An insight into short- and long-term mechanical circulatory support systems.

Cardiogenic shock due to acute myocardial infarction, postcardiotomy syndrome following cardiac surgery, or manifestation of heart failure remains a clinical challenge with high mortality rates, despite ongoing advances in surgical techniques, widespread use of primary percutaneous interventions, and medical treatment. Clinicians have, therefore, turned to mechanical means of circulatory support. At present, a broad range of devices are available, which may be extracorporeal, implantable, or percutaneous; temporary or long term. Although counter pulsation provided by intra-aortic balloon pump (IABP) and comprehensive mechanical support for both the systemic and the pulmonary circulation through extracorporeal membrane oxygenation (ECMO) remain a major tool of acute care in patients with cardiogenic shock, both before and after surgical or percutaneous intervention, the development of devices such as the Impella or the Tandemheart allows less invasive forms of temporary support. On the other hand, concerning mid-, or long-term support, left ventricular assist devices have evolved from a last resort life-saving therapy to a well-established viable alternative for thousands of heart failure patients caused by the shortage of donor organs available for transplantation. The optimal selection of the assist device is based on the initial consideration according to hemodynamic situation, comorbidities, intended time of use and therapeutic options. The present article offers an update on currently available mechanical circulatory support systems (MCSS) for short and long-term use as well as an insight into future perspectives.

Prediction of the external work of the native heart from the dynamic H-Q curves of the rotary blood pumps during left heart bypass.

The ventricular performance is dependent on the drainage effect of rotary blood pumps (RBPs) and the performance of RBPs is affected by the ventricular pulsation. In this study, the interaction between the ventricle and RBPs was examined using the pressure-volume (P-V) diagram of the ventricle and dynamic head pressure-bypass flow (H-Q) curves (H, head pressure: arterial pressure minus ventricular pressure vs. Q, bypass flow) of the RBPs. We first investigated the relationships in a mock loop with a passive fill ventricle, followed by validation in ex vivo animal experiments. An apical drainage cannula with a micro-pressure sensor was especially fabricated to obtain ventricular pressure, while three pairs of ultrasonic crystals placed on the heart wall were used to derive ventricular volume. The mock loop-configured ventricular apical-descending aorta bypass revealed that the external work of the ventricle expressed by the area inside the P-V diagrams (EW(Heart) ) correlated strongly with the area inside dynamic H-Q curves (EW(VAD)), with the coefficients of correlation being R² = 0.869 ∼ 0.961. The results in the mock loop were verified in the ex vivo studies using three Shiba goats (10-25 kg in body weight), showing the correlation coefficients of R² = 0.802 ∼ 0.817. The linear regression analysis indicated that the increase in the bypass flow reduced pulsatility in the ventricle expressed in EW(Heart) as well as in EW(VAD) . Experimental results, both mock loop and animal studies, showed that the interaction between cardiac external work and H-Q performance of RBPs can be expressed by the relationships "EW(Heart) versus EW(VAD) ." The pulsatile nature of the native heart can be expressed in the area underneath the H-Q curves of RBPs EW(VAD) during left heart bypass indicating the status of the level of assistance by RBPs and the native heart function.

Development of a disposable maglev centrifugal blood pump intended for one-month support in bridge-to-bridge applications: in vitro and initial in vivo evaluation.

MedTech Dispo, a disposable maglev centrifugal blood pump with two degrees of freedom magnetic suspension and radial magnetic coupling rotation, has been developed for 1-month extracorporeal circulatory support. As the first stage of a two-stage in vivo evaluation, 2-week evaluation of a prototype MedTech Dispo was conducted. In in vitro study, the pump could produce 5 L/min against 800 mm Hg and the normalized index of hemolysis was 0.0054 +/- 0.0008 g/100 L. In in vivo study, the pump, with its blood-contacting surface coated with biocompatible 2-methacryloyloxyethyl phosphorylcholine polymer, was implanted in seven calves in left heart bypass. Pump performance was stable with a mean flow of 4.49 +/- 0.38 L/min at a mean speed of 2072.1 +/- 64.5 rpm. The maglev control revealed its stability in rotor position during normal activity by the calves. During 2 weeks of operation in two calves which survived the intended study period, no thrombus formation was seen inside the pump and levels of plasma free hemoglobin were maintained below 4 mg/dL. Although further experiments are required, the pump demonstrated the potential for sufficient and reliable performance and biocompatibility in meeting the requirements for cardiopulmonary bypass and 1-week circulatory support.

