Preparation of a skeletal muscle ventricle in sheep: severe damage to the Latissimus dorsi muscle due to mobilization before preconditioning

As part of a study examining the use of a skeletal muscle ventricle for cardiac assistance in sheep, a new concept of muscle preconditioning was put into practice. We aimed to produce a latissimus dorsi muscle (LDM) capable of performing chronic work immediately after the construction of a skeletal muscle ventricle. The left LDM was detached from the thoracic wall, divided longitudinally and reattached in situ to achieve vascular delay. The right LDM was left unaffected. Thereafter, preconditioning of both LDM was started according to the clinically approved stimulation protocol for cardiomyoplasty. Preconditioning of the unaffected right LDM in situ resulted in a complete muscle fiber transformation with no signs of degeneration or necrosis. Mobilization of the left LDM before preconditioning led to a distinct damage of the muscle. During conditioning, the increase in burst duration from 2 to 3 impulses in sheep A and from 3 to 5 impulses in sheep B resulted in a homogenous degeneration of the muscle fibers of the left LDM. Histomorphological analysis showed a dramatic increase in the percent perimysial and endomysial connective tissue. The applied concept of muscle prefabrication proved to be a failure. Muscle splitting and mobilization followed by vascular delay and in situ conditioning as a concept of muscle prefabrication should be strictly avoided.     

Use of tactile stiffness to detect fatigue in the latissimus dorsi muscle

In clinical settings, no method has been established to examine the fatigue of a latissimus dorsi muscle (LDM) preconditioned for cardiomyoplasty. We examined the feasibility of measuring muscle stiffness (tactile stiffness) to evaluate muscle fatigue in situ using our tactile sensor. We stimulated canine LDM with burst pacing and monitored both stiffness and tension to determine their relationship. In both dissected LDM and LDM in situ, the decrements of these parameters during burst pacing were compared between preconditioned and unconditioned LDM. In measurement in situ, the sensor probe was placed on the LDM through a small incision. Strong statistical correlation was shown between stiffness and tension (r = 0.935). In decrements of stiffness in situ, there were statistically significant differences between preconditioned and unconditioned LDM. Our tactile sensor system can provide an efficient method for evaluating fatigue of muscles in situ without measuring muscle tension.     

Muscle contraction and relaxation described by tactile stiffness

We developed a tactile sensor system that measures the stiffness of objects (tactile stiffness) and used it to describe the time course of muscle contraction and relaxation. We examined fatigue resistance of the latissimus dorsi muscle (LDM), which is preconditioned for cardiomyoplasty. Time to peak, ripple of LDM, and time constant were calculated from the time course of LDM contraction and relaxation as described by tactile stiffness. We compared conditioned and unconditioned LDMs using these 3 parameters. The time course can be described by tactile stiffness. Tactile stiffness fell exponentially during LDM relaxation. In mean values, time to peak increased 230%, ripple decreased 20%, and time constants increased 424%. Significant differences were shown in 3 parameters between conditioned and unconditioned LDMs (p < 0.05). Our tactile sensor system can describe the time course of LDM contraction and relaxation. Examining the difference in time courses, we might detect the level of LDM preconditioning for cardiomyoplasty.     

Deferoxamine enhances neovascularization and recovery of ischemic skeletal muscle in an experimental sheep model

