Haemocompatibility and biological course of carbonaceous composites for cardiovascular devices.

A new class of carbonaceous composites has been developed for cardiovascular devices. The aim of the present study, performed in dogs, was to test the immediate blood compatibility of these materials when inserted within the vascular bed. Biocompatibility studies were performed on vascular cylinders (6 mm i.d.) and intra-atrial implants. The specimens were examined sequentially by SEM at 10, 20, 30, 180 s and 10 min after re-establishment of the blood flow. Patency of the vascular cylinders was tested during the second and third postoperative month by Doppler ultrasound investigations; specimens were examined by light and electron microscopy (scanning and transmission) at 15, 60 and 110 d following implantation. As early as 10 s after re-establishment of the blood flow platelet adhesion and a limited fibrin mesh with few erythrocytes developed on the material. Platelet aggregates were only observed on intravenous implants. Except in the case of the intravenous insert, no thrombosis developed at the contact of intra-arterial or intracardiac implants. After 15 d it was completely covered by a fibrocellular layer (3-5 cells thick) consisting of large myofibroblasts with microfilaments, newly synthesized collagen and elastin. Endothelial-like cells developed and were completed 2 mnth after implantation. However, deposits present inside and outside the fibrocytic cells of the newly developed tissue were observed corresponding to carbon peaks as indicated by wavelength dispersive X-ray microanalysis.

Haemocompatibility of Ti6A14V alloy.

Ti6A14V alloy has been mainly used as a biomaterial in the orthopaedic field. The present study describes the surface state of the Ti6A14V material and evaluates its in vitro haemocompatibility in terms of protein adsorption, platelet retention and haemolysis. The behaviour of the Ti6A14V alloy towards albumin and fibrinogen was compared to that of a reference medical-grade elastomer. The platelet retention test gave better results than those achieved with the elastomer. The haemolysis percentage of the alloy was almost zero. These results indicate that the Ti6A14V alloy is well tolerated by blood.

Blood haemolysis by ceramics.

Ceramics are more and more frequently under consideration for construction of blood-contacting devices, i.e. cardiac valves or cardiac assist devices. This study evaluated the haemolysis eventually initiated in vitro by ceramic powders (Al2O3, ZrO2/Y2O3, AlN, B4C, BN, SiC, Si3 N4, TiB2, TiN, TiC), graphite and diamond. The chemical composition of the powders was studied by X-ray microprobe and various other methods, and BET specific areas were determined. The haemolysis was almost zero for all powders, except AlN which showed slight haemolysis and TiB2 which had high haemolytic power.

TiN coating: surface characterization and haemocompatibility.

The left ventricular assist device under consideration is based on the principle of the Maillard-Wankel rotary pump. The construction materials must meet stringent requirements. Titanium nitride was chosen for its surface properties and graphite for its bulk characteristics. The purpose of this study was to characterize the chemical vapour deposition titanium nitride coating via morphology, roughness, crystallinity, chemical composition, to report and discuss the results of in vitro haemocompatibility tests (protein adsorption, platelet retention, haemolysis) and to discuss physico-chemical and biological results. This chemical vapour deposition titanium nitride coating is well tolerated by the blood despite its surface irregularities, and appears as a good candidate material after improvements.

Late results of double-valve replacement with biologic or mechanical prostheses.

BACKGROUND: We previously showed that the risk of reoperation for structural degeneration of bioprostheses was higher in cases involving patients older than 65 years (p = 0.003) and double-valve replacement (p = 0.02). The purpose of this study was to compare late outcome of mitral-aortic valve replacement using bioprostheses or mechanical valves. METHODS: The bioprosthesis group included all mainland France residents (n = 48) between 55 and 65 years old operated on between 1980 and 1995 for mitral-aortic valve replacement using bioprostheses. The mechanical valve group was obtained by matching each of these patients with a patient operated on using mechanical valves at approximately the same time during the study. RESULTS: In the bioprosthesis group, 10-year survival was 45%+/-8% versus 62%+/-7% in the mechanical valve group (not significant). The linearized reoperation rate was 6.8 per patient-year versus 1.1 per patient-year (p = 0.001), and the linearized reoperative mortality rate was 1.8 per patient-year and 0.7 per patient-year (not significant), respectively. CONCLUSIONS: The reoperative mortality risk after mitral-aortic valve replacement using two bioprostheses does not significantly decrease overall survival after age 65 years.

