METHOD AND DEVICE FOR ARRHYTHMIA DETECTION

Abstract

A method for arrhythmia detection within a heart signal of a patient, wherein the method is executed by a processor and comprises steps of: providing an input signal which refers to the heart signal of the patient, wherein the input signal comprises cardiac events and noise events, wherein the cardiac events are related to cardiac activity of interest of the heart of the patient, and wherein the noise events are not related to cardiac activity of interest of the heart; determining the cardiac events from the input signal in an arrhythmia detection window; evaluating the arrhythmia detection window by taking into account at least one of: (i) at least one noise event occurring before a start of the arrhythmia detection window, or (ii) at least one noise event occurring after an end of the arrhythmia detection window. Also, a device for arrhythmia detection is provided.

Claims

1. A method for arrhythmia detection within a heart signal of a patient, wherein the method is executed by a processor and comprises steps of: providing an input signal which refers to the heart signal of the patient, wherein the input signal comprises cardiac events and noise events, wherein the cardiac events are related to cardiac activity of interest of the heart of the patient, and wherein the noise events are not related to cardiac activity of interest of the heart; determining the cardiac events from the input signal in an arrhythmia detection window; evaluating the arrhythmia detection window by taking into account: at least one noise event occurring before a start of the arrhythmia detection window, and/or at least one noise event occurring after an end of the arrhythmia detection window.

2. The method of claim 1, wherein the step of determining the cardiac events from the input signal in the arrhythmia detection window is terminated if a noise event is detected in the arrhythmia detection window.

3. The method of claim 1, wherein the step of determining the cardiac events from the input signal in the arrhythmia detection window is terminated if a predetermined number of cardiac events is detected in the arrhythmia detection window.

4. The method of claim 1, wherein the arrhythmia detection window is followed by a confirmation period after the end of the arrhythmia detection window, wherein the arrhythmia detection window is confirmed when no noise event is detected during the confirmation period, and wherein the arrhythmia detection window is discarded when a noise event is detected during the confirmation period.

5. The method of claim 4, wherein duration of the confirmation period is determined by a predetermined number of cardiac events after the end of the arrhythmia detection window, and wherein the predetermined number of cardiac events after the end of the arrhythmia detection window depends on the number of noise events occurring before the start of the arrhythmia detection window.

6. The method of claim 1, further comprising: providing an event counter which is configured to count cardiac events and noise events, before the start of the arrhythmia detection window: increasing the event counter by a first value for each detected cardiac event; decreasing the event counter by a second value for each detected noise event, starting the arrhythmia detection window when the event counter is equal to or more than a first predetermined value.

7. The method of claim 6, wherein the second value is twice as high as the first value.

8. The method of claim 6, further comprising: after starting the arrhythmia detection window, increasing the event counter by the first value for each detected cardiac event; decreasing the event counter by a third value if a noise event is detected, terminating the arrhythmia detection window either if the event counter is lower than the first predetermined value or if the event counter is equal to or more than a second predetermined value.

9. The method of claim 8, wherein after the arrhythmia detection window is terminated because the event counter is equal to or more than the second predetermined value, a termination period is started by setting the event counter to a fourth value, wherein during the termination period, the event counter is decreased with every cardiac event that does not indicate the presence of an arrhythmia, and wherein an arrhythmia detection sequence is terminated as soon as the event counter is equal to or less than the first predetermined value.

10. The method of claim 1, further comprising: providing a first event counter which is configured to count cardiac events, providing a second event counter which is configured to count noise events, before the start of the arrhythmia detection window: increasing the second event counter by a fifth value for each detected noise event; decreasing the second event counter by a sixth value for each detected cardiac event, starting the arrhythmia detection window when the second event counter is equal to or less than a third predetermined value, wherein the first event counter is started when the arrhythmia detection window is started.

11. The method of claim 10, further comprising, after starting the arrhythmia detection window, increasing the first event counter by a seventh value for each detected cardiac event; increasing the second event counter by the fifth value for each detected noise event, terminating the arrhythmia detection window either if the first event counter is equal to or more than a fourth predetermined value or if the second event counter is more than the third predetermined value.

12. The method of claim 11, wherein after the arrhythmia detection window is terminated because the first event counter is equal to or more than the fourth predetermined value, a confirmation period is started by setting the second event counter to an eighth value, and during the confirmation period the second event counter is decreased by one with every cardiac event and successful arrhythmia detection result is confirmed as soon as the second event counter is equal to or less than zero.

