Centrifugal pumps and heparin-coated circuits in surgical treatment of giant cerebral aneurysms

Giant cerebral aneurysms may be untreatable by conventional neurosurgical techniques. Early attempts to use circulatory assistance and deep hypothermia were abandoned due to hemorrhagic complications. More recently, interest in circulatory support for complex neurosurgical procedures has been renewed. A consecutive series of 8 patients were operated on for giant cerebral aneurysms with the combined use of deep hypothermia. The protocol included careful preoperative cardiovascular assessment, perfect intraoperative synergy between neurosurgical and cardiac teams, minimally invasive peripheral vascular access including two femoral vein (21 F) and single arterial (17 F) femoral cannulation, use of total Carmeda coating on BioMedicus pumps in closed circuits, and reduced heparinization without Protamine reversal. All cerebral aneurysms were successfully treated through deep hypothermia (15-18 degrees C) as assessed by intraoperative fluoroscopic controls and Doppler vascular assessment. Mean circulatory support time was 174.2 +/- 29.6 min. Circulatory arrest period was 20 +/- 12 min. All patients survived and were extubated within 48 h. No major deficit was observed clinically or on postoperative CT scan. No hemorrhagic complications occurred (mean transfusions was 2.2 blood units). This work supports an extensive use of heparin-coated surfaces for complex circulatory assist techniques, either for cardiac or extra cardiac complex procedures.

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.

Rescue revascularization for acute coronary occlusion late after radiotherapy

Because radiation-induced coronary artery stenoses are frequently severe and located proximally, some patients are admitted in emergency. This report describes the case of a 47-year-old woman with radiation-induced stenosis of the left main coronary artery who presented with cardiac arrest during angiography. The patient was successfully treated using circulatory assistance and percutaneous transluminal coronary angioplasty as a bridge to coronary artery bypass grafting.

Study of left ventricular bypass using Wankel type semipulsatile blood pump

The influence of the Wankel type semipulsatile left ventricular assistance on hemodynamics was investigated with a computer simulation and an animal experiment. A simulation circuit was constructed to express the circulatory system. A current source was added to create a semipulsatile blood pump. The left and right ventricles were replaced by variable compliances. Left heart failure was simulated by decreasing the amount of compliance change of the left ventricle. Under the condition of heart failure when semipulsatile assist flow increased, the mean aortic pressure (AoP), tension time index (TTI), and diastolic pressure time index (DPTI) increased, and the cardiac output, pulse pressure (PP), and pulsatility indicator (PI) decreased. In an animal experiment, a Wankel type blood pump was used in a calf. With the increase of the assist flow, AoP curves became less pulsatile, and PP and PI decreased in accordance, which was predicted by the numerical simulation.

Aortic valve or root replacement with cryopreserved homograft for active infectious endocarditis

Active aortic endocarditis is a serious condition that carries a high mortality and morbidity. The aim of this study was to analyse results obtained from 24 patients who underwent aortic valve or root replacement with cryopreserved homograft for aortic endocarditis. Eleven patients had native valve endocarditis, and 13 had prosthetic valve endocarditis. The mean age was 47.7 years: there were seven women and 17 men. Causative organisms were staphylococci (12), streptococci (four), serratia (one), candida (one), pneumococci (one), while no organisms were isolated in the remaining five patients. Complete reconstruction of the aortic annulus with homograft conduits was necessary in 20 patients (six total root and 14 mini-root). Infracoronary homograft aortic valve replacement was performed in the remaining patients. One patient died 1 day after the operation from ventricular failure, and two others died after 4 and 6 months as a result of arrhythmia. One patient died of recurrent endocarditis 1 year after surgery. The actuarial survival rate at 3 years was 83.4%. All survivors are symptom-free, with no evidence of recurrent endocarditis. Doppler echocardiography showed minimal aortic regurgitation in four patients.

Value of Doppler echocardiography in the detection of low-grade rejections after cardiac transplantation

Modifications of the diastolic parameters pressure half-time (PHT) and isovolumic relaxation time (IVRT), recorded using cardiac Doppler echocardiography (CDE), were studied in 23 heart transplant recipients and compared to the results of 345 endomyocardial biopsies (EMB) performed on the same day. Two different protocols, analyzing respectively (1) a decrease of 20% or more in IVRT and/or PHT with respect to the mean and (2) a decrease of 20% or more in IVRT and/ or PHT with respect to its preceding value, were used to evaluate the efficiency of CDE in diagnosing mild and moderate rejections. When a mild rejection was detected by EMB, a statistically significant decrease was found in the average CDE parameter values of the patient population. However, these variations were weak and did not differ from the spontaneous variations observed in each patient in the absence of rejection. Thus, it is not surprising that the sensitivity of CDE in the detection of mild rejections was very low (45%) using the most sensitive protocol (variations of the parameters from their preceding value). We conclude that CDE alone does not seem to be sufficient to perform the noninvasive diagnosis of low-grade rejections and must be complemented by other noninvasive methods.

