Patent Description:
Mechanical Circulatory Support Devices ("MCSDs") are commonly used to assist the pumping action of a failing heart. Typically, an MCSD includes an implantable blood pump that is surgically implanted in a patient's body. The MCSD may include a housing with an inlet, an outlet, and a rotor mounted therein. The inlet is connected to a chamber of the patient's heart, typically the left ventricle, whereas the outlet is connected to an artery, such as the aorta. Rotation of the rotor drives blood from the inlet towards the outlet and thus assists blood flow from the chamber of the heart into the artery. One exemplary MCSD is the MVAD® Pump. The MVAD® Pump is further discussed in <CIT> and <CIT>. Unfortunately, determining a heart rate of a patient having an operating MCSD implanted within the patient's body may be difficult, particularly when there is a non-linear relationship between a blood flow rate through the blood pump and a motor current of the blood pump. <CIT> discloses a blood pump system and method of operation.

The techniques of this disclosure generally relate to determining a heart rate of a patient having an implanted blood pump during operation of the blood pump.

In an example, the present disclosure provides a method (not claimed) of determining a heart rate of a patient having an implanted blood pump including applying a voltage to a plurality of coils of a stator of the blood pump to produce an electromagnetic force to rotate a rotor in communication with the plurality of coils; displaying a waveform associated with a back electromotive force in the plurality of coils of the blood pump, the waveform being proportional to an axial position of the rotor relative to the stator; determining a time interval between a first alteration in the waveform relative to a baseline and a second alteration in the waveform relative to the baseline; and determining the heart rate of the patient based on the determined time interval.

In another example (not claimed), the disclosure provides the axial position of the rotor relative to the stator being proportional to a thrust through the blood pump, and the thrust is proportional to a fluid flow through the blood pump.

In an example (not claimed), the disclosure provides determining the heart rate of the patient in a presence of a non-linear relationship between the fluid flow through the blood pump and a motor current of the blood pump.

In another example (not claimed), the disclosure provides the time interval corresponding to a complete heartbeat of the patient.

In another example (not claimed), the disclosure provides including correlating the time interval to a predetermined figure.

In another example (not claimed), the disclosure provides dividing the time interval by the predetermined figure of sixty to determine a number of heart beats per minute.

In another example (not claimed), the disclosure provides the baseline being an upper hysteresis band, and the rise in the waveform includes a crossing of the upper hysteresis band.

In another example (not claimed), the disclosure provides correlating the waveform to a lower hysteresis band separate from the upper hysteresis band, and wherein the fall in the waveform includes a crossing of the lower hysteresis band.

In another example (not claimed), the disclosure provides calculating the heart rate of the patient based on a frequency analysis of the waveform.

In another example (not claimed), the disclosure provides determining a variability with respect to the determined heart rate of the patient over a select duration.

In one aspect, the present disclosure provides a system for determining a heart rate of a patient having an implantable blood pump, according to claim <NUM>.

In another aspect, the disclosure provides recording one or more-time intervals between one or more rises in the waveform relative to the baseline and calculating the heart rate based on the time intervals.

The baseline is an upper hysteresis band.

In another aspect, the disclosure provides the axial position of the rotor relative to the stator being proportional to a thrust through the blood pump, and the thrust is proportional to a fluid flow through the blood pump.

In another aspect, the disclosure provides determining the heart rate of the patient in a presence of a non-linear relationship between the fluid flow through the blood pump and a motor voltage of the blood pump.

Before describing in detail exemplary embodiments, it is noted that the embodiments reside primarily in combinations of system components and processing steps related to a system for determining a heart rate of a patient having an implanted blood pump. Accordingly, the system components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

Referring now to the drawings in which like reference designators refer to like elements there is shown in <FIG> a block diagram of an exemplary system <NUM> constructed in accordance with the principles of the present application and designated generally "<NUM>. " The system <NUM> includes an implantable blood pump <NUM> in communication with a controller <NUM>. The blood pump <NUM> may be the MVAD® Pump or another mechanical circulatory support device fully or partially implanted within the patient. The controller <NUM> includes a control circuit <NUM> having control circuitry for monitoring and controlling startup and subsequent operation of a motor <NUM> implanted within the blood pump <NUM>. The controller <NUM> may also include a processor <NUM> having processing circuitry, a memory <NUM>, and an interface <NUM>. The memory <NUM> stores information accessible by the processor <NUM> and processing circuitry, including instructions <NUM> executable by the processor <NUM> and/or data <NUM> that may be retrieved, manipulated, and/or stored by the processor <NUM>.