13. The method of claim 12, further comprising starting a termination period, by setting the first event counter to a ninth value; during termination period, decreasing the first event counter by one with every cardiac event that does not indicate the presence of an arrhythmia and terminate the arrhythmia detection sequence as soon as the first event counter is equal to or less than the third predetermined value.

14. A device for arrhythmia detection comprising: a sensing element which is configured to determine a heart signal of a heart of a patient, and a processor which is configured to provide an input signal which refers to the heart signal, wherein the input signal comprises cardiac events and noise events, wherein the cardiac events are related to cardiac activity of interest of the heart of the patient, and wherein the noise events are not related to cardiac activity of interest of the heart; determine cardiac events from the input signal an arrhythmia detection window, and evaluate the cardiac events in the arrhythmia detection window by taking into account: at least one noise event occurring before a start of the arrhythmia detection window, and/or at least one noise event occurring after an end of the arrhythmia detection window.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In the following, exemplary embodiments are described.

[0044] FIG. 1 shows a schematic representation of a cardiac device,

[0045] FIG. 2A shows a diagram of a first scenario according to a first embodiment,

[0046] FIG. 2B shows a diagram of a second scenario according to the first embodiment,

[0047] FIG. 3 shows a diagram of a first scenario according to a second embodiment,

[0048] FIG. 4 shows a diagram of a second scenario according to the second embodiment,

[0049] FIG. 5 shows a diagram of a third scenario according to the second embodiment.

DETAILED DESCRIPTION

[0050] FIG. 1 shows an exemplary embodiment of a cardiac device 1. In this embodiment, the cardiac device 1 is an implantable cardiac monitor and comprises a sensing element 3, for example a sensing electrode. A processor 2 is arranged within a housing of the cardiac device 1. The cardiac device 1 may comprise further sensing electrodes. In one embodiment, the cardiac device 1 comprises three sensing electrodes (not shown). The cardiac device 1 may include three input channels that receive different projections of the mean heart signal as input signals. Each input channel may use a single pair of the three sensing electrodes and each input channel may sense a different planar projection of the mean heart signal, wherein the projections are coincident in time. Noise on each input channel may be determined, in part, by the local activity around the sensing electrodes in that particular pair. Combining the three input channels into a single input channel may increase the signal to noise ratio by smoothing some of the random noise associated with each input channel, while emphasizing the QRS-signals or QRS complexes.

[0051] The following discussion refers to a single input channel and a single signal, respectively as well as to a combined input channel and a combined signal, respectively. The present disclosure relates to single and combined signals.

[0052] The cardiac device 1 monitors the electrocardiogram (ECG) for QRS events, arrhythmia events and noise events. Detected QRS events and arrhythmia events are marked by a sense marker and noise events are marked by a noise marker. The markers are part of an input signal to the method. In the following Figures, such input signals including sense markers and noise markers are depicted.

[0053] A first scenario of a first embodiment is shown in FIG. 2A. FIG. 2A shows a timeline from an input signal 5 including the related sense markers or cardiac events (also called noise-free events) 6 and noise markers or noise events 7. Further depicted is an event counter 8 which counts cardiac events 6 and noise events 7. Each noise event 7 decreases or decrements the event counter 8 and each cardiac event 6 increases or increments the event counter 8. A scale for the value of the event counter 8 is given at the left side of the diagram.

[0054] Further depicted in FIG. 2A are arrhythmia detection windows 9. During the arrhythmia detection windows 9 the actual detection of an arrhythmia takes place. While the method concerns arrhythmia detection it can be seen as focusing on defining or creating an arrhythmia detection window 9. Here, three arrhythmia detection windows 9a, 9b and 9c are shown. The left arrhythmia detection window 9a can be seen as a preceeding or lapsed arrhythmia detection window. The middle arrhythmia detection window 9b can be seen as a current or active arrhythmia detection window. The right arrhythmia detection window 9c can be seen as a subsequent arrhythmia detection window.

[0055] The following rules may be implemented in the method. In addition to noise conditions within an active arrhythmia detection window 9b, noise conditions or noise events 7 right before the start of the active detection window 9b are monitored as well.

[0056] If a noise event 7 is detected and the event counter 8 is larger than 0 which means that there is an active arrhythmia detection window 9b, instead of decrementing or setting the event counter 8 to 0, a fixed value, in this example of 16, is subtracted. Therefore, the event counter 8 can result in a negative value. The rational for this modification is that noise detection within the active arrhythmia detection window 9b most likely hints towards more and probably undetected noise and needs to be counter-acted aggressively.

