SYSTEM AND METHOD FOR THE DETECTION OF QRS COMPLEXES IN ELECTROCARDIOGRAPHIC SIGNALS.

Abstract

The present invention describes a system and method for detecting QRS complexes in electrocardiographic signals, thereby providing real-time QRS complex detection; and furthermore, it allows for QRS complex detection even in the presence of ECG signals contaminated with noise. This is achieved by using a "Haar-k" type wavelet function.

Description

FIELD OF INVENTION The present invention relates to methods for processing electrocardiographic signals, and more particularly to a system and method for detecting QRS complexes in electrocardiographic signals. BACKGROUND OF THE INVENTION An electrocardiogram (ECG) is defined as the graphical representation of the heart's electrical activity over time, obtained from the body surface on the chest using an electrocardiograph as a continuous strip. With the advent of digital data storage, it is common practice to sample the electrocardiogram, convert it to binary code, and store it as digital values. The resulting sequence of values ​​is also called an electrocardiographic signal or ECG signal. The ECG signal corresponds to an electrical potential difference measured between two electrodes, at least one of which is placed on a user's chest. The ECG signal can be divided into cycles, one cycle for each heartbeat. Each cycle consists of a short, high-amplitude pulse called the QRS complex, which contains high-frequency components. The QRS complex corresponds to the depolarization of the right and left ventricles of the human heart and the contraction of the large ventricular muscles. The QRS complex is divided into a Q wave, an R wave, and an S wave, with the R wave being the central part of the QRS complex and exhibiting the highest amplitude peak. The QRS complex is usually the central and most visually prominent part of the graph; it is the main peak seen in an ECG tracing.The ECG signal also contains other waveforms of longer duration and lower amplitude called P wave and T wave, which have fewer high-frequency components than the QRS complex. Automatic detection of the QRS complex has applications in vital signs monitoring systems and for diagnosing heart conditions. A wavelet transform (WT) is a widely used signal processing technique, often a key step in QRS complex detection algorithms. The WT involves convolving (or correlating) an input signal, such as an ECG signal, with a function called a wavelet. The WT uses the wavelet function as a pattern to search for similar waveforms within the ECG signal being analyzed. Any wavelet function must have a mean of zero so that, during correlation with the input signal, it acts as a bandpass filter. Furthermore, the wavelet function must have a finite duration and bounded amplitude. In this case, automatic QRS complex detection essentially involves finding the location of its peak, which is typically within the R wave. This same task can be performed manually by a cardiologist. Among the difficulties encountered in determining the QRS complex are: low-frequency noise over which the ECG signal is superimposed; high-frequency noise due to muscle activity (electromyographic noise); noise due to changes in conductivity at the electrode / skin interface; 60 Hz power line noise; and other sources of electromagnetic interference. There are different systems used for QRS complex detection, such as the one described in patent document US8725238B2, which describes a system for processing an ECG signal that, in addition to detecting the R point of the QRS complex, performs tasks such as removing low-frequency components, reducing high-frequency noise, compression, and predicting the heart rate.However, when applying the patent to try to detect the QRS complex in real time, we found a detection delay that is inherent to the described method; this is because the method requires calculating the TW on different scales using the correlation technique with respect to a wavelet function in conjunction with the correlation with respect to a scale function, but, because the scale function used is non-causal, delays are introduced in the output signal of magnitude proportional to the scale of the TW; the described method makes it necessary to use memory elements to equalize the delay of the TW on all scales. Additionally, patent document US6561986B2 describes a method and apparatus for detecting ventricular activity parameters by means of thoracic impedance measurements combined with ECG measurements. However, it employs a method for QRS complex detection that is not real-time, as it requires creating a sample window containing the entire QRS complex; then, starting from the end of the QRS interval, the method works backward, sample by sample, comparing adjacent points until it finds the peak point, called R. Patent document CN107951482A describes a method for leveling an ECG signal to a baseline based on wavelet decomposition. Although the first steps of the described method involve detecting the QRS complex starting points, it is not a real-time method, as