BACKGROUND: Iron chelators have been reported to interfere with inflammatory cells and possibly enhance vascular growth factor expression. The objective of this study was to investigate the efficacy of the iron chelator deferoxamine mesylate in preventing skeletal muscle ischemia. METHODS: The latissimus dorsi muscle (LDM) was mobilized in 20 adult sheep. Two separate pockets were created in each sheep. Autologous fibrin sealant with or without 100 mg/mL of deferoxamine mesylate (10 pockets) was added to the pockets. Deferoxamine mesylate alone was also applied to another 10 pockets, whereas the 10 other pockets served as controls. RESULTS: Conventional, indirect immunofluorescent enface staining showed that in nonmobilized, nonischemic LDM the capillary density was 196 +/- 14 capillaries/mm2 in the distal and 207 +/- 19 capillaries/mm2 in the middle part. After severe ischemic shock (subtotal mobilization), the muscle did not recover completely even after 2 months (149 +/- 15 capillaries/mm2 in the distal part and 177 +/- 16 capillaries/mm2 in the middle part of the LDM). Fibrin application only increased muscle neovascularization. The number of capillaries per mm2 of muscle increased to 250 +/- 25 in the distal part and to 271 +/- 24 in the middle part of the LDM. However, when fibrin was applied with added deferoxamine mesylate, the capillary density increased to 361 +/- 25 capillaries/mm2 in the distal part (p < 0.05 vs fibrin only; controls) and to 401 +/- 20 capillaries/mm2 in the middle part of the LDM (p < 0.05 vs fibrin only and p < 0.001 vs controls). The data are concordant with the blood flow estimation before and after mobilization (severe ischemic shock) in the different parts of the LDM. CONCLUSIONS: Local application of deferoxamine mesylate enhances neovascularization and recovery of surgically induced skeletal muscle ischemia in a sheep model.     

Comparison of Different Regimens of Electrical Stimulation Applied to Nonmobilized and Newly Mobilized Latissimus Dorsi Muscle

Abstract We investigated the possibility of preventing further aggravation of muscle ischemia and necrosis in newly mobilized, unconditioned latissimus dorsi muscle (LDM) by utilizing short increments of stimulation with intervening rest periods. Adult St. Croix sheep (N = 12) weighing 30 ± 8 kg were used in this study. Fatigue tests (30 min) using different stimulation regimens before and after LDM mobilization were performed on all animals; the length of time to return to baseline levels was also measured. Our investigation yielded results that contradict the conventional wisdom that any electrical stimulation damages newly mobilized LDM and will cause a considerable decrease in contractile force (CF). Stimulation regimens using continuous contractions at 30 and 60 contractions per minute (CPM) for 30 minutes were damaging to the LDM. CF also dropped significantly and returned slowly to baseline values: at 60 CPM, CF dropped to 50 ± 4% and did not return to baseline even after 90 minutes of rest; at 30 CPM, CF dropped to 61 ± 4% and baseline was restored after 80 minutes of rest. Electrical stimulation using continuous contractions at a slower rate (15 CPM) was tolerable, although a 23% decrease in CF was noted (p < 0.05 when compared to 60 CPM). These results did not satisfy us that such a regimen would be useful for cardiac assistance immediately after cardiomyoplasty. The work-rest regimen at 30 CPM also gave poor results: CF decreased to 75 ± 2% and baseline was restored after 80 minutes of rest. Promising results were seen when utilizing a work-rest regimen at 15 CPM. The newly mobilized LDM showed no visible signs of fatigue: CF decreased minimally to 92 ± 3% (p < 0.05 when compared to 30 CPM), and light microscopic analysis of biopsies revealed no morphological damage exceeding that typically seen after subtotal mobilization. Such results open avenues for future investigations: beginning electrical stimulation immediately after cardiomyoplasty (using a single impulse and a slow rate of contraction); decreasing the length of time necessary to obtain full cardiac assistance; and beginning partial cardiac assistance immediately after cardiomyoplasty (if needed) for approximately 30 minutes several times a day.     

Latissimus dorsi dynamic cardiomyoplasty of the right ventricle. Potential for use as a partial myocardial substitute