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.

Type A dissection of the thoracic aorta: use of MR imaging for long-term follow-up

PURPOSE

To evaluate routine magnetic resonance (MR) imaging for long-term follow-up in patients who undergo surgery for type A aortic dissection.

MATERIALS AND METHODS

Ninety-two MR examinations were performed in 36 patients. Standard spin-echo images were obtained with electrocardiographic gating (n = 92) and rapid images with a fast low-angle shot sequence and intravenous administration of gadopentetate dimeglumine (n = 25). All segments of the native thoracic aorta were evaluated. Anastomoses of the prosthesis and periprosthetic hematoma were carefully analyzed.

RESULTS

Of 22 complications that occurred in 18 patients, 18 were diagnosed at MR imaging (nine false aneurysms and nine aneurysms distal to the graft). Nine patients underwent reoperation. The findings at MR imaging correlated with those at surgery.

CONCLUSION

Routine follow-up with MR imaging should improve long-term survival in patients who survive emergency surgical repair of type A aortic dissection.

Experimental use of a semipulsatile rotary blood pump for cardiopulmonary bypass

We tested our valveless pulsatile rotary blood pump (CORA) extensively in animals, but only as a temporary implantable left ventricular assist device. To expand the scope of future clinical applications, we recently undertook experiments to assess the feasibility of our pump for use in a standard cardiopulmonary bypass circuit. We conducted 4 experiments in adult sheep (body weight, 40 kg): 2 with CORA and 2 with the BioMedicus pump (BP) for comparison. In all experiments, a currently used extracorporeal circuit with reservoir, filter, and membrane oxygenator (Sorin monolith) was installed, and open chest extracorporeal circulation (ECC) was performed for 6 h. Hemodynamic performance and hemolysis were evaluated. CORA provided semipulsatile systemic flow at a level comparable to that of the BP. Free plasma hemoglobin levels were slightly higher with CORA, but the decrease in platelet count was the same for both devices. There was no significant difference in the extent of blood trauma. We conclude that CORA could be successfully used for ECC with an oxygenator. Negative pressure can be prevented by our specially designed control system.

Clinical situations and results of cardiopulmonary support by peripheral access for resuscitation and recovery

Use of cardiopulmonary support (CPS) by peripheral access with a membrane oxygenator has made considerable progress as a result of the development of centrifugal pumps, percutaneous cannulation, and preheparinized circuits. We have used CPS for resuscitation in 3 cases, for recovery after cardiotomy in 6 cases (myocardial insufficiency, 4; pulmonary arterial hypertension, 1; respiratory insufficiency, 1), and after heart transplantation in 1 case. Of these 10 patients, 3 died during CPS, 5 were successfully weaned, and 2 underwent heart transplantation. Use of CPS is expanding for emergency cardiac assistance. Installation is simple and rapid. It allows recovery of organs pending more invasive and costly techniques.

[Repeated heart valve replacements: prognosis and results]

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.

Development of the Marseilles pulsatile rotary blood pump for permanent implantable left ventricular assistance

We have developed a low-speed, double-lobed hypocycloidal pump that furnishes a pulsatile flow without valves. The pump is coupled to a specially designed electric motor. The motor/pump unit is totally implantable and has been extensively tested in vitro and in vivo in animals. Because this pump is volumetric, it is necessary to control speed precisely to avoid overpumping. Our control system, which is based on analysis of the motor current wave form, can detect and prevent negative pressures before they occur. The physical properties and hemocompatibility of several construction materials have been studied to determine their suitability for clinical use. These materials include a graphite substrate, titanium nitrate surface coating, boric carbon, and amorphous diamond. The pumps currently being tested are made of titanium, but clinical versions will be made of composite materials selected from this preliminary study. In vivo testing of this pump confirmed its good hemodynamic performance, low hemolysis rate, and biocompatibility (i.e., low heat, noise, and vibration levels). Animal experiments were terminated after 15 days because of mechanical failure related to the accumulation of blood components on moving parts. A new pump in which the mechanism is completely sealed from the blood flow has been designed and will soon be tested. If this sealed design is effective, the pump should be ready for use as a permanent implantable ventricular assistance device.

