Latissimus dorsi dynamic cardiomyoplasty.

Cardiomyoplasty is a new surgical technique that uses an electrostimulated skeletal muscle to reinforce or partially replace the heart muscle. Since the first clinical case performed in 1985, long-term beneficial cardiac effects of latissimus dorsi cardiomyoplasty have been documented in patients with various myocardial diseases (ischemic, neoplastic, dilated cardiomyopathy). In this article we describe the surgical technique that we have developed to biomechanically assist severe and irreversible ventricular failure.

Aortomyoplasty counterpulsation: experimental results and early clinical experience.

BACKGROUND: Presently the only clinical method of skeletal muscle augmentation of the heart is achieved by wrapping muscle around the cardiac ventricles and then stimulating the muscle to contract synchronously with cardiac systole. Intraaortic balloon counterpulsation provides diastolic counterpulsation in the short-term with the known benefits of increasing diastolic pressure and reducing ventricular afterload. Using protocols already in existence for dynamic cardiomyoplasty we have investigated the long-term use of extraaortic skeletal muscle-powered counterpulsation. METHODS: In five alpine goats the right latissimus dorsi muscle (LDM) was used to achieve a wrap around the ascending aorta, which had been augmented with an elliptic pericardial patch. Electrostimulation protocols were commenced after 2 weeks and continued for 12 to 24 months. At this time baseline hemodynamic measurements were made with and without stimulation of the LDM. Acute cardiac depression was induced and further measurements were made, again with and without stimulation of the LDM. RESULTS: Results in the basal state demonstrated improvement in all parameters with stimulation and a 23% increase of the subendocardial viability index. After induction of cardiac depression there was a 52% increase in cardiac output, 39% decrease in systemic vascular resistance, and 27% increase in subendocardial viability index. Histologic studies demonstrated tight adhesion between the aortic wall and the LDM, no dilatation of the aortic wall, and no deleterious effects in the aortic wall of the chronic intermittent constriction. Histochemical staining demonstrated transformation of the muscle fibers of the LDM flap into type 1 oxidative muscle fibers. CONCLUSIONS: In conclusion, our present study demonstrates that in this animal model aortomyoplasty produces a chronic counterpulsation with preservation of aortic architecture. With induction of heart failure aortomyoplasty provided an effective means of cardiac assistance. The use of the ascending aorta to achieve diastolic counterpulsation may be an efficient use of skeletal muscle energy to augment the heart in selected clinical cases. Early clinical experience is described in this article.

Dynamic aortomyoplasty to assist left ventricular failure.

The efficacy of skeletal muscle contractile force to augment left ventricular function has been demonstrated experimentally and clinically by the cardiomyoplasty procedure. Another approach in biomechanical cardiac assistance is the use of electrostimulated skeletal muscle in an extracardiac position. We describe an autologous counterpulsating device using the native ascending aorta as a ventricular chamber wrapped by an electrostimulated latissimus dorsi muscle flap (LDMF). This model avoids thrombotic complications observed in skeletal muscle neo-ventricles associated with prosthetic chambers. In 8 goats, a right LDMF was transferred to the thoracic cavity by removal of the second rib. In 4 goats, the diameter of the aorta was enlarged by surgical implantation (using lateral clamping) of an autologous pericardial patch. The LDMF was wrapped around the ascending aorta and electrostimulated using an external diastolic pulse generator connected to a sensing myocardial lead and to LDMF pacing electrodes. Hemodynamic studies were performed (left ventricular, aortic, and pulmonary artery pressures and rate of rise of left ventricular pressure). The LDMF diastolic counterpulsation was performed using a burst of 30 Hz, with a delay from the R wave adjusted to provide optimal diastolic augmentation. Percent increase in the subendocardial viability index was calculated during unassisted and assisted cardiac cycles (1:2) at baseline and after acute heart failure induced by the administration of high doses of propranolol hydrochloride (3 mg/kg intravenously). Diastolic aortic counterpulsation by the stimulated LDMF resulted in a significant improvement in the subendocardial viability index both at baseline and after induced cardiac failure in both groups, though the increase was greater in the group with aortic enlargement.