Full-thickness right ventricular latissimus dorsi dynamic cardiomyoplasty with the Medtronic Cardiomyostimulator (Medtronic, Inc., Minneapolis, Minn.) was performed in a chronic canine model. In one group (n = 2) the latissimus dorsi was electrically preconditioned before cardiomyoplasty. In a second group (n = 3) cardiomyoplasty was performed and the muscle was progressively stimulated, with conditioning accomplished while the latissimus dorsi was functioning on the ventricle. The contribution of the stimulated latissimus dorsi to global ventricular function was assessed, and the effects of varying muscle stimulation parameters on latissimus dorsi function and hemodynamics were examined. Right ventricular systolic pressure increased 8%, from 23.2 +/- 0.95 to 25.1 +/- 1.5 mm Hg. The rate of pressure rise increased 37% from 226 +/- 13 to 309 +/- 12 mm Hg/sec. Right ventricular ejection fraction was measured in two dogs and increased 29% with latissimus dorsi stimulation, from 51.5% +/- 13.5% to 66.5% +/- 14.5%. Although the sample size was small, there was no difference observed between the preconditioned and nonpreconditioned groups. Right ventricular systolic pressure, rate of pressure rise, and percent latissimus dorsi fiber shortening increased as voltage and burst frequency of the muscle stimulus increased, whereas increasing the burst duration had little effect in two dogs so studied. Latissimus dorsi dynamic cardiomyoplasty can function as a partial myocardial replacement in a chronic canine model, apparently without preconditioning of the muscle. The degree of cardiac assist obtained with cardiomyoplasty appears to be influenced by the voltage and frequency of the stimulus applied to the muscle. Although it is unclear whether these results can be extrapolated to the left ventricle, this technique may find application in the treatment of ventricular aneurysm or ventricular tumor.     

Avoiding ischemia in latissimus dorsi muscle grafts: electrical prestimulation versus vascular delay

Background. Surgical mobilization of the latissimus dorsi muscle produces regional ischemic damage that may compromise its function in clinical applications such as cardiomyoplasty. We compared the effectiveness of two procedures designed to maintain blood flow throughout the mobilized muscle.

Methods. Adult pigs were assigned to two experimental groups: an electrically prestimulated group (n = 10) and a vascular delay group (n = 10). In the prestimulated group the left latissimus dorsi muscle was activated in situ at 2 Hz for 24 h/d. In the vascular delay group, the intercostal perforating arteries to the left latissimus dorsi muscle were divided. Two weeks later, hyperemic blood flow was measured by means of fluorescent microspheres immediately before and after mobilizing the latissimus dorsi muscle and again after recovery for a further 2 days.

Results. In the prestimulated group, blood flow was not significantly depressed in any region of the muscle immediately after mobilization, and blood flow increased significantly in proximal (p = 0.01), middle (p = 0.02), and distal (p = 0.007) regions following recovery. In muscles subjected to vascular delay the proximal and middle regions showed no significant changes in blood flow after mobilization or recovery, but flow in the distal region was 50% lower after mobilization (p = 0.003), and it remained significantly depressed even after recovery (p = 0.008).

Conclusions. Prestimulation was significantly more effective than vascular delay in preserving distal blood flow. Because it is also less invasive and initiates metabolic transformation before mobilization, this technique should allow cardiac assistance to be introduced at an earlier postoperative stage without compromising the viability of the grafted muscle.     

Preservation of the Latissimus Dorsi Muscle During Cardiomyoplasty Surgery

A bstract Background : Cardiomyoplasty surgery has been shown to be associated with damage and degeneration of the assisting skeletal muscle. The purpose of this study was to use ischemic (short-term) and thermal (long-term) preconditioning to protect the muscle during surgery and the subsequent ischemia. Methods : Three 10-minute cycles of ischemia-reperfusion were accomplished noninvasively on goat latissimus dorsi muscle (LDM) immediately prior to surgery. In another experiment, LDM was noninvasively heat shocked for 20 minutes at 42°C 24 hours prior to surgery. LDM damage was evaluated 5 days postsurgery using enzyme activities (β-glucuronidase, β-GLN; citrate synthase), hydroxyproline, morphology, and blood flow. Results : The lysosomal enzyme, β-GLN, was significantly increased (43%, p < 0.05) by surgical dissection and remained high in the ischemic preconditioned LDM (58%, p < 0.05) and in the heat shocked LDM (57%, p < 0.05). Conclusion : These findings show that these two protective protocols do not reduce the muscle damage that occurs during surgical preparation of the LDM for cardiomyoplasty.     

