Arrangement for determining a heart rate by automatically establishing the optimal refractory time for heart rate determination

Abstract

An arrangement for determining the heart rate (f RR ) or the refractory time of the cardiac tissue, particularly for detecting tachycardia or fibrillation, has an electrode (E) for sensing heart action signals (SIG), an input stage, connected to the electrode, for processing the heart action signals, a refractory member for ascertaining a refractory time value of the arrangement, in each case after a predetermined segment of a heart action signal, and a processing device, connected to the output of the input stage or of the refractory member, for determining the rate of the heart action signals, processed with blanking of the component that occurs during the refractory time, or for determining the refractory time value of the cardiac tissue. The arrangement further includes a device which is connected at least indirectly to the output of the processing device or of the input stage for automatically adjusting the refractory time of the refractory member as a function of a previously determined value of the heart rate or of a signal parameter of a previously determined heart action signal.

1. A system for determining the heart rate and for detecting a medical condition of a heart, comprising:
 an electrode for sensing heart action signals;  
 an input stage connected to the electrode for processing the heart action signals;  
 a refractory member for ascertaining a refractory time of the system after a predetermined segment of a heart action signal, said refractory member connected to an output of the input stage;  
 a processing device connected to an output of the input stage for determining the rate of the heart action signals which includes a means responsive to the refractory member for processing the heart action signals by blanking a component of a heart action signal that occurs during the refractory time, and a counter of detected heart signals for determining the heart rate; and  
 adjusting means connected between an output of the processing device and said refractory member for automatically adjusting the refractory time of the refractory member which includes an arithmetic calculation unit for calculating the refractory time (T ref ) as a function of a previously determined value of the heart rate in accordance with the following equation (1): 
   T ref =QT=QTc−1.75(T n −60) 
   T ref   =QT=QTc− 1 . 75   ( T   RR   − 60   )   (1)  
 
 
       wherein T ref  is the refractory period, T rr  is the previously calculated refractory period  T RR    is the time period between adjacent R - peaks of a heart action signal , and QTc is a set period. 
     
     
       2. The system of  claim 1 , wherein a value slightly greater than the value determined by equation (1) of the arithmetic calculation unit is used to adjust the refractory time. 
     
     
       3. The system of  claim 1 , wherein the value for QTc is determined for each patient based on an electrophysiological examination. 
     
     
       4. An implantable cardiac pacemaker, for treating tachyarrhythmias, comprising a system according to  claim 1 . 
     
     
       5. An implantable defibrillator comprising a system according to  claim 1 . 
     
     
       6. The system of  claim 1 , wherein the adjusting means includes a refractory time memory addressable at least indirectly through the processing device and connected on an output side to a control input of the refractory member, the memory having a plurality of memory spaces for predetermined refractory time values.