1. DESCRIPTION by ert634

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									1.                                                                          DESCRIPTION

     1.1        OVERVIEW
     The Novacor® Left Ventricular Assist System (LVAS) from World Heart Inc. provides
     circulatory support for patients with profound left ventricular failure.
     All implantable components are supplied sterile. If a component's sterile packaging appears
     damaged, or a package is inadvertently opened, that component must be replaced. System
     components should not be sterilized by the user.
     The primary components of the LVAS are illustrated in Figure 1.1. The integrated pulsatile
     pump and electromechanical driver (Pump/Drive Unit) is implanted in the left anterior
     abdominal wall. The pump receives blood from the left ventricle via a conduit which
     cannulates the apex of the left ventricle (LV). Blood pumped from the device travels through
     an outflow conduit anastomosed to the ascending aorta. A single percutaneous lead connects
     the implanted Pump/Drive Unit to the external Controller. This tubular lead carries the
     electrical wires leading from the implanted device and vents the air space within the
     Pump/Drive Unit encapsulation shell.




                 Figure 1.1   System Configuration: Novacor® LVAS

                    Pump/Drive Unit                          Vent Filter
                    Inflow Conduit                           Controller
                    Outflow Conduit                      ,   Power Packs
                    Percutaneous Lead/Pump Cable

     The components of the wearable control and power system are shown in Figure 1.2.


N20075 Rev. A                                 1-1
Operator’s Manual Novacor® LVAS


        The Controller:

        •    Independently operates the Pump/Drive Unit.

        •    Monitors the state of the Pump/Drive Unit.

        •    Calculates pump volume and fill rate for display.

        •    Uses the volume and flow information to coordinate the pump operation with the
             activity of the natural heart.

        •    Regulates the flow of power to the driver, controlling pump actuation.

        •    Detects and alarms for out-of-limit or abnormal operation.




                  Figure 1.2 Wearable Components: Controller (center) and Power Packs


        Wearable Power Packs:

        •    Provide power to the Controller, allowing the recipient untethered mobility.

        •    Incorporate charge monitoring circuitry, charge status lights, and audible and visual
             low power alarms.

        •    Are recharged by a separate Power Pack Charger, which can charge up to four Power
             Packs.
     Two Power Packs constitute redundant power sources during untethered operation (for
     explanation of untethered operation, see page 4-8.




                                                 1-2                                    N20075 Rev. A
                                                                                              Description


        The LVAS Monitor:
        •   Connects to the Controller by a Monitor/Controller connecting cable [6 m, (20 ft.)] in
            place of a Power Pack.
        •   Permits evaluation of LVAS function, and set up and adjustment of the control
            parameters and alarm limits, as necessary.
        •   Provides power to the Controller while connected.
        •   Can be powered by the AC line or by its internal rechargeable battery.
        •   Displays pump volume and flow waveforms on the screen, along with numeric values
            for pump rate, stroke volume and output.
        •   Displays the recipient's ECG waveform and heart rate on the screen when connected to
            an ECG source.

        The Personal Monitor:
        •   Is a small unit designed to be placed on a table or nightstand.
        •   Is intended to support system operation in the latter post-operative period when the
            recipient has stabilized and adjustments/diagnostics are not needed.
        •   Provides information on pump operation and system alarm status.
        •   Is linked to the Controller by a Monitor/Controller Cable [6 m, (20 ft.)] during tethered
            operation.