Use of a multi-modality life support system.

The purpose of this study was to describe the design and utilization of a multi-modality life support system (MMLSS), which is used to provide extracorporeal support for cases such as left heart bypass (LHB), extracorporeal life support (ECLS), veno-venous bypass, and hypothermic resuscitation. The design of the MMLSS consisted of a mobile cart outfitted with a centrifugal pump, heater cooler, an in-line blood gas monitor, oxygen blender/flow meter, and assorted safety devices (pressure sensors and level and bubble detectors). A single disposable circuit was used for all procedures and designed to be easily modifiable to support a variety of clinical scenarios, with and without the use of an oxygenator. The system was designed for rapid deployment throughout the hospital. From January 1, 2006 to December 31, 2007, the MMLSS has been used in three LHB procedures (63 +/- 72 minutes), four adult ECLS cases (57.2 +/- 56.9 hours), four veno-venous bypasses (72 +/- 35 minutes), and one hypothermic resuscitation (182 minutes). The MMLSS was designed to be used in patients > 20 kg and could achieve flows in the range of 1-5.5 L. There were no complications associated with the device. The MMLSS is a versatile system that can be used throughout the hospital with a single disposable circuit, accommodating a diverse caseload in a safe and reproducible manner.

Suction detection for the MicroMed DeBakey Left Ventricular Assist Device.

The MicroMed DeBakey Ventricular Assist Device (MicroMed Technology, Inc., Houston, TX) is a continuous axial flow pump designed for long-term circulatory support. The system received CE approval in 2001 as a bridge to transplantation and in 2004 as an alternative to transplantation. Low volume in the left ventricle or immoderate pump speed may cause ventricular collapse due to excessive suction. Suction causes decreased flow and may result in patient discomfort. Therefore, detection of this critical condition and immediate adaptive control of the device is desired. The purpose of this study is to evaluate and validate system parameters suitable for the reliable detection of suction. In vitro studies have been performed with a mock loop allowing pulsatile and nonpulsatile flow. Evidence of suction is clearly shown by the flow waveform reported by the implanted flow probe of the system. For redundancy to the implanted flow probe, it would be desirable to use the electronic motor signals of the pump for suction detection. The continuously accessible signals are motor current consumption and rotor/impeller speed. The influence of suction on these parameters has been investigated over a wide range of hydrodynamic conditions, and the significance of the respective signals individually or in combination has been explored. The reference signal for this analysis was the flow waveform of the ultrasonic probe. To achieve high reliability under both pulsatile and nonpulsatile conditions, it was determined that motor speed and current should be used concurrently for suction detection. Using the amplified differentiated current and speed signals, a suction-detection algorithm has been optimized, taking into account two different working points, defined by the value of the current input. The safety of this algorithm has been proven in vitro under pulsatile and nonpulsatile conditions over the full spectrum of possible speed and differential pressure variations. The algorithm described herein may be best utilized to provide redundancy to the existing flow based algorithm.

Repair of the torn descending thoracic aorta using the centrifugal pump for partial left heart bypass.

