Fetal cardiac bypass using an in-line axial flow pump to minimize extracorporeal surface and avoid priming volume

BACKGROUND

Progressive metabolic acidosis, hypoxia, and hypercarbia develop rapidly after fetal cardiac bypass mainly as a result of an increase in placental vascular resistance and a decrease in placental blood flow. A number of factors including fetal stress, priming substances, and extracorporeal surfaces have been identified as possible stimuli causing this placental dysfunction. The purpose of this study was to examine the effects of avoiding priming volume and minimizing extracorporeal surface area on placental hemodynamics and function.

METHODS

Fetal sheep (n = 16) at 118 to 122 days of gestation were subjected to cardiac bypass for 30 minutes using either an in-line axial-flow pump (Hemopump group: n = 8, no prime) or a roller pump with a venous reservoir (control group: n = 8, priming volume = 150 mL). After bypass, the fetuses were observed for 90 minutes. Placental blood flow and combined ventricular output were continuously measured with ultrasonic flow probes, and fetal blood gases were measured at specific intervals.

RESULTS

Three fetuses in the control group died during the study, whereas all 8 fetuses in the Hemopump group remained in stable condition throughout the study period. During and after bypass, placental blood flow was significantly higher (p < 0.0001) and placental vascular resistance was significantly lower (p < 0.0001) in the Hemopump group than in the control group. Arterial pH and partial pressure of arterial oxygen declined significantly less (p < 0.0001), and partial pressure of arterial carbon dioxide increased significantly less (p = 0.0002) in the Hemopump group than in the control group.

CONCLUSIONS

Reducing the extracorporeal surface area and avoiding external priming substances preserves placental hemodynamics after fetal cardiac bypass. An in-line axial-flow pump is useful in miniaturizing the bypass circuits for potential use in fetal cardiac surgery.

Long-term outcome after fetal cardiac bypass: fetal survival to full term and organ abnormalities

BACKGROUND

Earlier work suggests that fetal cardiac bypass is technically feasible but results in significant placental dysfunction. Many of the stimuli that initiate this placental dysfunction have been identified in the past several years and these involve fetal stress, extracorporeal surfaces, priming substances (maternal blood), and flow characteristics. Fetal survival with conventional methods of bypass has been far less than optimal. A novel fetal bypass circuit requiring no priming volume was designed incorporating an in-line axial flow pump (Hemopump, Johnson & Johnson Interventional Systems, Rancho Cordova, Calif.) and was demonstrated to have a marked beneficial effect on placental function.

OBJECTIVE

The purpose of this study was to investigate the effect of this newly developed customized fetal bypass circuit on fetal survival and developing fetal organs.

METHODS AND RESULTS

Nine fetuses at 122 to 126 days of gestation were subjected to fetal cardiac bypass via a transsternal approach, with a 16F single right atrial venous cannula and a 12F arterial cannula. Normothermic cardiac bypass was continued for 30 minutes at flow rates of 320 +/- 32 ml/kg. Of the nine fetuses, one fetus was stillborn 4 days after bypass and eight (89%) were delivered alive after progressing to term gestation. One lamb died of blunt trauma 1 day after birth. All other lambs (n = 7) thrived normally, and at 1 week of age they were subjected to autopsy. No gross hemorrhagic or thromboembolic lesions were detected in the organs examined including the brain. Microscopic examination of representative sections from all organs revealed mild pleural reaction in two lambs, and in two other lambs the hepatocytes showed evidence of mild increase in glycogen content, the significance of which is unknown in relation to fetal bypass. In one fetus that was aborted there was evidence of mild to moderate neuronal loss in the cerebral cortex.

CONCLUSION

This study demonstrates that with improvements in fetal extracorporeal circuitry and techniques very favorable fetal outcome can be achieved. Further studies are necessary to evaluate the effects of bypass on fetal brain in an appropriate animal model. Advances in extracorporeal circuitry to suit the unique fetal physiology increase the possibility of future clinical application.

Circulatory support of cardiac interventional procedures with the Hemopump cardiac assist system

The Hemopump is a catheter-mounted mechanical circulatory assist device which can support the majority of the circulation and significantly reduce left-ventricular work. It can be introduced via a peripheral artery or the ascending aorta. The following is an overview of the operation of the Hemopump and the results of a clinical trial in which the Hemopump was used to treat cardiogenic shock. In addition, the results of pilot experiences using the Hemopump for circulatory support during aorto-coronary artery surgery and high-risk angioplasty will be discussed.