     1.2        FUNCTION
     The implanted Pump/Drive Unit incorporates a seamless polyurethane sac blood pump and
     symmetrical pulsed solenoid electromechanical driver. Bioprosthetic valves at the pump inlet
     and outlet maintain forward flow. The blood pump fills passively at low pressure, receiving
     blood from the left ventricle via the inflow conduit. The Pump/Drive Unit can eject from all
     fill volumes (from 25 ml to its maximum capacity of 70 ml), to match the stroke volume
     received from the left ventricle. The Controller provides electrical energy, via the
     percutaneous lead, to actuate the driver during the ejection cycle. The driver's balanced,
     symmetrical solenoid (electromagnet) converts this electrical energy to mechanical energy,
     stored in a pair of springs. The spring forces act directly on the blood pump's dual opposed
     pusher plates, pressurizing the blood within the pump, and propelling it into the aorta to
     support systemic circulation. A small residual blood volume, proportional to afterload
     (systemic pressure), remains in the blood pump at the end of ejection. The Controller
     terminates the flow of electrical energy to the solenoid at the end of the ejection cycle, and the
     pump is free to fill again. The low filling resistance of the pump provides a reduced afterload
     for the left ventricle, resulting in substantial decompression. Typically, there is no flow
     through the aortic valve, as the pump captures the entire cardiac output.




N20075 Rev. A                                    1-3
Operator’s Manual Novacor® LVAS


     Position sensors within the Pump/Drive Unit provide continuous pump volume information to
     the Controller. Pump volume and fill & eject flow rates derived from this information are
     used to control timing in the various run modes. The system can thereby adapt to the natural
     heart’s function without dependence on an ECG signal or other physiologic measurement.
     The pump volume information is also used to compute the values of pump stroke volume and
     pump output displayed on the LVAS Monitor or Personal Monitor when connected to the
     Controller. Figures 1.3, 1.4 and 1.5 show mechanical drawings of pump/drive unit in three
     phases of the pump cycle.




                        Figure 1.3 Pump Filled (End Of Pump Filling Phase)




                                  Figure 1.4 Solenoid Closed (Start Of Eject Phase)




                          Figure 1.5 Pump Nominally Empty (End Of Eject Phase)



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     1.3        CONTROL ALGORITHMS
     The LVAS provides ventricular unloading. The low filling resistance of the pump provides a
     reduced afterload for the left ventricle in systole, resulting in substantial decompression. To
     provide maximum ventricular unloading, the LVAS should fill during left ventricular systole
     and should eject during left ventricular diastole, that is, operate in synchronous
     counterpulsation to the natural heart. The timing of initiation of the LVAS ejection controls
     loading and unloading. Typically, there is no flow through the aortic valve, as the pump
     captures the entire cardiac output.


     AUTOMATIC MODE
     The automatic mode controls the pump for fill-to-empty operation. As in all modes, the pump
     fills passively. Ejection is triggered when the pump reaches full fill, and terminated when the
     pump nominally reaches the end of its eject stroke (as detailed below). The system thereby
     operates with a nominal full eject stroke, with the pump rate – and, therefore, pump output –
     automatically adapting to varying preload. Pump operation is typically asynchronous; the
     degree of ventricular unloading will fluctuate as the phasing between the LVAS and the native
     heart varies cyclically between counterpulsation and co-pulsation.

     The termination of the pump ejection cycle is triggered by a decreasing rate of flow from the
     pump. When the eject rate falls below a predetermined value, the electrical energy into the
     driver is turned off, and the pump is free to fill. When pumping against a higher afterload,
     ejection will terminate at a higher residual volume. Therefore, the net stroke volume will
     decrease (from the nominal 70 ml) with increasing afterload.

     Normally, a one-second maximum cycle time ensures a minimum pump rate of 60 beats per
     minute (bpm), even if, due to low preload, the pump does not reach full fill. During device
     implantation, when very low filling may be encountered (e.g., during weaning from
     cardiopulmonary bypass), rates as low as 10 bpm are allowed. At Low flow rates, when
     filling takes longer than 800 msec, the pump will dwell for a brief time after reaching full fill,
     before ejecting. This provides some time for the left ventricle to fill before ejection is
     triggered, minimizing the chance of negative pressures in the inflow conduit and the
     associated possibility of air entrainment through the graft or apical cannulation.

     The only control adjustment associated with automatic mode is the Pump Output Limit
     control. Particularly, it may be desirable to limit the pump output, to reduce the possibility of
     overloading the right side of the heart. If the Pump Output Limit is enabled, the pump rate
     will be limited to prevent the pump output from exceeding the setting of the Pump Output
     Limit.


