NATIONAL COUNCIL OF SCIENTIFIC AND TECHNOLOGICAL RESEARCH CLINICAL RESEARCH AND DEVELOPMENT OF CARDIAC PROSTHESIS PROGRAM

ASSISTED CIRCULATION FOR CHRONIC INTRACTABLE HEART FAILURE
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Domingo Liotta, MD ; Jorge Gonzalez Zuelgaray, MD; Raúl Oliveri, MD; Eng.Daniel F. Sánchez; Eng. Luis A. Pinchete; Eng. Laureano Nava.

A multidisciplinary effort is under way at the National Council for Scientific and Technological Research (CONICET) in Argentina working on Mechanical Circulatory Support System (MCSS) for patients suffering from advanced chronic heart failure.

LIOTTA - VAD ProCor Model 1


What is the contribution of VAD - ProCor Model 1 to the existing pneumatically driven systems?

  1. It has a symmetrically opposed dual pusher plate mechanism allows the blood chamber to deform in a circular rolling fold thus minimizing strain in the sac material. It also avoids the formation of thrombi in the blood sac after long implants.

  2. New bioprostheses: the anatomy of the aortic root is maintained.

  3. It has a safe portable air driven unit that allows the patient's hospital discharge in an approximate 6-8 days' time. This must be followed by a sound and efficient clinical protocol.

System Description:


Mechanical Circulatory Support System (MCSS ), Liotta-VAD ProCor Model 1, consists of an intracorporeal blood pump pneumatically driven. The blood pump is 92 mm. diameter and 52 mm. thickness at the pump's equator, and 35 mm. at the lower pole. The overall volume of the implantable unit is 260 ml. and the blood displacement by 20-22 mm. linear motion is 65-70 ml. The pneumatic driving line is 6 mm. ID. The cross-section of the inflow and outflow tracts of the blood pump has 3.8 cm2. (Fig. 1). 13 KB

With a systolic period from 170 to 230 ms. (approximately 20-30 % of the cardiac cycle), dp/dt of 1600-2.400 mm.Hg/sec, and at 70 beats/min, with a dynamic ejection fraction of approximately 0.55-0.60, the pump flow output is from 4.2 to 4.5 l/min. With this setting, the peak systolic blood velocity at the outflow tract of the blood pump is 90 cm/sec (normal: 90-100 cm / sec).

The performance of the blood pump is highly remarkable and its values get near to the normal circulation. Besides, a 4 l/min pump output of circulating blood is a good enough figure to support a failing heart during a prolonged period.

The blood chamber is made of a segmented polyurethane obtained by dipping a wax mold coated with a silica-free silicone rubber material. The resulting blood chamber is seamless and it has an extremely smooth blood interphase.

The blood chamber deforms in a circular rolling fold which expands in a concentric way during the ejection systolic phase that minimizes strain in the sac material. (Fig.2). 8 KB

The blood sac is mounted free inside a rigid titanium housing attached only to the inlet and outlet ports . A unique valving system has been redesigned for the VAD-ProCor Model 1. The porcine aortic root anatomy; including the valvular system, the complex of the sinuses of Valsalva, the aortic ridge and the first 5 mm length of the ascending aorta; is placed in a highly flexible stent. (Fig.3, A and B).16 KB

The intracorporeal segment of the pneumatic driving line is covered with teflon felt fabric and it has two buttony teflon discs. One of the teflon discs is placed under the skin, in the subcutaneous tissue. The second is a sliding disc that is sutured to the aponeurosis of an external oblique muscle, at the exit point of the pneumatic line. The blood pump is placed between the transversalis muscle and the transversalis fascia.

The technical implant of VAD - ProCor Model 1 can be performed either in an intracorporeal or paracorporeal position by simply changing the position of the inflow and outflow pump connectors. The inflow via can be connected either to the left atrium or to the apex of the left ventricle; and the outflow connector can be sutured to the descending thoracic aorta or to the ascending aorta.

This shows how versatile VAD-ProCor Model 1 system is.


External Drive:

VAD actioned by a pneumatic driver has evidenced its effectiveness for more than three decades. Although, the biggest problem lies in the fact that the pneumatic system must be used together with a transcutaneous transmission power. The problem lessens when a portable unit with hours of autonomy is used.

VAD - ProCor Model 1 is powered by an external pneumatic console consisting of an electronic module and a compression unit. (Fig.4).14 KB

It has been designed to work in a synchronous mode, this means in counterpulsation with an external R-wave signal from the patient and in an asynchronous mode, which sets a fixed frequency.

As to electronics; a microprocessor based circuit controls the frequency, the systolic percentage, the alarm system (pressure, vacuum, motor temperature) and a digital display. It is prepared to commute automatically from synchronous to asynchronous mode, for example when the patient's frequency is too low (below 40 bpm).

The compressor unit that includes the pneumatic valves, is in an almost noiseless insulated cabinet .

The console has an Uninterruptible Power Supply (UPS) that provides the necessary protection against electrical power failures or against possible variations in line voltage.

It has been developed with an acquisition computer system and it has been checked during VAD-ProCor Model 1 in vitro model test.

