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

In Vivo and in Vitro Experience with the PUCA-II, a Single-Valved Pulsatile Catheter-Pump

The Pulsatile Catheter (PUCA) pump is a trans-arterial pulsatile ventricular assist device that can be used for short-term left ventricular support. The separate inflow and outflow valves in the first version of the device (PUCA-I) were replaced by a single inflow/outflow valve in the latest PUCA pump version (PUCA-II). The new combined valve was tested during in vitro (mock circulation) and in vivo experiments for valve leakage, flow resistance, and thrombus formation. During the in vitro experiments a maximum valve leakage of 6% during ejection and 21% during aspiration was found. The maximum flow resistance coefficient (K) was 4. The animal experiments demonstrated that the PUCA-II could be positioned within a few minutes into the left ventricle without X-ray guidance and without using a vascular graft. Thrombi were not found in the combined valve after total pump time of 3 hours, which proved the good washout of the valve. Initial experiments to position the pump in the right ventricle through the pulmonary artery were successful and contributed to the development of a new application for the device.

Hemodynamic Properties of the Hemopump HP14

Background

The Hemopump HP14 is a catheter-mounted, transvalvular, left ventricular assist device intended for femoral percutaneous insertion. The pump was developed for patients with postoperative or postinterventional low cardiac output and for CABG surgery on the beating heart. Little is known about the effect of afterload and hematocrit on the pump performance.

Methods

The influence of hematocrit and afterload on the pump flow was tested using an in vitro model filled with heparinized bovine blood. Regression analysis of the pump flow with respect to three hematocrit values (20%, 30%, 40%) and ten afterload levels (30 mmHg-120 mmHg in 10 mmHg increments) was performed for all pump speed levels (n = 7).

Results

At all pump speed levels reduction of afterload and hematocrit were significant predictors for increasing pump flow (p<0.001). For hematocrit values between 40% and 20% and highest pump speed, mean pump flow at lowest afterload ranged between 2.34 and 2.53 L/min; and at highest afterload between 1.31 and 1.53 L/min. For speed level 1, afterload of 120 mmHg and hematocrit of 40% there was a maximal retrograde flow of 230 ± 35 ml/min.

Conclusions

Pump performance is significantly improved by both afterload and hematocrit reduction. In the weaning phase and during the removal of the device, the pump should run at a speed level of at least three to prevent retrograde flow in the pump. Estimates for pump flow in vivo can be extrapolated from our diagrams. Our results show that the Hemopump HP14 is a valuable alternative to intra-aortic balloon counterpulsation.

Mechanical support for postcardiotomy cardiogenic shock

Postcardiotomy cardiogenic shock (PCCS) results in substantial morbidity and mortality. Despite intraaortic balloon pump and inotropic support, some patients with PCCS continue to have a refractory low cardiac output. For these patients, more effective ventricular assistance is imperative to prevent death. Multiple systems are available for the short-term support of patients with PCCS. Regardless of the device employed, only 25% of these patients survive and are discharged home. Two strategies, however, may improve the outcome of PCCS. One is long-term support by an implantable assist device, which can allow optimal ventricular unloading. Unfortunately, not all cardiac surgery centers offer this type of support. Therefore, the other strategy is the creation of postcardiotomy referral centers that offer long-term support or heart transplantation. Such centers would conserve scarce donor organs, maximize the chance of myocardial recovery, and yield expertise applicable not only to device recipients but also to critically ill heart-failure patients who do not need an implantable pump.

[Reperfusion therapy and mechanical circulatory support in patients in cardiogenic shock]

