Opto-electrical coherence detection of hemodynamically compromising arrhythmia

Abstract

System and methods for assessing sensed signals for determining a reliability measure of their accuracy with respect to a patient's true physiological status. As one example, the signals can include multiple, independently obtained signals, such as an electro-chemically based measure of cardiac activity and a plethysmography based measure of hemodynamic output which typically exhibit different morphologies and varying phase shifts with respect to each other. One manner of assessing the signals is to transform them into the frequency domain, such as via a Fast Fourier Transform (FFT), and evaluate them, such as by a coherence determination, to determine the degree of their mutual agreement. This can be used to assess the reliability of the sensing. Therapy can be delivered under certain observed conditions, such as a condition of hemodynamic insufficiency where anti-tachycardia pacing and/or shocking therapy can be delivered.

1 . A method of evaluating a patient condition and determining delivery of therapy comprising:
 monitoring a first signal indicative of a first patient condition;   monitoring a second signal indicative of a second patient condition;   transforming the first and second signals into a frequency domain;   evaluating the transformed signals in the frequency domain to determine a degree of correlation between the signals; and   delivering therapy based at least in part upon the determination of the degree of correlation between the signals.   
     
     
         2 . The method of  claim 1  wherein monitoring the first signal indicative of the first patient condition comprises monitoring electrical, time based signals indicative of cardiac activity. 
     
     
         3 . The method of  claim 2  wherein the first signal defines an intracardiac electrogram. 
     
     
         4 . The method of  claim 1  wherein monitoring the signal indicative of the second patient condition comprises monitoring time based volumetric-pressure variations indicative of hemodynamic output. 
     
     
         5 . The method of  claim 1  wherein transforming the first and second signals into the frequency domain comprises performing a Fast Fourier Transform (FFT) algorithm on the first and second signals. 
     
     
         6 . The method of  claim 1  wherein evaluating the transformed signals in the frequency domain to determine the degree of correlation between the signals comprises calculating a coherence of the signals defined as a ratio of a cross-power spectrum of the signals to auto-power spectra of each of the signals. 
     
     
         7 . A method comprising:
 obtaining a first signal indicative of electrophysiologic cardiac activity of a patient;   obtaining a second signal indicative of hemodynamic output of the patient;   obtaining a third signal Indicative of patient activity; and   performing a frequency domain evaluation of the signals to determine whether the second signal is frequency related to the first signal and whether the second signal is frequency related to the third signal;   upon determining that the second signal is frequency related to the first signal, and the second signal is frequency related to the third signal, determining that the second signal is providing a reliable indication of the patient's physiological condition; and   upon determining that the second signal is frequency related to the first signal, and the second signal is not frequency related to the third signal, determining that the second signal is providing a reliable indication of the patient's physiological condition.   
     
     
         8 . The method of  claim 7  wherein, upon determining that correlation is lacking between the first and second and the second and third signals, determining a ventricular tachycardia condition. 
     
     
         9 . The method of  claim 7  wherein, upon determining that correlation is lacking between the first and second, but does exist between the second and third signals, determining that the lack of correlation between the first and second signals is due to an elevated activity level. 
     
     
         10 . The method of  claim 9  further comprising inhibiting delivery of a therapy to the patient. 
     
     
         11 . The method of  claim 10  further comprising continuing to inhibit therapy until there is a correlation between the first and second signals. 
     
     
         12 . The method of  claim 7  wherein performing a frequency domain evaluation comprises:
 correlating the signals in the frequency domain by transforming the signals from a time domain into the frequency domain; and   evaluating the degree to which they share frequency components.   
     
     
         13 . The method of  claim 12  wherein transforming the signals from a time domain into the frequency domain comprises performing a Fourier transform to transform the first and second signals into the frequency domain. 
     
     
         14 . The method of  claim 12  wherein correlating the signals comprises performing a coherence calculation of the transformed first and second signals. 
     
     
         15 . The method of  claim 12  wherein transforming the signals from a time domain into the frequency domain comprises decomposing the first and second signals from a time domain into a corresponding composition of sinusoids in the frequency domain. 
     
     
         16 . The method of  claim 7  wherein performing a frequency domain evaluation comprises calculating a coherence value defined as a scalar ratio of a cross-power spectrum of the two signals to auto-power spectra of each of the two signals.