WO2014064267A1

WO2014064267A1 - Control system for a cardiac assist device

Info

Publication number: WO2014064267A1
Application number: PCT/EP2013/072435
Authority: WO
Inventors: Per Steinar Halvorsen; Erik Fosse; Andreas Espinoza
Original assignee: Oslo Universitetssykehus Hf
Priority date: 2012-10-25
Filing date: 2013-10-25
Publication date: 2014-05-01
Also published as: GB201219168D0

Abstract

A control system for a cardiac assist device includes a sensor 10, 12 implantable in the body at the heart for monitoring movement of the heart. The control system is arranged to, in use: receive signals from the sensor 10, 12, the signals providing information on movement of the heart muscle; process the signals to identify heart dysfunction indicative of inadequate or excessive flow rate from the cardiac assist device; and adjust the flow rate from the cardiac assist device based on the identification of such heart dysfunction in order to optimise the performance of the cardiac assist device.

Description

CONTROL SYSTEM FOR A CARDIAC ASSIST DEVICE

The current invention relates to a control system for a cardiac assist device, such as a ventricular assist device (VAD), and to a related method.

Cardiac assist devices are devices used to augment or replace the blood circulatory function of a failing heart. Such devices are to be distinguished from artificial hearts, which completely replace cardiac function and are typically used when the patient's heart has been removed. Cardiac assist devices generally provide a blood pumping function to increase the flow of blood from a ventricle to the corresponding artery and hence are often known as ventricular assist devices (VADs). Some VADs are intended for short term use, for example during recovery from heart attacks or heart surgery, while other implantable devices are intended for long term use (months to years and in some cases for life), typically for patients suffering from end stage heart failure.

VADs are designed to assist either the right (RVAD) or left (LVAD) ventricle, or both at once (BiVAD). The type of VAD selected for a particular patient depends on the patient's condition, the underlying heart disease and on the pulmonary arterial resistance that determines the load on the right ventricle. LVADs are most commonly used, but when pulmonary arterial resistance is high and/or right ventricular function is reduced, then right ventricular assistance or the use of a BiVAD can be required. Long term VADs are used to provide patients with a good quality of life while they wait for a heart transplantation (known as a "bridge to transplantation") or as destination therapy for end stage heart failure.

Cardiac assist devices including VADs of various types are well known and utilise various different types of pumps and control systems. There are however common requirements to all types, being a power source, a pumping device with appropriate connections for surgical implantation at the heart and a control system. The control system in newer pumps typically controls the pump to provide a constant flow and provides the ability for the flow rate to be adjusted. The flow rate might be set by the physician or surgeon.

When using implantable cardiac devices it is necessary to monitor the effect of the treatment on an ongoing basis in order to identify complications and ensure that the patient is receiving optimal treatment. For example 20-40 % of the patients treated with LVAD to assist the failing left ventricle suffer from right ventricular (RV) failure after implantation of the assist device. It is difficult to predict which patients will develop this RV dysfunction, but signs of high pulmonary vascular resistance increase the likelihood of RV failure. Those who experience RV failure will stay approximately 8 days longer in the ICU than those who do not. Each patients cost approximately 90 000 US$ more if he/she needs inotropic support during the ICU stay. The need for RVAD due to RV failure increases the cost by an average of 272 000 US$. RV failure increases the risk of death in LVAD patients, 1 1 .9% vs. 23.4% with RV failure. (Preliminary report presented at the ACC conference 201 1 : Iribarne A et al. Incremental cost of right ventricular failure after left ventricular assist device placement. J Am Coll Cardiol. 201 1 ).

A problem is that one has to rely on indirect or intermittent methods for the evaluation of the effect of the treatment. Cardiac performance can be evaluated by invasive blood pressures, cardiac output measurements and intermittently with

echocardiography in the intensive care unit (short term management), serum-levels of cardiac function markers (pro-BNP, bilirubin, transaminases), clinical markers (ankle edema, ascites, hepatic enlargement) for long term management. These techniques all require a medical professional and the presence of the patient at a medical facility. In addition, as the patient is improving and discharged to the home, only the pump flow and pressure delivered by the cardiac assist device can presently be used for monitoring the patient on an ongoing basis after discharge from the medical facility.

