Cardiac assist device

Abstract: A single device (1), which is intended to integrate the functions of a ventricular assistance device (V A D ) proper and of an aortic balloon pump (IABP), includes a single energy source (24) which causes the simultaneous rhythmic contraction of two chambers (5 , 6) which are intended to be filled with blood. One (6) of the contractible chambers has two one-way valves for the inlet (8) and outlet (9) of the blood respectively, whilst the other (5) has a single inlet-outlet connector (12) without valves for connection to the outlet of the first chamber (6) downstream of its outlet-valve portion (9).

Description: The present invention relates to devices for use in the treatment of acute or chronic mono- or bi-ventricular myocardial insufficiency. In general terms, two different kinds of device are known for the treatment of this condition. The first kind of device is that currently known as an aortic pulsator (an I A B P , that is, an intra-aortic balloon pump). Its operation is based on the reduction of the so-called post-loading (the overall resistance of the vascular system) in synchronism with the systolic expulsion from the left ventricle in order indirectly to increase the output of the heart. This device usually takes the form of a hollow catheter with a spindle-shaped balloon about 25-30 cm long at its end which, in its inflated condition, can occupy a volume of about 40 cm³. The catheter in question is positioned in the thoracic aorta by being passed along the femoral artery. The catheter is connected to a driver unit with a compressor and a system for synchronising it with the patient's electrocardiogram or arterial pressure. The driver unit inflates and deflates the balloon in the thoracic aorta in synchronism with the stages of the heart's activity. In general, at the beginning of the ventricular systole (the emptying of the left ventricle and the corresponding expulsion of a quantity of blood), the intra-aortic balloon is deflated so as to reduce the telediastolic pressure (the "minimum" pressure) which is equivalent to the reduction of the peripheral resistance of the vascular system, that is, the so-called post-loading. It is thus possible to create conditions favourable to the admission of a greater quantity of blood to the arterial system. The difference between the volume of the systolic output with and without the balloon pump represents the gain in terms of the efficiency of the system (15-20% on average). During the diastole, that is, when the aortic valve is closed, the intra-aortic balloon is inflated and consequently pushes back a quantity of blood approximately equal to its own volume (about 40 cm³) in both a cranial direction (that is, towards the upper part of the body ) and a caudal direction (that is, towards the lower part of the body). This raises the arterial pressure which has the positive result of an increase in the coronary flow-rate. The other kind of device is essentially that currently known as a ventricular assistance device (V A D ). It is based on the bypassing of the right and/or left ventricles by the withdrawal of blood from the atria or directly from the ventricles and its readmission to the pulmonary artery and/or to the aorta. Devices of this type can be divided further into alternating V A D s (for example, electropneumatic, electromagnetic, electromechanical systems, etc.) which effect intake stages followed by compression stages so as to create a pulsed blood-flow, and continuous V A D s which create a continuous flow by means of a system with a centrifugal pump. The main advantage of these devices is their ability to keep a patient alive even when the heart has stopped or is fibrillating. For this reason, V A D systems are used most successfully for mechanically supporting circulation whilst a heart transplant is awaited (a transplant bridge). They have been found to be much less effective, however, when used in parallel with the heart in an attempt to compensate for temporarily weakened heart function. A plausible explanation for this ineffectiveness is that all V A D s reduce the preloading of the heart muscle but increase the aforementioned post-loading (an increase in the average arterial pressure). With an inadequate ventricle (that is, a ventricle without functional reserve) the increase in the post-loading reduces the volume of blood expelled during the ventricular systole until, in certain extreme cases of weakened contractile activity of the heart, the aortic valve fails to open (the volume of blood expelled is zero). The resulting increased post-systolic volume creates a series of physical-metabolic conditions in the ventricles which create conditions unfavourable to the functional recovery of the heart. From US-A-4 581 029 a device is known for use as a blood pump comprising: an inlet tube connected to the right or left atrium of the patient's heart; an outlet tube connected to the patient's pulmonary artery or aorta; a contractible chamber which is intended to be filled with a quantity of blood and is associated with the inlet tube and first valve means for admitting the quantity of blood to the chamber and with the outlet tube and second valve means for discharging it therefrom; and operating means for causing the chamber to contract in a