[ Scientific Activities - Actividades Científicas ]
Cardiomyoplasty for chronic heart failure
Juan C. Chachques, MD, PhD, Alain Carpentier, MD, PhD
The Department of Cardiovascular Surgery
|Electrostimulation of the heart and skeletal muscles|
|Cardiomyoplasty: clinical experience|
Congestive cardiac failure is caused by a decrease in myocardial contractility due to
mechanical overload or by an initial defect in the myocardial fibre. The alteration in
diastolic function is inextricably linked with the pathophysiology of cardiac
insufficiency. Despite a widely varying and diverse aetiology of congestive cardiac
failure, the pathophysiology is to great extent constant. The predominant factor is the
alteration of myocardial contractility. This contractility defect causes an elevation of
the ventricular wall tension resulting in a progressive decline in the contractile state
of myocardial fibres.
The aim of cardiomyoplasty (CMP) is to restore or enhance the myocardial contractility using the patients latissimus dorsi muscle (LDM) which is wrapped around the ventricles and electrostimulated in synchrony with the contractions of the heart. This technique has been used world-wide in clinical medicine on more than 1500 patients of which 112 were treated at Broussais Hospital.
The biological support of this operation consists of chronic muscle electrostimulation which induces a physiological adaptation of skeletal muscle to cardiac work (« myocardisation of the LDM »). The metabolism of the rapid glycolytic fatigue-sensitive muscle fibers (type II) are transformed into slow oxydative fatigue-resistant muscle fibers (type I).
The electronic stimulation materials consist of an implantable Cardio-Myostimulator, muscle stimulation electrodes and systole detection electrodes which allow the synchronisation of muscle contractions to the heart beat. In order to imitate the duration of a systolic contraction, the skeletal muscle should be electrostimulated using train impulsions with a duration close to the ventricular ejection time span.
CMP is recommended to patiens suffering from severe chronic cardiac deficiency. The ischemic myocardial deficiency (patients presenting successive infarctions or one largely extended), as well as the dilated cardiomyopathies (generally of unknown origen) are considered to be indications for CMP. Hypertrophic or obstructive cardiomyopathies, however, are excluded for CMP (TABLE 1).
CRITERIA FOR CARDIOMYOPLASTY PATIENT SELECTION
The time to perform a CMP can be concluded from the postoperative results. The hemodynamic advantage of the CMP is only achieved after a delay of several weeks corresponding to the adaptation period of the LDM to its new cardiac assistance function. Therefore, the residual myocardial function has to be taken into account in patient selection.Top Surgical technique
An oblique incision is made in the postero-lateral region of the thorax in order to
dissect the left LDM. Its vascular-nervous pedicule, originating from the axillary region,
is carefully preserved. After implantation of two stimulation electrodes, a window is
created in the thoracic wall by partial resection of the second rib. The LDM is then
transferred through the window to the inside of the thorax.
The patient is placed in decubitus dorsal position. An extracorporeal circulation is technically not necessary during this type of surgery. A medial sternotomy allows to open the pericardium and expose the heart. The LDM is fixed around the ventricles. The 2 most frequent intraoperative complications during the heart wrapping are malignant ventricular arrhythmias and hemodynamic deterioration resulting from manipulation of the dilated heart. To avoid this complications, the LDM is passed posteriorly around the ventricles without lifting the heart. This maneuver is performed using two long curved hemostatic clamps, afterwards the LDM is fixed with interrupted sutures to the pericardium. The wrapping is completed by fixing the anterior part of the LDM to itself (in a pocket fashion) and to a pericardial flap, tailored from the right edge of the pericardiotomy. Care is taken to ensure that the heart is not subjected to excess tension or compression from the LDM wrapping.
Before the completion of the ventricular wrapping, one or two sensing electrodes are implanted into the right or left ventricular walls, to synchronise the muscle contractions to the ventricular systole. Sensing and impedance are verified to assure proper positioning. The stimulator is placed in an epigastric pocket and connected to the muscular and cardiac leads.
In the CMP technique, the LDM can serve as enhancement of the ventricular systole in ischemic or dilated cardiomyopathies, as well as partial myocardial replacement after resection of a voluminous anevrysm or an extensive tumour. In the latter cases a pericardial patch is used as interface between the LDM and the ventricular cavity.
