Cardiac Assist Device

This invention relates to an apparatus to assist a patient's heart. More particularly the apparatus is a cardiac assist device capable of being adapted for use as a left or right ventricle assist device and, in a preferred embodiment, as an assist for the right ventricle substitute, that is a modified right atrium, subsequent to the Fontan operation.

The Fontan operation has become of increasing importance over the past two decades for younger patients with complex univentricular hearts. Prior to the Fontan procedure such a condition was considered inoperable and untreatable.

The main risk factors for the Fontan operation include decreased systolic function of the ventricle, increased pulmonary vascular resistance and valve regurgitation.

Long term difficulties are now more frequently observed. Surviving patients experience reduced systolic function and increased pulmonary vascular resistance.

There have been modifications of the operation. For example the fenestrated Fontan procedure reduces the initial mortality of high risk patients but may not reduce the long term complications. As a result there is a belief that the Fontan operation should be considered a temporary procedure, and patients will require a heart-lung transplantation at a later age.

In the Fontan operation the systemic venous return is connected to the pulmonary artery by by-passing an absent or defective ventricle. The operation takes two forms. First closure of the atrial septal defect and anastomosis of the right atrium to the pulmonary artery and, secondly, construction of a tunnel within the right atrium, connecting the inferior vena cava to the superior vena cava and then connecting the superior vena cava to the pulmonary artery.

The present invention seeks to further improve the art and provides an alternative to transplantation. The present invention provides a right atrial assist that has the capability of prolonging the duration and improving the quality of the life of many patients who otherwise would have a heart/lung transplantation as their only opportunity for survival.

Accordingly, the present invention provides an apparatus to assist a patient's heart comprising a main pump to be mounted on the patient's chest wall and able to reciprocate to generate a compression stroke and an expansion stroke, said pump including a pump chamber to contain a fluid; an atrial pump attached to the atrium of the patient's heart, said atrium receiving blood through the patient's inferior vena cava (IVC); a conduit communicating the pump chamber and the atrial pump; a bypass in the conduit to surround the IVC; whereby the compression stoke of the pump forces fluid in the bypass to restrict the IVC and compresses the atrium to pump blood towards the patient's pulmonary artery.

The invention is illustrated, by way of example, in the drawing in which:

FIG. 1 illustrates a heart with a right atrial tunnel type of the Fontan procedure;

FIG. 2 illustrates a heart with an atrial septal defect type of Fontan procedure;

FIG. 3 is a schematic view of the apparatus according to the present invention.

FIG. 4 is an external view of a heart fitted part of the apparatus of the present invention;

FIG. 4a is a detail of FIG. 4;

FIG. 5 illustrates operation of the device according to the present invention in the heart of FIG. 1;

FIG. 6 illustrates operation of the apparatus the present invention in the heart of FIG. 2; and

FIGS. 1 and 2 show a heart modified according to the Fontan operation. FIG. 1 shows an atrial septal defect 10 and a lateral tunnel 12 connecting the inferior vena cava IVC to the superior vena cava SVC. The superior vena cava SVC is connected to the pulmonary artery PA and the blood flow in the superior vena cava SVC thus re-directed. The aorta A is also shown. Thus FIG. 1 shows construction of a tunnel 12 inside an atrium 14 and connecting the inferior vena cava IVC to the superior vena cava SVC. The superior vena cava SVC is connected to the pulmonary artery PA.

In FIG. 2 the second Fontan technique is illustrated. The atrial septal defect 10 is repaired by a patch 16. Again the superior vena cava SVC is connected to the pulmonary artery PA. The right atrium 14 is connected to the pulmonary artery PA via the superior vena cava SVC.

FIGS. 3 to 6 illustrate the present invention.

FIG. 3 shows the apparatus schematically. There is a main pump 18 to be mounted on the exterior of the patient's chest wall 20. The main pump has a chamber 22 defined between a pump diaphragm 24 and the skin on the chest wall 20 of the patient. There is a magnet 26 attached to the diaphragm 24 and an electromagnet 28 attached to the skin of the patient.

On the interior of the patient's chest, immediately adjacent the main pump 18, there is a hydraulic pressure receiver 30 formed with a diaphragm 32 mounting a magnet 34 and having a chamber 36. There is an atrial pump 38 attached to an atrium 14 of the patient's heart. The atrium 14 receives blood from the patient's inferior vena cava IVC. A conduit 40 having rigid walls communicates the chamber 36 and the atrial pump 38. There is a by-pass 42 in the conduit 40 that surrounds the inferior vena cava IVC.

By-pass 42 includes a flexible inner wall or sleeve 43 that surrounds the inferior vena cava IVC. Electrodes 45 assesses heart activity. The electrodes 45 generates a signal which is transmitted to an internal sensor transmitter 44. The internal sensor transmitter 44 communicates with an internal transcutaneous signal transmitter 46 which, in turn, communicates with an external transcutaneous signal transmitter 48. A signal from the external transcutaneous signal transmitter 48 is sent to an electrical pulse generator 50 that includes a commutator, a timer and a power source. The electrical pulse generator is, in turn, in communication with the magnets 26 and 28 of the main pump 18.

