Method for determining and monitoring a cardiac status of a patient

Abstract

The present invention relates to a method for accurately and reliably determining a cardiac status of a patient. An implantable medical device, IMD, comprises a sensor arrangement adapted to sense signals related to mechanical activity of the heart and an activity level sensor arrangement adapted to sense an activity level of the patient. Further, the IMD calculates a percentage of left ventricular diastolic time (PLVDT) for a cardiac cycle corresponding to a relation between a diastolic time interval and a cardiac cycle time interval using the determined systolic and diastolic time intervals or a percentage of left ventricular systolic time (PLVST) for a cardiac cycle corresponding to a relation between a systolic interval time interval and a cardiac cycle time interval using. A cardiac status is determined based on the calculated PLVDT (or PLVST) and on an activity level of the patient.

What is claimed is: 
     
         1 . A method for determining a cardiac status of a patient in an implantable medical device being connectable to at least one medical lead for contact with tissue of a heart of the patient, the method comprising:
 sensing signals related to mechanical activity of the heart and producing an output signal related to the mechanical activity;   sensing an activity level of the patient;   identifying predetermined cardiac events in the cardiac signals and determining a systolic time interval and a diastolic time interval of a cardiac cycle using the identified cardiac events;   calculating a percentage of left ventricular diastolic time (PLVDT) for a cardiac cycle corresponding to a relation between a diastolic time interval and a cardiac cycle time interval using the determined systolic and diastolic time intervals or a percentage of left ventricular systolic time (PLVST) for a cardiac cycle corresponding to a relation between a systolic interval time interval and a cardiac cycle time interval using the determined systolic and diastolic time intervals;   calculating a rate of change of the PLVDT (or PLVST) and the activity level;   synchronizing the activity level with the calculated PLVDT (or PLVST) over time; and   determining a cardiac status based on the calculated PLVDT (or PLVST) and on the activity level and on a rate of change of the PLVDT (or PLVST) and on a rate of change of the activity level.   
     
     
         2 . The method according to  claim 1 , further comprising sensing a heart rate of the patient, and wherein the determining a cardiac status comprises synchronizing the heart rate with the PLVDT (or PLVST) over time and determining a cardiac status based also on a development of the heart rate over time. 
     
     
         3 . The method according to  claim 1 , wherein the determining a cardiac status comprises determining a gradually increasing or decreasing PLVDT (or PLVST) over time synchronized with a stable or gradually decreasing activity level to be an indication of an impaired cardiac status. 
     
     
         4 . The method according to  claim 1 , wherein the determining a cardiac status comprises determining a stable PLVDT (or PLVST) over time within a predetermined range defined by an upper and a lower limit to be an indication of a normal cardiac status and wherein a PLVDT (or PLVST) being outside the predetermined range at least a predetermined period of time is determined to be an indication of an impaired cardiac status. 
     
     
         5 . The method according to  claim 1 , wherein the sensing signals related to mechanical activity of the heart comprises emitting light into an artery or on vascular tissue and receiving light reflected in blood or transmitted in blood, and producing a signal corresponding to a light absorption of the blood over time. 
     
     
         6 . The method according to  claim 5 , wherein the identifying cardiac events comprises:
 identifying a significant increase in a rate of change of the light absorption in a light absorption waveform obtained from the light sensing module as the closure of tricuspid and mitral valves and to identify a first significant decrease in a rate of change of the light absorption as a closure of the aortic valve, and   determining the diastolic period as the period of time from the closure of the aortic valve of a cardiac cycle to the closure of tricuspid and mitral valves of the subsequent cardiac cycle and a cardiac cycle as the period of time from closure of tricuspid and mitral vales of a cardiac cycle to the closure of tricuspid and mitral valves of the subsequent cardiac cycle.   
     
     
         7 . The method according to  claim 1 , wherein the sensing signals related to mechanical activity of the heart comprises sensing heart sounds and producing a signal corresponding to an amplitude of the detected heart sounds over time. 
     
     
         8 . The method according to  claim 7 , wherein the identifying cardiac events comprises:
 identifying the first heart sound, S1, as the closure of tricuspid and mitral valves in a heart sound amplitude waveform and the second heart sound, S2, as the closure of the aortic valve; and   determining the diastolic period as the period of time from the occurrence of the second heart sound of a cardiac cycle to the occurrence of the first heart sound of the subsequent cardiac cycle and a cardiac cycle as the period of time from the occurrence of first heart sound of a cardiac cycle to the occurrence of the first heart sound of the subsequent cardiac cycle.   
     
     
         9 . The method according to  claim 1 , wherein the sensing signals related to mechanical activity of the heart comprises sensing electrical signals of the heart and producing an IEGM signal. 
     
     
         10 . The method according to  claim 9 , wherein the identifying cardiac events comprises synchronizing the IEGM signal with the heart sound amplitude signal, and using an identification of a cardiac event in the IEGM signal to identify the first and second heart sounds. 
     
     
         11 . The method according to  claim 1 , wherein the sensing signals related to mechanical activity of the heart comprises sensing an intracardiac pressure and producing a pressure amplitude signal. 
     
     
         12 . The method according to  claim 11 , wherein the identifying cardiac events comprises:
 identifying of a significant increase in a rate of change of a pressure amplitude in the pressure amplitude waveform as the closure of tricuspid and mitral valves and a significant decrease of a rate of change of the pressure amplitude as the closure of the aortic valve; and   determining the diastolic period as the period of time from the closure of the aortic valve of a cardiac cycle to the closure of tricuspid and mitral valves of the subsequent cardiac cycle and a cardiac cycle as the period of time from closure of tricuspid and mitral vales of a cardiac cycle to the closure of tricuspid and mitral valves of the subsequent cardiac cycle.   
     
     
         13 . The method according to  claim 1 , wherein
 the sensing signals related to mechanical activity of the heart comprises sensing an intracardiac impedance over at least one cardiac cycle using a first electrode vector having at least two electrodes placed in a right atrium, and/or a left ventricle, and/or a right ventricle and to produce an impedance signal; and wherein   the identifying cardiac events comprises identifying the closure of the mitral and tricuspid valve and the closure of the aortic valve using a reference impedance waveform.