Acute Muscle Damage in Latissimus Dorsi Grafts Mobilized for Cardiac Assist: Is Vasospasm an Important Factor?

Abstract Background: Muscle damage in latissimus dorsi grafts is known to occur following surgical mobilization for cardiomyoplasty. It is believed that ischemia may be a contributory factor. We tested the hypothesis that surgical manipulation of the muscle graft resulted in vasospasm of the intramuscular arteries that compromised muscle viability by examining the effects of vasodilators in the early ischemic period. Methods : Rat latissimus dorsi muscles were mobilized from all truncal attachments with preservation of the thoracodorsal neurovascular pedicle. Undisturbed contralateral muscles served as controls. After 24 hours, regional analysis of muscle viability was performed by enzyme macrohistochemistry and histologic assessment. The experimental interventions in four randomized groups (n=5 each) included: group A, control; group B, topical papaverine (1%); group C, intravenous hydralazine (0.5 mg/kg); and group D, intravenous verapamil (75 μg/kg). Results: All mobilized muscles showed loss of viability, as compared to controls, with damage most apparent in the distal part (mobilized vs control: viable area = 56.76% 151.26–62.261 vs 98.54% 197.87–99.211; p e 0.0011. All three vasodilators failed to prevent muscle necrosis whereas papaverine appeared to aggravate the damage (papaverine vs control: viable area = 53.60% 130.73–76.471 vs 76.60% [75.02–78.181 in the middle region; p e 0.05 and 44.27% 129.53–59.011 vs 56.76% 151.26–62.261 in the distal region; p e 0.05). Conclusions : The rodent model appears to be useful for studying latissimus dorsi muscle injury. The use of vasodilators at the time of surgical mobilization of the latissimus dorsi muscle does not appear to influence the degree of early muscle damage. Topical papaverine may be detrimental to the muscle in this regard. (J Card Surg 1998;13:70–78)     

Nitroglycerine reduces neutrophil activation and acute damage in latissimus dorsi muscle grafts

Background. Damage to the latissimus dorsi muscle (LDM) may jeopardize a successful outcome to dynamic cardiomyoplasty. We and others have demonstrated muscle damage in LDM in various species including humans. Ischemia is now recognized to be an important contributory factor. We postulated that glyceryl trinitrate, a nitric oxide donor, might protect against ischemic endothelial dysfunction and so reduce resultant muscle damage.

Methods. In 20 adult rats the left LDM was mobilized on its thoracodorsal neurovascular pedicle and maintained as an orthotopic graft. Half of the animals received glycerol trinitrate intraoperatively and postoperatively for 24 hours. The other half served as untreated controls. Each group was further subdivided into two groups (n = 5 in each): animals in which the LDM was excised after 4 hours for myeloperoxidase studies, and animals in which the LDM was excised at 24 hours for analysis of muscle damage by histology and enzyme macrohistochemistry. Blood samples were taken at 24 hours for assay of plasma nitrite and nitrate as nitric oxide metabolites.

Results. Glycerol trinitrate-treated animals had higher plasma nitric oxide metabolite levels after 24 hours (after nitrate reductase treatment, total nitrite, 78.3 ± 11.8 nmol/mL, mean ± SEM) than controls (42.1 ± 3.7 nmol/mL, p = 0.008). The proportion of viable LDM in glycerol trinitrate-treated animals was greater than in untreated animals, mainly in the middle and distal regions of the graft (middle region, 96.3% ± 0.5% versus 75.7% ± 4.1%, p < 0.001; distal region, 94.4% ± 0.8% versus 40.9% ± 3.1%, p < 0.001). Macrohistochemical findings correlated well with the histologic findings. Myeloperoxidase activity (U/g) was markedly lower in glycerol trinitrate-treated LDMs, mainly in the distal part of the graft (glycerol trinitrate versus control, 20.5 ± 2.1 versus 40.9 ± 3.1 U/g, p < 0.001).