Non-invasive motion sensors have been suggested for use in guiding the control of a heart pump. For example, US 7988728 discloses the use of non-invasive sensors to monitor heart rate (and patient movement) and to control a cardiac assist device accordingly. An accelerometer is used to measure heart rate and patient movement and these measurements are used in control of a rotary pump. However, the use of these sensors can only provide basic information relating to heart rate and physical activity. The non-invasive sensors provide no direct information on cardiac performance or the performance of the cardiac assist device and can by no means provide information on complications, such as, for example, failure of the right ventricle (occurring in 20-40 % of the patients with LVAD).

Control of the timing of a cardiac assist device using implantable sensors has also been described in the prior art. US 7513864 describes the use of an acoustic or mechanical sensor (e.g. accelerometer) implanted in the heart to monitor heart function, with the measurements of heart rate being used to provide timing input for a cardiac assist device. These measurements provide information on the timing of the heart. They are intended to ensure correct timing of counter-pulsation in an LVAD relative to the closure of the aortic valve.

Viewed from a first aspect, the present invention provides a control system for a cardiac assist device, the system including a sensor implantable in the body at the heart for monitoring movement of the heart and the control system being arranged to, in use: receive signals from the sensor, the signals providing information on movement of the heart muscle; process the signals to identify heart dysfunction indicative of inadequate or excessive flow rate from the cardiac assist device; and adjust the flow rate from the cardiac assist device based on the identification of such heart dysfunction in order to optimise the performance of the cardiac assist device.

Sensors used in this way provide continuous and direct information on cardiac performance. By means of a control system as described above it is possible to detect and address problems with the cardiac assist device and to address them before the patient is severely affected. The use of implantable sensors in this way also provides further advantages since as well as the optimisation of flow rate it is also possible to monitor the effects of pump settings and medical therapy including treatment of the patients by drugs to control, for example, pulmonary pressure or contractility. It is important to understand that the advances described herein relate to implantable sensors and not to sensors that are used outside of the body. The sensor should be implantable at the heart. The invention extends to a control system with sensors that are implanted in the body.

As noted above, known systems involving the control of cardiac assist devices via non-invasive sensors as in US 7988728 are not capable of such measurements. The system described above provides all the advantages of these non-invasive systems with the additional advantage of direct monitoring of movement of the heart muscle and consequent benefits in the detection of heart dysfunction. Moreover, the known systems using implantable sensors for control of cardiac assist devices as in US 7513864 involve merely timing input. The sensors described in US 7513864 and similar systems are not utilised for the detection of heart dysfunction but instead are used to match the operation of the cardiac assist device to the heart rate.

It is known to implant motion sensors at the heart for the purpose of post-operative monitoring of cardiac function. A system of this type is described in EP 1458290, in which implanted motion sensors are used to follow movements of the heart muscles following heart surgery, for example to detect ischemia.

The sensors and techniques described in EP 1458290 are similar to those required by the current invention, and in fact the teaching of EP 1458290 is useful technological background for one seeking to implement the current invention. However, like the other prior art documents referenced above the disclosure of EP 1458290 fails to suggest the use of implanted sensors in the control of a cardiac assist device. In particular EP

1458290 and similar earlier disclosures of heart monitoring with implanted sensors do not suggest monitoring for heart dysfunction indicative of sub-optimal operation of a cardiac assist device, and control of the cardiac assist device to address this.

Consequently the currently proposed system provides advances not taught or suggested in the prior art. Various serious problems with cardiac assist devices can be addressed by this system, as discussed in more detail below.

The optimisation of the performance of the cardiac assist device preferably comprises an adjustment to increase the flow rate if it is determined to be inadequate, or to decrease the flow rate if it is determined to be excessive. Optimisation may also in some circumstances involve adjustment to a pulsing speed of the cardiac assist device, where it is a device with a pulsatile pumping characteristic. Adjustments to the flow rate from the cardiac assist device may occur continuously or periodically at regular intervals. It is preferred for the flow rate to be adjusted based on a closed loop control of the flow rate in response to the identification of heart dysfunction indicative of inadequate or excessive flow rate.

