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Journal of Rehabilitation Research andDevelopment Vol . 33 No. 2, April 1996Pages 133-144

Dynamic myoplasty: Surgical transfer and stimulation ofskeletal muscle for functional substitution or enhancement

Pierre Grandjean, MS; Michael Acker, MD ; Robert Madoff, MD ; Norman S. Williams, MS, FRCS;Jean Woloszko, MD, PhD ; Carole Kantor, MSBakken Research Centre B.V., 6201 MP Maastricht, The Netherlands ; Hospital of the University of Pennsylvania,Philadelphia, PA 19104 ; University of Minnesota, Minneapolis, MN 55402 ; The London Hospital Medical College,University of London, London, England, El 18B; Tantalus, Inc ., Highland Park, NJ 08904

Abstract—Dynamic myoplasty combines muscle transferwith electrical stimulation to provide contractile function thataugments or replaces impaired organ function . Dynamiccardiomyoplasty was the first clinical application in which askeletal muscle, latissimus dorsi, was transferred and stimu-lated to provide cardiac assistance, a function different fromits original one . The problem of early muscle fatigue that wasencountered in the initial implementation of the method wassolved by training the muscle with electrical stimulation andthus changing its fiber composition . With intramuscularelectrodes, the conditioned latissimus dorsi is stimulated insynchrony with the heart muscle . Safeguards are built into thetwo-channel implanted stimulator to avoid excessively highpulse rates . Clinicians report that 80% of patients withmoderate to severe heart failure prior to operation showed aclinical improvement of 1 .6 New York Heart Associationclasses . Alternative methods of providing cardiac assistancethat are also being investigated include wrapping the musclearound the aorta, creating a skeletal muscle ventricle, andusing the muscle to power an implantable pump . These lattertechniques are still under preclinical investigation . Compared

This material is based upon work supported by the VA Cleveland FESCenter, Rehabilitation Research and Development Service, Departmentof Veterans Affairs, Washington, DC.Mr . Grandjean is Worldwide Research Manager for Medtronic Cardiac AssistSystems. Dr. Acker is an Assistant Professor of Surgery in the Department ofCardiovascular and Thoracic Surgery of the Hospital of the University ofPennsylvania. Dr . Madoff is a Clinical Assistant Professor of Surgery in theDepartment of Colon and Rectal Surgery of the University of Minnesota . Dr.Williams is Director of the Academic Surgical Unit of the Royal LondonHospital, University of London, England . Dr . Woloszko is WorldwideResearch Manager for Medtronic Interstim.Address all correspondence and requests for reprints to : Pierre Grandjean,MS, Bakken Research Centre B .V ., 6201 MP Maastricht, The Netherlands .

with heart transplant, cardiomyoplasty has the great advan-tage of not being subject to tissue rejection.

The second principal application of dynamic myoplastyis treatment of fecal incontinence through creation of anelectrically stimulated skeletal muscle neosphincter(ESMNS) . The gracilis muscle of the leg is mobilized,wrapped around the anal canal, and conditioned withelectrical stimulation to become more fatigue resistant . Toachieve continence, the muscle is continuously stimulatedexcept when the patient wishes to defecate . Overall successrates in achieving continence are 60-65% . Both cardiomy-oplasty and the ESMNS technique, and their associateddevices, are being refined through ongoing clinical trials.

Key words : cardiomyoplasty, dynamic myoplasty, fecalincontinence, FES, FNS, functional electrical stimulation,heart failure, urinary incontinence.

INTRODUCTION

Myoplasty encompasses a variety of clinical proce-dures involving transfer of skeletal muscle for replace-ment or enhancement of body parts . The main uses sofar have been for filling facial defects and for breastreconstruction . In dynamic myoplasty, the addition ofelectrical stimulation allows the transferred muscle alsoto provide contractile function . The two major applica-tions presently under clinical investigation are dynamiccardiomyoplasty for the treatment of heart failure anddynamic myoplasty for treatment of fecal or urinaryincontinence.

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Journal of Rehabilitation Research and Development Vol . 33 No. 2 1996

Dynamic cardiomyoplasty was the first clinicalapplication in which a skeletal muscle was transferredand stimulated to provide a function different from itsoriginal one (1) . In this procedure, skeletal muscle canbe transferred to reinforce the myocardium. Otherapproaches form pumping chambers called skeletalmuscle ventricles at points along the ascending ordescending aorta (2,3) . In these cardiac applications, thetransferred muscle is paced cyclically in such a way asto synchronize with a selected portion of the cardiaccycle. In treatment of fecal or urinary incontinence,skeletal muscle is wrapped around the anus, urethra, orbladder neck to founi a neosphincter . After conditioning,the muscle is stimulated continuously except when thepatient interrupts it to defecate or urinate . This paperreviews the technical and clinical experience with thesevarious applications of dynamic myoplasty.

