Implantable heart stimulator for measuring dyssynchrony using impedance
Implantable heart stimulator connectable to an electrode arrangement has a pulse generator adapted to deliver stimulation pulses to a heart of a subject; an impedance measurement unit adapted monitor at least one heart chamber of the heart of the subject to measure the impedance in the at least one monitored heart chamber for generating an impedance signal corresponding to the measured impedance. The impedance signal is applied to a processor where the signal is processed, according to specified criteria, and a fractionation index value is determined represented by the curve length of the impedance signal during a predetermined measurement period. The fractionation index value is a measure of different degrees of mechanical dyssynchrony of the heart.
1. An implantable heart stimulator comprising:
an electrode arrangement adapted for placement adjacent a heart of a subject;
a pulse generator adapted for connection to the electrode arrangement to deliver stimulation pulses to the heart;
an impedance measurement unit that monitors, through said electrode arrangement, a chamber of the heart by measuring impedance therein to generate an impedance signal corresponding to said impedance; and
a computerized processor supplied with said impedance signal, said computerized processor being configured to analyze said impedance signal according to predetermined criteria to determine a fractionation index value that represents a measure of a length of curve of the impedance signal during a predetermined measurement period of said impedance, said processor making said fractionation index value available at an output thereof as an indicator of a degree of mechanical dyssynchrony of the heart, wherein said processor determines said curve length by filtering the impedance signal to remove noise therefrom, averaging the impedance signal during the measurement period to generate an average waveform, storing the average waveform, storing an average R-R interval from heartbeats included in said impedance signal, dividing the stored average waveform by a maximum value thereof, sampling the stored average waveform to define the number of samples in a heartbeat summing a plurality of absolute difference values between adjacent samples in the stored average waveform that is divided by the maximum to obtain a sum that is a measure of the curve length during the measurement period, and dividing said sum by the stored average R-R interval to obtain a quotient that is said fractionation index value.
2. An implantable heart stimulator as claimed in claim 1 wherein said computerized processor is configured to determine said fractionation index value at regular intervals during a predetermined time period, and to store respective fractionation index values in a memory.
3. An implantable heart stimulator as claimed in claim 2 wherein said processor is configured to access the stored fractionation values and to compare the accessed fractionation index values to respective predetermined thresholds that respectively represent different degrees of heart failure.
4. An implantable heart stimulator as claimed in claim 3 wherein said processor is configured to emit an alert signal when in accessed fractionation index value exceeds one of said predetermined thresholds that represents a dangerous degree of heart failure.
5. An implantable heart stimulator as claimed in claim 1 wherein said processor is configured to adjust a timing between stimulation pulses emitted by said pulse generator to minimize said fractionation index value.
6. An implantable heart stimulator as claimed in claim 5 wherein said pulse generator is a biventricular pulse generator that generates pulses supplied to respective ventricles of the heart with a VV-delay therebetween, and wherein said processor adjusts said timing by adjusting said VV-delay.
7. An implantable heart stimulator as claimed in claim 1 wherein said processor determines said curve length only during a diastolic portion of a heart cycle of the heart.
8. An implantable heart stimulator comprising:
an electrode arrangement adapted for placement adjacent a heart of a subject;
a pulse generator adapted for connection to the electrode arrangement to deliver stimulation pulses to the heart;
an impedance measurement unit that monitors, through said electrode arrangement, a chamber of the heart by measuring impedance therein to generate an impedance signal corresponding to said impedance; and
a computerized processor supplied with said impedance signal, said computerized processor being configured to analyze said impedance signal according to predetermined criteria to determine a fractionation index value that represents a measure of a length of curve of the impedance signal during a predetermined measurement period of said impedance, said processor making said fractionation index value available at an output thereof as an indicator of a degree of mechanical dyssynchrony of the heart, wherein said processor determines said curve length by calculating, for each heartbeat in the measurement period, an absolute difference between measurement samples separated by a predetermined number of samples, summing the calculated differences for each heartbeat to obtain a sum, normalizing the sum, summing each normalized sum for all heartbeats during a measurement period to obtain a sum of normalized sums, and dividing the sum of normalized sums by the number of heartbeats occurring in said measurement period to obtain a quotient that is said fractionation index value.