Cora valveless pulsatile rotary pump: new design and control.

For decades, research for developing a totally implantable artificial ventricle has been carried on. For 4 to 5 years, two devices have been investigated clinically. For many years, we have studied a rotary (but not centrifugal) pump that furnishes pulsatile flow without a valve and does not need external venting or a compliance chamber. It is a hypocycloidal pump based on the principle of the Maillard-Wankel rotary compressor. Currently made of titanium, it is activated by an electrical brushless direct-current motor. The motor-pump unit is totally sealed and implantable, without noise or vibration. This pump was implanted as a left ventricular assist device in calves. The midterm experiments showed good hemodynamic function. The hemolysis was low, but serious problems were encountered: blood components collecting on the gear mechanism inside the rotor jammed the pump. We therefore redesigned the pump to seal the gear mechanism. We used a double system to seal the open end of the rotor cavity with components polished to superfine optical quality. In addition, we developed a control system based on the study of the predicted shape of the motor current. The new design is now underway. We hope to start chronic experiments again in a few months. If the problem of sealing the bearing could be solved, the Cora ventricle could be used as permanent totally implantable left ventricular assist device.

Papillary muscle rupture caused by bacterial endocarditis: role of transesophageal echocardiography.

A 22-year-old man had severe pulmonary congestion and required mechanical ventilation. Endocarditis was suspected because a 2/6 systolic murmur was heard at the apex and because Osler nodes were present. Transthoracic and transesophageal echocardiography allowed correct diagnosis of papillary muscle rupture causing massive mitral regurgitation. To our knowledge, this is the first reported case of papillary muscle rupture caused by bacterial endocarditis diagnosed by transthoracic and transesophageal echocardiography.

Multiple valve replacement increases the risk of reoperation for structural degeneration of bioprostheses.

BACKGROUND AND AIM OF THE STUDY: The study aim was to analyze the results of reoperations for structural degeneration of bioprostheses, and to define a high-risk population for reoperative procedures. METHODS: A series of 524 consecutive patients who had undergone a first reoperative replacement for a failed bioprosthesis between 1978 and 1998 was reviewed retrospectively. The reoperative procedure comprised 363 single valve replacements, and 161 multiple valve replacements. During the original procedure, 648 bioprostheses had been implanted in the mitral (n = 403), aortic (n = 220) and tricuspid (n = 25) positions. RESULTS: The mean interval between the original procedure and reoperation was 8.8 +/- 3.3 years. Tissue valve failure was revealed by recurrence of cardiac insufficiency in 70% of cases. The overall early mortality rate was 8%, but early mortality rates for elective single mitral and aortic reoperative valve replacements were only 3.9% and 4%, respectively. Early mortality following reoperation for single and multiple valve replacement was 6.0% and 12.4% respectively (p = 0.02). Other significant multivariable predictors for early mortality were old age (p = 0.003), NYHA functional class (p = 0.007), presence of ascites (p = 0.02) and reoperation performed before 1988 (p = 0.013). CONCLUSIONS: The risk of reoperation for structural degeneration of bioprostheses is acceptable for elective single reoperative valve replacement as opposed to multiple reoperative valve replacement. This may limit the use of bioprostheses during the original procedure when multiple valve replacement is required.

Circulatory assist techniques after cardiomyoplasty. Determinants for clinical outcome and later consequences.