DYNAMIC CARDIOMYOPLASTY

Dynamic cardiomyoplasty is a procedure aimed attreating patients with chronic heart failure, refractory tomedical therapy, that severely limits their daily life, aClass III or intermittent Class IV condition, according tothe New York Heart Association (NYHA) classification(4) . Besides medical therapy, treatment alternatives forsevere heart failure are heart transplant, mechanicalassists, and dynamic cardiomyoplasty . The last two arestill investigational methods . Heart transplant is the goldstandard for treatment of Class IV heart disease, butonly 8 percent of patients who would benefit from itreceive new hearts because of limited donors. Inaddition, this treatment requires lifelong immunosup-pression which may lead to problems with infection,kidney failure, and deterioration of other systems.

In the next 5 to 10 years, we will see advances invarious mechanical heart assist devices. The UnitedStates Food and Drug Administration (FDA) hasapproved the first such device, an implantable leftventricular assist system, as a "bridge" until a hearttransplant can be carried out . Such devices still requirebetter solutions to the problems created by externalpower sources and blood-surface interactions, especiallywhen long-term support is considered.

Cardiomyoplasty is the only method of skeletalmuscle cardiac assistance currently under clinical inves-tigation . Studies are ongoing worldwide, including theUSA, under an FDA investigational device exemption(IDE) . Because the method uses autologous tissue, there

are no rejection problems, thus no need for immunosup-pression, and no need for an external power source.

The major limitation in the initial application ofdynamic cardiomyoplasty was the early onset of musclefatigue as soon as a skeletal muscle was activated atcardiac rates . Pioneering work by Pette (5) and Salmons(6) showed that muscle fiber composition and resultingphysiologic and metabolic characteristics (e .g ., force,fatigue resistance, contraction, and relaxation times)depend on neural activity . By electrically controllingnerve and muscle activation with functional neuromus-cular stimulation (FNS), Peckham, et al . (7) producedincreased force and improved the fatigue resistance ofatrophied paralyzed muscle (with intact lowermotoneurons) in quadriplegic patients.

The possibility of combining knowledge gained inthe FNS field with anatomical and surgical consider-ations suggested a solution to the problem of earlymuscle fatigue in cardiomyoplasty . First, an innovativeprogressive muscle stimulation protocol was developedby Carpentier, et al . (4) . Second, the latissimus dorsiwas selected (8). This muscle is used in dynamiccardiomyoplasty as done today because it is a widemuscle, it is not necessary for normal activity, and itcan be easily transferred into the thorax . Latissimusdorsi has its neuromuscular pedicle in its proximal part,making its transfer possible without great disturbance ofthe nerve or blood supply.

Conditioning Skeletal Muscle for Cardiac AssistCardiac and skeletal muscles differ in their re-

sponse to electrical impulses . A single electrical pulseabove a given threshold will cause an action potential topropagate through the entire cardiac muscle mass,producing a smooth muscle contraction . On the otherhand, the magnitude and duration of skeletal musclecontraction varies with the characteristics of the electri-cal pulses : amplitude, width, and interpulse interval (orpulse frequency) . Pulse train stimulation grades themagnitude and duration of muscle force by varying therate of motor unit excitation (temporal summation).Only a train of pulses spaced to produce summation willresult in a prolonged (>50 milliseconds) and forcefulcontraction. The fatigue resistance of stimulated muscledepends on fiber composition, metabolism, stimulusparameters, and duty cycle.

By the early 1970s, Salmons (6), Pette (5), andPeckham (7) had shown that the fatigue resistance ofskeletal muscle could be increased by several weeks oflow-frequency electrical stimulation . To understand the

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source of the aerobic capacity of such conditionedmuscle, the group at the University of Pennsylvaniastudied the bioenergetic correlates of fatigue resistancein conditioned canine latissimus dorsi muscle using thetechnique of phosphorus 31 nuclear magnetic resonance(P-31 NMR) spectroscopy. An overall small change inphosphorylation with a lack of plateau in developedisometric tension was observed in the conditionedmuscle. This was similar to that seen in cardiac muscleduring increased energy demand. This study indicatedthat the markedly enhanced resistance to fatigue of theconditioned muscle is in part the result of its increasedcapacity for oxidative phosphorylation (9).

Oxygen consumption was also measured directly inconditioned muscle, and compared to its contralateralcontrol . It was found that electrically transformedcanine muscle is capable of generating more isometricwork while consuming less oxygen per amount oftension developed than its contralateral control muscle.Isometric tension is maintained by turnover of actin-myosin cross bridges without relative movement of thefilaments. The rate at which cross bridges cycledetermined the energy cost for the maintenance oftension. The fact that cross bridge cycling is more rapidin fast muscle than in slow muscle reflects differencesbetween rates of hydrolysis of the fast and slowisoforms of myosin. Since the conditioned muscle isuniformly slow, a given isometric tension can bemaintained at an expense of less ATP (adenosinetriphosphate) hydrolyzed . Therefore, less oxygen shouldbe consumed by the electrically conditioned muscle forthe same amount of isometric tension developed. Thesestudies demonstrated that the metabolic capacity to docardiac work is present in electrically conditionedskeletal muscle, and it has the potential to be afunctioning myocardial substitute.