Cardiogenic shock is a state of inadequate tissue perfusion due to cardiac dysfunction, which is most commonly caused by acute myocardial infarction. The pathophysiology of cardiogenic shock is characterized by a downward spiral: ischemia causes myocardial dysfunction, which, in turn, augments the ischemic damage and the energetical imbalance. With conservative therapy, mortality rates for patients with cardiogenic shock are frustratingly high reaching more than 80%. Additional thrombolytic therapy has not been shown to significantly improve survival in such patients. Emergency cardiac catheterization and coronary angioplasty, however, seem to improve the outcome in shock-patients, which most probably is due to rapid and complete revascularization generally reached by angioplasty. In addition to interventional therapy with rapid coronary revascularization, the use of mechanical circulatory support may interrupt the vicious cycle in cardiogenic shock by stabilizing hemodynamics and the metabolic situation. Different cardiac assist devices are available for cardiologists and cardiac surgeons: 1. intraaortic balloon counterpulsation (IABP), 2. implantable turbine-pump (Hemopump), 3. percutaneous cardiopulmonary bypass support (CPS), 4. right heart, left heart, or biventricular assist devices placed by thoracotomy, and 5. intra- and extrathoracic total artificial hearts. Since percutaneous application is possible with IABP, Hemopump and CPS, these devices are currently used in interventional cardiology. The basic goals of the less invasive intraaortic balloon counterpulsation (IABP; Figure 1) are to stabilize circulatory collapse, to increase coronary perfusion and myocardial oxygen supply, and to decrease left ventricular workload and myocardial oxygen demand (Figure 2). Since the advent of percutaneous placement, IABP has been used by an increasing number of institutions (Figure 3). In addition to cardiogenic shock, the system may be of use in a variety of other indications in the catheterization laboratory and intensive care unit, including weaning from percutaneous cardiopulmonary bypass, in ischaemic left ventricular failure, in unstable angina, in high risk PTCA, and in prophylactic support in patients with myocardial infarction and successful revascularization. Animal experimental data showed that IABP may improve success of thrombolysis and recent clinical data suggest that survival is enhanced and transfer for revascularization is facilitated when patients with myocardial infarction and cardiogenic shock undergo thrombolysis and IABP rather than thrombolysis alone. A lot of studies had demonstrated before, that combined use of counterpulsation and revascularization therapy (i.e. coronary bypass surgery or angioplasty) may improve prognosis in patients with myocardial infarction complicated by cardiogenic shock (Table 1). In such patients, early treatment with IABP is most important: Multivariate analysis identified early IABP-support with a duration of shock to IABP-treatment of > or = 4 hours as an independent predictor of a positive short-term outcome. In shock-patients with postinfarction ventricular septal defect, IABP provides a marked hemodynamic improvement, and a significant decrease in shunt-flow (Figure 5). However, despite initial stabilization with IABP, such patients need immediate surgical repair of the septal defect to avoid hemodynamic deterioration. The rate of complications related to percutaneous IABP was significantly attenuated by employing catheters of reduced size. Using 9.5-F catheters, a long duration of counterpulsation emerged as the most significant factor associated with complications. In our hospital, those patients with 9.5-F catheters in whom counterpulsation did not exceed 48 hours had a low complication rate of 3.9%. The Hemopump is a catheter-mounted transvalvular left ventricular assist device intended for surgical placement via the femoral artery (Figures 6 and 7). (ABSTRACT TRUNCATED)

The Hemopump in 1997: a clinical, political, and marketing evolution

BACKGROUND

The Hemopump (Medtronic, Inc, Minneapolis, MN) was conceived in 1975 and designed in 1982 as a temporary, extracorporeal cardiac assist system. Although it has been used clinically in Europe, it is not currently available in the United States.

METHODS

In vitro and in vivo testing of the Hemopump began in 1983. Clinical investigations have included studies of patients in cardiogenic shock, Hemopump-supported coronary artery bypass operations in Sweden, and European studies of percutaneous transluminal coronary angioplasty (PTCA) with Hemopump support.

RESULTS

The Hemopump has demonstrated positive hemodynamic effects in patients. Laboratory and clinical studies have shown that the nonpulsatile axial flow generates flows of up to 4.5 L/min while maintaining adequate perfusion of other organs. In Europe, hemopumps have been used successfully to support coronary bypass and PTCA.

CONCLUSIONS

The Hemopump system is simple, inexpensive, and well tolerated by the blood elements. Moreover, its design allows flexibility in supporting patients during cardiopulmonary bypass (in lieu of conventional techniques) and high risk angioplasty, as well as in rescuing patients with low cardiac output.

Clinical experience with the percutaneous hemopump during high-risk coronary angioplasty

The percutaneous Hemopump showed beneficial effects during coronary angioplasty in 32 high-risk patients with unloading of the left ventricle during ischemia and maintaining cardiac output with mean aortic pressures of 50 mm Hg in case of cardiac arrest (3 patients). High procedure-related morbidity (occlusion of femoral artery in 2 patients; bleeding with need of transfusion in 4 patients) and mortality (4 of 32 patients) rates demonstrate the need for a very careful selection of patients.

