Circulatory support devices

Blood compatible materials are essential to circulatory support devices. Numerous materials have been considered for use in prosthetic devices. 

FIGURE 76.1 Typical design process for a circulatory support device. 

Currently available devices are able to provide left ventricular support for a short duration only. Development of percutaneously or minimally invasive long-term support devices is also underway. At least three such devices are undergoing preclinical evaluation. The Synergy device (CircuLite, Inc., Hackensack, NJ) is being developed as a pocket circulatory assist (PAC) device that would sit in a subcuatenous pocket over the chest wall and use a micro-pump with cannulas in the subclavian artery and vein to withdraw blood from the left atrium through a transseptal approach and deliver it to the subclavian artery. The device is connected to a power... 

Vranckx P, Foley DP, Feijter PJ, Vos J, Smits P, Serruys PW. Clinical introduction of the Tandem-heart, a percutaneous left ventricular assist device, for circulatory support during high-risk percutaneous coronary intervention. Internat J Cardiovasc Intervent 2003 5 35-39... 

Artificial circulatory support can be broadly classified into two categories. The first category is for those patients who undergo open heart surgery to correct valvular disorders, ventricular aneurysm, or coronary artery disease. In several cases, the heart may not recover sufficiently after surgery to take over the pumping action. In such patients ventricular assist devices are used as extracorporeal devices to maintain circulation until the heart recovers. Other ventricular assist devices include intra-aortic balloon pumps as well as... 

The most commonly used means of mechanical circulatory support is the intra-aortic balloon pump (lABP). In 1990, it was estimated that lABP therapy was provided to 70,000 patients aimually (Kantrowitz, 1990). As described below, the lABP can provide only limited cardiovascular support, as its effects are limited to pressure unloading of the ventricle, in contrast to artificial hearts and ventricular assist devices, which provide volume unloading (Mehlhom et al., 1999). To be effective, the lABP requires that the patient maintain some native pumping capacity, as the movement of blood due to the balloon is minimal. 

Starling RC, Naka Y, Boyle AJ, et al. Results of the post-U.S. Food and Dmg Administration-approval study with a continuous flow left ventricular assist device as a bridge to heart transplantation a prospective study using the INTERMACS (Interagency Registry for Mechanically Assisted Circulatory Support). JAm Coll Cardiol May 2011 57(19) 1890-8. 

For long-term circulatory support in patients with advanced CFIF (mostly as bridge-to-transplantation or bridge-to-recovery, rarely as destination therapy), a mechanical left ventricular assist device (LVAD) is often required, which decreases the left ventricular afterload by creation of a cardioaortic bypass through which the blood is directly pumped from the left ventricle into the aorta. In these patients MDCT not only allows for identification of the exact position of the carmula tip of the assist device, but may also allow for the detection of local complications associated with device implantation, such as intra/cardiac thrombosis, mediastinal, pericardial, or pleural fluid or air accumulations as well as mediastinal or pulmonary infections (Jain et al. 2005 Knollmann et al. 1999 Knisely et al. 1997). 

If there is dear evidence of worsening prompt hospital admission for intensive therapy is necessary. As the availability of a suitable donor heart is not predictable, hemodynamic deterioration is first treated with intravenous inotropic support. When the low-cardiac-output syndrome continues to be refractory, patients are put on a mechanical circulatory device for temporary mechanical support. This bridge to transplantation concept enables patient stabilization, withdrawal of intravenous medication (inotropic agents, catecholamines, calcium sensitizers) and rehabilitation (Antretter et al. 2002a). During chronic mechanical circulatory support a low level of exercise is possible and the patients are able to walk around, to leave hospital and sometimes they are followed up by heart failure specialists in an outpatient clinic. Nearly 25% of the most recent cohort transplanted from 1 January, 2001 to 30 June, 2003 were on some type of mechanical circulatory support (Taylor et al. 2004). 

Hetzer R, Loebe M, Potapov EV et al (1998) Circulatory support with pneumatic paracorporeal ventricular assist device in infants and children. Ann Thorac Surg 66 1498-1506... 

Mehta, S. M., Pae, W. E., Jr., Rosenberg, G. et al. 2001. The LionHeart LVD-2000 A completely implanted left ventricular assist device for chronic circulatory support. Ann Thorac Surg 71 S156-... 

Ca.rdia.c-AssistDevices. The principal cardiac-assist device, the intra-aortic balloon pump (lABP), is used primarily to support patients before or after open-heart surgery, or patients who go into cardiogenic shock. As of the mid-1990s, the lABP was being used more often to stabilize heart attack victims, especially in community hospitals which do not provide open-heart surgery. The procedure consists of a balloon catheter inserted into the aorta which expands and contracts to assist blood flow into the circulatory system and to reduce the heart s workload by about 20%. The disposable balloon is powered by an external pump console. 

Treatment strategies for progressive pulmonary venous hypertension should focus on treatment of the underlying disease. For patients with advanced decompensated systolic heart failure and secondary pulmonary hypertension, it is essential to reduce the pulmonary vascular resistance prior to heart transplantation to prevent acute RV failure of the donor heart. The use of continuous milrinone, occasionally nesirit-ide, and earlier intervention with mechanical circulatory device support (19) as a bridge to cardiac transplantation is considered a standard approach for this group of patients. Earlier intervention with valve repair or replacement for patients with mitral valve disease and aortic valve disease with associated pulmonary hypertension is recommended. 

Several systems are now available for circulation support. Ventricular assist devices (VAD) are mechanical pumps that can take over the circulatory function of the left ventricle (LVAD), the right ventricle (RVAD) or both ventricles (biventricular assist device - BVAD). The patient s native heart remains in place, and the VADs are implanted in a heterotopic position. Connection between the heart chambers and the great vessds is usually achieved... 

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