Closed loop impedance-based cardiac resynchronization therapy systems, devices, and methods
First Claim
1. A machine-assisted method comprising:
- measuring a first impedance, during at least a portion of a cardiac cycle, between a first electrode associated with a first ventricle of a heart and a reference electrode;
measuring a second impedance, during at least the portion of the cardiac cycle, between a second electrode associated with a second ventricle of the heart, in which the second ventricle is different from the first ventricle, and the same or a different reference electrode;
measuring a phase difference between the first and second impedances; and
automatically adjusting in a closed loop manner, using the measured phase difference as an error signal, a cardiac resynchronization therapy parameter that synchronizes left and right ventricular heart contractions, the automatically adjusting tending to reduce the phase difference during a subsequent cardiac cycle, wherein the automatically adjusting comprises;
when the measured phase difference shows the second impedance leading the first impedance in phase by more than a first threshold value, then lengthening an atrioventricular (AV) delay; and
when the measured phase difference shows the first impedance leading the second impedance in phase by more than a second threshold value, then shortening the AV delay.
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Abstract
This document discusses, among other things, systems, devices, and methods measure an impedance and, in response, adjust an atrioventricular (AV) delay or other cardiac resynchronization therapy (CRT) parameter that synchronizes left and right ventricular contractions. A first example uses parameterizes a first ventricular volume against a second ventricular volume during a cardiac cycle, using a loop area to create a synchronization fraction (SF). The CRT parameter is adjusted in closed-loop fashion to increase the SF. A second example measures a septal-freewall phase difference (PD), and adjusts a CRT parameter to decrease the PD. A third example measures a peak-to-peak volume or maximum rate of change in ventricular volume, and adjusts a CRT parameter to increase the peak-to-peak volume or maximum rate of change in the ventricular volume.
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Citations
14 Claims
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1. A machine-assisted method comprising:
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measuring a first impedance, during at least a portion of a cardiac cycle, between a first electrode associated with a first ventricle of a heart and a reference electrode; measuring a second impedance, during at least the portion of the cardiac cycle, between a second electrode associated with a second ventricle of the heart, in which the second ventricle is different from the first ventricle, and the same or a different reference electrode; measuring a phase difference between the first and second impedances; and automatically adjusting in a closed loop manner, using the measured phase difference as an error signal, a cardiac resynchronization therapy parameter that synchronizes left and right ventricular heart contractions, the automatically adjusting tending to reduce the phase difference during a subsequent cardiac cycle, wherein the automatically adjusting comprises; when the measured phase difference shows the second impedance leading the first impedance in phase by more than a first threshold value, then lengthening an atrioventricular (AV) delay; and when the measured phase difference shows the first impedance leading the second impedance in phase by more than a second threshold value, then shortening the AV delay. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A system comprising:
an implantable medical device comprising; an impedance measurement circuit, including terminals configured to be coupled to electrodes for association with a first ventricle of a heart and a second ventricle of the heart, respectively, and configured to be coupled to a reference electrode location separate from each of the first and second ventricles, the impedance measurement circuit configured to measure a first impedance between the first ventricle and the reference electrode location, and to measure a second impedance between the second ventricle and the reference electrode location; and a processor circuit, coupled to the impedance measurement circuit to receive signals indicative of the first and second impedances during a cardiac cycle, the processor circuit configured to perform instructions to measure a phase difference between the first and second impedances to provide an indication of a degree of synchrony or asynchrony between the first and second ventricles, the processor further configured to perform instructions to automatically adjust in a closed-loop manner, using the measured phase difference as an error signal, a cardiac resynchronization therapy parameter that synchronizes left and right ventricular heart contractions in a way that tends to reduce the phase difference during a subsequent cardiac cycle, wherein the processor circuit is further configured to perform instructions such that; if the measured phase difference shows the second impedance leading the first impedance in phase by more than a first threshold value, then lengthening an atrioventricular (AV) delay; and if the measured phase difference shows the first impedance leading the second impedance in phase by more than a second threshold value, then shortening the AV delay. - View Dependent Claims (10, 11, 12, 13, 14)
Specification