it requires first capturing 10 seconds of the ECG signal at a rate of 1000 samples per second; then, wavelet decomposition (WD) is applied using a Daubechies wavelet at the smallest possible scale for the sampling rate used; next, with the resulting coefficients, and disregarding the WD coefficients at other scales, a total of 6 levels of the reconstruction algorithm are executed applying inverse discrete WD; finally, the resulting series is reordered in descending order according to its absolute value, and only the first 200 coefficients are considered to locate the QRS complex starting points. As a consequence of the above, efforts have been made to eliminate the drawbacks of the methods currently used for processing electrocardiographic signals, developing a method and system for the detection of QRS complexes in electrocardiographic signals that, in addition to detecting the QRS complex in real time, allows the detection of the QRS complex in the presence of ECG signals contaminated with noise. OBJECTS OF THE INVENTION Taking into account the shortcomings of prior techniques, it is an object of the present invention to provide a system and method for the detection of QRS complexes in electrocardiographic signals for the detection of QRS complexes in real time. Furthermore, it is an object of the present invention to provide a system and method for the detection of QRS complexes in electrocardiographic signals even in the presence of noise in contaminated ECG signals. These and other objectives are achieved through a system and method for detecting QRS complexes in electrocardiographic signals in accordance with the present invention. BRIEF DESCRIPTION OF THE INVENTION. To that end, a first aspect of the present invention relates to a method for detecting QRS complexes in electrocardiographic signals comprising the steps of: obtaining an electrocardiographic (ECG) signal by means of at least one pair of electrodes; receiving the ECG signal from the electrodes in an amplifier; amplifying the ECG signal by means of the amplifier into an amplified signal; sending the amplified signal by means of the amplifier to an analog-to-digital converter (ADC); converting the amplified signal by means of an ADC into a digital signal; sending the digital signal to a digital controller; sending a clock signal generated by means of a clock signal generator to a digital controller for synchronization; receiving the digital signal sent by means of the ADC and the clock signal sent by means of the clock signal generator in a digital controller; and processing the digital signal to detect the QRS complex by means of the digital controller.and generate a QRS complex detection signal using the digital controller. A second aspect of the invention relates to a system for detecting QRS complexes in electrocardiographic signals comprising: a power source for energizing the system; at least one pair of electrodes configured to obtain an ECG signal; an amplifier configured to receive the ECG signal, amplify it, and send an amplified signal to an analog-to-digital converter (ADC); an ADC configured to receive the signal amplified by the amplifier, convert it into a digital signal, and send it to a digital controller; a clock signal generator configured to send a clock signal to a digital controller for synchronization; and a digital controller configured to receive the digital signal sent by the ADC and the clock signal sent by the clock signal generator, and to process the digital signal to generate a QRS complex detection signal. BRIEF DESCRIPTION OF THE DRAWINGS The novel aspects considered characteristic of the present invention will be set forth in detail in the appended claims. However, some embodiments, features, and some objects and advantages thereof will be better understood in the detailed description when read in conjunction with the accompanying drawings, in which: Figure 1 illustrates a diagram of the method for detecting QRS complexes in electrocardiographic signals according to a first modality of the present invention. Figure 2 illustrates a diagram of the system for detecting QRS complexes in electrocardiographic signals according to a second modality of the present invention. Figure 3 illustrates a graph showing the detection of QRS complexes with the system and method according to a modality of the present invention. DETAILED DESCRIPTION OF THE INVENTION The present invention seeks to detect QRS complexes in electrocardiographic signals, thereby providing real-time QRS complex detection; and to allow the detection of the QRS complex in the presence of ECG signals contaminated with noise. Thus, in a first aspect of the invention, a method for detecting QRS complexes in electrocardiographic signals is described, comprising the steps of: obtaining an ECG signal by means of at least one pair of electrodes; receiving the ECG signal from the electrodes in an amplifier; amplifying the ECG signal by means of the amplifier into an amplified signal; sending the amplified signal by means of the amplifier to an analog-to-digital converter (ADC); converting the amplified signal by means of an ADC into a digital signal; sending the digital signal to a digital controller; sending a clock signal generated by means of a clock signal generator to a digital controller for synchronization; receiving the digital signal sent by means of the ADC and the clock signal sent by means of the clock signal generator in a digital controller; and processing the digital signal to detect the QRS complex by means of the digital controller.and generate a QRS complex detection signal using the digital controller. In one embodiment of the present application, the stage of processing the digital signal by means of the digital controller comprises in turn the following steps: receiving a new digitized sample of the ECG signal from the ADC converter; storing the digitized sample of the ECG signal in the register of the digital controller; obtaining the current value of a wavelet transform W by convolving a wavelet function with the stored digitized sample of the ECG signal; verifying whether the value obtained by the wavelet transform meets a value condition; if the value condition is met, activating a digital pulse signal by means of the digital controller, this signal indicating the peak of the R wave of the QRS complex; and generating a QRS complex detection signal by means of the digital controller in accordance with the digital pulse signal. Ideally, the detection signal is activated when the digital pulse signal is activated. However, the detection signal does not deactivate immediately when the digital pulse signal deactivates; it deactivates after the digital pulse signal has been off for a period longer than a specified delay. One way to implement this delay is with a counter that is initialized to a constant value in each processing cycle where the digital pulse signal is 1. This counter is then decremented by one in each iteration where the digital pulse signal is 0. Decrementing continues only if the counter has not yet reached zero. This delay is necessary because it reduces the likelihood of the detection signal being activated repeatedly in short intervals due to high-frequency interference. In one embodiment of the present invention, the step of receiving a new digitized sample of the ECG signal from the ADC converter may further comprise the steps of: shifting the data in a register of the digital controller by one position, where the first position is a more recent data point and the last position is an older data point; deleting the oldest data point; and freeing the first position of the digital controller register. The step of storing the digitized sample of the ECG signal in the register of the digital controller may further comprise the steps of: storing the new digitized sample of the ECG signal in the first position of the digital controller register. In an alternative embodiment of the present invention, the step of storing the digitized ECG signal sample in the digital controller register may further comprise the steps of: deleting an older data entry located in the digital controller register; and storing the new digitized ECG signal sample in the position of the older data entry in the digital controller register, thereby changing the location of the oldest data entry to the location of the most recent data entry. The digital controller register may be considered as a circularly addressable register, where the register comprises a list with its most recent and oldest data entries adjacent and shifting one position with each iteration. The step of storing the digitized ECG signal sample in the digital controller register avoids shifting the data stored in the register. Additionally, the value condition that is met to verify whether the value obtained by the wavelet transform is selected from W > Th or | W | > Th, where Th is a previously established and empirically determined threshold value. Preferably, the wavelet transform is a continuous-time transform that convolves the digitized ECG signal sample with respect to a continuous Haar-k wavelet function that is defined by: llk(t) = -1 . 0 < t < 1, < t < k + 1, otherwise. The Haar-k wavelet contains a single initial positive pulse of amplitude k in the time interval from 0 to 1, which subsequently takes the value of -1 during the time interval from 1 to k+1, where k can be any integer greater than 1. When the Haar-k wavelet is convolved with the digital signal, it produces a band-pass filter effect. Because the Haar-k wavelet contains only one high-value pulse located in the time interval from 0 to 1, the filter output contains a version of the original QRS complex with a single peak near the peak of the R wave. The wavelet function is causal, and since the high-value pulse starts at time 0, it ensures that there is no delay in the detection of the QRS complex. More preferably, the wavelet transform is a discrete-time transform that convolves the sequence of digitized ECG signal samples stored with respect to the discrete wavelet function Haar-k, which has k+1 elements and is defined by Hk[m] = {k, -1, -1, ..., -1}, where