Effects of the 14F hemopump on coronary hemodynamics in patients undergoing high-risk coronary angioplasty

BACKGROUND

The influence of the 14F Hemopump on coronary hemodynamics in patients with coronary artery disease remains unknown.

METHODS

Systemic and coronary hemodynamic measurements were obtained in eight patients among 13 who underwent high-risk coronary angioplasty in our institution with the support of the Hemopump. Coronary blood flow velocity was measured with a 0.014-inch Doppler-tipped guide wire both proximal and distal to the target lesion.

RESULTS

Angioplasty decreases the diameter coronary stenosis from 76% +/- 21% to 22% +/- 11%. Hemopump support did not change systemic hemodynamics either before or after angioplasty. During angioplasty Hemopump support decreased the pulmonary capillary wedge pressure from 23.5 +/- 8.5 mm Hg to 18.6 +/- 7 mm Hg (p = 0.013). No changes in either heart rate, mean and systolic aortic pressures, and cardiac index were observed throughout the procedure. After successful angioplasty was performed, the ratio of proximal to distal flow velocity decreased from 2.11 +/- 1 to 1.65 +/- 0.2 (p = 0.05). However, Hemopump did not affect absolute coronary blood flow velocities or the phasic pattern of flow velocities (diastolic systolic velocity ratio, diastolic and systolic velocity integrals) either in proximal or distal locations either before or after angioplasty.

CONCLUSIONS

This study shows that although the 14F Hemopump produces unloading of the left ventricle, it does not importantly alter coronary hemodynamics when systemic hemodynamics are stable. Whether the Hemopump would maintain or improve coronary blood flow in compromised patients remains to be determined.

PTCA with the use of cardiac assist devices: risk stratification, short- and long-term results

Percutaneous cardiopulmonary assist devices (PCPS) have become available in interventional cardiology within recent years. These tools offer the opportunity of performing percutaneous transluminal coronary angioplasty (PTCA) in high-risk patients characterized by significant stenoses of several coronary arteries and a poor left ventricular function. It is unclear for which patients PCPS are necessary and which patients will profit by PTCA as compared to coronary artery bypass grafting (CABG). Therefore, the anticipated risk of CABG and of PTCA without assist devices was calculated according to risk scores and compared with our results of assisted PTCA. In addition the long-term survival rate was investigated. In 35 patients (mean 65.5 years of age, 12 females, 23 males), we performed PTCA concomitant with the use of cardiac assist devices. The indications for the use of a cardiac assist device were severely impaired LV function (EF 30% +/- 8.9%) in combination with significant coronary artery disease (2.7 +/- 0.3 vessels) and a significant supply area of the vessel to be dilated. In 6 patients, PCPS was started before coronary angioplasty because of hemodynamic instability. In 21 cases, PCPS was on a standby basis without being connected to the patient's circulation. In 8 patients, a left heart assist device, the 14F-Hemopump, was inserted percutaneously. The patients were analyzed using risk scores of angioplasty and of coronary bypass graft surgery. The calculated risk of hemodynamic compromise during PTCA according to the risk scores was more than 50%. The anticipated risk of a fatal outcome following CABG would have been 19.8%. PTCA was performed on an average of 2.0 coronary arteries per patient and was successful in 85%. We observed a decline in angina pectoris classification (CCS) from 3.5 to 1.6. An average reduction of 1.1 NYHA class was achieved. The in-hospital mortality was 8.6% (3 patients: 1 x sepsis, 1 x early reocclusion, 1 x cerebral embolism). At 24 months follow-up, a re-PTCA was necessary in four cases because of restenosis. In the remainder, NYHA and CCS class were stable during the follow-up period. An additional five patients died during the first year and two patients in the second year. We conclude that PTCA with the use of a cardiac assist device shows favorable short-term results in a subset of patients with extended coronary artery disease and severely impaired LV function who are not suitable for nonsupported PTCA or CABG due to their risk profile. However, the long term results are not satisfying and stress the need for complete revascularisation with CABG once the patient's condition is stabilized by means of supported PTCA.