pulsed manner. There is thus a need to provide a device which can simultaneously achieve the following results: a reduction in preloading by the withdrawal of blood upstream of the ventricles, a blood-flow which can maintain adequate perfusion of a patient's organs even in the absence of heart activity, a reduction in post-loading during systolic expulsion, and an increase in the coronary flow-rate in the diastolic stage. Briefly, there is a need to provide a device which can combine the advantages of V.A.D. systems and of balloon-pump systems without incurring their respective disadvantages. The object of the present invention is to provide a device which satisfies this need in an optimum manner. According to the present invention, this object is achieved by virtue of a device having the characteristics recited in claim 1. Preferred embodiments of the invention are specified in the dependent claims. The invention will now be described, purely by way of non-limiting example, with reference to the appended drawings, in which: Figures 1 and 2 show two possible embodiments of the device according to the invention, and Figures 3 and 4 show the general arrangement of the device according to the invention in use and also with reference to its operating sequence. The device according to the invention, generally indicated 1, includes essentially a ventricular bag 6 (the first chamber) with two one-way valves 8 and 9 (constituted, for example, by heart-valve prostheses or valves of a similar structure) whose directions of opening are selected such that the alternate contraction and expansion of the ventricular bag 6 creates a blood-flow in the direction indicated by the arrows in Figures 1 and 2. In practice, the valve 8 acts as an inlet valve for admitting blood to the bag 6 and the valve 9 acts as an outlet valve for discharging it therefrom. A tube 11, for example, of the type currently used as a vascular prosthesis (a "vascular graft") is connected to the inlet valve 8 and is intended to be connected to the right or left atrium of the patient's heart according to the arrangement shown in Figures 3 and 4. The outlet valve 9 opens into an outlet tube 10 which has a structure generally similar to that of the tube 11, and is intended to be connected to the patient's pulmonary artery or aorta, again according to the arrangement shown in Figures 3 and 4. A further chamber or bag 5 (the second chamber) is associated with the bag 6, either in one unit (that is, within a single overall envelope 20 according to the arrangement shown in Figure 1) or in a spatially adjacent arrangement (according to the solution shown in Figure 2, which has two separate envelopes 22, 23), and has a single, free, communication opening 12, that is, an opening which enables the unimpeded flow of blood out of and into the bag 5, which opens into the tube 10 downstream of the outlet valve 9 with reference to the direction in which the blood is expelled from the bag 6. If the bags or chambers 5, 6 are housed in a single envelope 20, a soft or partially rigid dividing wall 21 is provided. Each chamber 5, 6 (which, like the tubes 10, 11 and the valves 8 and 9, are formed according to solutions widely known in the art and do not need to be described fully herein) is defined essentially by a bag, bladder or balloon of flexible material (for example, a polymeric material) housed in an envelope which is essentially rigid or relatively more rigid (the envelope 20 of Figure 1, the envelopes 22, 23 in the solution of Figure 2). The outer surface of the bag and the inner surface of its envelope thus define an operating chamber into which an operating or supply source (usually constituted by a pneumatic or hydraulic pump) rhythmically delivers a fluid under pressure through respective supply tubes 24, 25 and 26, causing the flexible walls of the bags to contract and consequently reduce the volumes of the chambers 5 and 6. The alternating supply and discharge of the pressurised fluid (that is, by a succession of pumping and discharge stages with the consequent alternating contraction and expansion of the bags) results in a pulsed pumping action on the blood circulating in the device 1. In particular, the chamber 6, which is intended to act as an artificial ventricle, takes in blood - during the expansion stage - from the tube 11 through the inlet valve 8 and then expels that quantity of blood - during the contraction stage - through the valve 9 into the tube 10. The chamber 5 (which is intended to play a functional role substantially comparable to that of an aortic balloon pump) can vary its volume in order selectively to vary the post-loading of the heart. The chambers 5, 6 are operated in synchronism by the same fluid supply so that, during their diastolic stage, that is, when the blood is flowing into the chamber 6 through the valve 8, the chamber 5 also expands to reach its maximum volume. Conversely, when the chamber 6 moves on to the systolic stage and contracts in order to expel the quantity of blood which has previously collected within it, the bag 5 also contracts to reduce its volume. Figures 3 and 4 refer explicitly to a possible arrangement for the connection of the device according to the invention in parallel with the left ventricle. This means that the inlet tube 11 is connected