Conclusions. Glycerol trinitrate significantly reduced acute damage to the distal two-thirds of the mobilized LDM, possibly by modifying leukocyte activation and endothelial dysfunction associated with ischemic injury.     

Cardiomyoplasty: Transformation of the Assisting Muscle Using Intermittent Versus Continuous Stimulation

A bstract Background : Dynamic cardiomyoplasty has been shown to result in muscle damage and necrosis. The purpose of this study was to compare the effects of intermittent versus continuous stimulation on the latissimus dorsi muscle (LDM) with and without surgical dissection. Methods : Surgically dissected and nondissected goat LDM were either stimulated continuously (24 hours/day) or intermittently (16 hours on/8 hours off/day) for 60 to 75 days. Results : The findings show that the continuous stimulation induced the most complete transformation of myosin isoforms and C_a² pump isoforms in the nondissected LDM, whereas, intermittent stimulation resulted in less muscle damage in the surgically dissected LDM. Intermittent stimulation of the dissected LDM resulted in larger fiber areas and a lower connective tissue concentration than did the continuous stimulation. Conclusions : It was concluded that surgically dissected muscle responds differently to electrical stimulation and that intermittent stimulation may result in less damage while transforming the LDM pedicle for use in cardiomyoplasty.     

Fiber length variability within the flexor carpi ulnaris and flexor carpi radialis muscles: implications for surgical tendon transfer

PURPOSE: The purpose of this study was to understand the detailed architectural properties of the human flexor carpi radialis (FCR) and flexor carpi ulnaris (FCU) muscles and their implications for tendon transfer surgery. METHODS: Muscle fiber length was measured in 6 separate regions of the FCU and FCR from 10 cadaveric specimens. Sarcomere length was measured by laser diffraction for normalization. Moment arms were estimated by measuring tendon excursion with respect to joint angle. The position of entry of the motor nerve branches into each muscle also was measured to establish limits for the safe length of muscle mobilization. RESULTS: Muscle fiber length varied significantly along both the FCU and FCR. Fiber length variability in the FCU was twice that of the FCR. Although the average fiber length for both muscles across all regions was similar (62.6 +/- 2.1 mm for the FCR and 63.1 +/- 4.0 mm for the FCU), the proximal fibers of the FCU were longer compared with the proximal fibers of the FCR and the distal fibers of the FCU were shorter compared with the distal fibers of the FCR. The 99% confidence interval for the second nerve branch entry into the muscles was located approximately 69 mm distal to the medial epicondyle for the FCU and approximately 73 mm distal for the FCR. CONCLUSIONS: These data show different designs of both the FCU and the FCR. The functional significance of fiber length variability is not clear but imply that, when used in tendon transfer, the properly mobilized FCU has a much greater excursion.     

Growth factors improve latissimus dorsi muscle vascularization and trophicity after cardiomyoplasty

BACKGROUND: Dynamic cardiomyoplasty consists of wrapping the electrostimulated latissimus dorsi muscle (LDM) around the failed heart. Partial ischemia followed by atrophy of the middle and distal part of the LDM were observed in 30% of clinical cases after LDM flap elevation from its origin. In the current study, we hypothesized that local administration of growth factors at the LDM/epicardial interface could improve muscle vascularization and trophicity. METHODS: In 24 sheep, dynamic cardiomyoplasty was performed using the left LDM. A multiperforated catheter was positioned at the LDM/epicardial interface for a weekly administration, during a 1-month period, of the following factors: basic fibroblast growth factor (bFGF, n = 6), vascular endothelial growth factor (VEGF, n = 6), and regenerating agent (RGTA, n = 6). Six sheep injected with phosphate-buffered saline (used for dilution of the growth factors) were used as a control group. At 3 months, angiographic, histologic, and histomorphometric studies were performed. RESULTS: Angiographic studies of the animals treated with growth factors demonstrated hypervascularization due to the development of new vessels. Histomorphometric and histologic studies showed a significant increase in the number of capillaries and arterioles (100 fields/muscle) in the groups treated with bFGF (443.0 +/- 101.2, p < 0.01), RGTA (293.2 +/- 29.3, p < 0.05), and VEGF (246.5 +/- 45.9, p < 0.05), as compared with the control group (81.5 +/- 11.4). A significantly lower atrophy score was observed in the groups treated with bFGF (1.4 +/- 0.18, p < 0.05), RGTA (1.59 +/- 0.17, p < 0.05), and VEGF (1.96 +/- 0.14, NS), as compared with the control group (2.48 +/- 0.16). CONCLUSIONS: Local administration at the heart/muscle interface of growth factors increases muscle vascularization and avoids muscle atrophy in an experimental cardiomyoplasty model, both of which are advantageous to the contracting LDM. The local growth factors delivery system used in this study appears efficient, easy to implant, and manipulate and safe.     