Dynamic cardiomyoplasty.

Dynamic cardiomyoplasty is a promising new technique that appears to effect symptomatic improvement in patients with NYHA class III heart failure. Objective improvement in systolic performance of the left ventricle appears small but remains to be further defined. No survival advantage has yet been realized, although this may be seen as the technique is further refined and operative risk curtailed. Mechanism of action may include a girdling effect that prevents progressive left ventricular dilatation. This effect may be independent of any role in augmenting systolic performance. Randomized clinical trials currently in progress will provide definitive answers within the next few years to these important questions.

Dynamic cardiomyoplasty for long-term cardiac assist.

The principle of cardiomyoplasty is long-term electrostimulation of a latissimus dorsi muscle (LDM) wrapped around the failing heart. Technically, this procedure consists of placing the left LDM flap around the heart via a window created by partial resection of the 2nd or 3rd rib, and subsequent muscle electrostimulation in synchrony with ventricular systole. The aim of cardiomyoplasty is to support ventricular function in ischemic or dilated cardiomyopathies, or to partially replace the ventricular myocardium after large aneurysm or tumor resections. Our clinical experience at Broussais Hospital involves 44 patients. The functional class and quality of life improved after cardiomyoplasty. Improvement of the ventricular performance and limitation of cardiac dilatation were demonstrated over the long-term. The actuarial survival at 6 years was 71%. Risk factors influencing perioperative mortality were: age > 65 years, associated surgical procedures, pulmonary vascular hypertension, and patients hemodynamically unstable or on inotropic drug support. Preoperative risk factors influencing the long-term mortality were: permanent NYHA functional class 4, cardiothoracic ratio > 0.60, LV ejection fraction < 15%, bi-ventricular heart failure, and atrial fibrillation. Cardiomyoplasty does not preclude the use of future orthotopic heart transplantation.

[Cardiomyoplasty. Experimental bases, operative technic, indications]. / Cardiomyoplastie. Bases expérimentales, technique opératoire, indications.

Dynamic cardiomyoplasty aims at restoring ventricular contractility by means of a skeletal muscle sutured around the heart. It consists of transferring a latissimus dorsi muscle flap onto the heart through a window created in the thoracic wall by partial resection of the second rib. The skeletal muscle may be used to reinforce the ventricular systole in ischemic or dilated cardiomyopathy, or to replace the myocardium after resection of a large aneurysm or an extensive tumour. The electronic pacing material includes an implantable cardiomyostimulator, muscle stimulating electrodes and R wave detecting electrodes. Muscular pacing begins 2 weeks after the operation, this being the time required for adhesions to be formed between the heart and the muscle. A progressive and sequential electrostimulation procedure results in the transformation of glycolytic muscle fibres that are fatigue-sensitive into fatigue-resistant oxidative fibres. The purpose of this biomechanical cardiac assistance system, where cardiac surgery is combined with plastic surgery and biomedical engineering, is to prolong life and improve its quality in patients with severe heart failure.

[Circulatory assistance through cardiomyoplasty and aortomyoplasty. Experience and first clinical results]. / Assistance circulatoire par cardiomyoplastie et aortomyoplastie. Expérience et premiers résultats cliniques.

The finding that skeletal muscles can be made resistant to fatigue by progressive electrical stimulation has been used as a means of providing circulatory support in cardiac surgery. The first application of this discovery was dynamic cardiomyoplasty, performed for the first time in man in 1985 at the Broussais Hospital, Paris. The latissimus dorsi muscle is transposed into the thorax, then attached around the heart and finally stimulated synchronously with the ventricular systole. So far, more than 200 patients in the whole world (including 57 at the Broussais Hospital) have undergone this operation with results that are increasingly encouraging. In these cases the muscle is used to reinforce or replace the left or right ventricle, but other applications are being studied, such as double cardiomyoplasty (left latissimus dorsi and right pectoralis major muscles), cardiomyoplasty of the right atrium and aortomyoplasty which produces aortic counterpulsation. The development of these techniques underlines the ever growing interest raised by this type of autologous circulatory support.