m takes values ​​from 1 to k+1. Additionally, the Haar-k wavelet function can have a dilated version of Hk[m] denoted by Hkn[m]. The dilated wavelet function contains (k+1)xn elements, where m ranges from 1 to (k+1)xn, n being any integer greater than or equal to 1; the first n elements are equal to ak, and the last kxn elements are equal to -1. If we set n equal to 1, then the dilated wavelet function Hkn[m] reduces to the wavelet function Hk[m]. The wavelet function Hk[m] and the dilated wavelet function Hk¿m] as defined here are normalized, that is, their last ky kxn elements, respectively, have the value of -1.However, it is possible to use non-normalized versions of these wavelets, where all their elements are multiplied by a constant that can be any positive or negative integer or decimal number. To obtain the current value of the wavelet transform W, a convolution defined by W = d[l] x Hkn[l] + d[2] x Hkn[2] + ... + d[(k+l)xn] x Hkn[(k+l)xn] can be performed; where d[l] is the digitized sample of ECG signal in the current iteration, d[2] is the digitized sample of ECG signal in the previous iteration, d[3] is the digitized sample of ECG signal from two iterations ago, and in general, d[j] is the digitized sample of ECG signal from j - 1 iterations ago. Additionally, it is possible to perform multiple convolutions of the digital signal against several versions of the wavelet Hkn[m] that are dilated to different values ​​of n, resulting in a set of Wn values. Each of these values ​​is compared against its own threshold level Thn, resulting in several digital pulse signals. The value of the detection signal will depend on at least one activation function of these digital pulse signals. Using multiple convolutions allows us to process the ECG signal when it is contaminated with high levels of noise. Furthermore, the convolution to obtain the value of the wavelet transform W can be derived from the value of a wavelet transform W' obtained in a previous iteration, in order to reduce the number of operations required to calculate W. This is achieved by taking advantage of the fact that the values ​​of the function Hkn[m] show little change for consecutive values ​​of m. The value of the wavelet transform W is calculated using the equation W = W'+d[l] xk - d[n+l] xk - d[nl] + d[(k+l)xn+l], where d[l] is the digitized ECG signal sample in the current iteration; d[n+l] is the digitized ECG signal sample from n iterations ago; and d[(k+l)xn+l] is the digitized ECG signal sample from (k+l)xn iterations ago. An additional embodiment of the present invention, the wavelet transform W, may employ two or more Hkn[m] filters, with kn values ​​that may be different or even the same. A first filter performs the wavelet transform of the digitized ECG signal samples stored in a record; a second filter performs the wavelet transform of the digitized samples output from the first filter; and so on. The output of the final cascaded filter is the output of the combined wavelet transform, thus obtaining an equivalent wavelet function with a more selective frequency response. The values ​​of the combined equivalent wavelet function may be obtained, if desired, by convoluting the coefficients of the respective individual Hkn[m] filters involved. A second aspect of the present invention describes a system for detecting QRS complexes in electrocardiographic signals comprising: a power source for energizing the system; at least one pair of electrodes configured to obtain an ECG signal; an amplifier configured to receive the ECG signal, amplify it, and send an amplified signal to an analog-to-digital converter (ADC); an ADC configured to receive the signal amplified by the amplifier, convert it into a digital signal, and send it to a digital controller; and a clock signal generator configured to send a clock signal to a digital controller for synchronization.and a digital controller that is configured to receive the digital signal sent by the ADC converter and the clock signal sent by the clock signal generator, and to process the digital signal to generate a QRS complex detection signal. In one embodiment of the present invention, each pair of electrodes preferably has a configuration known as modified limb lead II or MLII. Additionally, one of the electrodes in each pair can be considered the reference ground for the purpose of amplifying the obtained ECG signal. Additionally, in one embodiment of the present invention, the amplifier is configured to provide a gain to the ECG signal of up to 300. In another embodiment of the present invention, the ADC converter preferably has a minimum resolution of 8 bits and a minimum input voltage range of 0 to 3.3 V. The input voltage range is divided by the resolution of the ADC converter, and each part of the input voltage is assigned a binary code the size of the converter's resolution; for example, for a resolution of 8 bits and an input voltage of 0 V, the binary code is 0000 0000. Additionally, the ADC converter is configured to receive a control signal sent by the digital controller. The