The blood pump <NUM> may be a continuous flow blood pump, such as, without limitation, the MVAD® Pump referenced above, and may include a housing having a rotor therein. The system <NUM> and the blood pump <NUM> may be used in conjunction with a method of determining a heart rate of a patient having the blood pump implanted with the patient's body based upon an axial position of the rotor with respect to the housing, as discussed in further detail below.

<FIG> is an exploded view of the blood pump <NUM> include a housing <NUM> having an inlet cannula <NUM> and a rotor <NUM> such as an impeller, proximate the inlet cannula <NUM> to impel the blood. The inlet cannula <NUM> includes an inner tube <NUM> formed from a non-magnetic material, such as a ceramic. The inner tube <NUM> includes an interior surface <NUM> defining a cylindrical bore <NUM> for receiving the rotor <NUM> therein. The inner tube <NUM> also includes a cylindrical outer surface <NUM> surrounded by a stator <NUM> having one or more coils <NUM>. A voltage is applied to the coils <NUM> from a drive circuit (not shown) to produce an electromagnetic force to rotate the rotor <NUM>. In particular, the electromagnetic force of the coils <NUM> exhibits an electromagnetic field which interacts with a magnetic field of the rotor <NUM> to suspend the rotor <NUM> within the cylindrical bore <NUM> and rotate the rotor <NUM>. In addition to or in lieu of the magnetic forces, the rotor <NUM> may be suspended within the housing <NUM> using one or more hydrodynamic forces.

Rotation of the rotor <NUM> impels the blood along a fluid flow path from an upstream direction U to a downstream direction D through the inner tube <NUM>. The fluid flow path may be referred to as a blood flow path. Further details associated with rotary blood pumps are described in <CIT>. The blood pump <NUM> defines a housing axis "A" extending therethrough and along the fluid flow path from the upstream to the downstream direction. The rotor <NUM> moves in an axial direction relative to the housing <NUM> along the housing axis. When fluid, such as blood, passes through the blood pump <NUM>, the fluid imparts a thrust on the rotor <NUM> which causes the rotor <NUM> to move. A magnitude of the thrust is related to the fluid flow rate through the blood pump <NUM>. In other words, the axial position of the rotor <NUM> relative to the housing <NUM> is proportional to the fluid flow rate through the blood pump <NUM>, which is proportional to the thrust.

The patient's heart beat is determined by analyzing the axial position of the rotor <NUM> relative to the housing <NUM>, and particularly the stator <NUM>. For example, a back electromotive force ("BEMF") is produced in the coils <NUM> when the voltage is applied to the coils <NUM> to rotate the rotor <NUM>. In other words, the BEMF is the voltage induced in the coils <NUM> by rotating the rotor <NUM>. The axial movement of the rotor <NUM> alters the alignment between the rotor <NUM> and the coils <NUM> which alters the BEMF. The slope of the BEMF is analyzed to derive the patient's heart beat. In addition to or in lieu of using the BEMF, a sensor (not shown) disposed within the housing <NUM> may be used to determine the axial position of the rotor <NUM> relative to the stator <NUM>.

<FIG> is a graph that illustrates an exemplary waveform <NUM> of the BEMF in a pulsatile flow system over approximately ten seconds at sixty beats per minute. The term approximately includes a deviation within plus or minus five seconds. The control circuit <NUM> and the control circuitry (<FIG>) are configured to generate the waveform <NUM>. The waveform <NUM> shows alterations in the BEMF signal's amplitude relative to a baseline <NUM> over time. The alterations in the waveform <NUM> are detected and viewed and/or recorded to determine the patient's heart beat. For example, a time interval between adjacent pairs of rises and/or falls in the waveform <NUM> relative to the baseline <NUM> represent a duration of an individual heartbeat. In other words, the time interval is the time it takes to complete a single complete heartbeat. The heartbeat is correlated to a predetermined figure to determine the patient's heart rate in beats per minute. For example, the predetermined figure may be the number <NUM> with the time interval being divided by the number <NUM> to output the heart rate in beats per minute. The number of time intervals used to determine the heart rate may vary. The heart rate may be determined regardless of a speed of the blood pump <NUM>, such as when there is a non-linear relationship between the fluid flow through the blood pump <NUM> and the speed, which may occur in the MVAD® Pump.

In another configuration, the heart rate may be determined by performing a frequency analysis of the waveform <NUM>. The time interval calculations and/or the frequency analysis are performed using one or more algorithms or other calculation methods. The waveform <NUM> may be displayed on a monitor of the controller <NUM> or a remote location, such as a remote location viewable by a clinician. The waveform <NUM> is provided for illustrative purposes as the duration and number of beats per minute may vary in accordance with individual patients. The determined heart rate may be used to derive additional parameters, such as the patient's heart rate variability over time, for clinical or other use. For example, the variability with respect to the patient's heart rate may be determined over weeks, months, and/or years to determine whether the patient's health condition is deteriorating.