When the flow delivered by the pump is excessive the pump can empty the blood from the heart. This gives rise to a risk of pump failure (suction problems) with

corresponding circulatory collapse. This problem may initially be detected by the sensors as a pathological increase in motion in the contracting "healthy" myocardium (reduced afterload), until a sudden decrease occurs due to suction (acute increase in afterload). Thus, in a preferred embodiment processing of the signals from the sensor to identify heart dysfunction may comprise monitoring for a progressive reduction in afterload (progressive increase in systolic motions) of the ventricle and/or monitoring for an acute increase in afterload of the ventricle (acute decrease in systolic motions), and determining that there is a potentially excessive flow rate when one or both of these occurs, with the flow rate then being adjusted downwards.

When the flow delivered by the pump is inadequate this increases the demand to the remaining contracting myocardium. This may also cause circulatory collapse. This problem can be detected by a gradual decrease in contractility (motion) in the "healthy" myocardium. Eventually it will result in the occurrence of a pathological motion of the contracting myocardium in the form of reduced systolic contraction and increased post systolic contraction. In animal models a decrease in systolic motion more than 40% indicates myocardial ischemia with a sensitivity of 94% and specificity of 92%. However, it remains to be tested whether this also applies in patients treated with VAD. Thus, in a preferred embodiment processing of the signals from the sensor to identify heart dysfunction may comprise monitoring for a progressive reduction in contractility and/or monitoring for heart motion indicating reduced systolic contraction and increased post systolic contraction, and determining that there is a potentially inadequate flow rate when one or both of these occurs, with the flow rate then being adjusted upwards.

The control system may advantageously also be used to detect pump failure from other causes. For example the pump may operate inefficiently or fail completely due to clotting, tube dislodgement, acute Atrial Septal Defect (ASD) and Ventricular Septal Defect (VSD), for example. These problems will affect the motions on the "healthy" myocardium. Clotting or tube dislodgement may cause pump failure resulting in inadequate flow detectable as above, ASD and VSD may cause suction detectable by its effect on the after load as discussed above. ASD and VSD may also cause acute unloading or overloading, which may be detected by the control system as increased or decreased motion of the myocardium.

Thus, in preferred embodiments the control system may be arranged to measure the corrective effect of changes in the flow rate of the cardiac assist device and to determine that there is a problem in addition to the underlying heart defect when corrective adjustments to the flow rate do not result in an expected improvement in heart function. For example if an increase in flow rate in response to heart dysfunction indicative of inadequate flow rate does not result in an expected improvement in heart function then the control system may determine that there is a potential clotting or tube dislodgement. Also, if a decrease in flow rate in response to heart dysfunction indicative of excessive flow rate does not result in an expected improvement in heart function then the control system may determine that there is a potential ASD or VSD. The control system may be arranged to monitor for increased or decreased motion of the myocardium indicative of acute unloading or overloading and to determine that there is a potential ASD or VSD when this occurs.

It is important for the patient and/or supervising medical authority to be made aware of such potential problems and hence preferably the control system is arranged to provide an alert when a problem of this nature is determined to be potentially present.

Typically a cardiac assist device delivers a fixed pump rate (RPM) giving an almost constant flow depending on pre- and afterload. However, patients may benefit from increased flow during physical activity and rehabilitation. A motion sensor placed at the heart (or alternatively a separate sensor placed elsewhere on the body) can provide information about body motion and position. For example, such a sensor may function as a "step counter". In preferred embodiments the control system is arranged to process signals from the sensors at the heart (or optionally from a separate sensor on the body) to determine the level of physical activity of the patient and to adjust the flow rate of the cardiac assist device in response to changes in physical activity. Thus, the flow rate may for example be increased when the sensor movement indicates an increased level of physical activity by the patient.

Whilst just one sensor may be used, in preferred embodiments there are multiple sensors, for example sensors on both of the left and the right ventricle. More than two sensors could be used, for example to also provide information about movement of the left or right atrium. The sensors may include an ECG sensor in addition to the motion sensor(s). The ECG and motion sensors could be combined into a single sensor device, which can hence be implanted in a single operation. Advantageously, the use of a combined ECG and motion sensor allows for more information to be provided on heart function. ECG data can be used in conjunction with motion sensor data to allow for a more informed decision making process for the control system. Such an arrangement may also be utilised for pacing the heart using the control system. Thus, in situations where the patient has a pacemaker wire or could advantageously be provided with one, the control system may be arranged to provide an output for pacing the heart.