Perfusion therapy to reduce myocardial ischemia en route to emergency coronary artery bypass grafting for failed percutaneous transluminal coronary angioplasty

Despite improvements in operator technique, catheter technology, and the development of new devices, emergency coronary artery bypass grafting (CABG) is still required in 1%-4% of attempted catheter based revascularization procedures. Patients who require such emergency CABG after failed percutaneous transluminal coronary angioplasty (PTCA) have worse acute outcomes than those undergoing elective CABG, with a higher incidence of Q wave myocardial infarction (MI) and a higher operative mortality. In patients with otherwise refractory abrupt closure, maintenance of antegrade coronary blood flow using perfusion catheters lessens the incidence of Q wave MI and lowers peak creatinine phosphokinase. Direct maintenance of coronary flow thus appears to provide more definitive control of myocardial ischemia than purely adjunctive measures, such as intra-aortic balloon pumping, cardiopulmonary support, or coronary sinus retroperfusion. Although the recent introduction of coronary stents holds great promise for definitive percutaneous reversal of abrupt closure and a dramatic decrease in the incidence of emergency CABG for failed PTCA, maintenance of antegrade flow via perfusion technology remains the cornerstone of management in reducing the perioperative mortality and morbidity of patients who still require emergency bypass surgery after failed PTCA.

Transvalvular left ventricular assistance in acute myocardial infarction with cardiogenic shock and high risk angioplasty: experimental and clinical results with the Hemopump

The Hemopump has been shown to be an effective left ventricular assist device. It is capable of supporting the circulation in patients with profound left ventricular dysfunction in the setting of cardiogenic shock. In experimental animals it seems possible that supporting the circulation immediately prior to reperfusion will produce a significant decrease in infarct size, which has important clinical ramifications, particularly in the setting of patients with large anterior myocardial infarction. The mechanism for this infarct salvage is unclear at the present time and requires further investigation, at a more basic level. The current tools available to the cardiologist include the intraaortic balloon pump and the cardiopulmonary support system (CPS), (PCs, BARD, Inc.). The Hemopump is available in Europe, but not in the United States at the present time. Clearly, the CPS system is the most powerful of the devices available, producing up to 61/m of flow. Unfortunately, there are a number of drawbacks with the CPS system, including its need for an oxygenator, which limits its useful period of support to approximately 8 hours. Additionally, support with the PCS system may be associated with adverse physiological events. The intraaortic balloon pump requires synchronization with the cardiac cycle, and hence, is not suitable for patients with significant tachyarrhythmias. Patients with overt cardiac arrest, similarly, cannot be supported with the intraaortic balloon pump. Nonetheless, the balloon pump has been associated with improved infarct salvage in an experimental animal model. On the other hand, the Hemopump, in its first version, required a surgical incision and placement of a graft onto the femoral artery.(ABSTRACT TRUNCATED AT 250 WORDS)

Pulmonary and left ventricular decompression by artificial pulmonary valve incompetence during percutaneous cardiopulmonary bypass support in cardiac arrest

BACKGROUND

In cardiac arrest, use of percutaneous cardiopulmonary bypass support (PCPS) may lead to left ventricular loading, with deleterious effects on the myocardium, and is often accompanied by an increase in pulmonary artery pressure. The present study was designed to assess the potential of artificially induced pulmonary valve incompetency to retrogradely decompress the left ventricle during PCPS in ventricular fibrillation.

METHODS AND RESULTS

Studies were performed using a standardized experimental animal model in sheep (n = 12; body weight, 77 to 112 kg). When PCPS was used during fibrillation, an increase in left ventricular pressure (from 21.4 +/- 5.0 mm Hg after 1 minute to 28.4 +/- 9.5 mm Hg after 10 minutes of fibrillation) was observed in all animals, with a simultaneous increase in pulmonary artery pressure in 6 animals, from 15.5 +/- 3.8 to 24.3 +/- 5.4 mm Hg (group A). In these animals, artificial pulmonary valve incompetency, which was induced by a special "pulmonary valve spreading catheter," led to effective decompression of both the pulmonary circulation (decrease in pulmonary artery pressure from 24.3 to 11.3 mm Hg) and the left ventricle (decrease in left ventricular pressure from 30.5 to 17.7 mm Hg). We simultaneously measured a decrease in the myocardial release of lactate (increase in arterial coronaryvenous difference in lactate content from -0.01 to 0.14 mmol/L), demonstrating the myocardial protective effect of the procedure. In contrast, in 6 animals without an increase in pulmonary artery pressure during PCPS (group B), artificial pulmonary valve incompetency did not reduce left ventricular loading, which was probably because of competent mitral valves in these animals.

CONCLUSIONS

In case of increasing pulmonary artery pressure during PCPS in cardiac arrest, artificial pulmonary valve incompetency might be a useful tool for effective pulmonary and retrograde left ventricular decompression.