Closed loop impedance-based cardiac resynchronization therapy systems, devices, and methods

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.

1 . A system comprising:
 an implantable medical device comprising:   a physiological conductivity characteristic measurement circuit, including terminals configured to be coupled to electrodes for association with different first and second regions of a same first ventricle of a heart, respectively, and configured to be coupled to a reference electrode location separate from each of the first and second regions, to provide first and second conductivity characteristics respectively associated with the first and second regions; and   a processor circuit, coupled to the conductivity characteristic measurement circuit to receive signals indicative of the first and second conductivity characteristics during the cardiac cycle, the processor configured to perform instructions to measure a phase difference between the first and second conductivity characteristics to provide an indication of a degree of synchrony or asynchrony between the first and second regions, 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 contraction of the first and second regions in a way that tends to reduce the phase difference during a subsequent cardiac cycle.   
     
     
         2 . The system of  claim 1 , in which the automatically adjusting the cardiac resynchronization therapy parameter includes adjusting an atrioventricular (AV) delay. 
     
     
         3 . The system of  claim 1 , in which the automatically adjusting the cardiac resynchronization therapy parameter includes adjusting a left ventricular offset. 
     
     
         4 . The system of  claim 1 , in which the automatically adjusting the cardiac resynchronization therapy parameter includes adjusting an intraventricular delay. 
     
     
         5 . The system of  claim 1 , in which the automatically adjusting the cardiac resynchronization therapy parameter includes adjusting an interventricular delay. 
     
     
         6 . The system of  claim 1 , in which the implantable device includes the reference electrode, and wherein the reference electrode is located on a hermetically sealed housing of the implantable device or located on an insulating header extending from the housing of the implantable device. 
     
     
         7 . The system of  claim 1 , further comprising an intravascular lead including a supraventricular electrode serving as the reference electrode. 
     
     
         8 . The system of  claim 1 , further comprising a telemetry circuit, coupled to the processor, the telemetry circuit configured for transmitting from the implantable device data indicative of the phase difference. 
     
     
         9 . The system of  claim 8 , further comprising an external user interface device that is configured to receive the data indicative of the phase difference from the implantable device, the external user interface device including a display monitor configured to display information about the phase difference. 
     
     
         10 . The system of  claim 1 , in which the physiological conductivity characteristic measurement circuit is an impedance measurement circuit configured to measure respective impedances of the first and second regions of the same first ventricle, and in which measuring the respective impedances includes:
 injecting a current through each of the first and second regions; and   measuring a responsive voltage characteristic of the first and second regions.   
     
     
         11 . The system of  claim 10 , wherein the first region is a septum region and the second region is a left ventricular freewall region. 
     
     
         12 . A system comprising:
 an implantable medical device comprising:   a physiological impedance measurement circuit, including terminals configured to be coupled to electrodes for association with different septal and freewall regions of a same first ventricle of a heart, respectively, and configured to be coupled to a reference electrode location separate from each of the septal and freewall regions, to provide first and second impedances respectively associated with the septal and freewall regions; and   a processor circuit, coupled to the impedance measurement circuit to receive signals indicative of the first and second impedances during the cardiac cycle, the processor 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 septal and freewall regions, 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 contraction of the septal and freewall regions in a way that tends to reduce the phase difference during a subsequent cardiac cycle.   
     
     
         13 . The system of  claim 12 , in which the automatically adjusting the cardiac resynchronization therapy parameter includes adjusting an atrioventricular (AV) delay. 
     
     
         14 . The system of  claim 12 , in which the automatically adjusting the cardiac resynchronization therapy parameter includes adjusting a left ventricular offset. 
     
     
         15 . The system of  claim 12 , in which the automatically adjusting the cardiac resynchronization therapy parameter includes adjusting an intraventricular delay. 
     
     
         16 . The system of  claim 12 , in which the automatically adjusting the cardiac resynchronization therapy parameter includes adjusting an interventricular delay. 
     
     
         17 . A system comprising:
 an implantable medical device comprising:   a physiological impedance measurement circuit, including terminals configured to be coupled to electrodes for association with different septal and freewall regions of a same first ventricle of a heart, respectively, and configured to be coupled to a reference electrode location separate from each of the septal and freewall regions, to provide first and second impedances respectively associated with the septal and freewall regions; and   a processor circuit, coupled to the impedance measurement circuit to receive signals indicative of the first and second impedances during the cardiac cycle, the processor 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 septal and freewall regions, 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 contraction of the septal and freewall regions in a way that tends to reduce the phase difference during a subsequent cardiac cycle, in which the automatically adjusting the cardiac resynchronization therapy parameter includes adjusting an intraventricular delay.   
     
     
         18 . The system of  claim 17 , comprising:
 a left ventricular lead, configured to be coupled to the implantable medical device, the left ventricular lead configured to be inserted into a coronary sinus to dispose an electrode in association with the free-wall, wherein the freewall is a left ventricular freewall.   
     
     
         19 . The system of  claim 18 , comprising:
 a right ventricular lead, configured to be coupled to the implantable medical device, the right ventricular lead configured to be inserted into a right ventricle to dispose an electrode in association with the septum.   
     
     
         20 . The system of  claim 18 , comprising an electrode located at a header or housing of the implantable medical device to serve as a reference electrode for measuring the first and second impedances.