[0057] If a noise event 7 is detected and the event counter 8 is equal to or less than 0, the event counter 8 is decremented by a programmable value, in this example 2. Decrementing the event counter 8 is limited to a fixed negative limit.

[0058] If no noise event 7 is detected and the interval's rate is below the HVR threshold and event counter 8 is less than 0, the event counter 8 is incremented by a programmable value, in this example 1.

[0059] If no noise event 7 is detected and the interval's rate is above the HVR threshold, the event counter 8 is incremented by 1.

[0060] In the following, the function of the method according to an embodiment of the present invention is explained with regard to the curve of the event counter 8, i.e. at the end of the window 9a. The starting point for this discussion is the first noise event 7 at which the event counter 8 is decremented by two from the value of zero to the value of minus two. The next noise event 7 decrements the event counter 8 further to minus four. The next four cardiac events 6 which may include QRS and arrhythmia events each increment the event counter 8 by one which results in a value of zero for the event counter 8.

[0061] Having reached the predetermined limit of zero for the event counter 8, the active arrhythmia detection window 9b starts. During the arrhythmia detection window 9b the event counter 8 is incremented by cardiac events 6 to a value of fourteen. Then, a noise event 7 is detected inside the arrhythmia detection window 9b which leads to a decrease of the event counter 8 by a third value, in this example of sixteen. The event counter 8 is thus reduced to the negative value of minus 2. As the event counter 8 is below the predetermined limit of zero the active arrhythmia detection window 9b is terminated and discarded as it includes noise. Two cardiac events 6 (without noise) are needed to start the next arrhythmia detection window 9c as the event counter 8 starts with a value of minus two after the active arrhythmia detection window 9b.

[0062] FIG. 2B shows a second scenario of the first embodiment. The beginning is similar to the situation shown in FIG. 2A. After the end of the preceding arrhythmia detection window 9a, the event counter 8 has a value of 0. Two successive noise events 7 lead to a reduction of the event counter 8 to a value of 4. Following, four cardiac events 6 are registered, each cardiac event 6 increasing the event counter 8 by a value of 1 which results in a value of 0 for the event counter 8. Having reached the predetermined limit of 0 for the event counter 8, the active arrhythmia detection window 9b starts. During the arrhythmia detection window 9b the event counter 8 is incremented by cardiac events 6 until it reaches a predetermined value (here 16, other values are possible).

[0063] With the termination of the active arrhythmia detection window 9b because the predetermined number of cardiac events 6 (with arrhythmia indication) has been reached, a confirmation period or confirmation state 11 starts. The length or duration of the confirmation state 11 is set to a value of 2 (other values are possible). The event counter 8 decrements during the confirmation state 11 by one for each detected cardiac event. After two cardiac events (without noise), the confirmation state 11 is ended successfully.

[0064] At the end of the confirmation state 11 the event counter 8 is set to a predetermined value, in this example to a value of 5. A termination period or termination state 12 follows the confirmation state 11. During the termination state 12 the event counter 8 is incremented for each cardiac event 6 (without arrhythmia indication) by the value of 1. The termination state 12 ends when the event counter 8 reaches the value of 0. Then, the next arrhythmia detection window 9c commences. In the example of FIG. 2B, the detection window 9b was successful as no noise event 7 was detected inside the confirmation state 11.

[0065] If a noise event 7 would have been detected in the confirmation state 11, the arrhythmia detection window 9b would be discarded.

[0066] FIGS. 3 to 5 represent a second embodiment of an implementation of the method by utilizing a first event counter 13 and a second event counter 14 (also called noise counter). Instead of allowing negative event counter values in case of noise events as done in the first embodiment, the noise counter now counts the noise events. This approach supports the extension of the algorithm towards considering noise events after the end of the active arrhythmia detection window.

[0067] The method according to the second embodiment (as shown in FIGS. 3 to 5) is extended with regard as shown in FIG. 2A in the way that noise events right after the active arrhythmia detection window are taken into account as well. Depending on the existence of noise events right before the start of an active arrhythmia detection window, the time will vary for how long the algorithm looks for noise events right after the active arrhythmia detection window.

[0068] Different states can be defined, namely a detection state, a confirmation state, and a termination state. The detection state replicates the behavior of FIG. 2A. In other words, FIG. 2A shows detection states only since confirmation and termination states do not show up due to the circumstances of the situation (noise during active detection terminates immediately the current detection sequence and starts a new detection sequence).