Cardiomyoplasty, in spite of recent improvements, remains a high risk operation. The early postoperative period is sometimes very critical, even for patients selected from preoperative New York Heart Association functional class IV. During the surgical period, poor hemodynamics may be responsible for early death, as well as influence latissimus dorsi muscle long-term viability. Circulatory assist, including pharmacologic support with enoximone, intraaortic balloon counterpulsation (IABP), and ventricular assist devices (VAD), may be needed. From February, 1993 to September, 1994, 14 clinical dynamic cardiomyoplasty procedures were performed using the Medtronic (Minneapolis, MN) system at Hôpital La Timone, Marseille, France. Eight patients suffered from early and severe postoperative heart failure. Enoximone was used in three patients and IABP in five patients. Two days after cardiomyoplasty, one of the IABP patients required an implantable left VAD (Thermocardio Systems, Woburn, MA) as a bridge to cardiac transplantation. Overall hospital mortality was 7%. The authors studied the preoperative clinical data and surgical techniques to find specific risk factors that could have influenced postoperative events. Another aim of this study was to evaluate long-term benefits in these particular patients. Results showed that cardiomyoplasty patients may require complex means to overcome postoperative hemodynamic failure, but without necessarily poor long-term results. This should be an important step in improving future patient selection.

Control of a rotary pulsatile cardiac assist pump driven by an electric motor without a pressure sensor to avoid collapse of the pump inlet.

Our ventricular assist device uses a valveless volumetric pump operating on the Maillard-Wankel rotary principle. It is driven by an electric motor and provides a semi pulsatile flow. At each cycle, blood is actively aspirated into the device, and overpumping results in collapse at the pump inlet. To prevent overpumping, it is necessary to ensure that pump intake does not exceed venous return. Poor long-term reliability rules out the use of current implantable pressure sensors for this purpose. To resolve this problem, we have developed a method of control based on monitoring of the intensity of electric current consumed by the motor. The method consists of real time monitoring of current intensity at the beginning of each pump cycle. A sudden change in intensity indicates underfilling, and motor speed is reduced to prevent collapse. The current consumed by the motor also depends on the afterload, but the form of the signal remains the same when afterload changes. After demonstrating the feasibility of this technique in a simulator, we are now testing it in animals. We were able to detect and prevent collapse due to overpumping by the cardiac assist device. This system also enables us to know the maximum possible assistance and to thus adapt assistance to the user.

Hemocompatibility of titanium nitride.

The left ventricular assist device is based on the principle of the Maillard-Wenkel rotative pump. The materials which make up the pump must present particular mechanical, tribological, thermal and chemical properties. Titanium nitride (TiN) because of its surface properties and graphite because of its bulk characteristics have been chosen. The present study evaluated the in vitro hemocompatibility of TiN coating deposited by the chemical vapor deposition process. Protein adsorption, platelet retention and hemolysis tests have been carried out. In spite of some disparities, the TiN behavior towards albumin and fibrinogen is interesting, compared with the one of a reference medical grade elastomer. The platelet retention test gives similar results as those achieved with the same elastomer. The hemolysis percentage is near to zero. TiN shows interesting characteristics, as far as mechanical and tribological problems are concerned, and presents very encouraging blood tolerability properties.

A new model to test platelet adhesion under dynamic conditions. Application to the evaluation of a titanium nitride coating.

In order to evaluate under dynamic circumstances the in vitro platelet adhesion induced by rigid materials such as ceramic coatings deposited on selected substrates, a new model simulating a tube has been designed. In vitro platelet adhesion was assessed with this new model: the material was titanium nitride (TiN) deposited on Ti6A14V (TA6V) titanium alloy by a physical vapor deposition (PVD) process. The results were compared to those obtained with complete titanium carbide (TiC) graphite tubes coated with TiN by a chemical vapor deposition (CVD) process. The difference observed (less than 25%) in favour of the new system, could be due to the better surface state of the construction materials of this system. In fact it is a systemic error. However TiN confirms its good performance as a blood-contacting biomaterial.

Biological evaluation of mechanical circulatory support systems in calves.

