurcation graft have been divided, tailored, and rejoined to prevent kinking.
irreversible and extensive loss of cardiac muscle contractility, such as ischemic cardiomyo p a t h y , dilated c a r d i o m y o p a t h y , C h a g a s myocarditis, dysplastic myocardial disease (ie, Uhl’s anomaly), and myocardial tumors. In most patients, symptoms of heart failure have improved dramatically after the surgery and the muscle conditioning period. In some patients, surgery has increased the cardiac ejection fraction.” Although these improvements often are
small, patients feel much better when the muscle is stimulated. Some patients’ symptoms are worse when the stimulator is temporarily s w i t c h e d o f f . O n e can speculate that f o r patients with dilated hearts, even a small increase in ejection fraction may cause a comparatively significant increase in the cardiac output resulting in improvement of symptoms. T h u s f a r , the measured hemodynamic improvements following cardiomyoplasty have 1013
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been variable and usually less than would have been expected from the improvements in the patients’ symptoms. This reflects uncertainties about the way the procedure works. These uncertainties remain because of the lack of a good experimental model for cardiomyoplasty. Most animal research has been performed on healthy animal hearts, and the effect of cardiomyoplasty on a healthy heart is likely to differ significantly from the effect on a dilated and failing heart. In trying to explain the clinical observations, some have suggested that an external wrap of skeletal muscle provides an accessory contractile layer that assists in the ejection of blood.’8 Others think that the stimulated latissimus dorsi muscle graft prevents the heart from further di1atati0n.I~An improvement in the blood supply to the heart via skeletal muscle graft collaterals also may play an important role. As the mechanisms of action of cardiomyoplasty are better understood, improved patient selection criteria will develop. Some predict that this procedure may become an alternative for patients with heart failure in whom cardiac transplantation is contraindicated.20
Skeletal Muscte Ventricles
T
he second approach using skeletal muscle for heart assist is to construct separate skeletal muscle pumping chambers or SMVs. A number of investigators over the years have studied skeletal muscle pumps. Dr Spotnitz constructed an SMV from the canine rectus abdominis muscle and demonstrated that some characteristics were similar to those of the heart as described earlier. Unfortunately, all of these muscle pouches fatigued rapidly. After the demonstration that electrical preconditioning was able to transform skeletal muscle into fatigue-resistant muscle, a number of skeletal muscle ventricle systems were designed. In our laboratory, SMVs usually are constructed from the latissimus dorsi muscle. The surgeon completely mobilizes the muscle from its chest wall and back attachments, leaving the neurovascular bundle intact. After the mobilization, the surgeon wraps the muscle around a 1014
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Teflon stent, which is cylindrical or conical in shape. The shape of the mandrel will become the shape of the ventricular cavity. The surgeon places a pacing electrode around the proximal thoracodorsal nerve while implanting a sensing electrode into the left ventricular wall, Both electrodes are connected to an implantable Rwave-synchronous cardiomyostimulator.*’ It is important to understand that mobilizing the latissimus dorsi requires division of many chest wall blood vessels, which leads to ischemia of the distal half of the muscle graft. To allow for recovery of this initial ischemia, the muscle should be rested after the surgery, for a so-called “vascular delay period.” Usually, this takes three to four weeks.22The combination of a vascular delay period and electrical conditioning allows for the development of a fatigue-resistant SMV. In a second surgical procedure, the surgeon removes the Teflon mandrel and connects the SMV to the cardiovascular system. To test the ability of an SMV to function for long periods of time, a totally implantable “mock circulation system” was developed which allowed for control of both preload (ie, filling pressure) and afterload (ie, vascular resistance), and for measurement of SMV output in chronic experiment^.^^ Some SMVs pumped fluid in this mock circulation for as long as nine weeks. The S M V s were able to generate stroke work between that of the canine left and right ventricle^.^^ Much effort has been put forth to define the best stimulation patterns of electrical conditioning, the optimal length of vascular delay, and the best shape of an SMV. In a recent study, after SMV construction, experimental animals were placed in three groups to test different delay and conditioning protocols. The best results were obtained from the group that received the longest vascular delay period, demonstrating the importance of recovery of the blood ~ u p p l y . ~ ~ Oofn ethe ways in which SMVs can be used for cardiac assistance is as arterial diastolic counterpulsators. Michael A. Acker, MD, from our laboratory, constructed a tube-shaped SMV and connected it to the descending thoracic aorta.26By stimu-
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Carotid 200
Femoral 100 Pressure
(mmHg)
ECG
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25 Hz
0
Fig 3. Arterial pressure and electrocardiogram traces taken at one year in one dog whose SMV had been pumping continuously for more than one year. Asterisks mark diastolic augmentation. The SMV contracts every other heartbeat. lating the muscle during diastole, the SMV produced arterial pressures similar to those produced by the intra-aortic balloon pump. During the assisted cardiac cycle, the SMV increased forward blood flow by up to 63%. The longest surviving animal lived 11 weeks. Since that first set of experiments, we have been connecting conical or cylindrical SMVs to the thoracic aorta via a bifurcated graft anastomosed to the neck of the SMV (Fig 2). In ongoing experiments, the aorta was ligated between the proximal and distal limbs of the bifurcated graft so there was obligatory blood flow through the SMV. This type of SMV-counterpulsator caused less thromboembolic complications than the first one tested.*’ One of the dogs with such a device is alive after more than a year, and the SMV continues to function effectively. There has been no evidence of throm1016
boembolism at the time of this writing (Fig 3). Charles R. Bridges, Jr, MD, ScD, also working in our laboratory, recently studied the possibility of using S M V s to completely bypass the right heart.28 He connected the S M V to the vena cava (inflow) and to the proximal pulmonary artery (outflow), so that the right heart was excluded from the circulation. For several hours, the SMVs performed the work of the right ventricle.