     FILL RATE TRIGGER MODE
     In Fill Rate Trigger mode the LVAS is typically intended to operate in synchronous
     counterpulsation to the left ventricle (LV). In this mode the LVAS responds to small changes
     in the pump filling rate due to the left ventricular contraction. The rate of pump filling will
     typically increase at the start of systole and decrease near the end of systole. By detecting a
     decreasing Fill rate, pump ejection can be triggered to coincide with the end of LV systole,


N20075 Rev. A                                    1-5
Operator’s Manual Novacor® LVAS


     establishing counterpulsation to the left ventricle and optimal phasing for unloading. The
     primary control adjustment is the End of Fill Threshold, which sets the percentage by which
     the fill rate must decrease (from it’s peak) before ejection is triggered. The secondary control,
     the Eject Delay, delays pump ejection for a set interval after the End of Fill Threshold is
     crossed, and is used to fine-tune the phasing of the pump to the left ventricle. The automatic
     Fill tracking works on a beat to beat basis, accommodating the rapid changes in
     hemodynamics common during implant surgery.

     If there is no systole, the decrease in fill rate needed to trigger pump ejection will occur when
     the pump reaches its full-fill limit. Thus, if the left ventricle arrests while the LVAS is
     operating in Fill Rate Trigger mode, the pump will automatically default to fill-to-empty
     pumping.

     A minimum stroke volume function prevents the pump from ejecting until it has filled by at
     least 25 ml. This is intended to ensure the establishment of good flow patterns within the
     pump and complete washing of the pump's blood-contacting surfaces. If the stroke volume
     from the left ventricle is less than the minimum stroke volume, the pump will fill (and unload
     the ventricle) for two or more beats, responding to the eject trigger only after the minimum
     stroke volume requirement is satisfied. In this case, the system may automatically provide
     every-other, or every-third, heartbeat synchronous operation.

     In Fill Rate Trigger mode, if the expected trigger does not appear within one second of the
     start of a the previous ejection, the pump will then eject. Thus, the LVAS has a minimum
     pump rate of 60 beats/minute (bpm). During extraordinarily poor pump filling conditions, the
     one-second maximum cycle time will take precedence over the minimum stroke volume,
     maintaining 60 bpm regardless of small stroke volumes.


     FIXED RATE TRIGGER MODE
     The LVAS can be operated asynchronously in the Fixed Rate Trigger mode. Here, the LVAS
     will operate at a rate set by the operator, independent of heart action. This function may be
     useful during implantation, periods of ventricular fibrillation or low cardiac flow, when the
     pump rate can be adjusted to maintain the desired pump stroke volume.
     The 25 ml minimum stroke volume parameter is active in Fixed Rate Trigger, and takes
     priority over the Pump Rate setting. If there is insufficient preload to fill the pump 25 ml per
     beat at the set pump rate, the pump will cycle at a rate less than the Pump Rate setting.


     SINGLE STROKE
     In this mode, individual cycles of the pump are commanded by the operator. The Single
     Stroke command is used during implant surgery to purge air from the pump and conduits and
     to establish initial (low) pump flows before continuous pumping is initiated.




                                                 1-6                                     N20075 Rev. A
                                                                                      Description


     The control parameters associated with each run mode, their adjustment range, and their
     factory-set values are listed below. See Section 4 for a complete description of the
     operating mode selection and adjustment. Single-stroke and Halt modes are also available,
     however there are no adjustable parameters associated with these modes.
     Here follows a table of the parameters, their range and factory-set values:


          Run Mode, Parameter             Adjustment            Initial, Factory-
                                          Range                 Set Value

          Automatic:
          Pump Output Limit               3 – 8 L/min &         Disabled
                                          Unlimited
                                          (i.e., disabled)
          Fill Rate Trigger:
          End of Fill Threshold           0 – 95 %              20 %
          Eject Delay                     0 - 500 msec          80 msec
          Fixed Rate Trigger:
          Pump Rate                       30 - 150 bpm          80 bpm




N20075 Rev. A                                1-7

								
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