The choice of the LDM in the CMP technique has been justified by the following anatomical and physiological conditions: 1) its proximity to the heart, 2) the extent of muscular mass with the possibility of intrathoracic transposition whilst keeping the vascular-nervous pedicule intact, 3) absence of important functional sequelae at the level of the superior limbs after removal of the LDM. The third condition has also been observed by plastic surgeons who frequently use the LDM to reconstruct the thoracic wall, the cervical region or the upper limb.
Cardiac and skeletal muscles differ in their structure and their
response to electrostimulation. The depolarisation of a single cell of the myocardium
induces an action potential which travels through the whole cardiac muscle which, in turn,
leads to an instantaneous contraction of atria and ventricles. Only one single impulsion
below a given threshold can start this process.
Skeletal muscle also shows electrophysiological differences. The amplitude and duration of the contractions can be influenced by stimulation parameters. The modulation of the amplitude and/or of the impulsion size modifies the number of motor units activated (spatial recruitment) whereas the number of impulsions and the duration between each impulsion modifies the excitation frequency of motor units (temporal recruitment). A train of impulsions produces, therefore, a contraction, variable in force, which is supported in time by an additional effect.
The electrical activation of skeletal muscles is known in other clinical applications: in the treatment of respiratory paralysis (stimulation of the diaphragm or more precisely the phrenic nerve); in colorectal surgery (surgical creation of a neosphincter using the gracilis muscle, electrostimulation of this muscle allows an efficient continence); in urology (vesicomyoplasty and neosphincter); in the correction of scoliosis (stimulation of the paravertebrae muscles); in the treatment of paraplegia (stimulation of inferior limb muscles); and in orthopedia (rehabilitation of the musculature after prolonged inactivation).
CMP improves cardiac performance by several mechanisms:
CMP leads to an increase in ventricular mass by adding a new contractile muscular wall which allows, in turn, to reestablish the ratio between the mass and the ventricular diameter in dilated cardiomyopathies.Place cardiomyoplasty
The surgical treatments actually proposed for severe cardiac deficiency unresponsive to medical treatment are:
Certain developed countries have benefited from the cardiac transplantation and
mechanical circulatory assistance programmes. Nevertheless, cardiac transplantation is
still limited in many countries because of legal, cultural and religious problems,
difficulties in follow-up, as well as the price and risk of immunosuppressive treatment.
Mechanical assist devices are also expensive, which reduces their development.
On the other hand, the insufficient number of organ donors does not face up to the needs of all cardiac transplantation patients. The number of patients on waiting lists also increase annually, as well as the waiting period. Therefore, it is logical to propose to these patients, with a high risk of mortality, other therapeutic possibilities.
CMP has the advantage of constituting a complete implantable cardiac assistance system which is entirely biocompatible. Recent progress in biology and skeletal muscle electrostimulation have demonstrated that the latter could transform the muscle resistant to fatigue and, hence, become an important source of circulatory assistance.
The biomechanical system is a combination of cardiac and plastic surgery with biomedical engineering. Its aim is to prolong and improve the quality of life of patients who suffer from severe chronic cardiac deficiency and who are unresponsive to medical treatment. In CMP, the musculature of the same subject is used which excludes the risk of rejection and, therefore, no immunosuppressive treatment is necessary. The clinical follow-up is simple since the function of the cardiomyostimulator is essentially checked. Long-term results are encouraging, particularly since the indications are more precisely identified.
The management of patients with end stage heart fallure is a daily
challenge in cardiac surgery. Cardiac transplantation and mechanical assist devices do not
cover all the needs.
Patient Population: Between 1985 and 1999, 112 patients aged 15 to 72 years (mean 51 years) were operated on in our Institution. All patients presented a severe cardiac deficiency refractory to maximal pharmacological therapy; 86 were in NYHA class III and 26 in class IV. Ejection fraction averaged 17%, EDLV volume 178 ± 31 ml/m2. The cause of heart failure was ischemia in 59 patients, dilated cardiomyopalhy in 46 patients and ventricular tumors in 7 patients. Associated pathology (pulmonary hypertension, diabetes...) was present in 60%. The technique has evolved from "open fixation" (58 patients), to "non-suture wrapping" (41 patients), to "mini-invasive technique" (13 patients). Two-stage operations in high risk patients with mitral valve insufficiency or severe arrhythmia were performed in 6 patients. Associaled procedures were necessary in 24 patients (CABG=14, valve=10).