Data from animal experiments with mechanical circulatory support systems (MCSS) performed in Groningen and Marseille over the past years were used to obtain normal values of hematological, coagulation, rheological and blood chemistry parameters in calves. These parameters were divided between two groups: a limited number of parameters necessary to assess biocompatibility properties of MCSS quickly and a more extensive number of parameters suitable for more detailed biological evaluation of blood pumps. All applied tests can be examined in calf blood as well as in human blood. Parameters were selected on clinical relevance and usefulness for standardization procedures. The obtained data were compared with normal values in human beings derived from the literature.

[Mitral valve replacement with bioprosthesis in children]. / Remplacement valvulaire mitral par bioprothèse chez l'enfant.

Forty seven bioprostheses were used for mitral valve replacement between January 1975 and June 1980, with no operative mortality, in children under 19 years of age. This study was undertaken to evaluate the medium and longterm outcome of 43 patients followed up for at least 2 years. The late mortality was higher in children under 13 years of age (11.1% per patient/year) than in older children (3% per patient/year). The incidence of reoperation for deterioration of the bioprosthesis was 5,5% per patient/year. The actuarial longevity of bioprostheses without any complications was 48 +/- 16% at 5 years. After a review of the literature, the authors discuss their present therapeutic attitude: whenever possible, mitral valvuloplasty is the operation of choice, but when valve replacement is necessary, two criteria must be considered: the age of the patient and conditions of follow up. If medical follow-up facilities are good: mechanical prostheses are preferred in patients under 13 years of age: after puberty especially in girls, the bioprosthesis is the valve of choice. If medical follow-up facilities are poor: the valve of choice is a bioprosthesis at all ages because of the risk of thromboembolism and the relatively slow clinical aggravation in cases of bioprosthetic deterioration.

[Compression of the right pulmonary artery by a dissecting aneurysm of the ascending aorta. Apropos of a case occurring long after aortic valve replacement]. / Compression de l'artère pulmonaire droite par un anévrysme disséquant de l'aorte ascendante. A propos d'un cas survenu à distance d'un remplacement valvulaire aortique.

The authors report the case of a dissecting aneurysm of the ascending aorta compressing the right pulmonary artery in a 62 year old man, 6 years after aortic valve replacement. The clinical presentation was that of pulmonary embolism. The diagnosis was confirmed by angiopneumography and CT scanning. The ascending aorta was successfully replaced with a Dacron prosthesis. One other case was found in a review of the literature. After discussing the predisposing factors of aortic dissection during cardiac surgery, the authors underline the diagnostic value of CT scanning in cases of suspected aneurysms of the thoracic aorta.

[Repeated heart valve replacements: prognosis and results]. / Remplacements valvulaires itératifs; pronostic et résultats.

In order to determine the prognosis of reoperation for valvular replacement, we reviewed the results of a consecutive series of 124 patients operated in the department between 1974 and 1992 (163 multi redo operations). There were 69 women and 55 men, with a mean age 48 years; 77% of the patients were in functional class III or IV. Operations were performed as an emergency in 30% of cases. Endocarditis was found in 24% of cases and was an important risk factor in this content. The main indications for reoperation were periprosthetic leakage in 28.8% of cases and failure of bioprostheses in 23.7%. The valvular replacement was simple in 61%, double in 32% and triple in 7% of cases. An associated procedure was necessary in 27% of cases. Mechanical devices were implanted in 62.3% of cases. Peroperative mortality was 3% and hospital mortality, mainly from cardiac causes, was 21.7% for the second, 20% for the third and 55.6% for the fourth reoperations. Operative mortality was dependent on the number or reoperations, functional class, emergency surgery, duration of bypass and cross-clamping time. Four per cent of patients were lost to follow-up and 30 patients died secondarily. The actuarial survival rate was 52% at 5 years and 33% at 10 years, actuarial survival rate without valvular complication was 41% at 5 years and 19% at 10 years but the functional results remained good with over 90% of patients in functional class I or II at the end of follow-up.