Surgical ProcedureSurgery begins with the patient in the lateral

position . Through a large incision the latissimus dorsimuscle is freed from its distal insertions, the muscle islifted, and the electrodes (cathode and anode) areinserted near the nerve branches of the muscle (4).Then, the muscle is inserted inside the thorax through awindow made by resection of part of the second rib(Figure 1).

The second phase of the procedure is carried out inthe supine position through an incision of themediastinatum. The muscle is brought under the heartand wrapped, in most cases, in a posterior to anterior

wrap, also called clockwise fashion (Figure 1) . Themuscle is sutured to the myocardium or to thepericardium sack . Patients with chronic heart failureusually have dilated hearts, and the heart coverage thatthe muscle can provide is sometimes insufficient . Insuch cases, a piece of the pericardium is used tocomplete the wrapping.

The procedure is done in different ways dependingon the nature of the heart failure . If the heart is onlydilated, the muscle is used as a reinforcement ; this typeof surgery can be done without the use of circulatorysupport . If the patient is suffering from a largeaneurysm, the aneurysm can be resected and the muscleused as a patch, taking care that there is a surfacebetween the muscle and the blood to prevent clottingproblems.

DeviceThe device is an implantable pulse generator

(cardiomyostimulator), powered with a single lithiumbattery and sealed in a titanium case . This second-generation device weighs 60 grams and is connected to

Figure I.In cardiomyoplasty, the latissimus dorsi muscle is mobilized,transposed into the chest through the rib cage, and wrapped aroundthe ventricles of the heart. The muscle is then stimulated insynchrony with the heart to augment its pumping function.Permission to reprint this figure has been granted by Medtronic, Inc .

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mill ni imii , Muscle Channel

Cardiac Channel

Synchronization Circuit

4,

the muscle via intramuscular electrodes . Intramuscularrather than nerve or epimysial electrodes were selectedto ensure that a wide range of surgeons would be able toimplant the device easily.

Anodic and cathodic electrodes are placed near thenerve branches of the latissimus dorsi . In most patients,there is no need to do nerve mapping, since the nervebranches are clearly visible and can be used aslandmarks . The lead is composed of a nickel alloy(MP35N) coil that ends with an electrode coil made ofplatinum-iridium. The lead is enclosed in a pair ofpolyurethane sheaths, one of which slides on the otherto permit adjustment of the lead length to differentmuscle sizes. The electrode is inserted inside the musclenear the nerve branches by means of a suture with anattached needle; this is done in such a way as tominimize the energy requirement, taking care not to beso close to the nerve branches as to damage them . Twosilicon disks and plastic clips secure the lead in positiononce the sliding sheath has been adjusted after thepositioning of the electrode (Figure 2). For the cardiacchannel, a smaller version of the skeletal muscleelectrode and lead are used and inserted into themyocardium to ensure proper detection of the heartfunction.

The muscle is stimulated in synchrony with theheart function by the cardiomyostimulator ("Trans-form" Model 4710, Medtronic, Inc ., Minneapolis, MN)that senses the heart function and paces the muscle withtrains of impulses (Figure 2). The device is a two-channel system with one channel dealing with the heartand the other with the transplanted muscle . The heartchannel senses the heart and paces it if necessary . Thesignal from the heart channel is processed via asynchronization circuit that senses the ventricular con-traction and, after a synchronization delay, puts out aburst of pulses.

Triggering the muscle by the heart alone maycreate problems, because most of these patients havevery high resting heart rates of 90–100 beats per minute.Stimulating the muscle at this rate could lead to fatigueand consequently muscle damage, depending on theindividual patient . This problem has been addressed byproviding means to program the device within thefollowing parameters:

1 . synchronization ratio : enables augmentation orreduction of muscle activity by synchronizing themuscle on different heart beats, for instance, onevery three heart beats

4750 Lead : maximal electrode exposure

minimal electrode exposure

Figure 2.(Top) Schematic of operation of the cardiomyostimulator . Inresponse to signals from the heart, the cardiomyostimulator pacesthe transferred muscle with trains of impulses . Permission to reprintthis figure has been granted by the W .B . Saunders Company.(Bottom) Adjustable lead mechanism.

2. muscle upper rate : enables programming the maxi-mum muscle contraction rate allowed

3. synchronization upper rate : enables programminga cardiac upper rate above which the muscle isdisabled

4. adaptive burst duration : enables the burst durationto automatically adapt to heart rate (burst lengthdecreases as heart rate increases).

In addition, cardiac sensitivity, refractory period,and synchronization delay (time from cardiac event tomuscle burst initiation) are programmable to adjustmuscle activation to cardiac contraction.

Many characteristics of the stimulator are adjust-able: The muscle channel is bipolar and can be turnedon and off. The pulse amplitude can be programmed upto 9 V; pulsewidth and frequency within pulses can beregulated ; burst durations can be adjusted by program-

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ming the number of pulses and the pulse interval . Amagnet mode has been included to enable the cardiolo-gist to easily assess the unstimulated performance of theheart by applying the magnet to inhibit the musclechannel . The system can be programmed with radiofrequency (RF), using standard cardiac pacemakermethods.