Moreover, there is a portable knapsack system that works with a mini compressor power unit, with the same electronic microprocessor (hardware and software) described above. This knapsack system includes a battery that gives some hours of free movement to the patient. Its main characteristics are that it is easy to transport, it is a light unit and that its performance is smooth. The VAD- ProCor Model 1 pump has been designed for slow rate frequency during a prolonged period.



New Bioprosthesis for VAD : a unique advancement in VAD


The Anatomy of the Aortic Root Maintained


Introduction:


Either porcine or pericardial bioprostheses and the currently available mechanical valvular prostheses mounted in VAD, result in the formation of thrombotic deposit at the leaflet nadirs. In fact, the base of the valvular leaflets in the prosthetic area is excluded from the blood stream during the opening and closing phase, thus favouring the production of lethal thromboembolic material deposit.

This complication has been reported with both the experimental and the clinical use of VAD.


Objectives:

The new bioprosthesis maintains the entire anatomy of the porcine aortic root in a designed frame which includes the sinuses of Valsalva and the critical aortic ridge: that is the even structure that connects anatomically and functionally the three aortic commissures. The smooth and uniform anatomy of the sinuses of Valsalva, avoids the dangerously tortuous angular formation during the valvular opening phase between the nadirs of the biological material and the foreign material.

In order to secure the valve to the VAD conduits system, two cuffs prolong the dacron fabric that covers the bioprosthesis body, at both the inlet and outlet of the valvular opening


Conclusion:

Bioprostheses are the main alternative to be incorporated to VAD. Blood damage and thromboembolic complications are minimized when compared to those due to mechanical prostheses.

The new bioprosthesis that maintains the aortic root will be extremely helpful to avoid the thromboembolic complications that currently plague available bioprostheses when incorporated to VAD conduits, either in an intracorporeal or paracorporeal position.

VAD - ProCor Model 1 has adopted the new bioprosthesis as the alternative valving system.


A Brief History


The 33rd Anniversary
demonstrates the experience of the ProCor group in the achievement of both VAD and total artificial heart.

  1. 18th July 1963, first implantation of an intrathoracic left artificial ventricle in a human being, with Dr. E. Stanley Crawford, Baylor University College of Medicine, Methodist Hospital, Houston Tx. USA (1,2).

    The original prototype is kept and exhibited at the Smithsonian Institution, Washington, DC.

  2. 21st April 1966, first paracorporeal left artificial ventricle implantation with Dr. Michael E. DeBakey, Baylor University College of Medicine, Methodist Hospital, Houston Tx., USA. (3,4).

  3. 4th April 1969, first Total Artificial Heart used as a bridge to heart transplantation with Dr. Denton A. Cooley, Texas Heart Institute, Houston Tx. USA (5,6).



The opening of this investigation gave way to the research of mechanical circulatory devices to be used worldwide in the treatment of patients with a failing heart.

The CONICET-PROCOAR program was created in 1991 and it was born out of this historical roots. Today, the program is working on 4 different lines of research. (7).

It has been transferred the manufacturing of Liotta VAD-ProCor Model 1 to the industry. 2


References:

  1. Liotta D., Taliani T., Giffoniello A.H., Sarria Deheza F., Liotta S., Lizarraga R., Tolocka L., Pagano J.: Biancciotti E.: Artificial Heart in the chest: Preliminary report. Trans Amer. Soc. Int. Organs, 7:318,1961.

  2. Liotta D., Hall C.W., Henly W.S., Beall A.C., Cooley D.A., DeBakey M.: P Prolonged assisted circulation after cardiac surgery. Prolonged partial left ventricular bypass by means of intracorporeal circulation. This paper was finalist in The Young Investigators Award Contest of the American College of Cardiology, Denver, May 1962. Amer.J.Cardiol. 12:399,1963.

  3. DeBakey M.E., Liotta D., Hall C.W.: Prospects for implications of the artificial heart and assistive devices. J.Rehab., 32:106,1966.

  4. Hall W., Liotta D., DeBakey M.E.: Bioengineering efforts in developing artificial hearts and assistors. Amer,J.Surg. 114:24,1967.

  5. Cooley D.A., Liotta D., Hallman G.L., Bloodwell R.D., Leachman R. Milan J.D.: First human implantation of cardiac prosthesis for total replacement of the heart. Trans. Amer. Soc. Artif. Int. Organs. 15:252, 1969.

  6. Cooley D.A., Liotta D., Hallman G.L., Bloodwel R.D. Leachman R. Nora J.D., Fernbach D.J., Milan J.D.: Orthotopic cardiac prosthesis for two - staged cardiac replacement. Am. J. Cardio. 24:723 - 730, 1969.

  7. Liotta D., Alvarez C.B. and CONICET - PROCOAR Investigators. Chronic Heart Assist System, Assisted Circulation IV, 217-232 , 1995. Editor, F.Unger-Verlag Berlin,




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This study is funded by CONICET-PROCOAR Program. PMT-SID 0423 and Domingo Liotta Foundation.
F.O.C. MEDICAL S.A. Hipólito Irigoyen 2321 (1089) Buenos Aires, Argentina


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