control signal preferably instructs the ADC converter to repeat the procedure of receiving an amplified signal from the amplifier, converting it into a digital signal, and sending it to the digital controller. Furthermore, in one embodiment of the present invention, the clock signal generator is selected from the group comprising a quartz crystal circuit, an astable oscillator, among others. In one embodiment of the present invention, the digital controller is further configured to receive an initialization signal that instructs the digital controller to initialize its internal memory registers to a suitable initial value, preferably zero. The digital controller is further configured to send a control signal that instructs the ADC to repeat the procedure of receiving an amplified signal, converting it into a digital signal, and sending it to the digital controller. The digital signal processed by the digital controller is preferably a one-bit pulse signal whose rising edge indicates the location where the system detected the peak of the R wave of the QRS complex. In a further embodiment of the present invention, the system components—the amplifier, the ADC converter, and the clock signal generator—used for QRS complex detection may be included in an analog module within an integrated circuit which also contains the digital controller. Additionally, in one embodiment of the present invention, a Field Programmable Gate Array (FPGA) is used for the implementation of the digital controller hardware, while the amplifier, ADC converter, and clock signal generator can be internal or external to the FPGA. Several preferred embodiments of the invention are described for illustrative purposes, it being understood that the invention can be carried out in other ways not specifically shown in the drawings. Referring now to Figure 1, which illustrates a method 100 for the detection of QRS complexes in electrocardiographic signals comprising the steps of: obtaining 110 an ECG signal by means of at least one pair of electrodes; receiving 120 the ECG signal from the electrode in an amplifier; amplifying 121 the ECG signal by means of the amplifier into an amplified signal; sending 122 the amplified signal by means of the amplifier to an ADC converter; converting 130 the amplified signal by means of an ADC converter into a digital signal; sending 131 the digital signal to a digital controller; sending 140 a clock signal generated by means of a clock signal generator to a digital controller for synchronization; receiving 150 the digital signal sent by means of the ADC converter and the clock signal sent by means of the clock signal generator in a digital controller; processing 151 the digital signal to detect the QRS complex by means of the digital controller;and generate a QRS complex detection signal using the digital controller. Now, Figure 2, which illustrates a system 200 for detecting QRS complexes in electrocardiographic signals comprising: a source 210 for powering the system; at least one pair of electrodes 220 configured to obtain an ECG signal 221; an amplifier 230 configured to receive the ECG signal 221, amplify it, and send an amplified signal 231 to an ADC converter 240; an ADC converter 240 configured to receive the amplified signal 231 from the amplifier 230, convert it into a digital signal 241, and send it to a digital controller 250; a clock signal generator 260 configured to send a clock signal 261 to a digital controller 250 for synchronization;and a digital controller 250 that is configured to receive the digital signal 241 sent by the ADC converter 240 and the clock signal 261 sent by the clock signal generator 260 and to process the digital signal 241 to generate a QRS complex detection signal 251.; Figure 3 illustrates the results of laboratory measurements of the system. The top portion shows a section of an ECG signal 221 encompassing three QRS complexes 222. The middle portion shows a QRS complex detection signal 251, where the rising edge indicates the location where the QRS complex was detected 252. The bottom portion shows an EXPERT signal 253 where the rising edge indicates the point at which a cardiologist has confirmed the presence of a QRS complex. In accordance with the foregoing, it may be observed that a system and method for the detection of QRS complexes in electrocardiographic signals has been devised to detect the QRS complex in real time and to allow the detection of the QRS complex in the presence of ECG signals contaminated with noise, and it will be evident to any person skilled in the art that the modalities of the system and the method for the detection of QRS complexes in electrocardiographic signals as described above and illustrated in the accompanying drawings are merely illustrative and not limiting to the present invention, since numerous substantial changes in their details are possible without departing from the scope of the invention. Therefore, the present invention shall not be considered restricted except as required by prior art and within the scope of the appended claims.