A 2-week postsurgery rest period is allowed togive time for the muscle flap to heal and the muscle-heart interface to begin to develop adhesions . Stimula-tion synchronized on the heart function is begun withsingle pulses on every other heartbeat . The number ofpulses in the burst is then progressively increased every2 weeks, ultimately producing a burst of 6 pulses lastingabout 185 ms (Figure 3) . In some cases, after 2 to 3months of training, the stimulation mode may beswitched to pulses on every heartbeat, depending on thepatient's clinical condition . This type of stimulationprotocol enables long-term cyclic muscle contraction atcardiac rates . Muscle biopsies in animals have shownthat the trained muscle converted to type I fibers(aerobic metabolism) . With new knowledge in this field,we may find that complete conversion of this sort is notnecessary for adequate function (10).

The device is tuned by changing the synchroniza-tion delay. Mitral flow regurgitation is avoided bymaking sure the stimulation burst never occurs beforethe mitral valve closure . In patients with more than 3months follow-up, the settings are typically : pulseamplitude, 4 .3 V; pulsewidth, 200 ps ; number of pulses,6; pulse interval, 33 ms; average delay, 50 ms . Averagemuscle lead impedance is approximately 390 ohms . In

WEEK 1 .2

WEEK 3,4

WEEK 5 .6

WEEK 7,8

AFTER 2 MONTHS

CLINICAL DEMAND

Figure 3.Stimulation protocol used for training the transposed latissimus dorsiafter cardiomyoplasty.

order to minimize risks of muscle overuse, most patientsare programmed at a synchronization rate of 2 :1.

Evaluation of First Generation DeviceTo date, two cardiomyostimulation systems have

been developed by Medtronic and used in clinicalstudies . The first-generation (Medtronic ModelSP1005/A) has been described earlier by Grandjean, etal . (11) and is summarized below.

Overall performance of the system has been goodin 515 implant-years of cumulative experience . Of 353systems, 99 have required replacement due to batterydepletion (mean time to replacement : 28 months) . Thelongest implant of a single device has been 41 months.There were eight cases of inadequate synchronization,mostly in the first series of devices, caused byinadequate signal filtering . This was solved by retuningthe cardiac circuit to adapt to the very weak signalssometimes found in dilated hearts . There were 16 casesof premature end-of-life of the device, mostly happen-ing after patients were subjected to multiple defibrilla-tion shock.

Of 707 intramuscular leads with a total of 1,030lead-years of cumulative experience, there has beenno lead failure (breakage or displacement) . The long-est implant has been in place for 110 months . Therehave been only six cases of failure to evoke mus-cle contraction: as the leads remained integral, itwas concluded that perhaps muscle transfer had causednerve damage . Three of these cases had no recoveryof muscle function. Others recovered evoked mus-cle contraction after 3 to 9 months, indicating nervedamage and subsequent repair . Selectivity of stimulationwas good; there has been no lead displacement orbreakage . However, there were several cases of leaddamage perioperatively when the lead caught in aretractor; such leads were repaired or exchanged duringsurgery.

In order to meet new requirements as investigationexpanded, a new (second-generation) system was devel-oped that is easier to manufacture and meets additionalneeds realized in early clinical experience . Changes tothe cardiac elements of the device are : 1) it uses ademand pacemaker with a larger range of cardiacpacemaking amplitude ; 2) it is programmable, andunipolar and bipolar to help in situations where wecombine devices (e .g ., using it in combination with adual pacemaker, or implantable defibrillator) ; 3) itssynchronization range has been extended up to 1 :8; 4) itmay be disabled in case the cardiac rate exceeds a

TIME AFTERSURGERY TYPE

ECG

CONTRACTIONSTIMULATION MUSCLE

EU 11811

111111 11101 111111

Jk

NO STIMULATION(FLAP HEALING:VASCULAR DELAY,MUSCLE-HEARTADHESIONS)

SINGLE PULSES, 2 :1

DOUBLE PULSES . 2:1

TRIPLE PULSES . 2 :1

PULSE TRAINS. 2 :1

PULSE TRAINS. 1 :1

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programmed value ; and 5) it has an increased range ofdelay .

Changes to the muscle elements of the device are:1) unipolar and bipolar polarization, 2) adjustable burstlength by programming number of pulses and pulse in-terval, 3) adaptation mode where burst shrinks as heartrate increases to prevent diastolic filling impairment,and 4) upper rate to prevent muscle overstimulation.

Specially developed components make this newdevice smaller and lighter, and give it greater longevitythan the previous generation. Safety features include : 1)runaway protection on cardiac and muscle channels, 2)full protection for electrocautery and defibrillation, 3)special connectors that prevent lead misconnection, and4) progressive battery depletion indicator which can bemonitored by telephone. To retrofit patients with earlierdevices, adapters were made for connecting previousleads to new stimulators . Packaging is recyclable andeach device has a unique tag that is visible on X-ray.

