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Clinical application of BVS5000 left ventricular assist device in heart failure patients

LUO, Xin-jin; HU, Sheng-shou; SUN, Han-song; XU, Jian-ping; LIU, Ping; ZHENG, Zhe; MA, Wei-guo; ZHANG, Yan

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Abstract

Mechanical support for the heart failure patients has interested and challenged cardiac specialist for decades. A variety of ventricular assist devices have been designed for use, so have the variety of cannulating methods.

The Abiomed BVS5000 began its clinical trials in 1987 in the USA, and got USA Food and Drug Administration (FDA) approve for clinical using in 1994. The BVS5000 is a pneumatically driven pulsate extracorporeal asynchronous ventricular assist device capable of providing cardiac output of 5–6 L/min, which consists an atrial (filling) chamber and a ventricular (pumping) chamber. The blood pump fills passively by gravity. There are two 25-mm trileaflet polyurethane valves, situated between the atrial and ventricular chamber, to ensure the direction of blood flow.1 Abiomed BVS5000 LVAD has been used in Fu Wai Hospital as a means of left ventricular support for several years. In order to mitigate myocardium injury and simplify the weaning procedure, a modified cannulating method has been used since 2004. This retrospective review described our clinical application of BVS500 LVAD in heart failure patients and also compared this modified technique with the routine way.

METHODS

From February 2004 to April 2006, 12 male patients, ranging in age from 39 to 68 years (average (55.2±9.6) years), with mean body surface area (1.76±0.1) m2 (range 1.6 to 1.9 m2), implanted Abiomed BVS5000 LVAD (Abiomed Inc., Danvers, MA, USA) for left ventricular support in Fu Wai Hospital. Except one patient with dilated cardiomyopathy was supported for ‘bridge to transplantation’ because of acute cardiogenic shock, the other 11 were the post-cardiotomy patients after coronary artery bypass graft (CABG), which were supported for ‘bridge to recovery’.

Seven patients were cannulated in modified method (Group Modified), the other 5 patients were cannulated in routine way (Group Routine). Patients’ information in both groups was displayed in Table. The indication for ventricular assistance was same in both groups.

Table
Table:
Comparison of modified group with routine group

The indication for ventricular assistance was described by Norman et al.2 That included a cardiac index <2.0 L•min−1•m−2, an arterial blood pressure < 80–90 mmHg, left or right atrial filling pressure >20 mmHg, urine output <20 ml/h, despite maximal pharmacological support.

In our experience, for high risk ischemic myopathy patient (the left ventricular diameter in diastole (LVDD) >60 mm, left ventricular ejection fraction (LVEF) <35%, no obvious ventricular aneurysm) with CABG operation, the decision for LVADs insertion was made within 1 hour of the first failure attempt to wean from cardiopulmonary bypass (CPB). After a trial of stopping CPB support, if the left atrial filling pressure rose over 16 mmHg, preparation for device insertion was made instantly. In these 12 patients, the pre-operative LVDD was (68.0±6.7) mm (range 60–81 mm), LVEF was (31±4)% (range 25%-35%).

BVS5000 management followed the guidelines described in the Abiomed training manual. All patients were treated with protamine sulfate intra-operatively to reverse the effects of heparin. After patients entering intensive care unit (ICU), activated clotting time (ACT) was measured. ACTs were maintained at 180–200 s with pump flow rate greater than 3.0 L/min by heparin administration during the supporting period.

The routine cannulation techniques used for BVS5000 implantation is inserting the inflow cannulae directly into the left atrium through inter-atrial grove, and connecting the arterial cannulae to the ascending aorta. Five patients used this cannulating method (Group Routine), were considered to have a longer supporting duration or companied with severe periphery arterial sclerosis. Atrial cannulae of 32 Fr or 36 Fr was used for inflow. Arterial outflow cannulae included the 42 Fr atrial cannulae with 10-mm Hemashield graft (Meadox Medicals Inc., Oakland, CA, USA) attached. In routine group, re-entering the operating room and general anesthesia were needed for weaning devices through re-sternotomy.