Claims

1. A method for detecting QRS complexes in electrocardiographic (ECG) signals, characterized in that it comprises the steps of: obtaining an ECG signal by means of at least one pair of electrodes; receiving the ECG signal from the electrodes in an amplifier; amplifying the ECG signal by means of the amplifier into an amplified signal; sending the amplified signal by means of the amplifier to an analog-to-digital converter (ADC); converting the amplified signal by means of an ADC into a digital signal; sending the digital signal to a digital controller; sending a clock signal generated by means of a clock signal generator to a digital controller for synchronization; receiving the digital signal sent by means of the ADC and the clock signal sent by means of the clock signal generator in a digital controller; and processing the digital signal to detect the QRS complex by means of the digital controller.and generate a QRS complex detection signal using the digital controller.

2. The method according to claim 1, further characterized in that the step of processing the digital signal by means of the digital controller comprises in turn the following steps: receiving from the ADC converter a new digitized sample of the ECG signal; storing the digitized sample of the ECG signal in the register of the digital controller; obtaining the current value of a wavelet transform W by convolving a wavelet function with the stored digitized sample of the ECG signal; verifying whether the value obtained by the wavelet transform meets a value condition; if the value condition is met, activating by means of the digital controller a digital pulse signal, this signal indicating the peak of the R wave of the QRS complex; and generating a QRS complex detection signal by means of the digital controller in accordance with the digital pulse signal.

3. The method according to claim 2, further characterized in that the detection signal is turned on when the digital pulse signal is turned on.

4. The method according to claim 3, further characterized in that the detection signal does not turn off immediately when the digital pulse signal turns off, the detection signal turns off when the digital pulse signal has been off for a time longer than a delay time.

5. The method according to claim 4, further characterized in that the delay time is implemented by means of a counter that is loaded to a constant value in each processing where the digital pulse signal results in a value of 1 and whose value is decremented by one in each iteration where the digital pulse signal results in a value of 0.

6. The method according to claim 5, further characterized in that the decrement is only continued if the counter has not yet reached the value of zero.

7. The method according to claim 2, further characterized in that the step of receiving a new digitized sample of the ECG signal from the ADC converter further comprises the steps of: shifting the data in a register of the digital controller by one position, wherein a first position is a more recent data and a last position is an older data; deleting the older data; and releasing the first position of the register of the digital controller.

8. The method according to claim 7, further characterized in that the step of storing the digitized sample of the ECG signal in the register of the digital controller further comprises the steps of: storing the new digitized sample of the ECG signal in the first position of the register of the digital controller.

9. The method according to claim 2, further characterized in that the step of storing the digitized sample of the ECG signal in the register of the digital controller may further comprise the steps of: deleting an older data item located in the register of the digital controller; and storing the new digitized sample of the ECG signal in the position of the older data item located in the register of the digital controller, converting the location of the older data item to the location of the newer data item.

10. The method according to claim 9, further characterized in that the digital controller register is considered as a circular address register, wherein the circular address register comprises a list with its most recent data and its oldest data adjacent and moving one position with each iteration.

11. The method according to claim 2, further characterized in that the value condition that is met to verify whether the value obtained by the wavelet transform is selected from W > Th or | W | > Th, where Th is a previously established and empirically determined threshold value.

12. The method according to claim 2, further characterized in that the wavelet transform is a continuous-time transform that convolves the digitized ECG signal sample with respect to a continuous wavelet function Haar-k defined by: Hk(V = k -1 0 0 < t < 1, 1 < t < k + 1, otherwise. which contains a single initial positive pulse of amplitude k in the time interval from 0 to 1, which subsequently takes the value of -1 during the time interval from 1 to k+1, where k is any integer greater than 1.

13. The method according to claim 12, further characterized in that the wavelet transform is a discrete-time transform that convolves the sequence of digitized ECG signal samples stored with respect to a discrete wavelet function Haark having k+1 elements and defined by Hk[m] = {k, -1, -1, ..., -1}, where m takes values ​​from 1 to k+1.

14. The method according to claim 13, further characterized in that the Haar-k wavelet function is a dilated wavelet function of Hk[m] denoted by Hkn[m]; the dilated wavelet function contains (k+l)xn elements; wherein the range of m is from 1 to (k+l)xn, n being any integer equal to or greater than 1; the first n elements are equal to ak, and the last kxn elements are equal to -1; the dilated wavelet Hkn[m] is normalized.

15. The method according to claim 14, further characterized in that the current value of the wavelet transform W is obtained by performing a convolution defined by W = d[l] x Hkn[l] + d[2] x Hkn[2] + ... + d[(k+l)xn] x Hkn[(k+l)xnJ; wherein d[l] is the digitized sample of ECG signal in the current iteration; d[2] is the digitized sample of ECG signal in the previous iteration; d[3] is the digitized sample of ECG signal from two iterations ago; and in general, d[j] is the digitized sample of ECG signal from j - 1 iterations ago.

16. The method according to claim 15, further characterized in that several convolutions of the digital signal are performed against several versions of the wavelet function Hkn[m] that are dilated to different values ​​of n, resulting in a set of values ​​Wn; each of these values ​​is compared against its own level of a threshold Thn, resulting in several digital pulse signals; wherein the value of the detection signal will depend on at least one activation function of these digital pulse signals.