[0069] The confirmation state extends the behavior of the algorithm. At the end of an active arrhythmia detection window a time window or confirmation period is used to identify noise events. If noise events are detected within this time window, the current detection is classified as failed and is aborted. The next state will be a new detection state. On the other side, if no noise event is detected, the detection is classified as confirmed or successful and the next state will be the termination state.

[0070] The termination state is started with the end of a successful confirmation state. The end or termination of the termination state is decided as known, i.e. a predefined number of intervals with rates below the HVR rate threshold are detected. Then, a new detection state is entered again.

[0071] FIGS. 3 to 5 depict behavior for different noise scenarios.

[0072] FIG. 3 shows a diagram with no noise events. The situation shown in FIG. 3 demonstrates that in the absence of noise events at the beginning of the active arrhythmia detection window 9, only a short period of intervals (2 intervals in the above case) is used to confirm the arrhythmia detection.

[0073] A detection state 10 ends with the termination of the active detection window 9 because the predetermined number of cardiac events 6 (with arrhythmia indication) has been reached. Directly after the detection state 10, a confirmation state 11 starts. The length or duration of the confirmation state 11 is determined by the noise counter 14. The noise counter 14 is not amended in this example since no noise was encountered before the start of the active detection window. Nevertheless, an offset value of two is added to the noise counter 14 at the end of the detection window 9 or the end of the detection state 10. For each cardiac event (without noise) the noise counter 14 is decremented by one. As the noise counter 14 reaches zero, the confirmation state 11 is ended successfully. During the confirmation state 11 the first event counter 13 is not altered.

[0074] At the end of the confirmation state 11 the first event counter 13 is set to a predetermined value, in this example to a value of five. A termination state 12 follows the confirmation state 11. During the termination state 12 the first event counter 13 is decremented for each cardiac event 6 (without arrhythmia indication) by the value of one. The termination state 12 ends when the first event counter 13 reaches zero. Then, the next detection state 10 commences. In the example of FIG. 3, the detection window 9 was successful as no noise event was detected inside the confirmation state 11.

[0075] FIG. 4 shows a diagram with noise events 7 before the start and a successful confirmation. FIG. 4 shows noise events 7 before the start of an active arrhythmia detection window 9, inhibiting the start of the arrhythmia detection window 9. The noise counter 14 is incremented in the example by a value of two for each noise event and decremented by a value of one for each cardiac event 6. As soon as the noise counter is decremented below the value of 2, the active arrhythmia detection window 9 starts because of intervals having rates higher than the HVR rate threshold. Once the first event counter 13 reaches the event counter limit of sixteen, the confirmation state 11 starts. Because of the initial noise events 7 at the start of the active arrhythmia detection window 9, the confirmation state 11 is elongated to five intervals. This is due to the noise counter remaining value of one at the start of the actual detection window. Because of that an offset value of 4 is added to the noise counter 14 at the end of the detection window 9 or the end of the detection state 10. As soon as the confirmation state 11 for this episode is established, the regular termination state 12 takes over.

[0076] FIG. 5 shows a diagram with noise events 7 before the start and a failed confirmation. As in FIG. 4, FIG. 5 shows noise events 7 before the start of an active arrhythmia detection window 9, inhibiting the start of the arrhythmia detection window 9. After that, in the absence of noise events, the active arrhythmia detection window 9 starts because of intervals having rates higher than the HVR rate threshold. Once the first event counter 13 reaches the event counter limit of sixteen, the confirmation state 11 starts. Because of the initial noise events 7 at the start of the active arrhythmia detection window 9, the confirmation state 11 is elongated to five intervals. This is due to the noise counter remaining value of one at the start of the actual detection window. Because of that an offset value of 4 is added to the noise counter 14 at the end of the detection window 9 or the end of the detection state 10. Later, still within the confirmation state 11, a noise event 7 causes a fail of the confirmation for this episode. Now, the next regular detection state 10 starts with the noise counter value set to two.

[0077] It will be apparent to those skilled in the art that numerous modifications and variations of the described examples and embodiments are possible in light of the above teachings of the disclosure. The disclosed examples and embodiments are presented for purposes of illustration only. Other alternate embodiments may include some or all of the features disclosed herein. Therefore, it is the intent to cover all such modifications and alternate embodiments as may come within the true scope of this invention, which is to be given the full breadth thereof. Additionally, the disclosure of a range of values is a disclosure of every numerical value within that range, including the end points.