Summary
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resently, only cardiomyoplasty has been used clinically. This is not surprising because it is a relatively safe operation to perform, avoids problems of thrombosis, and is unlikely to do harm. Evidence is beginning to emerge that clinical improvement may be due
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to enhanced cardiac output and not simply to limiting ventricular distension or to a placebo effect. We consider skeletal muscle ventricles to be experimental; however, our experiment in which one dog continues to do well after one year demonstrates that long-term function is achievable. Many problems remain. Further refinement may enable SMVs to work at even lower filling pressures. Although the great majority of cardiac failure occurs in adults, a significant number of children are born with congenital cardiac deficiencies for whom skeletal muscle assist also may offer potential therapy. 0 Notes 1. J G Copeland et al, “The role of mechanical support and transplantation in treatment of patients with end-stage cardiomyopathy,” Circulation 72 (September 1985) I1 7-12. 2. S Salmons, J Jarvis, “Cardiomyoplasty: The basic issues,” Cardiac Chronicle 4 (February 1990) 1-7. 3. F R De Jesus, “Breve concideraciones sobre un case de herida penetrante del corazon,” Asociacion Medica De Puerto Rico Boletn 23 (August 1931) 380-382. 4. C S Beck, “A new blood supply to the heart by operation,” Surgery, Gynecology & Obstetrics 6 1 (September 1935) 407-410. 5. B V Petrovsky, “The use of the diaphragm grafts for plastic operations in thoracic surgery,” Journal of Thoracic and Cardiovascular Surgery 4 1 (March 1961) 348-355. 6. A Kantrowitz, W McKinnon, “The experimental use of the diaphragm as an auxiliary myocardium,” Surgical Forum 9 (1959) 266-268. 7. H M Spotnitz, C Merker, J R Malm, “Applied physiology of the canine rectus abdominis: Forcelength curves correlated with functional characteristics of a rectus powered ‘ventricle’: Potential for cardiac assistance,” Trans American Society of Artificial Internal Organs 20 (July 1974) 747-756. 8. J C Buller, J C Eccles, R M Eccles, “Interactions between motor neurons and muscles in respect of the characteristic speeds of their responses,” Journal of Physiology 150 (February 1960) 418439. 9. S Salmons, G Vrbova, “The influence of activity on some contractile characteristics of mammalian fast and slow muscles,” Journal of Physiology 210 (May 1969) 535-549. 10. F R Armenti et al, “Transformation of skeletal muscle for cardiac replacement,” Surgical Forum 35 1018
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(1984) 258-260; J A Macoviak et al, “Electrical conditioning of in situ skeletal muscle for replacement of myocardium,” Journal of Surgical Research 32 (May 1982) 429-439; J D Mannion, L W Stephenson, “Potential uses of skeletal muscle for myocardial assistance,” Surgical Clinics of North America 65 (June 1985) 679-687. 11. Armenti, “Transformation of skeletal muscle for cardiac replacement,” 258-260. 12. M A Acker et al, “Oxygen consumption of chronically stimulated skeletal muscle,” Journal of Thoracic and Cardiovascular Surgery 94 (November 1987) 702-709. 13. M A Acker et al, “An autologous biologic pump motor,” Journal of Thoracic and Cardiovascular Surgery,” 92 (October 1986) 733746; M A Acker et al, “Skeletal muscle as the potential power source for a cardiovascular pump: Assessment in vivo,” Science 236 (April 17, 1987) 324-327; M A Acker et al, “Skeletal muscle ventricles in circulation: One to eleven weeks’ experience,” Journal of Thoracic and Cardiovascular Surgery 94 (August 1987) 163-174; R C Chiu et al, “Implantable extra-aortic balloon assist powered by transformed fatigue-resistant skeletal muscle,” Journal of Thoracic and Cardiovascular Surgery 94 (November 1987) 694-701; M L Dewar et al, “Synchronously stimulated skeletal muscle graft for myocardial repair: An experimental study,” Journal of Thoracic and Cardiovascular Surgery 87 (March 1984) 325-331. 14. A Carpentier, J C Chachques, “Myocardial substitution with a stimulated skeletal muscle: First successful clinical case,” (Letter) The Lancet 1 (June 1, 1985) 1267. 15. J C Chachques, P A Grandjean, A Carpentier, “Latissirnus dorsi dynamic cardiornyoplasty,” Annals of Thoracic Surgery 47 (April 1989) 600604. 16. Ibid; Carpentier, Chachques, “Myocardial substitution with a stimulated skeletal muscle: First successful clinical case,” 1267; J C Chachques et al, “Dynamic cardiomyoplasty: A new approach to assist chronic myocardial failure,” Life Support System 5 (October/December 1987) 323-327; J C Chachques et al, “Effect of latissimus dorsi dynamic c ardi om y o p I a s t y on vent r i c u 1ar function, ” Circulation 78 supplement 111 (November 1988) 203-216; J C Chachques et al, “Dynamic aortomyoplasty to assist left ventricular failure,” Annals of Thoracic Surgery 49 (February 1990) 225-230. 17. A Carpentier, “In discussion of: R L Kao et al, ‘The importance of skeletal muscle fiber orientation for dynamic cardiomyoplasty,’ ” Journal of Thoracic and Cardiovascular Surgery 99 (January 1990) 134140. 18. S Salmons, J C Jarvis, “Cardiomyoplasty: The