OBJECTIVE: To describe the relevant anatomy and sequential technical maneuvers to repair blunt injuries to the descending thoracic aorta with partial left heart bypass. SUMMARY BACKGROUND DATA: Blunt injury to the descending thoracic aorta remains among the most lethal and morbid of anatomic injuries. Of the techniques of repair which have evolved, "clamp and sew" is simple but has an unacceptable risk of paraplegia. In contrast, partial left heart bypass is more complex but virtually eliminates the risk of paraplegia. METHOD: We present a detailed management plan for treating blunt injury to the descending thoracic aorta using partial left heart bypass that has evolved over the past 25 years. Preoperative Aza-blockade to reduce the risk of rupture and use of the centrifugal pump to reduce the incidence of paraplegia without the risk of systemic anticoagulation are essential. RESULTS: We present a detailed description of our management of injuries to the descending thoracic aorta. In our experience, no episodes of postoperative paraplegia have occurred with the use of this technique. CONCLUSION: Blunt injury to the descending thoracic aorta can be safely repaired using partial left heart bypass.

Bypass balloon pumping: a newly developed device for mechanical circulatory support in heart failure.

Various types of assist devices have been developed for severe heart failures. Among them, intra-aortic balloon pumping (IABP) has achieved popularity, mainly in the treatment of patients with either severe cardiac infarction or low cardiac output syndrome (LOS) after open-heart surgery. However, IABP has a limitation in that although it acts as a pressure support, it cannot directly support flow volume. In cases of severe pump failure, stronger pump support would be required. However, there is a limit in the clinical use of temporary mechanical support using a pump because of the costs of the expensive equipment. With this in mind, we came up with a new idea in which the motion of a balloon in IABP system is converted into a power source for creating a one-way stream. In order to realize our idea, we made a J-shaped sample model of pulsating chamber incorporating two ball valves. In the hydrodynamic experiment using our new device, flows over 2500 ml/min (Max. 3475 ml/min) were obtained. The percent changes in parameters such as TTI, DPTI and bypass flows obtained by the experiment of left ventricular bypass have demonstrated that our assist system is effective for reducing cardiac work.

Oxygenator support for partial left-heart bypass.

Partial left-heart bypass provides circulatory support and distal perfusion for repair of thoracic and thoracoabdominal aortic disease without requiring full anticoagulation. Unfortunately some patients, such as those with significant lung contusion in the setting of trauma or those with severe chronic obstructive pulmonary disease and degenerative aneurysms, do not tolerate single-lung ventilation. We have recently modified our left-heart bypass circuit in selected cases to provide supplementary oxygenation, making this technique more broadly applicable.

Mechanical bridge to recovery in fulminant myocarditis.

A patient with acute fulminant lymphocytic myocarditis and cardiogenic shock was successfully treated by mechanical off loading of the left ventricle. A nonpulsatile left-heart bypass was undertaken with an implantable centrifugal blood pump. Careful weaning resulted in device removal on the seventh day. Left and right ventricular function is sustained at 7 months. Widespread application of this method depends on the availability of an inexpensive user friendly blood pump, appropriate weaning protocols and emerging strategies to promote sustainable myocardial recovery.

[The left atrial-femoral bypass in operations on the descending aorta]. / Levopredserdno-bedrennyi obkhod pri operatsiiakh na niskhodiashchei aorte.

Fifteen patients were operated on for aortic aneurysms and were fitted with prostheses of the thoracoabdominal portion of the aorta in March 1997-February 1999. The operations were performed under conditions of a left atrial-femoral bypass with a centrifuge pump with a working heart. The patients were divided into 2 groups. In group 1 (10 pts), standard extracorporeal shunting and Cell-Saver were used, in group 2 (5 pts) the extracorporeal contour included an original system for rapid collection and return of autoblood. A left-atrial bypass prevented ischemia of the organs of the abdominal cavity and lower part of the body. Incorporation of a system for rapid collection and return of autoblood into the extracorporeal contour maintained stable hemodynamics, decreased heparin dose, preserved autoblood, and decreased the amount of transfused donor blood and its components.

Recent clinical experience with left heart bypass using a centrifugal pump for repair of traumatic aortic transection.