<FIG> depicts a first alteration in the waveform <NUM> as a first rise <NUM> in the waveform <NUM> relative to the baseline <NUM>. The baseline <NUM> is an upper hysteresis band which is separate from a lower hysteresis band <NUM> by a filter <NUM>. The baseline <NUM> or the upper hysteresis band and the lower hysteresis band <NUM> are used to reduce the occurrence of faulty triggers in the rises, which may otherwise occur due to outside factors, such as noise. The rise in the waveform <NUM> refers to the waveform <NUM> crossing the baseline <NUM>. Once the first rise <NUM> is detected, a timer runs until a second rise <NUM> in the waveform <NUM> is detected relative to the baseline <NUM> and the timer stops. A time interval, designated as an "n-n interval", is recorded between the first rise <NUM> and the second rise <NUM> and stored in the memory <NUM> (<FIG>). The time interval between the first rise <NUM> and the second rise <NUM> represents the time duration between individual heart beats.

<FIG> is a graph that illustrates a first alteration of the waveform <NUM> as a first fall <NUM> in the waveform <NUM> relative to the baseline <NUM>. The fall in the waveform <NUM> refers to the waveform <NUM> crossing the lower hysteresis band <NUM>. Similar to the first rise <NUM> in the waveform <NUM> (<FIG>), when the first fall <NUM> is detected a timer runs until a second fall <NUM> in the waveform <NUM> is detected relative to the baseline <NUM>, at which time the timer stops. A time interval between the first fall <NUM> and the second fall <NUM>, such as the n-n interval, is recorded and stored in the memory <NUM>. Two or more of the time intervals may be determined and recorded to determine the average heart rate.

<FIG> is a flow chart depicting steps of an exemplary method <NUM> of determining the heart rate of a patient having an implanted blood pump. The control circuit <NUM> and the control circuitry (<FIG>) may be configured to execute the steps of the method. In one exemplary configuration, the method begins with step <NUM> and proceeds to step <NUM> of applying a voltage to the coils <NUM> of the stator <NUM> of the blood pump <NUM> to produce an electromagnetic force to rotate the rotor <NUM> in communication with the coils <NUM>. As mentioned above, the voltage is applied through a drive circuit (not shown). At step <NUM>, the method includes displaying the waveform <NUM> associated with the back electromotive force in the coils <NUM> of the blood pump <NUM> with the waveform <NUM> being proportional to an axial position of the rotor <NUM> relative to the stator <NUM>. The waveform <NUM> may be generated using the controller <NUM> and control circuit <NUM> (<FIG>) and displayed on a monitor of the controller <NUM> (not shown) or at another remote location. At step <NUM>, the method <NUM> includes determining the time interval between the first alteration in the waveform <NUM> relative to the baseline <NUM> and a second alteration in the waveform <NUM> relative to the baseline <NUM>. The first and second alterations are the rise and/or the fall with respect to the baseline <NUM>. At step <NUM>, the method <NUM> includes determining the heart rate of the patient based on the determined time interval as discussed in further detail above.

It should be understood that various aspects disclosed herein may be combined in different combinations than the combinations specifically presented in the description and accompanying drawings, insofar as encompassed by the scope of the accompanying claims.

Claim 1:
A system (<NUM>) for determining a heart rate of a patient having an implanted blood pump (<NUM>) including:
a controller (<NUM>) including a processor (<NUM>), the processor (<NUM>) having processing circuitry configured to:
apply a voltage to a plurality of coils (<NUM>) of a stator (<NUM>) of the blood pump (<NUM>) to produce an electromagnetic force to rotate a rotor (<NUM>) in communication with the plurality of coils (<NUM>);
display a waveform (<NUM>) associated with a back electromotive force in the plurality of coils (<NUM>) of the blood pump (<NUM>);
determine a time interval between a first alteration in the waveform (<NUM>) relative to a baseline (<NUM>) and a second alteration in the waveform (<NUM>) relative to the baseline (<NUM>);
wherein the baseline (<NUM>) is an upper hysteresis band,
wherein the first alteration is a first rise (<NUM>) in the waveform (<NUM>) relative to the baseline (<NUM>) and the second alteration is a second rise (<NUM>) in the waveform (<NUM>) relative to the baseline (<NUM>), and
determine the heart rate of the patient based on the determined time interval.