As of July 1994, this second-generation system hada cumulative experience of 15 implant-years. Of the 58systems, 13 were replacements of the previouscardiomyostimulators which had reached expected bat-tery depletion . Premature end of life of the device hasnot been a problem, even in cases of frequent defibrilla-tion. Of 90 leads with a total experience of 30 years, thelongest follow-up time has been 8 months . No lead ordevice failures have been observed.

Clinical OutcomesIn Phase I studies of cardiomyoplasty, surgeons

treated 118 patients with various degrees of heart failureusing single or multiple procedures (combiningmyoplasty with ventricular aneurysectomy or coronaryartery bypass graft surgery) . Preoperatively, the patientswere 75 percent Class III and the rest Class IV(confined to bedrest) . The average ejection fraction(percentage of blood emptied from the ventricle duringcontraction) was 20 percent, compared with normalvalues of 60–70 percent. This low fraction is anindication of advanced heart failure resulting in markedlimitation in daily activities and usually poor quality oflife .

After cardiomyoplasty, based on subjective clinicalevaluations, 80 percent of patients showed a clinicalimprovement of an average of 1 .6 NYHA classes . Thehospital mortality of Class III patients was less than 10percent at most centers . Patients whose conditions wererated Class IV experienced a higher hospital mortality(–30 percent) . In most centers, it was concluded that

Class IV patients are too sick for this procedure . Whilethere was no overall objective evidence of cardiacfunction improvement in the total group, two centersshowed improved systolic function in subgroups of theirpatients.

When expansion of the trials was requested, theFDA required a Phase II clinical protocol that wouldconfinn the safety of the first-generation device andbetter document the efficacy of the cardiomyoplastyprocedure . The Phase II trials focused on cardio-myoplasty as an isolated procedure . Between May 1991and September 1993, 68 patients were enrolled . Theirmean age was 57 and most of them (91 percent) were inNYHA class III. Eight patients (12 percent) died priorto discharge from initial hospitalization . At the end of12 months, 47 percent moved to Class II and 41 percentto Class I. A reference group, not prospectivelyrandomized, was given only medical treatment.

This Phase II trial, a pooled multicenter study,showed objective evidence of systolic improvement : leftventricular ejection fraction rose from 22 .7 percentpreoperatively to 26 .1 percent at 6 months, a small butstatistically significant (p<0 .05) 15 percent relativeincrease . At one year, there was no decrease in ejectionfraction. Improvements in left ventricular stroke workindex and stroke volume were statistically significant.Disappointingly, the maximal increase in oxygen con-sumption did not reach statistical significance . Again,patients showed a clear improvement of quality of life,as documented in questionnaires . To investigate ifcardiomyoplasty improves survival, a randomized trialis currently underway . Deaths in the first year have beenmostly sudden, due to arrhythmias in half the cases.This emphasizes the possibility of an automatic defibril-lator combined with a myostimulator.

Other Applications Under InvestigationIn addition to placing the transferred muscle

around the heart, alternate methods of providing cardiacassist are: 1) wrapping the muscle around the aorta(Figure 4), 2) creating a skeletal muscle ventricle(SMV, see Figure 5), and 3) using the muscle to poweran implantable pump . These applications are beingstudied in animal tests . In dynamic aortomyoplasty, thelatissimus dorsi is wrapped on the descending orascending aorta. In the SMV approach, the latissimusdorsi muscle is shaped into a pumping chamber whichis then connected, for example, to the aorta. It can bestimulated in a counterpulsation mode, contracting whenthe heart relaxes . The "aortic chamber" or the SMV

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Figure 4.In aortomyoplasty, the latissimus dorsi muscle is wrapped aroundthe aorta and stimulated to contract during cardiac diastole(counterpulsation) to augment diastolic pressure, which will improvecoronary perfusion . Aorta during cardiac systole (left bottom) andduring cardiac disatole (right bottom) . Permission to reprint thisfigure has been granted by Medtronic, Inc.

empties during the diastolic phase and fills during thesystolic phase, augmenting diastolic pressure and de-creasing systolic pressure . This decreases the afterloadof the heart, decreases wall tension on a failing heart,and improves perfusion of the myocardium. Bothapproaches aim to reproduce chronically the acutebenefits of the intra-aortic counterpulsation balloonpumping that is frequently used in intensive care.

Since the relation of the stimulation to the cardiaccycle is different than with cardiomyoplasty, coun-terpulsation approaches require a more sophisticatedstimulation system. It must account for the facts thatheart systolic and diastolic times decrease as heart rateincreases, and that the time of onset of musclestimulation (synchronization delay) and burst durationneed to be adjusted as heart rate varies . Medtronic has

Figure 5.The latissimus dorsi muscle can alternatively be fashioned into amuscle pouch or skeletal muscle ventricle and coupled to thecirculation using vascular grafts . When the muscle relaxes (top left),the pouch will fill with blood . When the muscle contracts (bottomright), blood will be ejected from the pouch . Thus it acts as a"neoventricle ." Permission to reprint this figure has been grantedby Medtronic, Inc.

developed a software-based device, similar to animplantable microcomputer (12) . The device function isdefined by a program (algorithm), which is loaded intoits random access memory (RAM) by RF link . Thealgorithm permits adaptation of synchronization delayand burst duration as heart rate is changing . Tests of thissystem have examined the effect of different burstpatterns, pulse intervals, and change in number of motorunits recruited . Arrhythmia can be detected during ,muscle stimulation and the pulse burst can be aborted.The system can then wait a few cycles until the heartrate stabilizes and then start to pace again.