Mechanical left ventricular unloading during high risk coronary angioplasty: first use of a new percutaneous transvalvular left ventricular assist device

A new catheter mounted, transvalvular left ventricular assist device has been designed for percutaneous transfemoral access. The device, the Hemopump [14 French (Fr.) outer diameter], is based on a mixed flow rotary pump and is capable of flow rates of 1.5-2.2 l/min. The pump is inserted using a specialized 16 Fr. femoral introducer sheath. The first application of the percutaneous Hemopump in man was performed in two patients with hemodynamic compromise during high risk coronary angioplasty. In these patients, Hemopump support resulted in hemodynamic stabilization (increase in aortic pressure from 60/42 to 87/61 and from 80/60 to 100/70 mm Hg, respectively) and marked left ventricular unloading (decrease in pulmonary capillary wedge pressure from 25 to 10 and from 14 to 10 mm Hg) during balloon inflation. In both patients, percutaneous transluminal coronary angioplasty (PTCA) could be accomplished successfully. Using the system for periods of about 2 hr in each patient, we observed no vascular, hemorrhagic, or embolic complications. In both patients, only a minor increase in both plasma free hemoglobin and lactate dehydrogenase levels was noted. Our preliminary experiences suggest that the percutaneous Hemopump is safe and effective and may be a powerful alternative to other devices used for supported angioplasty.

The Sternotomy Hemopump. A second generation intraarterial ventricular assist device

The first generation Hemopump is a VAD based on a catheter mounted intraarterial axial flow blood pump that is placed through the femoral artery. Blood is withdrawn from the left ventricle through a transvalvular inflow cannula and pumped into the aorta. Clinical trials have demonstrated hemodynamic efficacy, improved survival, and low hemolysis in cardiogenic shock. The incidence of non-insertion of the device and fracture of the flexible drive cable limited its utility, however. In addition, some processes used in pilot production could not be adapted to volume manufacturing. A second generation device, the Sternotomy Hemopump, has been developed for insertion through the ascending aorta. Design changes include a shortened inflow cannula, higher flow hydraulics, and a more durable flexible drive cable. In addition, more efficient manufacturing processes were implemented. In a pulsatile mock loop the flow was 5.7 L/min at 100 mmHg. In vivo experiments of up to 2 weeks demonstrated a mean plasma free hemoglobin of 8.7 mg/dl, minimal valve injury, and an acceptable incidence of renal infarction. In vitro endurance demonstrated a 7 day reliability of 99.9% with a 95% confidence. A new clinical trial will evaluate the use of the Sternotomy Hemopump for nonoxygenator support during aorto-coronary artery bypass surgery.

Peripheral organ perfusion augmentation during left ventricular failure. A controlled bovine comparison between the intraaortic balloon pump and the Hemopump

Despite the use of inotropic therapy and the intraaortic balloon pump (IABP), inadequate peripheral organ perfusion and subsequent multiorgan failure from left ventricular dysfunction is a major cause of death following cardiac surgery. To compare the end-organ perfusion provided by the IABP with that of the recently developed Hemopump Cardiac Assist System, blood flow from visceral organs was measured by ultrasonic flow probes during separate periods of support with each of these pumps. Ten calves underwent coronary artery ligations with beta-receptor blockade; hemodynamic parameters were recorded before the induction of failure, during unsupported cardiac failure, and during Hemopump and IABP support. Improvement in mean cardiac output, mixed venous oxygen saturation, and pulmonary artery wedge pressure was significantly greater (p < 0.05) during Hemopump support than during IABP support. Renal artery flow was significantly greater during Hemopump support (276 +/- 74.2 cc/min) than during IABP support (164 +/- 79.6 cc/min). Hepatic artery flow was significantly greater during Hemopump support (34.7 +/- 25.7 cc/min) than during IABP support (24.4 +/- 18.9 cc/min), and portal vein flow was significantly greater during Hemopump support (1588 +/- 315 cc/min) than IABP support (1259 +/- 310 cc/min). There were no significant differences, however, between carotid artery flow during Hemopump support (292 +/- 171 cc/min) and that during IABP support (317 +/- 204 cc/min). We conclude that renal, hepatic, and mesenteric perfusion provided by the nonpulsatile Hemopump is superior to that of the IABP in this bovine model of left ventricular failure. Therefore, the Hemopump may be more effective in preventing multiorgan failure during recovery of ventricular function.