If patients did not have severe atherosclerosis of femoral artery, modified cannulating method would be chosen. Seven patients accepted this cannulating method (Group Modified).

In modified group, we inserted the arterial cannulae in femoral artery. It was easy to wean out. A segment of bovine jugular vein (diameter 18 mm) almost 15 cm length was firstly anastomosed to the inter-atrial grove incision by continuous suture with 4-0 prolene. Two purse-string sutures (4-0 prolene) were prepared beforehand around the vessel wall of the bovine jugular vein, with a segment of sterile silastic casing kept on each suture for tightening the purse-string. Then the inflow cannulae was inserted into the left atrial through the bovine jugular vein. The purse-string sutures were tightened for immobilization the cannulae and prohibition of bleeding. The inflow cannulae pierced out the skin at the right epigastrium through a subcutaneous canal, and was connected to the pump. In order to simplify the weaning procedure, the ends of those two purse-string sutures were located just below the xiphoid before closing the incision.

During the weaning procedure, a small incision (almost 8 cm) below xiphoid process was went through, and the inflow cannulae with those two purse-string sutures were exposed easily. After successfully terminating the assistance of LVADs, the casings on the purse-string sutures were loosen temporarily, so the inflow cannulae could be quickly pulled out through the bovine jugular vein. Next, the casings were tightened completely and fixed firmly with the distant end of the bovine jugular vein. The whole procedure of the weaning device was able to be finished bedside in the ICU. Re-sternotomy was not performed anymore. Only local anesthesia was needed. However, in this way, patients’ movement was limited during the support period. It is more suitable for short-term support patients.

Weaning was not begun before the third day of support, and was started only when extra-cardiac organ recovery (eg: lungs, liver, kidneys) was demonstrated clinically, chemically, or radiographically. The weaning protocol required a stable cardiac rhythm and minimal inotropic drug support. The LVADs flow was decreased by 0.5 L every 30 minutes until a flow of 2.0 L-min−1 was achieved with stable hemodynamics or stopped earlier if hemodynamics become unstable. Inotropic drugs may be added or titrated upward at moderate doses.

All patients were remained in the ICU during BVS5000 support. Transthoracic echocardiography was performed daily or every other day. LVDD and LVEF served as the main parameters to assess changes in cardiac performance.

The data were expressed as mean ± standard deviation (SD) and were analyzed using SPSS10.0 statistical software (SPSS, Inc., Chicago, IL, USA). Student's t test was used to compare the mean values, and the differences of P <0.05 were considered significant.

RESULTS

In these 12 patients, the BVS5000 support duration was (8.8±11.2) days ((3–43) days), with support flow rate of (3.8–4.5) L/min. The respiratory support duration was (2.7±2.2) days ((0.5–6) days). After BVS5000 implantation, the thoracic drainage for the first three days was (2078±1015) ml. The successful weaning rate was 75% (9 cases) and the discharge rate was 67% (8 cases).

Four patients were lost, with mortality of 33%. Three patients died of cerebral embolism during the support period and 1 patient died of ventricular tachycardia after the weaning of BVS5000. The most common morbidity was adverse neurological events. Bleeding and infection were major complications. Two patients were re-operated for hemostasia. Three patients had positive bacteria culture results in their sputum.

For those 8 discharged patients, their LVDD decreased to (53.3±7.7)mm and LVEF increased to (48.0±8.1)% when they left the hospital. Which were improved obviously compared with that of pre-operative (pre-operative: LVDD (69.0±6.4)mm, LVEF (31.0±4.0)%.

There is no statistical difference between two groups on average BVS5000 support duration, assisted flow rate, mechanical ventilation duration, ICU stay and thoracic drainage in first three days (Table).

