Systems and methods to monitor and treat heart failure conditions

Abstract

An implantable device monitors and treats heart failure, pulmonary edema, and hemodynamic conditions and in some cases applies therapy. In one implementation, the implantable device applies a high-frequency multi-phasic pulse waveform over multiple-vectors through tissue. The waveform has a duration less than the charging time constant of electrode-electrolyte interfaces in vivo to reduce intrusiveness while increasing sensitivity and specificity for trending parameters. The waveform can be multiplexed over multiple vectors and the results cross-correlated or subjected to probabilistic analysis or thresholding schemata to stage heart failure or pulmonary edema. In one implementation, a fractionation morphology of a sensed impedance waveform is used to trend intracardiac pressure to stage heart failure and to regulate cardiac resynchronization therapy. The waveform also provides unintrusive electrode integrity checks and 3-D impedancegrams.

What is claimed is: 
     
         1 . An implantable device, comprising:
 a waveform generator to create a waveform for application along each of multiple vectors through a bodily tissue of a patient via electrodes, wherein the duration of each waveform is less than a charging time constant of an electrode-electrolyte interface between each electrode and the bodily tissue and wherein at least one of the vectors is confined to within the patient's heart tissue or pericardium;   a multiplexor to apply and process the waveform over the multiple vectors;   an impedance measurement module to obtain multiple impedance measurements at least in part via the multiplexor such that one of the multiple impedance measurements is obtained for each of the multiple vectors; and   an evaluator to interpret the multiple impedance measurements in order to estimate a bodily parameter of the patient.   
     
     
         2 . The implantable device as recited in  claim 1 , wherein the multiplexor uses time multiplexation to apply and process the waveform over the multiple vectors. 
     
     
         3 . The implantable device as recited in  claim 2 , wherein the multiplexor signals the impedance measurement module to sense an impedance result for each of the vectors in rapid succession, wherein the speed of the rapid succession emulates simultaneous measurement across the multiple vectors. 
     
     
         4 . The implantable device as recited in  claim 3 , wherein the multiplexor sequentially times a measurement of each of the applied waveforms to occur within a time interval of a physiological circumstance. 
     
     
         5 . The implantable device as recited in  claim 3 , wherein the physiological circumstance comprises an intracardiac pressure state. 
     
     
         6 . The implantable device as recited in  claim 3 , wherein the multiplexor applies a different frequency of the waveform for each of the multiple vectors; and
 wherein the multiplexor senses an impedance result associated with each of the multiple waveforms by frequency.   
     
     
         7 . The implantable device as recited in  claim 1 , further comprising a network selector for determining the multiple vectors. 
     
     
         8 . The implantable device as recited in  claim 7 , wherein the network selector weights each of the multiple vectors according to an importance of each vector with respect to the bodily parameter to be estimated. 
     
     
         9 . The implantable device as recited in  claim 1 , further comprising an alert module to actuate an alarm or a patient notification in response to an estimate of the bodily parameter exceeding a threshold, wherein the alarm or patient notification is delivered via the implantable device or via a device external to the patient 
     
     
         10 . The implantable device as recited in  claim 1 , wherein the implantable device interprets the multiple impedance measurements to estimate a degree of heart failure or a degree of pulmonary edema of the patient.