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basic issues,” Cardiac Chronicle 4 no 2 (1990) 1-7. 19. Chachques, “Dynamic cardiomyoplasty: A new approach to assist chronic myocardial failure,” 323-327; Chachques, “Effect of latissimus dorsi dynamic cardiomyoplasty on ventricular function,” 203-216; Carpentier, “In discussion of: R L Kao et al, ‘The importance of skeletal muscle fiber orientation for dynamic cardiomyoplasty,’ ”134- 140. 20. Chachques, “Latissimus dorsi dynamic cardiomyoplasty,” 600-604. 21. Acker et al, “Skeletal muscle ventricles in circulation: One to eleven weeks’ experience,” 163174. 22. Chachques, “Latissimus dorsi dynamic cardiomyoplasty,” 600-604; J D Mannion, R Hammond, L W Stephenson, “Hydraulic pouches of canine latissimus dorsi: Potential for left ventricular assistance,” Journal of Thoracic and Cardiovascular Surgery 91 (April 1986) 534-544; J D Mannion et al, “Transmural blood flow of multi-layered latissimus dorsi skeletal muscle ventricles during circulatory assistance,” Trans American Society of Artificial Infernal Organs 32 (July/September 1986) 454-460;
J D Mannion et al, “Effects of collateral blood vessel ligation and electrical conditioning on blood flow in dog latissimus dorsi muscle,” Journal of Surgical Research 47 (October 1989) 332-340. 23. Buller, Eccles, Eccles, “Interactions between motor neurons and muscles in respect of the characteristic speeds of their responses,” 417-439. 24. Ihid; Salmons, Jarvis, “Cardiomyoplasty: The basic issues,” 1-7. 25. A Pochettino et al, “Skeletal muscle ventricles for total heart replacement,” Annals of Surgery 212 (September 1990) 345-352. 26. Acker et al, “Skeletal muscle ventricles in circulation: One to eleven weeks’ experience,” 153174. 27. C R Bridges, Jr et al, “Functional right-heart replacement with skeletal muscle ventricles,” Circulation 80 supplement I11 (November 1989) 183-191. 28. D R Anderson et al “Autogenously lined skeletal muscle ventricles: Up to nine months’ experience,” Journal of Thoracic and Cardiovascular Surgery (1991) in press.
Quality Standards for Medical Gloves
Average Malpractice Award Increases
The US Food and Drug Administration (FDA) announced minimum quality levels and methods to test rubber and plastic gloves worn by health care workers. Manufacturers of medical gloves now conduct their own testing programs. The FDA action standardizes the testing and defines the maximum failure rate. Random samples of gloves will be inspected for tears, holes, and any foreign matter embedded in the gloves. The gloves also will be subjected to a water leak test. This test involves pouring 1L of water into the glove and checking for leaks. Gloves will not be sold for medical use if more than 25 per 1,000 surgeons’ gloves or 40 per 1,000 patient examination gloves are found to have leaks. The criteria are more stringent for surgeons’ gloves because they come in contact with internal areas of the body and may be exposed to bodily fluids for longer periods of time. The FDA regulations were published in the Dec 12, 1990, Federal Register.
It takes nearly five years to resolve a malpractice claim against an obstetrician/gynecologist. This is ajump from 3.5 years in 1987. These are results of a recent study of 2,200 physicians conducted by the American College of Obstetricians and Gynecologists, Washington, DC. The results were reported in the Nov 5 , 1990, issue of Hospitals. The results of the study also show that about 40% of all claims were dropped or settled without any payment on behalf of the physician. The average payment increased 33% to $21 1,320, according to the article. The most costly malpractice suits during 1987 and 1988 involved failure to diagnose a hemorrhage. The average award in those cases was $145,300. Other expensive malpractice settlements were failure to diagnose a bowel lesion, improper treatment related to birth, misdiagnosis of diabetes, and failure to detect a myocardial infarction.
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