The sensor or sensors may be attached on the heart (epicardium), within the heart muscle (myocardium) or within the heart (heart chambers). Thus, the sensors on the left or right ventricle as mentioned above may be on the heart surface, within the myocardium or within the heart cavity and there may be sensors in more than one of these locations. A sensor may be attached at the apex of the heart.

The particular form of the sensors is not of great significance provided that they are susceptible to operation implanted within the body and provided that they are capable of providing signals that directly indicate heart motion or can be processed to determine heart motion. The sensors may for example take the form of accelerometers, inertia based sensors, electro-mechanical position sensors, acoustic sensor elements such as ultrasound sensors, gyroscopic sensors and so on, including combinations of sensor types.

Movement of the heart and characterisation of this movement can be carried out by any suitable means. Acceleration data can be integrated to provide movement data and movement data can be derived from the differential of position data. The control system is preferably arranged to use position, motion and/or acceleration data to determine heart muscle activities and parameters such as afterload, contractility, heart rate and so on.

The control system and/or sensors may be capable of wireless transmission of data. For example, hemodynamic data may be transferred wirelessly from this system to the hospital treating the patient. The implantable cardiac assist device may be a LVAD, RVAD and BiVAD, used in the treatment of heart failure. The control system may be integrated as a part of the cardiac device and hence the invention extends to a cardiac assist device comprising the control system described above. Power to the sensors may be delivered by the power source for the cardiac assist device, for example a battery pack, with all leads incorporated into a single set of wiring for the cardiac assist device and extending between the parts external to the body including a controller of the cardiac assist device and the power source and the parts internal to the body including the implantable elements of the cardiac assist device, such as a pump and tubing, and the implantable sensors.

The systems described above can function over long time periods, providing valuable clinical information to the increasing number of patients having permanent or long- term devices. After hospital discharge such a system gives continuous information on heart rate, arrhythmias, ventricular performance and occurrence of ischemic events during daily activities. This offers promise for better diagnosis, earlier treatment of complications and improved guidance of interventions (medications) and pump settings. The system, including signal processing algorithms, may also be used in the follow up of patients, and to risk classify patients to "bridge to transplant" or to receive permanent implantable cardiac devices.

Viewed from a second aspect, the invention provides a method comprising use of the control system described above for cardiac assistance, monitoring of cardiac function and/or guidance of medical treatment in the acute phase or the follow-up phase. In some cases it may be beneficial to use the system for monitoring of cardiac function even when cardiac assistance is not continually required. In a preferred method, the control system is used to determine the need for a BiVAD by use of the signals from the sensor to identify ventricular failure.

Viewed from a third aspect the invention provides a method of controlling a cardiac assist device comprising: monitoring of cardiac function by measuring movement of the heart using implanted sensors; based on the measured movement of the heart, identifying heart dysfunction indicative of inadequate or excessive flow rate from the cardiac assist device; and adjusting the flow rate from the cardiac assist device based on the

identification of such heart dysfunction in order to optimise the performance of the cardiac assist device.

This method provides advantages similar to those from the control system described above. The method may involve use of a control system as described above in relation to the first aspect and preferred features thereof. The optimisation of the performance of the cardiac assist device preferably comprises increasing the flow rate (for example by increasing pump speed) if it is determined to be inadequate, or decreasing the flow rate if it is determined to be excessive. Optimisation may also in some circumstances involve adjusting a pulsing speed of the cardiac assist device, where it is a device with a pulsatile pumping characteristic.

Adjustments to the flow rate from the cardiac assist device may occur continuously or periodically at regular intervals. It is preferred for the flow rate to be adjusted based on a closed loop control of the flow rate in response to the identification of heart dysfunction indicative of inadequate or excessive flow rate.

The method may comprise monitoring for a progressive reduction in afterload of the ventricle and/or monitoring for an acute increase in afterload (ventricular dilatation) of the ventricle, and determining that there is a potentially excessive flow rate when one or both of these occurs, with the flow rate then being adjusted downwards. The method may also or alternatively comprise monitoring for a progressive reduction in contractility and/or monitoring for heart motion indicating reduced systolic contraction and increased post systolic contraction, and determining that there is a potentially inadequate flow rate when one or both of these occurs, with the flow rate then being adjusted upwards.