Right-sided aortic arch: surgical treatment of an aneurysm arising from a Kommerell's diverticulum and extending to the descending thoracic aorta with an aberrant left subclavian artery

The case of a 44-year-old black man who presented with severe dysphagia, cough and chest pain caused by a 12-cm aneurysm developing from a Kommerell's diverticulum at the origin of an aberrant retro-oesophageal left subclavian artery is reported. The aortic arch and descending thoracic aorta were right sided. Diagnosis was established before operation by computed tomography, magnetic resonance imaging and arteriography. The aneurysm extended a considerable distance down the descending aorta and therefore the risk of postoperative paraplegia was considered to be high. Accordingly selective arteriography was performed to locate the Adamkievicz's artery which arose only 2 cm below the end of the aneurysm. Resection grafting of the aneurysm including the upper third of the descending aorta via right thoractomy was performed. The patient made an uneventful recovery and was discharged 20 days later. This case appears to be the first successful operation for this pathology.

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.

Diagnosis of prosthetic heart valve thrombosis. The respective values of transthoracic and transoesophageal Doppler echocardiography

Early diagnosis of acute prosthetic thrombosis remains a challenge. In 20 patients with 23 thrombosed cardiac valves, we evaluated the respective value of transthoracic (TTE) and transoesophageal (TEE) Doppler echocardiography. According to the presence or absence of prosthetic obstruction by continuous-wave Doppler, prostheses were separated into two groups. Group 1 included nine thrombosed prostheses (8 mitral, 1 aortic) with severe obstruction. All patients presented with severe symptoms of heart failure. Transthoracic Doppler echocardiography allowed immediate diagnosis of prosthetic thrombosis, even in critically ill patients, showing (1) eccentric transprosthetic colour flow jets in all eight mitral prostheses, (2) severe obstruction on Doppler examination (mean gradient = 18 to 36 mmHg in eight mitral prostheses, and 69 mmHg in one aortic valve), and (3) direct echocardiographic evidence of thrombosis (i.e. thrombus or abnormal disc or leaflet motion) in four patients. All nine patients were immediately treated by surgery (n = 8) or fibrinolysis (n = 1) on the basis of TTE results only. TEE allowed better visualization of thrombus and restricted leaflet or disc motion, but had little influence on patient management. Group 2 included 14 thrombosed prostheses (10 mitral, 4 aortic) with mild or absent obstruction. In three patients with massive mitral prosthetic thrombosis, an associated minimal thrombosis of a prosthetic aortic valve was found at surgery, but was detected neither by TTE, nor by TEE. The 11 remaining patients with isolated partial mitral (n = 10) or aortic (n = 1) thrombosis. Clinical presentation was fever, cerebral embolism, or mild dyspnoea, but no heart failure. TTE was normal in all.(ABSTRACT TRUNCATED AT 250 WORDS)

[Plasma glycosylated residues demonstrated by proton NMR spectroscopy. Value in the detection of heart graft rejection]

In conjunction with biopsy and Doppler studies, we analysed by high resolution proton NMR spectroscopy the blood plasma of 22 heart transplant recipients. There was a significant variation in the glycosylated residues of proteins with the development of acute cardiac rejection. A more extensive study is underway to assess the sensitivity and specificity of this approach for the early diagnosis of acute cardiac rejection.

[Right intra-atrial extension of hydatid cyst mimicking cardiac thrombosis. Apropos of a case]

The authors describe an unusual case of hydatid cyst inserted in the inferior vena cava and extending into the right atrium. The transoesoesophageal echocardiographic appearances were similar to those of a thrombus: the tumour was very mobile, echogenic, polylobular with a cord-like pedicle in the inferior vena cava. The pathological examination revealed a ruptured hydatid cyst. The mass and its insertion were not visible on CT scan or cavography. Transoesophageal echocardiography would therefore seem to be a very useful diagnostic method for tumours arising in the inferior vena cava and extending into the right atrium.

First significant animal survival with a Wankel-type left ventricular assist device

The authors' laboratory is developing a device for heterotopic left ventricular assistance. It consists of a titanium Wankel-type rotary pump, driven by an hermetically sealed electric motor. In our animal experiments, the motor-pump unit was implanted in the thoracic wall. The pump was connected to the left heart chambers by left atrial cannulation, and to the descending aorta. The motor was connected to the power and control unit by an electric wire through the skin. In this report, the authors describe the first significant animal survival with this system. Laboratory results were encouraging for hemolysis. The pump failed at 13 days due to a deposit of fibrin and blood cells in the gear housing. This problem was not surprising since similar events have been encountered with centrifugal devices. However, further design improvements should allow longer animal survival and clinical application.

Control of pulsatile rotary pumps without pressure sensors

When ventricular assistance is achieved with a volumetric pump driven by an electric actuator, overpumping can cause venous collapse. To prevent this problem, pump speed must be monitored and controlled. The authors developed a regulatory system based on the current intensity signal from the electric motor. This signal is processed and compared with predicted values calculated according to a mathematical model at the beginning of each ejection phase. If a difference is detected, pump speed is adequately adjusted. The great advantage of this system is elimination of the need for an implantable pressure sensor. It requires a simple and ubiquitous electronic component, i.e., a resistor, that can be easily integrated into the motor control circuit and does not require calibration.

