ACCOUNT FOR PRELOAD CHANGES IN THE LEFT VENTRICLE
A method of estimating a patient's cardiac preload in a patient having an implantable blood pump. The method includes generating a current waveform from operation of the implanted blood pump. A beat-to-beat pump filling index (PFI) is calculated, the PFI is calculated by dividing a current amplitude component by a time component, the amplitude component being calculated by subtracting a trough of the current waveform from an inflection point divided by an amplitude difference of peak to trough of the waveform, the time component being calculated by dividing a time between the trough and the inflection point by a time between the peak and the trough. An alert is generated if the PFI deviates from predetermined thresholds.
1 . A method of preventing ventricular suction in a patient having an implantable blood pump, the method comprising:
generating a current waveform from operation of the implantable blood pump;
calculating a beat-to-beat pump filling index from the current waveform;
determining whether the pump filling index indicates low cardiac preload; and
automatically decreasing a speed of an impeller of the implantable blood pump when the pump filling index indicates low cardiac preload to prevent ventricular suction.
2 . The method of claim 1 , further comprising comparing the pump filling index to a lower threshold to determine whether the pump filling index indicates low cardiac preload.
3 . The method of claim 1 , further comprising determining whether the pump filling index indicates high cardiac preload, and automatically increasing the speed of the impeller when the pump filling index indicates high cardiac preload to prevent ventricular overfilling.
4 . The method of claim 3 , further comprising comparing the pump filling index to an upper threshold to determine whether the pump filling index indicates high cardiac preload.
5 . The method of claim 1 , wherein the pump filling index has a linear relationship with cardiac preload levels.
6 . The method of claim 1 , wherein the pump filling index has a linear correlation with pulmonary capillary wedge pressure.
7 . The method of claim 1 , wherein the current waveform includes cardiac beat-to-beat peaks and troughs.
8 . The method of claim 7 , wherein calculating the beat-to-beat pump filling index from the current waveform includes identifying inflection points between the beat-to-beat peaks and troughs.
9 . The method of claim 8 , wherein identifying inflection points in the current waveform comprises identifying a point at which the current waveform changes from positive to negative current between the beat-to-beat peaks and troughs.
10 . The method of claim 1 , further comprising applying a median filter to consecutive pump filling index calculations.
11 . A method of monitoring cardiac activity in a patient having a blood pump, the method comprising:
receive a current waveform from operation of the blood pump;
identify peaks, troughs, and inflection points in the current waveform corresponding to cardiac beats;
calculate a pump filling index for each cardiac beat by dividing a current amplitude component by a time component; and
generate a preload status indicator based on the pump filling index.
12 . The method of claim 11 , wherein the instructions further cause the processing circuitry to apply a median filter to consecutive pump filling index calculations.
13 . The method of claim 11 , wherein the inflection points comprise a points at which the current waveform changes from positive to negative current.
14 . The method of claim 11 , wherein the preload status indicator indicates one of high cardiac preload, normal cardiac preload, or low cardiac preload.
15 . The method of claim 14 , further comprising automatically increasing or decreasing a speed of an impeller of the blood pump based on the preload status indicator.
16 . The method of claim 15 , wherein:
automatically increasing the speed of the impeller occurs when the preload status indicator indicates high cardiac preload; and
automatically decreasing the speed of the impeller occurs when the preload status indicator indicates low cardiac preload to prevent ventricular suction.
17 . A ventricular assist device for assisting a heart of a patient, comprising:
a housing defining a blood flow path from an inlet to an outlet;
a rotatable impeller disposed within the housing;
a motor configured to rotate the impeller at a set speed; and
a controller configured to:
monitor a current waveform of current drawn by the motor,
calculate a relative index of cardiac preload from the monitored current, and
adjust the set speed of the impeller based on the relative index of cardiac preload to maintain physiologically suitable output.
18 . The ventricular assist device of claim 17 , wherein the controller is configured to adjust the set speed to prevent at least one of ventricular overfilling and ventricular suction.
19 . The ventricular assist device of claim 17 , wherein calculating the relative index of cardiac preload from the monitored current includes calculating a beat-to-beat pump filling index from the current waveform.
20 . The ventricular assist device of claim 19 , wherein the controller is further configured to: generate a preload status indicator based on the pump filling index.