Although not shown in the drawings, main pump 18 has a diaphragm that seals the chamber 22 and contacts the skin of the chest wall 20. Diaphragm 32 seals chamber 36 of the hydraulic pressure receiver 30. Similarly atrial pump 38 is closed with a diaphragm that contacts the atrium wall. Thus the system of hydraulic pressure receiver 30, conduit 40, atrial pump 38 and by-pass 42 with sleeve 43 forms a closed circuit. This arrangement is necessary to avoid leakage of the fluid contained within the system by which pressure is transmitted.

An external view of the by-pass 42 is shown in FIG. 4 and operation of the device is shown in FIGS. 4a, 5 and 6.

FIG. 4 illustrates the atrial pump 38 located on the right atrium 14 of the patient and the rigid conduit 40 that extends from the hydraulic pressure receiver 30 to the atrial pump 38 with the by-pass 42 extending around the inferior vena cava IVC.

The apparatus of FIG. 4 functions as follows: The main pump 18 receives an electrical pulse from the electrical pulse generator 50 which activates the magnets 26 and 28. The diaphragm 24 moves in a manner controlled by the direction of the current from the electrical pulse generator 50 by attraction and repulsion of magnets 26 and 28. Movement of the diaphragm 24 generates positive and negative hydraulic pressure in the chamber 22 of the main pump 18. The chamber 28 is in contact with the skin surface which reacts to those internal pressure changes by moving inwards and outwards. This movement is transmitted to the diaphragm 32 of hydraulic pressure receiver 30. The movement is accentuated by the presence of magnet 34 in the hydraulic pressure receiver 30. That is the magnet 34 is repulsed or attracted, depending on the variation of the polarity of the magnets 28. Thus diaphragm movement by hydraulic pressure is assisted by magnetic force. Movement of the diaphragm 32 creates alternatively positive and negative pressure within the hydraulic pressure receiver 30 as a result of movements in the main pump 18. Hydraulic pressure in the hydraulic pressure receiver 30 is transmitted through the conduit 40, through the by-pass 42 that surrounds the inferior vena cava IVC and to the atrial pump 38.

When pressure is applied to the conduit 40 the inferior vena cava IVC is restricted by that pressure (as shown in FIG. 4a). Similarly, of course, when there is reduced pressure in the hydraulic pressure receiver 30 then the inferior vena cava is opened as pressure within the inferior vena cava exceeds the pressure within the by-pass 42. The rigidity of conduit 40 means that it does not change volume with pressure changes in receiver 30. Similarly atrial pump 38 and by-pass 42 have rigid walls (as emphasized by the use of double lines in FIG. 3).

The increased hydraulic pressure in receiver 30 is transmitted to the atrial pump 38 and to the atrial chamber. The motion of the atrial pump 38 will increase the pressure in the right atrium and, because of the closure of the inferior vena cava, forward flow from the right atrium toward the pulmonary artery will occur.

When the pressure is reduced and the inferior vena cava opened by the reduced pressure, the atrial pump 38 will move the atrium wall outwardly, reducing pressure within the atrium 14. Blood flow from the inferior vena cava to the right atrium 14 will then fill the atrium. The cycle can then be repeated.

The electrodes 45 and the hydraulic pressure sensors sense the electrophysiology of the heart and the function of the hydraulic pressure received, the atrial pump 38 and the by-pass 42. This information is amplified and transmitted by the internal sensor transmitter 44, which is powered by an internal battery. The signal generated is transmitted through the skin using transcutaneous induction coils as known in the art. The external sensor 48 transmits a signal to the electrical pulse generator 50. The electrical pulse generator 50 contains a timer which coordinates the function of the atrial pump 38 and the by-pass 42 to the patient's heart function, thus maximizing the forward flow from the inferior vena cava to the right atrium and from the right atrium toward the pulmonary artery. The information received from the pressure sensors assists this function. The electrical pulse generator 50 contains a commutator (not shown) which, by reversing direction of electrical current to the magnets 26 and 28 in the main pump 18, changes the hydraulic pressure in the pump 18. This variation results in a similar change throughout the hydraulic system. Repetitive cycles of the change create the pumping action of the device. The electrical pulse generator 50 has a power source which is, of course, easily renewable.

Thus the apparatus of the present invention enhances the forward flow of blood from the IVC to the left atrium via pulmonary artery circulation. It does this by pumping blood forward from the right atrium, or right atrium lateral tunnel, to the pulmonary artery. Power generated outside the body is transmitted by hydraulic force. The alternating pressure in the conduit 42 is generated by electromagnetic energy and mechanical energy transmitted through the skin surface.

The invention has been described with reference to assisting a heart that has undergone the Fontan procedure. The invention is also related to extraluminal hydraulic valve and implanted systolic and diastolic assist devices.

Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be readily apparent to those of ordinary skill in the art in light of the teachings of this invention that certain changes and modifications may be made thereto without departing from the spirit or scope of the appended claims.