to the left auricle or atrium whilst the outlet tube 10 is connected to the ascending portion of the aorta A. The connections are formed according to known criteria, for example, by insertion or anastomosis. At the beginning of the ventricular systole of the heart, the pneumatic source (the pump) which supplies the tubes 24, 25 and 26 is operated (by a vacuum, spring, etc.) in a condition of active pressure reduction so as to cause the maximum expansion of the chambers 5 and 6 which fill with blood. In particular, the chamber 6 receives blood from the tube 11 connected to the left atrium, thus reducing the preloading of the ventricle. The chamber 5 which communicates with the aorta A through the tube 10 fills with blood as a result of the pressure gradients prevailing in the two regions (the aorta A and the chamber 5), reducing the post-loading of the left ventricle. At the end of the ventricular systole of the heart or during the diastole, the operating source supplies the tubes 24, 25 and 26 so that both the chambers 5 and 6 are compressed and the quantity of blood collected therein during the preceding stage is admitted to the aorta A through the tube 10, increasing the arterial pressure with a consequent increase in coronary perfusion. In the event of heart fibrillation, the chamber 5 does not fulfil an active haemodynamic role and the valved chamber 6 which is arranged to bypass the ventricles can maintain the vital body functions on its own. It is clear from the foregoing that the device according to the invention simultaneously satisfies, in a wholly satisfactory manner, all the functional requirements which are normally satisfied - separately - by V A D s and aortic balloon pumps, without giving rise to the problems demonstrated by those devices.

Claims: A cardiac ventricular assistance device comprising, in a single functional combination: an inlet tube (11) for connection to the right or left atrium of the patient's heart, an oulet tube (10) for connection to the patient's pulmonary artery or aorta, a first selectively contractible chamber (6) which is connected to said inlet tube (11) and to said outlet tube (10) and is intended to be filled with a quantity of blood; said first chamber having associated therewith first valve means (8) for admitting the quantity of blood to the first chamber and second valve means (9) for discharging it therefrom, a second selectively contractible chamber (5) which can also be filled with a quantity of blood and has a communication opening (12) which opens into said outlet tube (10) downstream of the discharge valve means (9) of the first selectively contractible chamber (6), with reference to the direction in which the blood is expelled from said first chamber (6) for enabling the unimpeded passage of blood out of and into the second selectively contractible chamber (5), and operating means (24, 25 and 26) causing the first (6) and second (5) chambers to contract in synchronism in a pulsed manner. A device according to Claim 1, characterised in that it includes a common envelope (20) defining the first (6) and second (5) selectively contractible chambers and having dividing means (21) which separate the first (6) and second (5) selectively contractible chambers. A device according to Claim 2, characterised in that the dividing means (21) are soft. A device according to Claim 2, characterised in that the dividing means (21) are at least partially rigid. A device according to Claim 1, characterised in that it includes two separate envelopes (22, 23) defining the first (6) and second (5) selectively contractible chambers, respectively. A device according to any one of the preceding claims, characterised in that at least one of the first (6) and second (5) selectively contractible chambers is defined by a bag of flexible material. A device according to any one of the preceding Claims 1 to 5, characterised in that at least one of the first (6) and second (5) selectively contractible chambers is defined by a rigid envelope and a membrane of flexible material. A device according to Claim 6, characterised in that the bag of flexible material is housed in an at least rigid envelope (20; 22, 23) so that the outer surface of the bag and the inner surface of the envelope define an operating chamber with dimensions which vary as a result of the contraction of the bag, and in that the operating means (24, 25, and 26) are constituted by means for supplying a fluid under pressure to the interior of the operating chamber. A device according to any one of the preceding claims, characterised in that the first (8) and second (9) valve means are constituted by valves with pivoting obturators. A device according to Claim 2, characterised in that the operating means include a single tube (24) for supplying a quantity of fluid under pressure to the common envelope (20). A device according to any one of the preceding claims, characterised in that the operating means achieve a direct mechanical effect and are moved by any source of energy, such as a biological, magnetic or electrical source.

Inventors: ARPESELLA GIORGIO, MAMBRITO BRUNO, ZAGARA MAURIZIO, ARPESELLA, GIORGIO, MAMBRITO, BRUNO, ZAGARA, MAURIZIO
Applicants: MINI RICERCA SCIENT TECNOLOG
Application year: 1991
Main classification: A61M1
IPC codes: A61M1