DISCUSSION

Tremendous progress has been made in the management of acute cardiogenic shock, whether pre- or post-cardiotomy in nature. However, a subset of patient remains problematic because of profound ventricular dysfunction that is associated with post-cardiotomy failure or acute failure of cardiomyopathy. Several publications2–4 have previously reported a 0.5%—1.0% incidence of post-cardiotomy ventricular dysfunction refractory to both maximal pharmacological support and intra aortic balloon pump therapy. Mechanical ventricular assistance remains an important therapeutic method in treating such kinds of patients.

In 1962, Dennis et al5 first described the left atrium-to-femoral artery bypass system by jugular approach. Consecutively, left atrial-to-femoral arterial VAD were mostly used in patients who could not be weaned from CPB after cardiothoracic operation.6,7 For these ‘bridge-to-recovery’ patients, it is important to take consideration of minimal invasive for myocardium and convenient weaning procedure for VADs. Compared with other kind of LVADs, BVS5000 has longer cannulae which connect to extracorporeal pump. It facilitates to cannulate in left atrial and femoral artery at the same time. Using modified cannulating method described in this study, re-sternotomy for weaning the BVS5000 device can be avoided. The whole weaning procedure is accomplished just bedside in ICU.

Restoration of heart function may be obtained by prolonged unloading of heart with mechanical ventricular assistance.8,9 Recovery of the myocardium occurs by diverting blood from left atrium to the systemic circulation, which will result in reducing filling pressure in the left ventricle, cardiac workload, and oxygen demand. Patients after left ventricular assist devices (LVADs) implantation are noted to have decreased LVDD, improved LVEF, decreased pulmonary capillary wedge pressure10 and decreased immunoreactivity to atrial natriuretic polypeptide and brain natriuretic polypeptide.11

Although, there are many kinds of LVADs used all over the world, which are much better and more convenient than that we used in this group. Meanwhile, they are too expensive for patients in the mainland of China. The choice of LVADs is dependent upon the financial condition of the patient and approval by the state Food and Drug Administration. It is important to choose LVADs products that satisfy the criteria of “Safe, Effective, and Cheaper”. In our experience, Abiomed BVS5000 is a kind of supporting device which is simple and safe with minimal mechanical failure. It is efficient for short-term support. Much more importantly, it is not so much expensive, it can be afforded by patients in developing country, such as China. Till now in the mainland of China, this group of patients we reported is the biggest group of patients who were supported by BVS5000 LVAD.

The timing of insertion is crucial for positive outcomes.12 An error is often made in trying too many interventions before an assist device inserted. Patients who have their device implanted in an elective setting enjoyed better survival than those in more urgent scenario.13,14 Abiomed Registry of June 2000 has shown, wean and discharge rates can be doubled (40% vs 20%) by adhering to the principle of early insertion. In some center, the timing of post-cardiotomy shock insertion has also decreased from 6 hours to 1 hour from the first attempt to wean from CPB,15,16 just as we did in our institute. It is important to keep in mind that use of three or more inotropic drugs at maximal dosages is associated with an unacceptable mortality if hemodynamic situation is not rapidly improved. Mechnical assist should be inserted before multiple organ system failure occurs. Willams et al17 have indicated that renal failure is the strongest predictor for mortality in patients bridged with devices.

Neurological events are among the most commonly reported complications after placement of LVADs.18 It was also the main complication in this study. Cerebral embolism is the most frequent brain event, with reports ranging from 3% to 47%, especially in cases in which the device was used as a bridge for a limited period of time. The use of textured blood-contacting surfaces in devices may result in a lower incidence of neurological events.19–20

Within the epidemic of heart failure, ventricular assist devices have become an important means for preserving end-organ function and provide effective decompression of the failing ventricles. With the progress, in technology there is great anticipation for even better devices for cardiac mechanical assistance, also the even better result.

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Keywords:

heart failure; surgical treatment; left ventricular assist devices

© 2008 Chinese Medical Association