Results: Hospital mortality was 53% between 1985-1987, 13% between 1988-1997, and 8% since the introduction of mini-invasive techniques. Actuarial survival at 10 years was 70% for preop class III patients and 28% for class IV patients. Average NYHA class was 3.3 preop and 1.4 postop. Nine patients required transplantation. Hemodynamic investigations in the survivors showed significant improvement in ejection fraction (21% to 31%) and cardiac index (1.9 to 2.8 L/mn/m2).
The clinical evaluation and the postoperative studies show that CMP is an efficient technique to assist chronic patients who suffer from severe cardiac deficiency. The technique allows a functional improvement of the patients of their capacity during exercise, as well as a decrease in medication. In operated patients a decrease was noted in deterioration of their state which would have required hospitalisation.
The quality of life of the patients, evaluated every six months postoperatively by questionnaire, significantly improved since most patients had increased their daily and social activities and 62% had started working again. The CMP results improved through experience, through rigorous patient selection, through progress in the operation technique, and through improved postoperative care. The post-operative course was often critical (30 % low cardiac output syndrome), particularly in ischemic etiology.
In conclusion: Cardiomyoplasty has been associated with better results due to technical improvements, the most significant being mini-invasive techniques, the latest the use of growth factors to enhance muscle vascularisation. Cardiac transplantation is technically feasible after a CMP. Risk factors have been identified resulting in more precise indications, a lower hospital mortality and a wider use of this operation.
Electrophysiological treatments associated with CMP
The patients who have been subjected to a CMP, suffering from an ischemic or severe idiopathic cardiomyopathy, present a great risk ventricular arrhythmias which is potentially responsable for the occurence of sudden death. At the same time, electrical and mechanical asynchronisms between the ventricles are frequently observed in these patients. In recent clinical cases, CMP has been associated with an implantable defibrillator or biventricular stimulation (multisite pacing). The positive results obtained foresee an important expansion of this associated techniques.
Video-assisted mini-invasive techniques
In cardiovascular surgery, the recent clinical experiences (in the case of coronary and valve surgery) have demonstrated the interest of using mini-invasive techniques. Fundamentally, the advantage for the patient is aesthetic, however, rehabilitation is much quicker and it avoids the risk of complications of a sternotomy. Since October 1997, thirteen CMPs have been carried out in our department using reduced access ways with very encouraging results.
Growth factors and cardiomyoplasty
The LDM which is fixed around the heart can cause cellular alterations due to the dissection, intrathoracic transposition and electrostimulation. Growth factors (agents which increase cell proliferation and induce cell migration) could have a beneficial effect on muscle fibres. In our department, we have started a research study to evaluate the action of growth factors on a CMP model: basic Fibroblast Growth Factor (bFGF), Vascular Endothelial Growth Factor (VEGF), as well as Heparin Sulphate (RGTA). The use of these factors improve the development of the collateral circulation between the heart, the LDM and the mediastin structures by stimulation of angiogenesis.
Cellular cardiomyoplasty is an approach to implant cells and grow new muscle fibers in
the damaged myocardium that potentially may contribute to the contractile performance of
Since cardiomyocytes cannot regenerate after ischemia, the injury is irreversible. Therefore, the aim of cellular cardiomyoplasty is the repair of injured myocardium by cell transplantation, either in ischemic or idiopathic cardiomyopathies. Two types of cells have mainly been used for this purpose:
1) Foetal cardiomyocytes, an approach which presents two major disadvantages: - the availability of embryonic (or foetal) tissue is limited.
- an immunosuppressive treatment is required after implantation of cardiomyocytes.
2) Autologous myoblasts obtained from skeletal muscles of the same individual. The satellite cells or myoblasts can be obtained in large quantities, furthermore the autologous implantation does not cause any immunological rejection problems.
Cellular cardiomyoplasty research is at a developping stage in our department. The main questions are how satellite cells integrate into myocardiac tissue and whether the cells can provide an improvement in contractile force.
Fig. 1: Cardiomyoplasty technique: the left latissimus dorsi muscle
(LDM) is transposed into the chest through a window created by
resecting the anterior segment of the 2nd rib (5 cm). The LDM is
then wrapped arround both ventricles. Sensing and pacing
electrodes are connected to an implantable cardiomyostimulator.