Potential for left ventricular assistance by latissimus dorsi myograft--sequential effects of electrical preconditioning on skeletal muscle fiber type, blood flow and metabolic status

In order to evaluate the possibility of left ventricular assistance by latissimus dorsi (LD) myograft, we have studied contractile property and fatigue rates of skeletal muscle ventricle (SMV) constructed using canine LD muscles. Twenty three dogs were divided into 3 groups depending on the conditioning protocol of LD muscles; Group I (Control n = 12), Group II (Vascular delay n = 4) and Group III (Vascular delay and electrical preconditioning n = 7). SMVs in GIII dogs generated sufficient pressure and forward flow in a hydraulic test system with muscle stimulation at a burst-frequency of 50 Hz (SMV pressure 131 +/- 42 mmHg, Stroke volume 7.0 +/- 3.0 ml/beat). Although SMVs in GI and GII dogs could sustain flow for only 4.0 +/- 1.1 minutes and 32.4 +/- 14.0 minutes, respectively, SMVs in GIII were able to pump continuously for 107.5 +/- 15.0 minutes (p less than 0.01, vs GI and GII). Thermography surface temperature mapping revealed marked improvement of blood distribution of LD muscles in GII and GIII dogs. Flow rates of thoracodorsal artery during SMV stimulation were GI: 10.0 +/- 3.1 ml/minute/LD 100 g, GII: 15.0 +/- 3.7 ml/minutes/100 g and GIII: 20.7 +/- 2.5 ml/minutes/100 g (p less than 0.01 vs GI). The ratio of oxygen consumption to lactate output was GI: 0.33 +/- 0.10, GII: 0.36 +/- 0.09 and GIII: 1.56 +/- 0.97 (p less than 0.01 vs GI, p less than 0.05 vs GII). Histochemical examination of LD muscles using alkaline ATPase stain revealed muscle fiber type transformation of GIII muscles. These results suggest electrically preconditioned LD muscles have sufficient contractile property for partial left ventricular assistance, and highly fatigue-resistant properties resulted from muscle fiber transformation, improved muscle perfusion and metabolic changes.     

Adynamic cardiomyoplasty: effect on cardiac efficiency and contractile reserve in dogs with adriamycin-induced cardiomyopathy