[Surgical treatment of right-sided infective endocarditis]

Between 1980 and 1989, 8 patients (5 men, 3 women; mean age 30 years) were operated upon in our department of right-sided infective endocarditis. Six patients were heroin addicts and among these 3 were HIV positive and 2 had confirmed AIDS. The most frequently encountered microorganisms (6 cases) were staphylococci. It was decided to operate because of persistent infection and haemodynamic deterioration. The infection involved the pulmonary valve in only 1 of the 8 patients. Surgery was performed during the acute phase in 5 patients and was conservative in 6 patients, consisting of excision of the vegetations or valvulectomy combined or not with valvuloplasty. A high mortality rate (3/8 cases) was observed only among patients operated upon in the acute phase. This may be due to the underlying immunodeficiency and poor haemodynamic state of these patients. Among survivors, the long-term results were excellent, with no recurrent endocarditis and no death, and with only one subsequent operation, 4 years after the first one, for residual tricuspic valve regurgitation. This study shows that patients with right-sided infective endocarditis should be operated upon outside the acute phase of the disease and as soon as complications appear, and that surgery should preferably be conservative.

Another way of pumping blood with a rotary but noncentrifugal pump for an artificial heart

This article describes an alternative mode of pumping blood inside the body. The device is a non centrifugal, valveless, low speed rotary pump, electrically powered, based on Wankel engine principle. The authors developed an implantable electrical actuator resulting in a compact, sealed motor-pump unit with electrical and magnetic components insulated from fluids. The results in the flow curve and in the pumping action show some common points but also some basic differences compared to classical pulsatile pumps or centrifugal pumps. The blood coming from the atrium follows a continuous movement without any stop flow but with variations creating pulsatility. Ejection and filling of the pump are simultaneous. It is always an active filling. Hydraulic efficiency depends on clearance in the pumping chamber and outlet port pressure. A 60 cc device allows flows up to 8-9 liters. The implantable motor is cyclindrical in shape, has a moderate weight (490 grams) and presents a good efficiency (32% for a rotary speed of 90 rpm against a mean aortic pressure of 150 mm of Hg). The authors conclude that their device could be proposed after further experimental studies, as an LVAD for shortterm assistance with a good promise for permanent application.

Thromboembolytic complications during circulatory assistance with a centrifugal pump in patients with valvular prostheses

This article describes two patients with artificial heart valves who suffered thromboembolytic complications during circulatory assistance using a Biomedicus centrifugal pump. The first case involved a 25-year-old man who presented acute blockage of a mechanical aortic valve. Emergency surgery was performed to replace this valve with a bioprosthesis. Postoperatively the patient developed severe left heart insufficiency and a Biomedicus centrifugal pump was placed between the left atrium and the ascending aorta. After 3 days of total left ventricular assistance, weaning was started and successfully completed with explanation on the 5th day. Two days later the patient died of multiple coronary embolism with thrombosis of the valve. The second case involved a 30-year-old man. Six months before, he underwent surgical procedure with placement of Bio-prosthesis for dissecting aortic aneurysm due to annuloectasia. Upon admission for terminal dilated myocardiopathy, the patient was in kidney failure almost requiring dialysis. Because of this patient's size (Marfan syndrome), no donor heart was immediately available and left circulatory assistance with a Biomedicus pump had to be initiated. The patient lived without mechanical ventilation, in good clinical condition until day 23 when he presented acute right heart failure due to extensive valvular and coronary thrombosis. From these two cases, several important comments can be made about anticoagulation therapy, partial unloading of left ventricle, or need for biventricular assistance, and efficiency of centrifugal devices in these clinical applications.

[Approaching the posterior wall of the aortic arch. Temporary division of the innominate artery]

Two cases of wound affecting the posterior wall of the aortic arch are reported. One wound occurred during mediastinoscopy, the other was caused by a bullet. During surgery under extracorporeal circulation, the approach and repair of the wounds was greatly facilitated by temporary division of the innominate artery: the ascending and horizontal portions of the aorta could be tilted to the left, giving a very satisfactory access to the posterior wall of the arch. The innominate artery was easily repaired, without neurological complications. The authors insist on the convenience of this technique to approach not only the aortic arch but also various mediastinal organs, such as the tracheal bifurcation, the right branch of the pulmonary artery and the roof of the left atrium.

[18 and one-half years' survival after cardiac graft. Clinical course and anatomical findings]

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.

[Use of elastic laces with attached needle in coronary surgery]

Using elastic laces with attached needle for surgery of the coronary arteries ensures adequate exposure, presentation and drying up of these vessels during distal anastomosis.