Areas for improvementWith any of these cardiac assist approaches that

rely on skeletal muscle power, close attention needs to

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be given to improvement of muscle graft function, tothe biomechanical energy transfer, and to the effect ofthe electrical stimulation regime. Long-term musclegraft function may by improved by better musclepreparation (preoperative, e .g., voluntary or evokedexercising, passive and active stretch, pharmacologicalsupport) and perioperative handling (e .g., to preventepisodes of muscle ischemia). Muscle status and activa-tion needs to be monitored closely to evaluate thebenefits of such preparations . To this end, research isbeing performed to monitor graft function by cineX-ray, CT/MRI scans, and echo-Doppler tissue imaging.The activation pattern should maximize power outputwhile minimizing muscle energy expenditure (i .e .,minimize fatigue) . An ideal way to do this could be tocustomize training, but that will depend on availabilityof muscle sensors and feedback methods that are not yetdeveloped. For cardiomyoplasty, improving muscleenergy transfer to the heart may require better heartcoverage by the transplanted muscle, improved muscle-heart coupling, and improved tissue interface character-istics .

Assessment of the effects of these new protocolsnecessitates more objective documentation than theclinical assessments used in previous studies (i .e ., moresophisticated methods such as pressure-volume investi-gations by conductance catheter techniques) . Someaspects of the extrinsic mechanism of action arediscussed above . In addition to continued study of thatarea, examination is also needed of the intrinsicmechanisms of myocardial recovery : decreasing wallstress, decreasing oxygen demand, cross-vascularizationof muscle and myocardium . Finally, the major roleplayed by arrhythmic events in the function of cardiacassist devices strongly suggests the combination ofdefibrillators with cardiomyostimulators.

DYNAMIC MYOPLASTY FOR FECAL ANDURINARY INCONTINENCE

Clinical Problem of Incontinence and WhereDynamic Myoplasty Fits Into Treatment

Fecal incontinence is an underreported conditionthat affects 2 .5 percent of the population (13) . One-thirdof nursing home patients in Minnesota have fecalincontinence' . It is a huge problem in human tends with

' Madoff R . Unpublished data .

high direct economic costs and indirect costs that resultfrom the unwillingness of people to leave their homes.

The anal sphincter mechanism consists of theinternal sphincter (smooth muscle that provides 80 per-cent of resting sphincter pressure), the external sphinc-ter (voluntary muscle), and the puborectalis muscle(voluntary muscle) . In addition to adequate sphincterfunction, normal continence depends on mental func-tion, stool volume and consistency, colonic transit,rectal distensiblity, anorectal sensation, and anorectalreflexes . Thus, even if the sphincter itself is normal,other abnormalities can cause fecal incontinence.

Among people with a normal pelvic floor, causesof incontinence are diarrheal states, overflow due toimpaction or neoplasm, and a wide range of neurologicconditions. For example, the peripheral neuropathysecondary to diabetes results in a 20 percent rate ofincontinence among diabetes clinic patients (14).Among people with an abnormal pelvic floor, causes ofincontinence include anorectal malformation, trauma,iatrogenic injury (particularly obstetrical injury), andinjury to pudendal nerves (due to childbirth or habitualstraining) . A third group of patients become incontinentfollowing anorectal resection for removal of malig-nancy . In this group, dynamic myoplasty may be donein conjunction with a perineal colostomy to approximatethe function of the anus.

Development of TreatmentIf there is sphincter injury, surgical repair is

effective in restoring continence for solids in about 80percent of patients (15) . If the sphincter is intact,biofeedback has reduced episodes of incontinence by 90percent in more than two-thirds of the patients treated(15) . If these therapies are unsuccessful, colostomy is aneffective option, but many patients will not accept it.

In the 1950s, surgeons developed a passive wrap ofgracilis muscle around the anal canal (16,17) . It failedbecause the patients were unable to maintain thenecessary contraction of the muscle voluntarily andbecause the muscle fatigued . To treat urinary inconti-nence, urologists have used a silastic cuff implantedaround the urethra and then inflated it from a reservoirof fluid . A similar device has been used for fecalincontinence with some success, but it is not commer-cially available . For these reasons, research has beenundertaken to create neosphincters from skeletal muscleusing mainly the gracilis and gluteus muscles.

The electrically stimulated, skeletal muscle neo-sphincter (ESMNS) was developed as a new option for

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patients whose conditions were not amenable to stan-dard available therapy (Figure 6) . The ESMNS proce-dure adds to the passive muscle wrap a neural orintramuscular electrode that stimulates the muscle(18,19). Conditioning with electrical stimulation in-creases the percentage of type I fibers in the muscle,improving its fatigue resistance . When conditioned, themuscle is continuously stimulated to achieve conti-nence . When the person wishes to defecate, he or sheuses a magnet to turn the stimulator off, and then backon afterward.