The girdling effect of the skeletal muscle wrap seems to be the primary mechanism of action of cardiomyoplasty. It is associated with a myocardial sparing effect. Myocardial sparing effect has been shown with an active muscle wrap or an active muscle wrap acutely turned "OFF". The purpose of the study was to evaluate the effect of a passive skeletal muscle wrap on cardiac energetics parameters and contractile reserve in a canine model of cardiomyopathy. Six dogs with adriamycin-induced cardiomyopathy were studied. Three dogs underwent right latissimus dorsi adynamic cardiomyoplasty and 3 served as controls. Cardiac and coronary sinus catheterizations were performed at 0 and 6 weeks. A dobutamine stress test was performed at 6 weeks. Myocardial oxygen consumption was not reduced in the cardiomyoplasty group (139.20+/-86.90 Joules/min) compared to the control group (95.10+/-12.60 Joules/min, P = 0.27) at 6 weeks. Mechanical cardiac efficiency was increased in the cardiomyoplasty group (33.15+/-4.40%) compared to the control group (24.50+/-2.70%, P = 0.049) at 6 weeks. Left ventricular end diastolic diameter index was reduced in the cardiomyoplasty group (38.00+/-1.70 mm/m2) compared to the control group (46.30+/-1.55 mm/m2, P = 0.049) at 6 weeks. Indices of diastolic function -dp/dt, and tau were not significantly affected by adynamic cardiomyoplasty. Max dp/dt was increasing more in the cardiomyoplasty group than in the control group (P = 0.07) during dobutamine stress test. Mechanical cardiac efficiency was better preserved by the adynamic cardiomyoplasty. Myocardial contractile reserve might be better preserved with cardiomyoplasty.     

Optimal Electrical Stimulation for Latissimus Dorsi Muscle After Cardiomyoplasty

A bstract The aim of this study was to evaluate the functional state of latissimus dorsi muscle (LDM) during electrical stimulation following cardiomyoplasty. Both single pulses and bursts of impulses were used for electrical stimulation. In 15 dogs, studies were carried out for 2 months, while in 19 patients, the follow-up period after cardiomyoplasty was 10 ± 3.1 months. The LDM was punctured by needle electrodes at various intervals following cardiomyoplasty, and the changes of the rheomyosignal (RMS) curve were registered on the "Reostim-06." During the follow-up study, it was found that: (1) signal amplitude decreased 30%; (2) the contraction duration of LDM increased 38%; (3) the contraction velocity decreased 43%; and (4) relaxation velocity decreased 61%. There is a correlation between LDM mechanical contractile force and RMS indices (r = 0.8). The RMS index was a function of the electrical burst duration and the number of impulses in the bursts. Thus, RMS parameters can characterize the functional state of LDM, and they may be used in designing a new generation of electromyostimulators for optimal LDM stimulation at different periods after cardiomyoplasty.     

Adynamic Cardiomyoplasty: Effect on Cardiac Efficiency and Contractile Reserve in Dogs with Adriamycin-Induced Cardiomyopathy

ASTRACT The girdling effect of the skeletal muscle wrap seems to be the primary mechanism of action of cardiomyoplasty. It is associated with a myocardial sparing effect. Myocardial sparing effect has been shown with an active muscle wrap or an active muscle wrap acutely turned"OFF". The purpose of the study was to evaluate the effect of a passive skeletal muscle wrap on cardiac energetics parameters and contractile reserve in a canine model of cardiomyopathy. Six dogs with adriamycin-induced cardiomyopathy were studied. Three dogs underwent right latissimus dorsi adynamic cardiomyoplasty and 3 served as controls. Cardiac and coronary sinus catheterizations were performed at 0 and 6 weeks. A dobutamine stress test was performed at 6 weeks. Myocardial oxygen consumption was not reduced in the cardiomyoplasty group (139.20 ± 86.90 Joules/min) compared to the control group (95.10 ± 12.60 Joules/min, P = 0.27) at 6 weeks. Mechanical cardiac efficiency was increased in the cardiomyoplasty group (33.15 ± 4.40%) compared to the control group (24.50 ± 2.70%, P = 0.049) at 6 weeks. Left ventricular end diastolic diameter index was reduced in the cardiomyoplasty group (38.00 ± 1.70 mm/m²) compared to the control group (46.30 ± 1.55 mm/m², P = 0.049) at 6 weeks. Indices of diastolic function-dp/dt, and tau were not significantly affected by adynamic cardiomyoplasty. Max dp/dt was increasing more in the cardiomyoplasty group than in the control group (P = 0.07) during dobutamine stress test. Mechanical cardiac efficiency was better preserved by the adynamic cardiomyoplasty. Myocardial contractile reserve might be better preserved with cardiomyoplasty.     