17. The method according to claim 16, further characterized in that the convolution to obtain the value of the wavelet transform W is obtained from the value of a wavelet transform W obtained in a previous iteration.

18. The method according to claim 17, further characterized in that the value of the wavelet transform W is calculated by the equation W = W'+d[l] xkd[n+l] xk - d[nl] + d[(k+l)xn+l]; where d[l] is the digitized sample of ECG signal in the current iteration; d[n+l] is the digitized sample of ECG signal from n iterations ago; and d[(k+l)xn+l] is the digitized sample of ECG signal from (k+l)xn iterations ago.

19. The method according to claim 16, further characterized in that the wavelet transform W employs two or more filters Hkn[m], with kn values ​​that are different or equal.

20. The method according to claim 19, further characterized in that a first filter performs the wavelet transform of the digitized ECG signal samples stored in a record; a second filter performs the wavelet transform of the digitized samples coming out of the first filter; and so on; wherein the output of a final cascaded filter is the output of the wavelet transform as a whole, this in order to obtain an equivalent wavelet function with a more selective frequency response.

21. A system for detecting QRS complexes in electrocardiographic signals characterized in that it comprises: a power source for energizing the system; at least one pair of electrodes configured to obtain an ECG signal; an amplifier configured to receive the ECG signal, amplify it, and send an amplified signal to an analog-to-digital converter (ADC); an ADC configured to receive the signal amplified by the amplifier, convert it into a digital signal, and send it to a digital controller; a clock signal generator configured to send a clock signal to a digital controller for synchronization; and a digital controller configured to receive the digital signal sent by the ADC and the clock signal sent by the clock signal generator, and to process the digital signal to generate a QRS complex detection signal.

22. The system according to claim 21, further characterized in that each pair of electrodes has a modified limb lead II (MLII) configuration.

23. The system according to claim 22, further characterized in that one of the electrodes of each pair of electrodes is considered as the reference ground for the purpose of amplifying the obtained ECG signal.

24. The system according to claim 21, further characterized in that the amplifier is configured to provide a gain to the ECG signal of a maximum of 300.

25. The system according to claim 21, further characterized in that the ADC converter has a minimum resolution of 8 bits and a minimum input voltage range of 0 to 3.3 V.

26. The system according to claim 25, further characterized in that the input voltage range is divided by the resolution of the ADC converter and each part of the input voltage is assigned a binary code the size of the converter's resolution.

27. The system according to claim 21, further characterized in that the ADC converter is configured to receive a control signal sent by the digital controller, the control signal instructing the ADC converter to repeat the procedure of receiving an amplified signal by the amplifier, converting it into a digital signal and sending it to the digital controller.

28. The system according to claim 21, further characterized in that the clock signal generator is selected from the group comprising: a quartz crystal circuit, or an astable oscillator.

29. The system according to claim 21, further characterized in that the digital controller is additionally configured to receive an initialization signal which is configured to instruct the digital controller to initialize its internal memory registers to a suitable initial value, 30. The system according to claim 29, further characterized in that the initial value for the internal memory registers of the digital controller is a value of zero.

31. The system according to claim 21, further characterized in that the digital controller is additionally configured to send a control signal instructing the ADC converter to repeat the procedure of receiving an amplified signal by the amplifier, converting it into a digital signal, and sending it to the digital controller.

32. The system according to claim 21, further characterized in that the digital signal processed by the digital controller is a one-bit digital pulse signal whose rising edge indicates the location where the system detected the peak of the R wave of the QRS complex.

33. The system according to claim 21, further characterized in that the system components: the amplifier, the ADC converter and the clock signal generator, used for the detection of QRS complexes are included in an analog module within an integrated circuit which also contains the digital controller.

34. The system according to claim 33, further characterized in that a Field Programmable Gate Array (FPGA) is used for the implementation of the digital controller hardware, while the amplifier, ADC converter and clock signal generator are internal to the FPGA.

35. The system according to claim 33, further characterized in that a Field Programmable Gate Array (FPGA) is used for the implementation of the digital controller hardware, while the amplifier, ADC converter and clock signal generator are external to the FPGA.

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