Management of patients supported on the Hemopump cardiac assist system

The Hemopump Cardiac Assist System is a relatively new intraarterial, axial-flow circulatory assist device that offers temporary left ventricular support to patients in refractory cardiogenic shock, without requiring major surgery for insertion. Use of the Hemopump is associated with a low complication rate. Device-related morbidity is extremely rare. Because the Hemopump is safe for use in community hospitals, the number of patients supported by this device is expected to increase. In this report, we present general guidelines for the care of patients supported by the Hemopump. We describe techniques for the management of afterload reduction, supravalvular dislodgement, device malfunction, ventricular ectopy, intracardiac shunting, and inflow cannula obstruction.

Treatment of cardiogenic shock with the Hemopump left ventricular assist device

A multiinstitutional study is in progress to evaluate the Hemopump in the treatment of cardiogenic shock. Fifty-three patients with refractory cardiogenic shock were selected for Hemopump assistance. The hemodynamic definition of cardiogenic shock included (1) a cardiac index of less than 2.0 L.min-1.m-2, (2) pulmonary capillary wedge pressure of greater than 18 mm Hg, and (3) a systolic blood pressure of less than 90 mm Hg or a left ventricular work index of less than 1,500 g-m.m-2.min-1. The Hemopump was successfully inserted in 41 of 53 patients (77.3%). A significant improvement in the hemodynamic status was seen during Hemopump assistance. A minimal level of hemolysis was observed. No leg ischemia was observed. The 30-day overall survival of the Hemopump group was 31.7%. Criteria establishing indications for use and clinical utility are proposed. We conclude that the Hemopump provides significant hemodynamic support of the patient in cardiogenic shock allowing for recovery from ventricular stunning in marginal ventricles, and that in select patients the Hemopump may offer a major improvement in survival over conventional therapy.

Treatment of cardiac allograft failure by use of an intraaortic axial flow pump

Since April 1988 we have used the Hemopump device, a new means of circulatory support, to successfully treat three orthotopic heart transplant recipients with biventricular failure refractory to conventional therapy. The Hemopump device is a 21F catheter-mounted, transvalvular, intraaortic axial flow pump. Power to the pump is percutaneously transmitted from an external electromechanical drive console by a flexible drive cable. We first used the pump in a 61-year-old man in whom severe steroid-resistant rejection developed 28 days after heart transplant, resulting in cardiogenic shock (cardiac index less than 2.0 L/min/m2) despite maximal inotropic support. In the second case a 49-year-old man with no evidence of pulmonary hypertension sustained cardiac arrest 2 hours after heart transplant, necessitating open chest massage and emergency cardiopulmonary bypass. The third patient was a 9-year-old boy in whom rejection developed 5 months after heart transplant, resulting in congestive heart failure that was unresponsive to maximal medical therapy. The device was implanted by way of the femoral artery approach in the first case, the ascending aorta in the second, and the distal abdominal aorta in the third. Duration of support was 46 hours, 65 hours, and 6 days, respectively. Increased blood flow provided by the pump ranged from 2 to 4 L/min. No device-related complications, such as hemolysis, infection, or thromboembolic events, occurred. All patients recovered normal heart function and were weaned from the device. The first patient is well after 12 months. The second patient died of metastatic lymphoma at 2 months, and the third died of Pseudomonas pneumonia after 2 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)

The Hemopump--a new cardiac prothesis device

A unique cardiac prothesis device is currently undergoing clinical trials. Called the Hemopump, this device is a radical new design of a temporary left ventricular assist blood pump. It uses a miniature (7 mm diameter) axial flow pump placed transvalvular across the aortic valve which pumps blood from the left ventricle to the aorta. Mechanical power from an external motor is transmitted percutaneously to the pump by a flexible cable contained within a catheter-like sheath. This arrangement allows the pump to be placed through a femoral artery cutdown without requiring major surgery. Development of the Hemopump concept presented significant challenges in pump hydraulic design, bearing, and seal design, as well as materials selection and miniature parts fabrication. Clinical trial results thus far indicate these challenges have been well met and that the Hemopump has the potential to become a widely used safe and effective clinical device.