A preferred method includes monitoring the corrective effect of changes in the flow rate of the cardiac assist device and to determine that there is a problem in addition to the underlying heart defect when corrective adjustments to the flow rate do not result in an expected improvement in heart function. This may be done as described above in relation to the control system of the first aspect.

Certain preferred embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:

Figure 1 shows an example of the use of implanted sensors in conjunction with a

LVAD device for the human heart;

Figures 2a-2e show systolic and diastolic function measured by accelerometer during different interventions;

Figure 3 has plots of sensor acceleration, velocity and displacement for various conditions and also shows ECG and ventricular pressure;

Figures 4a-4c show plots of ECG and sensed velocity for the right ventricle during a LVAD procedure;

Figures 5a and 5b show plots of ECG and sensed velocity with (a) pulmonary artery hypertension and (b) after surgery to fit a LVAD; and Figures 6a-6c are plots of various heart measurements for the right ventricle during (a) chest opening, (b) weaning from extra corporeal circulation and (c) chest closure with initiation of LVAD flow.

The LVAD device of Figure 1 is similar to conventional devices as regards its basic function in pumping blood to assist cardiac function. The LVAD consists of a controller 2, batteries 4 and a pump 6. The batteries 4 are held on the patient's body along with the controller by a harness. The controller 2 is linked to the batteries 4 by wires and control wires 8 link the controller 2 to the pump 6. The pump 6 is implanted inside the body and is connected between the left ventricle and aorta in order to provide ventricular assistance to the heart. The control wires 8 connect to the pump within the body and to the controller 2 outside of the body. They supply power and control signals from the controller 2 to the pump 6.

The example arrangement of this embodiment further includes motion sensors 10, 12. A first motion sensor 10 is connected to the wall of the right ventricle, and a second motion sensor 12 is connected to the wall of the left ventricle. The control of the pump 2 by the controller 2 involves the use of data from the motion sensors 10, 12. The motion sensors 10, 12 can be any suitable sensor, such as 3-axis accelerometers, miniaturized ultrasound sensors, inertia based sensors, electromechanical position sensors and/or gyrosensors, and may for example be sensors of a type similar to those disclosed in EP 1458290.

The motion sensors 10, 12 provide signals for functional assessment of the right and left ventricle to guide therapy management (cardiac assist device settings and medical therapy). Processing of these signals is integrated into the control system of the controller 2 to thereby enable backward supervision (closed loop feedback control) to optimize the treatment of heart failure and the operation of the cardiac assist device. The control system may for example use position, motion and/or acceleration data from the sensors to determine heart movement and then monitor for changes in afterload, contractility, heart rate and other parameters of heart movement in order to identify heart dysfunction indicative of potential sub-optimal operation of the cardiac assist device. Various examples of this are set out above. The control system can also take account of other parameters including those measured at the pump such as blood pressure and so on.

The possibility to provide continuous hemodynamic monitoring (contractility and pumping capacity) and hemodynamic feedback to cardiac devices to optimize pump settings, guide the effects of medical therapy, effects of physical activity (increased demand) and to detect complications (ventricular failure, device malfunction etc.) during use of cardiac devices. Known cardiac devices do not have direct feedback systems for evaluating cardiac performance.

Motion sensor systems as described herein, for example attached to the walls of right and left ventricle, will deliver highly clinical relevant signals on myocardial contractility and ventricular performance. The sensors have been tested in various models aimed to induce both global and regional ventricular dysfunction by inducing changes in contractility (ischemia, betablocade, septic and hypotermic cardiomyopathy), preload (volume unloading and pharmacological intervention) and afterload (outflow obstruction and pharmacological intervention). The sensors are capable of detecting heart failure earlier than routine hemodynamic monitoring, and with high sensitivity. The sensors provide information about heart function very similar to echocardiography, but have an obvious advantage as continuous monitoring is possible. Signals from such sensors may also be used for guidance of treatment with implantable cardiac devices. Automated signal analysis has proved feasible with the described sensor systems and hence is implemented in the proposed control system.