[Iron stores, iron deficiency and iron supplementation]. / Jerndepoter, jernmangel og jernberigelse.

In order to assess the prevalence of iron deficiency in the Danish population, a randomised cross sectional investigation was carried out one year after repealing of the order from 1939 concerning supplementing of corn products with iron. A randomised group of 198 persons divided into ten groups of 20 persons with equal numbers of men and women in the age group 20-69 years was submitted to determinations of serum-iron, serum-transferrin and serum-ferritin. The prevalence of iron deficiency as determined by serum-ferritin values of below 15 micrograms/l was 18% and 12% respectively, for women under and over 45 years while iron deficiency determined by transferrin saturation under 16% was 18% for both groups. 6% of the women under 45 years had severe iron deficiency as determined by low transferrin saturation and low ferritin. The prevalence among men was 1% and 3% as assessed by serum-ferritin levels and transferritin saturation. These results were compared with corresponding population investigations from Sweden where iron enrichment is the highest in the world and the sale of iron tablets is the greatest in the world. No significant differences in the frequency of latent iron deficiency could be demonstrated but the number of persons with severe iron depletion appears to be less in Sweden. Differences in the methodological procedures, however, cannot be excluded.

Recruitment properties of monopolar and bipolar epimysial electrodes.

Muscle force was studied as a function of stimulus parameters, epimysial electrode position relative to nerve supply, and muscle length to provide insight into the properties of motor prostheses that employ epimysial electrodes. The results of the acute experiments indicated that the dependence of recruitment (force versus stimulus amplitude) on muscle length was minimal for a monopolar electrode positioned close to nerve entrance or 5 mm proximal to the motor point. The selectivity of stimulation (minimal activation of adjacent muscles) was best, and the recruitment rate the highest, for an electrode placed close to the nerve entrance. A bipolar pair of electrodes placed on the superficial surface of the muscle opposite to the nerve entrance gave better selectivity than the monopolar electrode at the low end of the recruitment range, and poorer selectivity at the high end. This electrode configuration required greater stimulus currents and exhibited a lower recruitment gain than was obtained for a monopolar electrode in the same position. Examination of tissue surrounding the electrode 30 days after implantation showed that the fibrous tissue encapsulating the electrode had been incorporated into the fascial layer. Slightly larger dependence on muscle length and lower selectivity of stimulation were measured after encapsulation than were measured in the acute experiments.

Patient management and clinical follow-up after cardiomyoplasty.

The purpose of this article is to provide an overview of patient management following latissimus dorsi cardiomyoplasty, based on clinical experience with 34 patients operated on between 1985 and 1990. Postoperative patient care includes: (1) clinical follow-up, (2) electrostimulation management, and (3) management of complications. The efficacy of cardiomyoplasty is principally evaluated by the quality-of-life before and after cardiomyoplasty (New York Heart Association [NYHA] functional class), number of rehospitalizations due to congestive heart failure, amount of pharmacological support, exercise capacity, postoperative reintegration and adaptation to working life, and late survival.

Dynamic cardiomyoplasty: clinical follow-up results.

From 1985 to April 1990, 78 clinical dynamic cardiomyoplasty procedures were performed using the latissimus dorsi muscle stimulated with the Medtronic Cardiomyoplasty System. Indications for surgery were mostly ischemic and idiopathic dilated cardiomyopathies with patients in severe cardiac insufficiency (NYHA Class III and IV). Results of this multicenter study (11 centers) indicate that the dynamic cardiomyoplasty procedure can be transferred and reproduced in many centers with low perioperative mortality and that it improves the functional status of patients who survive the procedure. The survival rate suggests a long-term benefit (average implant time: 11.7 months). Although clinical functional improvement was reported, actual hemodynamic augmentations could not be clearly demonstrated under the protocol. Further studies of functional and hemodynamic parameters are necessary to determine if dynamic cardiomyoplasty is efficacious for a well-defined group of congestive heart failure patients. These points will be addressed in forthcoming studies.