[Atrioventricular "sequential" stimulation by implantable "bifocal" stimulator]. / La stimulation "séquentielle" auriculo-ventriculaire par stimulateur "bifocal" implantable

The "bifocal pacemaker achieves a sequential" stimulation which reproduces the physiological atrio-ventricular sequence. This type of stimulation has the advantages of atrial stimulation without the disadvantages of being inefficient when an atrio-ventricular block exists or supervenes. The pacemaker was used by the endocavity route in 12 patients. The indications included a disease of the sinus node (8 cases), supra-ventricular arrhythmias associated to conduction disorders (3 cases) and a cardiomyopathy with conduction disorders (1 case). The preliminary results were appraised after two to twenty four months. One displacement of the ventricular electrode was noted. On the other hand no displacement of the atrial electrode was reported. One battery was worn out after 19 months. The "bifocal" pacemaker was efficient in the treatment of symptoms which justified its implantation. Or particular interest were the results obtained in patients with no supraventricular arrhythmias. This pacemaker may be of use: 1) in the disease of the sinus node, in particular in the tachycardia-bradycardia syndrome; 2) in supraventricular arrhythmias associated to paroxystic conduction disorders; 3)in patients with an alteration of the myocardial function and for whom the atrial contribution to cardiac output is essential.

[The mitral apparatus and surgery of sub-valvular aortic stenosis]. / L'appareil mitral et la chirurgie des sténoses aortiques sous-valvulaires

The authors present three eases of subvalvular aortic stenosis caused by an abnormality of the mitral valve mechanism which required placement of a prosthetic valve. They describe the types of mitral valve abnormality which are reported in the literature to have caused obstruction to the aortic outflow tract. They analyse the criteria for diagnosis of this condition, and the surgical treatment. The placement of a prosthetic mitral valve does not always remove the obstruction to the aortic outflow, especially if there is an abnormality in the position of the mitral ring.

[18 and one-half years' survival after cardiac graft. Clinical course and anatomical findings]. / Survie de 18 ans et demi après greffe cardiaque. Evolution clinique et constatations anatomiques.

Operated upon in November, 1968, the last survivor of heart transplant recipients in those times has died on May 11, 1987, having survived 18 years and 6 months. The active life of this patient, however, was marred by episodes of graft rejection during the first post-operative years and by various incidents. It was mainly the complications of the immunosuppressive treatment that hampered his activities (osteoporosis) and provoked his death. Post-mortem examination confirmed that the heart was in good condition, found an active bronchial epithelioma and revealed iatrogenic lesions, namely adenomas, adenocarcinoma of the kidney and "regenerative" nodular hyperplasia of the liver with portal hypertension. Such lesions are observed in patients under long-term treatment with immunosuppressants. A "sleep apnoea" syndrome might have accounted for the formation of pulmonary hypertension lesions. The authors wish to pay their respects to this man who devoted himself to the service of other men.

[Reintervention on heart valve prostheses. Apropos of 78 cases]. / Les réinterventions sur prothèses valvulaires cardiaques. A propos de 78 observations.

78 patients with one or more prosthetic heart valves were reoperated on between 1972 and 1978, and comprised 12% of the work load of valvular surgery. There were two postoperative periods in which the incidence of reoperation was high: the first year, 38%, and the period between the 5th and the 8th year, 41%. The main causes of reoperation could be divided into two groups: those common to all valves with paravalvular leaks (25%), endocarditis (12%) being the principal causes, and those associated with particular valves: deterioration of Beall prosthesis 33%, and thrombosis mainly affecting the Bjork and Beall prostheses (25%). The operative mortality was 12%. The fact that urgent operation is required in severe cases is underlined. In the light of these results, the surgical indications of reoperation should be discussed at an earlier stage. These indications are based essentially on the clinical condition of the patient and objective confirmation by further investigation should not delay the operation, which, in our experience, has never been unnecessary.