OBJECTIVE: To analyze the indications, results, and limitations of using left atrial to femoral artery (LA-FA) bypass to provide distal perfusion during repair of traumatic aortic injuries. SUMMARY BACKGROUND DATA: There is no consensus about the best method for repair of traumatic aortic transection. Distal aortic perfusion with LA-FA bypass and a centrifugal pump has been the authors' preferred technique for injuries to the aortic isthmus and descending thoracic aorta. METHODS: From 1988 to 1998, the authors operated on 30 patients with traumatic aortic transection using LA-FA bypass. The mean age of the group was 36+/-2 years. The mechanism of injury was from a motor vehicle accident in 97% of the cases. Distal aortic perfusion was maintained at 50 to 75 mm Hg with flow rates of 1.5 and 3 L/min. The mean aortic cross-clamp time was 38+/-2 minutes, and the mean bypass time was 49+/-2 minutes. RESULTS: No complications related to cannulation, arterial thromboembolism, renal failure, mesenteric ischemia, or hepatic insufficiency occurred. There were no cases of postoperative paraplegia and no deaths. CONCLUSION: Left atrial to femoral artery bypass is a safe, simple, and effective adjunct to the repair of traumatic injuries to the thoracic aorta. Active distal aortic perfusion preserves spinal cord, mesenteric, and renal blood flow and eliminates the potential catastrophic consequence of spinal cord ischemia from an unexpectedly prolonged aortic cross-clamp time.

Afferent and efferent nerve activity of arterial baroreceptor reflex under nonpulsatile systemic circulation.

We studied the changes in arterial baroreceptor reflex (ABR) afferent activity and efferent activity induced by nonpulsatile systemic circulation (NC) during total left heart bypass (TLHB) in rabbits. To evaluate the influence of the circuit priming fluid and exposure to NC, we directly measured aortic depressor nerve activity (ADNA) (n = 5) and renal sympathetic nerve activity (RSNA) (n = 5) before the start of partial left heart bypass (PLHB) (Before), after PHLB (After), and 5 min after the start of TLHB (During THLB) while maintaining the mean aortic pressure. The circuit priming fluid did not affect the ABR. ADNA exhibited periodic discharge at Before and After, but at During THLB, this periodic discharge transformed into a continuous discharge, and ADNA increased significantly. However, there were no significant differences in RSNA. Our results suggested that in the acute phase under NC, the ABR differed from that under natural circulation.

Detection of suction and regurgitation of the implantable centrifugal pump based on the motor current waveform analysis and its application to optimization of pump flow.

In this study, a detection algorithm for suction and regurgitation of the centrifugal pump during left heart bypass without relying on external flow or pressure sensors was developed and evaluated in acute studies using adult goats. The detection scheme relies on power spectral density (PSD) analysis of the motor current waveform through which the waveform deformation index (WDI) is obtained. This index is defined as the ratio of the fundamental component of the PSD to the higher PSD components, and its value increases with the deformation of the basic waveform. By assuming that the undistorted motor current waveform can be represented by a pure sine waveform, we theoretically synthesized various waveforms which have different second harmonic components. We were able to synthesize the waveform whose shape was close to the distorted motor current waveform under varying suction levels obtained in a mock loop study. From this study, we came to the conclusion that the WDI value of 0.2 can serve as a threshold level in deciding the suction and regurgitation speeds (rpm) during left heart bypass. In the study using adult goats, we were successful in minimizing both regurgitation and suction when the centrifugal pump speed was adjusted based on the WDI algorithm. The resultant bypass flow ranged from 1.5 to 2.0 L/min which was around 60% of the total flow. Further study is underway to evaluate the applicability of the WDI method in optimizing bypass pump flow.

[Diagnostic and therapeutic observations drawn from the surgical experiences of 108 traumatic ruptures of the descending thoracic aorta]. / Observations diagnostiques et thérapeutiques tirées d'une expérience chirurgicale de 108 ruptures traumatiques de l'aorte thoracique descendante.