What is the ideal pulse frequency for skeletal muscle stimulation after cardiomyoplasty?

Routinely the latissimus dorsi (LD) muscle is stimulated with bursts of pulses at 30 pulses/sec after cardiomyoplasty to assist the failing heart. At a lower pulse frequency the contractile force decreases and at higher frequencies the energy demand of the pacemaker increases rapidly. We investigated the effect of the stimulus frequency variation on contractile force in untrained LD muscles and in muscles after 12 weeks of continuous cyclic electrical stimulation. In six dogs, two electrodes (Medtronic SP5528) were implanted in the left LD muscle together with an Itrel muscle stimulator. The LD muscle was stimulated with 30 pulses/sec in bursts to deliver initially 30 and after 10 weeks 80 contractions per minute. Both before and after training of the LD muscle maximum force was observed by stimulating with a frequency of 36 to 130 pulses/sec in a burst. However, training induced a shift in the steep part of the force-frequency relation to lower frequencies. In particular, at 15 pulses/sec 60% of the maximal force was obtained in contrast to 40% before training. A fatigue test of 8 minutes duration was performed specified by 100 bursts/min and a burst duration of 0.25 sec at pulse frequencies of 30, 36, 50, and 85 pulses/sec. The contractile force decreased significantly during the course of the test at all frequencies. However, the force obtained with 30 pulses/sec stimulation was lower during the initial phase and approximately 10% higher at the end of the fatigue test as compared to 36, 50, and 85 pulses/sec stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

The rectus abdominis cardiomyoplastic procedure: preliminary results.

The rectus abdominis myofascial flap (RAMF) was investigated as a viable alternative to the latissimus dorsi flap for dynamic cardiomyoplasty. In human and animal cadaver experiments and live sheep, it was possible to use the RAMF for innervated intrathoracic use. The RAMF was stimulated by a specially designed cardiomyostimulator (Medtronic Inc., Maastricht, The Netherlands). The flap might be promising as an addition to the currently available dynamic cardiomyoplastic techniques.

Effects of carnitine on preconditioned latissimus dorsi muscle at different burst frequencies.

Exercise and electrical stimulation may result in a decrease in carnitine levels associated with preconditioned latissimus dorsi muscles. Therefore, the effects of exogenous carnitine were studied in a model of latissimus dorsi muscle contraction. Twelve dogs were studied. Under anesthesia, the latissimus dorsi was placed around an implantable mock circulation system. The muscle was made fatigue-resistant with the aid of chronic low-frequency electrical stimulation. Six animals received carnitine 0.15 mmol/kg; the other six served as control. The muscles were stimulated with 20, 43, and 85 Hz pulse training. During the 90-minute stimulation period, the pressure that developed in the mock circulation was measured at 15 minute intervals. The changes in ATP and lactate levels were measured every 30 minutes. Stimulations at 20 and 43 Hz did not result in any change in pressure or metabolic data over the course of 90 minutes of stimulation. When the 85 Hz burst was applied, ATP levels decreased, while lactate levels increased, with an associated drop in pressure in the control group. ATP and lactate levels were, respectively, 13.8 +/- 1.4 mumol/g and 15.0 +/- 4.0 mumol/g in the carnitine group and 10.3 +/- 1.1 mumol/g and 23.0 +/- 3.0 mumol/g in the control group at the end of 90 minutes (p < 0.06). The pressure at the same time interval was 74 +/- 4 mmHg in the control group, and 85 +/- 3 mmHg in the carnitine group (p < 0.05). In this study, we demonstrated that carnitine administration enhances muscle performance in terms of metabolic and pressure changes during high-frequency electrical stimulation at 85 Hz.

Dynamic cardiomyoplasty: a new approach to assist chronic myocardial failure.