Ischemic preconditioning of skeletal muscle: duration of late-phase protection

BACKGROUND: The time course of the late phase of ischemic preconditioning (IPC) was determined in latissimus dorsi muscle (LDM) flaps using viability and function as the endpoints. MATERIALS AND METHODS: LDM flaps from Sprague-Dawley rats were allocated into 6 groups. LDMs were preconditioned with 2 30-minute periods of ischemia separated by 10 minutes of reperfusion and subjected to a 4-hour ischemic insult after 24, 48, 72, and 96 hours from IPC. LDMs were evaluated for percent necrosis and muscle contractile function and compared with controls. RESULTS: The late phase of IPC provides significant protection against necrosis up to 72 hours. Conversely, when the end point used was muscle contractile function, the protection only lasted 48 hours. CONCLUSION: The time course of late-phase protection in skeletal muscle is 2-3 days. Late phase IPC appears to protect muscle flaps during the most critical time period following elevation.     

Electrical stimulation-induced changes in double-wrapped muscles for dynamic graciloplasty

HYPOTHESIS: Treatment of fecal incontinence has been greatly improved by electrical stimulation of gracilis muscle transposed around the anal canal. Various configurations of the muscle have been used: single alpha, gamma, epsilon muscle loops, split sling, or double wrap. We report herein experimental data on muscle transformation and damage induced by the latter surgical approach. DESIGN, INTERVENTIONS, AND MAIN OUTCOME MEASURES: This study was conducted on 4 groups of New Zealand white rabbits. Group 1 had unstimulated transposed gracilis muscles. Group 2 had left transposed gracilis muscles stimulated only. Group 3 had both right and left transposed gracilis muscles stimulated. Group 4 were the controls (not operated on). Muscle properties were studied by electrophysiological,immunohistochemical,and biochemical techniques. RESULTS: Transformation from fast-contractile glycolytic muscle fibers into fast-intermediate to slow-contractile oxidative muscle fiber types induced a fatigue resistance of the transposed muscle that has undergone long-term stimulation and muscle alterations characterized by fiber atrophy and fibrosis. CONCLUSIONS: Whatever technique of dynamic graciloplasty is used, muscle degeneration associated with mobilization might result primarily from the surgical dissection, whereby collateral blood supply to the gracilis is interrupted and exacerbated by long-term stimulation.     

Cardiomyoplasty: the benefits of electrical prestimulation of the latissimus dorsi muscle in situ.

BACKGROUND: Ischemic damage in the latissimus dorsi muscle may limit the success of cardiomyoplasty. Electrical prestimulation of the muscle in situ is known to enhance thoracodorsal perfusion to the distal latissimus dorsi muscle immediately after grafting. In this study we asked whether prestimulation was also beneficial under typical postoperative conditions. METHODS: Ten sheep were randomly assigned to two equal groups. In one group the latissimus dorsi muscle was stimulated continuously in situ at 2 Hz for 2 weeks; in the other group the muscle was not stimulated. Regional blood flows in the muscle were determined sequentially (1) under baseline conditions, (2) immediately after surgical mobilization, handling, and reattachment at 80% of the resting length, and (3) after 5 days. RESULTS: Manipulation of the unstimulated muscle resulted in an acute global reduction in blood flow with no improvement after 5 days. The distal region was most severely affected (26.2%+/-4.2% of baseline blood flow). Electrical prestimulation significantly reduced regional blood flow under baseline conditions but rendered the whole muscle more resistant to the surgical manipulations; blood flow was significantly better-preserved immediately afterwards, and there was complete recovery to baseline levels after 5 days. CONCLUSIONS: Electrical prestimulation of the latissimus dorsi muscle in situ reduces the acute distal ischemia caused by surgical manipulations, and promotes subsequent recovery of blood flow to baseline levels after a few days. Use of a prestimulated graft may therefore improve the outcome of skeletal muscle cardiac assistance.