Traumatic rupture of the thoracic aorta should be suspected when automobile (62.9%), motorcycle (11.1%), ski-doo (2.7%), deltaplane (0.9%), or skiing accidents (0.9%), cause a sudden and rapid deceleration. It was also encountered with a vertical fall of 10 meters and more (4.6%), when a pedestrian was struck by a vehicle (4.6%) or the chest damaged by a high velocity flying object (4.6%). A lateral impact was found in 33% of injured patients and 52.7% were not wearing seat belts. Ruptured aorta was found as a single lesion in only 12% of the cases and among associated orthopedic lesions (63.8%) and abdominal injuries (28.7%), about 2/3 of them involved the left side of the body. The most reliable clinical sign of descending aortic rupture is the pseudo-coarctation syndrome found in 53% in the acute phase by simple pulse palpation and in 56% with blood pressure measurements. As soon as the diagnosis is suspected, associated hypertension present in 50% should be medically treated to avoid sudden exsanguination. Surgical repair should be undertaken with a perfusion technique which is an integral part of the ressuscitation procedure. A Gott shunt was used in 81 patients and a partial left heart bypass with a Bio-Medicus pump in 25 cases. This active atrioaortic bypass is physiologically superior. The pump flow (3727 +/- 612 ml/min.) is superior to the shunt flow (2833 +/- 576 ml/min.). Proximal pressure with the pump is better controlled (111 +/- 20 mmHg) than with the shunt (152 +/- 30 mmHg) and the mean distal pressure obtained with the pump is higher (81 +/- 19 mmHg) than with the shunt (64 +/- 22 mmHg). One case of paraplegia occured (0.9%) with an unfunctionnal Gott shunt. The survival rate is 95.4% (63/66 cases) in the acute phase and 100% (42/42 cases) in the chronic phase.

Surgical results for thoraco-abdominal aneurysm by modified DeBakey method using centrifugal biopump and renal cryopreservation.

BACKGROUND: In this paper, we report the surgical results of our DeBakey and Crawford combined method. METHODS: From 1985 to 1995, 22 consecutive patients with thoraco-abdominal aneurysms underwent a modified DeBakey and Crawford combined procedure to minimize the ischemic time for the spinal cord and visceral organs. The extent of aneurysm as classified by Crawford was as follows: Group I, 12; Group II, 4, Group III, 3; Group IV, 3. The etiology of the aneurysm was atherosclerosis in 19, cystic medial necrosis in 2, and aortitis in 1. The aneurysm was approached through the spiral opening method. First, end-to-side distal anastomosis was performed above the bifurcation under partial aortic clamping, and this was followed by proximal anastomosis. During the end-to-end proximal anastomosis, a Gott shunt tube or heparinless left heart bypass was used. In two patients, left renal artery had been previously reconstructed by a saphenous vein graft extending from the left common iliac artery. Then aneurysm was opened, and the right renal artery and superiors mesenteric artery were perfused with cold blood. In two patients, partial cardiopulmonary bypass and selective perfusion were performed. In eight patients, renal artery, celiac artery, superior mesenteric artery, and intercostal artery were reconstructed with a branch graft. RESULTS: No patient died within 30 days of surgery, however, one patient died of acute myocardial infarction (POD 54) and another of ventricular fibrillation during hemodialysis (POD 60). Postoperative complications included paraplegia, and renal failure requiring dialysis each in two patients. Postoperative angiography revealed 18/19 (94.7%) of grafts were patent. CONCLUSIONS: In conclusion, by using different techniques for spinal cord and visceral protection, including the Gott shunt, Biomedicus pump, renal cryopreservation, and separate revascularization of viscera and intercostal arteries, good results could be obtained.

Left heart bypass in the pig with a centrifugal pump using cannulae prepared for percutaneous placement.