Preparation before Muscle TransferIn animal experiments with transfer of the sartorius

muscle to create a neosphincter stimulated by intramus-cular electrodes, the London group (NS Williams)measured flow through a loop of intestine surroundedby the neosphincter. They attached strain gauges to theneosphincter to measure its contraction. After 6 weeks,they observed that the fusion frequency could besignificantly reduced, suggesting fiber type conversion.They confirmed this on histology but also observedischemic damage and considerable reduction in thediameter of type I fibers (20).

Upon observation of distal ischemia of the mobi-lized gracilis muscle in humans, the London groupconducted radio contrast studies of the muscle's vascu-lar supply in cadavers . These studies showed that theblood supply was not entirely segmental, prompting the

Figure 6.Dynamic gracilis myoplasty for treatment of fecal incontinence .

colorectal surgeons to do a delay maneuver, similar tothat used by plastic surgeons . About one month beforemuscle transfer, the London surgeons divided the distalblood supply to the gracilis muscle . This has eliminateda greater than 50 percent incidence of ischemic necrosisand perineal sepsis . The Minnesota group (RD Madoff)and the Maastricht (Netherlands) group do not believethe delay maneuver is necessary and therefore do notuse it (21).

Surgical Procedure and Muscle ConditioningDynamic myoplasty for fecal incontinence uses the

gracilis muscle because it is easily transposable and notessential to lower limb function . It is a long, thin,ribbon-like muscle whose nerve and blood supply enterproximally . The muscle is mobilized up to that point.Through multiple incisions, the muscle is wrappedaround the anal canal and its tendon is secured to theischial tuberosity . There are two methods of stimulatingthe muscle . The London group places the electrode onthe main nerve to the gracilis at the point where thenerve comes off the obturator nerve and lies on theadductor brevis muscle. This location is well out of theway of contracting muscle, and is thus subject to littletension. In addition, it allows the whole muscle tocontract and requires a low voltage to produce contrac-tion. The lead is connected to a pulse generator(Neuromed Inc., Ft . Lauderdale, FL), which is placedconveniently in a subcutaneous pocket in the upperabdomen.

In the alternative technique practiced by theMinnesota and Netherlands groups (22), the main nerveto the gracilis is identified but not mobilized . Twointramuscular stimulating electrodes (Medtronic Model4300, Medtronic B .V., Kerkrade, The Netherlands) arewoven into the muscle 4 cm apart at the level of themain nerve branches to provide complete musclestimulation . The leads are tunneled subcutaneously tothe lower abdomen where they are connected to animplantable pulse generator (Itrel ® 7424, Medtronic,Inc., Minneapolis, MN). Like the London group'stechnique, this method also provides muscle stimulationat low voltages that remain stable over the long term.

The treatment protocols also vary with the sur-geons performing the procedure. At the Royal LondonHospital, the protocol starts with a frequency of 9 Hzand an intermittent pattern of stimulation . Over a periodof 8 weeks, the "off" period is gradually reduced untilconversion from fast-twitch to slow-twitch muscle hasoccurred and the muscle is stimulated continually .

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Journal of Rehabilitation Research and Development Vol . 33 No . 2 1996

Various training regimens that reach the same endpointseem to be equally good.

At the University of Minnesota, the protocol lasts14 weeks. The muscle transfer and implant are done atthe same time in patients with a pre-existing stoma ; butthe implant is delayed 6 weeks after the transfer inpatients with no stoma in order to limit infection.Muscle training begins at 6 weeks in all patients andcontinues for 8 weeks, using a frequency of 25 Hz . Theduty cycle starts with 0 .1 s on and 1 .2 s off for the first2 weeks, and is incrementally shifted at 2-weekintervals, reaching 1 .0 s on and 0.5 s off in the final 2weeks . After the training period, muscle is stimulatedcontinuously, typically at 15 Hz.

Demographics and Outcome of ESMNS Treatmentof Patients with Complete Fecal Incontinence

At the Royal London Hospital, the first series ofprocedures were done in patients with intact rectumsand used an external stimulator and no vascular delay.Of 11 patients, 5 became continent and 6 proceduresfailed. In the second series, using internal stimulatorsand vascular delay, of 16 patients, 15 achieved conti-nence and 1 failed . The overall success rate was 60 to65 percent, which includes both category 1 and 2continence (i.e ., patients who are continent for liquidand solids: category 1 ; and solids only: category 2) . Asthere has been a major insult to the sphincter, thecontinence can never be perfect . Average postoperativeanal pressures, measured by manometry, were 60 cmH 20, which is the lower limit of normal.