The surgical implantation of the pump 6 and the internal part of the control wires 8 can be carried out by conventional surgical techniques. Similarly, the implantation of the sensors 10, 12 can be done in conventional fashion.

It will readily be understood that although the above discussion and the Figure relate to the implanted sensors in the context of an LVAD device the sensors and control system could equally well be applied to aid the operation of an RVAD or BiVAD device, or any similar cardiac assist device for human or animal cardiac assistance and/or monitoring.

In addition, although the above example embodiment utilises two motion sensors there could alternatively be just one sensor or more than two sensors depending on the level of information required, the condition of the patient, and the cardiac assist device that is being used. In some example embodiments the sensor arrangement includes an ECG sensor as well as a motion sensor. The two sensors could be combined into a single sensor device. As noted above the use of a combined ECG and motion sensor allows for more information to be provided on heart function and hence can increase the accuracy of the device and allow for better optimisation of control of the cardiac assist device. It also allows for the possibility of pacing the heart using the control system, in situations where the patient has a pacemaker wire or could advantageously be provided with one.

Figures 2a to 6c show various animal data illustrating the use of the proposed device. Figures 2a-2e show systolic and diastolic function measured by an accelerometer at the heart during different interventions including (a) a baseline measurement for comparison, (b) administration of esmolol, (c) administration of epinephrine, (d) volume and (e) LAD occlusion. The vertical arrows indicate peak systolic contraction within a defined time interval of 150 ms (thick black lines in figure) after peak R on ECG, e' denotes early diastolic inflow velocity, and a' denotes atrial inflow velocity. In a normal state e'>a', whereas during diastolic dysfunction e'<a'. A large negative e' indicates increased preload or contractility. The plots also include pressure readings and ECG readings taken simultaneous with the measurements by the accelerometer.

Figure 3 has plots of sensor acceleration, velocity and displacement for various conditions and also shows ECG and ventricular pressure measurements taken

simultaneously with the accelerometer measurements. Figure 3a is a baseline for comparison, Figure 3b shows readings taken during pulmonary artery hypertension, and Figure 3c shows measurements during failure of the right ventricle. It will appreciated that the accelerometer measurements taken at the heart provide a substantial source of information about heart function.

Figures 4a-4c show plots of ECG and sensed velocity for the right ventricle during a

LVAD procedure. As with Figure 2 the vertical lines denote the systole. Figure 4a shows measurements during chest opening, Figure 4b shows right ventricular dysfunction, and Figure 4c shows measurements after closure of the chest, with operation of the LVAD.

Figures 5a and 5b show plots of ECG and sensed velocity with (a) pulmonary artery hypertension and (b) after surgery to fit a LVAD. In this case Figure 5a shows

measurements after administration of protamine (MPAP 35 mmHg). The vertical arrows denote systolic contraction.

Figures 6a-6c are plots of various heart measurements for the right ventricle during (a) chest opening, (b) weaning from extra corporeal circulation and (c) chest closure with initiation of LVAD flow. The vertical arrows denote systolic contraction. During weaning from extra corporeal circulation, depicted in Figure 6b, a 3-axis accelerometer detected a severely depressed right ventricular function by measuring systolic contraction velocities in circumferential, longitudinal and radial directions. By means of the sensed heart movement and control of the LVAD the right ventricular function was normalised before chest closure.

As will be appreciated from the example patient data shown in the Figures the use of accelerometers at the heart in a control system for a cardiac assist device as disclosed herein enables heart dysfunction to be determined and corrective action taken with the cardiac assist device. This optimises the performance of the cardiac assist device,

Claims

CLAIMS:

1 . A control system for a cardiac assist device, the system including a sensor implantable in the body at the heart for monitoring movement of the heart and the control system being arranged to, in use:

receive signals from the sensor, the signals providing information on movement of the heart muscle;

process the signals to identify heart dysfunction indicative of inadequate or excessive flow rate from the cardiac assist device; and

adjust the flow rate from the cardiac assist device based on the identification of such heart dysfunction in order to optimise the performance of the cardiac assist device.

2. A control system as claimed in claim 1 , arranged to optimise the performance of the cardiac assist device by adjusting the flow rate based on a closed loop control.