A rapid and efficient circulatory support system may save a patient in cardiogenic shock. Left heart bypass with percutaneous and trans-septal placement of the aspiration cannula simplifies the circuit and eliminates the need for an oxygenator. In this pre-clinical study we assessed left heart bypass support with a centrifugal pump using new cannulae prepared for percutaneous placement (14 F arterial catheter and 16 F left atrial aspiration line) in 5 anaesthetized pigs. Animals were supported for two hours at a mean flow of 3.2 l/min (4,033 rpm), a mean haematocrit of 29% and low heparinisation (ACT double baseline). Hemodynamic measurements and blood samples were taken at baseline (A), 10 minutes (B), one hour (C) and 2 hours (D) on support. Results show maintenance of hemodynamic parameters throughout the 2 hour support period. Only systolic arterial and left ventricular pressure decreased by 12% and 20% respectively from baseline to the end of the support period with a 13% increase in cardiac output. When the pump was turned on (0-3 l/min) there was usually a decrease in heart rate, systolic pressure and left ventricular pressure, with unchanged cardiac output (non failing model). Potassium increased from 3.9 to 4.2 mmol/l (ns), and plasma hemoglobin from 6.0 to 18.2 mg/dl (p<0.05). Thrombocytes decreased from 187 to 155 10(9)/l (ns). In conclusion, this preclinical study demonstrated the feasibility of an efficient left heart bypass of short duration with a centrifugal pump using cannulae prepared for percutaneous placement. Left heart bypass was well tolerated hemodynamically and no significant laboratory change occurred within the two hours of support. This opens several possibilities for the short term support of patients in cardiogenic shock and eventually also for patients submitted to minimally invasive cardiac surgery.

Initial experience with the Nikkiso centrifugal pump during thoracoabdominal aortic aneurysm repair.

PURPOSE: Several centers use atriodistal bypass (ADB) as a protective adjunct against distal ischemia during extensive thoracoabdominal aortic aneurysm (TAAA) repair. Most current ADB circuits use indirect-drive centrifugal pumps. The purpose of this report is to describe our initial clinical experience with the Nikkiso pump, a more compact direct-drive centrifugal pump recently developed at Baylor, for ADB during TAAA repair. METHODS: The Nikkiso pump was used for ADB perfusion in 10 consecutive patients during graft repair of TAAAs (six Crawford extent I and four extent II). Two patients had aortic dissection. In the four patients who had extent II repairs, selective renal and visceral perfusion was also performed with the Nikkiso pump. RESULTS: No mechanical pump malfunctions or adverse events related to the device occurred. All 10 patients survived and were discharged from the hospital. No patient had paraplegia after surgery. Two patients had delayed lower extremity weakness after undergoing extent I repairs; both recovered and were ambulating at the time of discharge. No complications were associated with bleeding or cerebral, respiratory, renal, or hepatic function. CONCLUSIONS: Our initial experience with the Nikkiso centrifugal pump during TAAA repair demonstrated excellent pump function that provided sufficient flow for both distal aortic and selective organ perfusion. The prevention of permanent spinal cord injury and distal organ failure was successful in this group.

Complete myocardial revascularization with left heart bypass without oxygenator on the beating heart.

BACKGROUND: Whereas the complete myocardial revascularization is necessary in high risk group patients, the CABG procedure on the beating heart on circumflex artery still presents a dilemma. METHODS: Between January 1994 and September 1996, we performed complete myocardial revascularization with left heart bypass in 62 patients (54 male, 8 female, mean age: 57) who had absolute or relative contraindications for CPB. RESULTS: The hospital mortality was 3.2%, late mortality was 1.6%. Peroperative MI was seen in 2 patients (3.2%). The mean number of distal anastomosis was 3.6 (ranged 2-6). CONCLUSION: Complete myocardial revascularization on the beating heart can be performed by using left heart bypass (LHBP) without using an oxygenerator safely in high risk patients.