Also in London, a second group of patientsreceived total anorectal reconstruction followingabdomino-perineal excision of malignancy . These pa-tients are examples of the 100,000 colostomy patients inthe United Kingdom, and five times that many in theUnited States, who find an abdominal stoma unsatisfac-tory and undesirable . In the procedure, the colon wasanastomosed at the perineum, and for three patientswithout a colon, the ileum was fashioned into a pouchand anastomosed at the perineum . The gracilis wasmobilized and transposed 1 to 2 months later . Eight to12 weeks later, the electrode, lead, and stimulator wereimplanted and conditioning was begun. The stoma wasclosed if satisfactory continence and defecation could beshown. Satisfactory anorectal function was achieved in50 percent of 12 patients.

Konsten, et al . of the Maastricht group were able torestore normal continence with their technique in 65percent of 26 patients . Biopsy showed an average fiber

conversion from 46 percent type I fibers to 64 percentafter electrical stimulation (23).

In a multicenter clinical evaluation of dynamic analmyoplasty, 165 patients have been enrolled so far ; 90suffered from idiopathic incontinence, 45 had perinealreconstruction after abdomino-perineal resection for lowrectal cancer, and 30 had congenital defects . Thepreliminary data show that continence could beachieved in more than 75 percent of perineal resectionpatients, and in more than 60 percent of the incontinentpatients . In a study involving 52 patients (most of whomtook part in the multicenter study cited above), Baetenreported that 73 percent were fully continent after amedian follow-up of 2 .1 years (18) . There was signifi-cant improvement in median time to defecation, andpatients reported an improvement in quality of life.

At the University of Minnesota, seven patients withcomplete fecal incontinence were treated with dynamicgraciloplasty and followed for 18 months . Six werefemale and the mean age of all seven was 45 years.Median duration of incontinence was 8 years (7 mos to51 yrs) . In three patients, the cause was obstetrical orsurgical injury; in one patient, cauda equina syndrome;in one, trauma; and in two, imperforate anus . Amongsix evaluable patients, two became fully continent, threeimproved markedly, and one remained incontinent.Complications encountered were cellulitis (inflamma-tion of cellular or connective tissue) in four, transientpain in two, and transient edema in one.

Factors that could be adjusted in the ESMNSprocedure are the vascular delay, whether or not tocreate a stoma, the type of electrode and lead, choice ofmuscle, the wrap configuration, and the conditioningregimen. The effectiveness of vascular delay has beenevaluated in a randomized animal study comparing : 1)muscle transposition and then a 6-week wait before thestart of stimulation, 2) vascular delay followed bytransposition and immediate stimulation, and 3) transpo-sition and immediate stimulation . Preliminary data showthat muscle damage occurs in 3), but methods 1) and 2)both minimize muscle damage and provide betterfunctional outcomes (24).

Other Applications Under InvestigationThe success of this method for treating fecal

incontinence led some investigators to explore a similarapproach to restoring urinary continence (25,26) . Be-cause this technique involves more complex phenomenawhich influence the efficacy of the muscle contraction(e.g ., muscle wrap technique, location), several surgical

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GRANDJEAN et at . Dynamic Myoplasty

options are being explored (27) . In other studies,dynamic myoplasty has been carried out to restoremicturition by wrapping innervated segments of therectus abdominis muscle around the bladder (28).

Recommendations for Further ResearchThe ESMNS represents a promising new therapy

for patients with fecal incontinence whose conditionsare not amenable to standard therapy . Needed areobjective measures of quality of life (18,28) andeconomic costs of incontinence to show that this is agood therapy. On a technical level, several modifica-tions would improve the device . If it were possible toinclude a sensory element in the device that wouldreceive afferent information and act in a closed-loopfashion, the device would work in a way moreanalogous to the native sphincter . Such an artificialreflex activity could eliminate the need for an externalmagnet.

In the current and future applications of thismethod, issues of muscle choice and surgical methodwill need to be evaluated . Muscles other than gracilis(e .g ., sartorius, gluteus) may be as good or better.Multiple muscles may produce better results than singlemuscles . The length of wrappable muscle could beincreased if a vascular anastamosis were done. If anerve anastomosis were done, the muscle could betransferred as a free flap . Arthroscopic techniques maysimplify the surgical procedures.

Basic study of transferred muscle and fiber conver-sion will continue to be important to the refinement ofdynamic myoplasty. The inherent force capacity of thetransferred muscle is reduced by 30 percent when thetendon is cut (29) . Force capacity is also lost when thefibers convert to type I (30) . Better understanding ofthese phenomena is needed to realize the full potentialof dynamic myoplasty.

ACKNOWLEDGMENTS

This paper arose from presentations at the Engi-neering Foundation Conference "Neural Prostheses:Motor Systems IV" on July 23-28, 1994 in Mt.Sterling, Ohio . The conference was supported by grantsfrom the Whitaker Foundation, the Paralyzed Veteransof America Spinal Cord Research Foundation, theNational Science Foundation, the University of Miamiand the Bakken Research Centre . The Public HealthService participated in the support of this meeting under

a grant from the National Institute of Child Health andHuman Development of the National Center for Medi-cal Rehabilitation and Research, and the NationalInstitute of Neurological Disorders and Stroke . Thedevelopment of this paper was supported by theCleveland FES Center, Cleveland OH.

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