3. A control system as claimed in claim 1 or 2, being arranged to process the signals from the sensor to identify heart dysfunction by monitoring for a progressive reduction in afterload of the ventricle and/or monitoring for an acute increase in afterload of the ventricle, and determining that there is a potentially excessive flow rate when one or both of these occurs; and being arranged to adjust the flow rate of the cardiac assist device downwards in response to the determination of potentially excessive flow rate.

4. A control system as claimed in claim 1 , 2 or 3, being arranged to process the signals from the sensor to identify heart dysfunction by monitoring for a progressive reduction in contractility and/or monitoring for heart motion indicating reduced systolic contraction and increased post systolic contraction, and determining that there is a potentially inadequate flow rate when one or both of these occurs; and being arranged to adjust the flow rate of the cardiac assist device upwards in response to the determination of potentially inadequate flow rate.

5. A control system as claimed in any preceding claim, being arranged to measure the corrective effect of changes in the flow rate of the cardiac assist device and to determine that there is a problem in addition to the underlying heart defect when corrective adjustments to the flow rate do not result in an expected improvement in heart function.

6. A control system as claimed in claim 5, wherein if an increase in flow rate in response to heart dysfunction indicative of inadequate flow rate does not result in an expected improvement in heart function then the control system determines that there is a potential clotting or tube dislodgement.

7. A control system as claimed in claim 5 or 6, wherein if a decrease in flow rate in response to heart dysfunction indicative of excessive flow rate does not result in an expected improvement in heart function then the control system determines that there is a potential ASD or VSD.

8. A control system as claimed in any preceding claim, being arranged to process signals from the sensors at the heart in order to determine the level of physical activity of the patient and to adjust the flow rate of the cardiac assist device in response to changes in physical activity.

9. A control system as claimed in any preceding claim, comprising one or more sensors for placement in the body on both of the left and the right ventricle.

10. A control system as claimed in any preceding claim, being arranged to use position, motion and/or acceleration data to determine heart muscle activities and cardiac parameters.

1 1 . A control system as claimed in any preceding claim, comprising an ECG sensor for implanting at the heart with the sensor for monitoring heart movement.

12. A cardiac assist device comprising the control system of any preceding claim.

13. A method comprising use of the control system of any of claims 1 to 1 1 for cardiac assistance, monitoring of cardiac function and/or guidance of medical treatment in the acute phase or the follow-up phase.

14. A method as claimed in claim 13, wherein the control system is used to determine the need for a BiVAD by use of the signals from the sensor to identify ventricular failure.

15. A method of controlling a cardiac assist device comprising: monitoring of cardiac function by measuring movement of the heart using implanted sensors;

based on the measured movement of the heart, identifying heart dysfunction indicative of inadequate or excessive flow rate from the cardiac assist device; and

adjusting the flow rate from the cardiac assist device based on the identification of such heart dysfunction in order to optimise the performance of the cardiac assist device.

16. A method as claimed in claim 15, comprising use of a control system or cardiac assist device as claimed in any of claims 1 to 12.

17. A method as claimed in claim 15 or 16, wherein the optimisation of the performance of the cardiac assist device comprises adjusting the flow rate based on a closed loop control.

18. A method as claimed in claim 15, 16 or 17, comprising monitoring for a progressive reduction in afterload of the ventricle and/or monitoring for an acute increase in afterload of the ventricle, and determining that there is a potentially excessive flow rate when one or both of these occurs, with the flow rate then being adjusted downwards.

19. A method as claimed in any of claims 15 to 18, comprising monitoring for a progressive reduction in contractility and/or monitoring for heart motion indicating reduced systolic contraction and increased post systolic contraction, and determining that there is a potentially inadequate flow rate when one or both of these occurs, with the flow rate then being adjusted upwards.

20. A method as claimed in any of claims 15 to 19, comprising monitoring the corrective effect of changes in the flow rate of the cardiac assist device and determining that there is a problem in addition to the underlying heart defect when corrective adjustments to the flow rate do not result in an expected improvement in heart function.

21 . A method of control of a cardiac device substantially as hereinbefore described.

22. A control system for a cardiac device substantially as hereinbefore described.