First human use of the Hemopump, a catheter-mounted ventricular assist device

The Hemopump, a catheter-mounted, temporary ventricular assist device, consists of an external electromechanical drive console and a disposable, intraarterial axial-flow pump (21F). Power is transmitted percutaneously to the pump by a flexible drive shaft within the catheter. The device is positioned in the left ventricle by way of the femoral artery approach or through the ascending aorta. Blood is drawn from the left ventricle through the transvalvular inlet cannula and pumped into the aorta. As of December 1988, the Hemopump had successfully supported the circulation of 7 patients (5 men, 2 women) ranging in age from 44 to 72 years (mean age, 59 years) and suffering from cardiogenic shock (cardiac index less than 2.0 L/min/m2). Indications for use included failure to be weaned from cardiopulmonary bypass in 4 patients, acute myocardial infarction in 1, severe cardiac allograft rejection in 1, and donor heart failure in 1. Duration of support ranged from 26 to 113 hours (mean, 66 hours). Although 5 patients demonstrated transient hemolysis, none experienced infection, thrombosis, or vascular injury. Hemodynamic variables improved in all patients during support by the device. As of December 1988, 5 of the 7 patients were alive more than 30 days after support had been discontinued, and 3 of these patients were discharged from the hospital. On the basis of our initial clinical results, the Hemopump, which does not require a major surgical procedure for insertion, provides effective, temporary circulatory support in patients with potentially reversible cardiac failure.

Effect of the hemopump left ventricular assist device on regional myocardial perfusion and function. Reduction of ischemia during coronary occlusion

The Hemopump is a new 7-mm diameter left ventricular assist device that provides as much as 3.5 l/min of nonpulsatile cardiac output after fluoroscopic placement into the left ventricle through a femoral artery cutdown. The purpose of this study was to measure the effects of Hemopump assist on hemodynamics, left ventricular function, and perfusion in the presence and absence of ischemia. Eight dogs were instrumented under pentobarbital anesthesia with left ventricular, left atrial, and aortic catheters, a loose silk ligature around the midleft anterior descending coronary artery, and sonomicrometer crystals in midwall myocardium within the left anterior descending and circumflex perfusion territories. Hemodynamic variables, regional systolic fractional shortening, and myocardial perfusion after left atrial injection of 15-microns radiolabeled microspheres were measured in the presence and absence of Hemopump assist before and after left anterior descending artery occlusion. In the absence of ischemia, Hemopump left ventricular assist resulted in reduced left ventricular end-diastolic pressure while aortic mean pressure was maintained, and there was significant reduction in regional systolic fractional shortening (reflecting systolic unloading) that correlated with an 18% decline in regional myocardial perfusion. During left anterior descending artery occlusion, left ventricular systolic and diastolic pressures were reduced during Hemopump assist while aortic mean pressure was maintained. Perfusion rose in the ischemic territory (from 13.0 +/- 8.7% to 26.2 +/- 19.8% of nonischemic flow, p = 0.045). Reduced fractional shortening was again seen in nonischemic tissue with Hemopump assist during left anterior descending artery occlusion, and this was often correlated with reduced perfusion (r = 0.67).(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo evaluation of a peripheral vascular access axial flow blood pump

More than 80 acute and chronic calf in vivo studies were utilized to develop a 3 L/min axial flow blood pump designed for intraarterial ventricular assist. The 7 mm diameter transvalvular inlet cannula of the cable driven pump receives blood from the left ventricle. The pump then discharges blood into the descending aorta. In the calf, the pump was introduced into the renal aorta. Safety and effectiveness of the device were demonstrated in three control and 21 implanted animals. Blood chemistry results showed an average plasma free hemoglobin of 3 mg/dl for control and 6.7 mg/dl for implanted animals. Platelets were 1.04 X 10(6) and 0.65 X 10(6), respectively, for control and implanted animals. Fibrinogen, BUN, creatinine, and bilirubin were essentially the same for both groups of animals. The hardware was typically free of deposits, and histopathologic examination revealed minimal injury to intracardiac structures, aortic valve leaflets, and aortic intima. The data indicates that the device may provide full support for a failing left ventricle with minimal trauma or risk.