The concept of 'reconstructive cardiac surgery' using a stimulated autologous skeletal muscle has been investigated in this research. Our approach has been to investigate the substitution or reinforcement of a ventricular wall by a contractile tissue. The experiments have demonstrated the feasibility of this technique and the long-term adaptability and adequate electrophysiological properties of the Latissimus Dorsi flap transferred to a heterotopic position over the heart. Long-term biocompatible fatigue resistant muscle stimulation has become possible in experimental and clinical cases as a result of the development of specially designed electrodes and the use of a progressive sequential stimulation protocol to adapt the skeletal muscle to a cardiac support function. Autologous pericardium treated with glutaraldehyde was found to be a suitable material to close the ventricular cavity. Cardiomyoplasty with autologous skeletal muscle to restore ventricular contractility seems to be a valid alternative in addition to current methods of treatment for irreversible myocardial failure.

Cardiac assistance by atrial or ventricular cardiomyoplasty.

Dynamic cardiomyoplasty was conceived to enhance cardiac performance by assisting myocardial contraction. Technically, this procedure consists of placing a pedicled latissimus dorsi muscle flap around the heart and subsequent muscle electrostimulation in synchrony with ventricular systole. Three types of dynamic cardiomyoplasty can be considered. (1) Atrial or ventricular reinforcement is accomplished by wrapping the latissimus dorsi muscle flap around the heart to support hypokinetic or akinetic areas secondary to congenital or acquired diseases. The atrial reinforcement may be performed to improve atrial output after Fontan-type procedures. (2) Ventricular substitution is performed to replace a portion of the ventricular wall. Autologous pericardium is used to create a neoendocardium and facilitate hemostatic closure of the ventricle. The pedicled latissimus dorsi is then secured to replace the resected myocardium. (3) The two previous techniques of ventricular substitution and reinforcement are combined. This reconstructive procedure, which normalizes the ventricular geometrical shape, is particularly useful after extended cardiac resections, such as is done in treatment of large ventricular aneurysms, cardiac tumors, or echinococcal cyst formations. At present, improvement in ventricular function has been obtained in 12 patients at our institution. Preoperative severe cardiac dysfunction was present in all of these patients (New York Heart Association functional class III or IV). Postoperative echocardiography, multigated acquisition scan, and hemodynamic studies demonstrate an improvement in ventricular function and no impairment of ventricular compliance by the muscle flap. After a mean follow-up period of 18 months, all patients are in functional class I or II. We believe that dynamic cardiomyoplasty prolongs and improves the quality of life of patients suffering from severe chronic and irreversible myocardial dysfunction by improving ventricular contraction and limiting cardiac dilatation.

Biomechanical characteristics of unconditioned and conditioned latissimus dorsi muscles used for cardiocirculatory assistance.

An understanding of the biomechanical characteristics of striated skeletal muscles involved in cardiocirculatory assistance is a prerequisite to assess their efficacy and to evaluate their haemodynamic benefits. Six goats had their latissimus dorsi muscles evaluated by isometric strain gauge testing. Total tension, and both active and passive force development at different preloads were measured. The relationship between muscle impedance and starting length was also studied. Four additional muscles were submitted to isometric and isotonic strain gauge testing after 3 months of chronic electrical stimulation (Broussais Hospital protocol) with the contralateral muscle serving as a control. In isometric testing, both conditioned and unconditioned goat latissimus dorsi displayed a Frank-Starling length-tension curve, and a linear relationship between muscle impedance and starting length was found. Chronic stimulation preserved muscle mass and isometric force. Transformed muscles showed a mean 59% reduction of maximal shortening velocity; means (s.d.) residual shortening velocity at maximal work and power output was 0.17(0.07) m/s. The work and power output were both reduced 65% after stimulation, and the residual maximal power at optimal preload varied from approximately 7.7 and 9.6 W/kg. It is concluded that, following the Broussais protocol, the goat latissimus dorsi muscle retained mass and most of its isometric force-generating capacity, but lost significant work and power potential. The residual power output did not, however, preclude the possibility of a significant cardiocirculatory contribution, providing that the conditions for optimal energy transduction are adequately delineated.