Patent Description:
During a cardiac procedure, the condition of the heart may be monitored, inter alia, by observing electrophysiological data in a graphical form, typically as potential vs. time graphs. While the heart is in a sinus condition, the periodic electrocardiogram (ECG) waveforms generated by the heart are relatively uncomplicated. However, in some non-sinus conditions of the heart, such as during atrial fibrillation, each periodic ECG signal may include one or more features that may only occur in some of the periodic signals, but not in every signal. Because of the irregularity of the signals, it is difficult to distinguish these features.

<CIT>, describes a method for visualization of electrophysiology data. Electroanatomic data representing electrical activity on a surface of an organ over a time period is stored. An interval within the time period is selected in response to a user selection. Responsive to the user selection of the interval, a visual representation of physiological information for the user selected interval is generated by applying at least one method to the electroanatomic data. The visual representation is spatially represented on a graphical representation of a predetermined region of the surface of the organ.

<CIT> describes a cardiac muscle excitation waveform detector. The detector includes a waveform acquisition section that acquires, in a preset period, a waveform from an intracardiac electrocardiogram measured in the middle of occurrence of atrial fibrillation. The disclosure is stated to show a result of a mean conduction time that is calculated under an analysis technique described in the disclosure.

<CIT>, describes a system for presenting information representative of patient electrophysiological activity, such as complex fractionated electrogram information. The disclosure describes a presentation device that presents electrogram information as associated with a location at which it was measured on a model of the patient's heart.

<CIT> discloses a method of displaying a periodically recurring electrocardiographic (EKG) signal. The EKG signals are applied to the Y-deflection circuits of a cathode ray oscilloscope (CRO). Free-running time base signals are generated and applied to the X- deflection circuits of the CRO. The r wave portions of the EKG signals are detected, delayed for a given period of time, and used to synchronize the timebase signals.

<CIT> discloses a system which processes semiperiodic electrical signals such as an electrocardiogram to produce a real time signal display on the face of a variable persistence cathode ray tube in an oscilloscope. Each cycle of the signal being processed is formed on a separate horizontal base line which is spaced vertically below the trace formed by the preceding cycle. Each of the waveforms is organized about a prominent cyclical event with all similar events aligning in approximately the same vertical plane.

<CIT> describes displaying successive electrograms on top of each other on a graphical display.

This invention is defined by the method of independent claim <NUM> and by the apparatus of independent claim <NUM>.

The present disclosure will be more fully understood from the following detailed description of the
embodiments thereof, taken together with the drawings, in which:.

In certain conditions of the heart, such as some types of atrial fibrillation, each periodic ECG (electrocardiogram) signal may include one or more waveform features that only occur in some of the signals, but not in every signal. These irregularly recurring waveforms are periodic, in the sense that when they do recur, the recurrence is at approximately the same position (in time) in the signal. Because of the irregularity, the waveforms are difficult to distinguish.

Embodiments of the present invention provide a method for viewing the ECG signals so that the irregularly recurring waveforms are made more visible. A set of signals is acquired from the heart of a subject, the set being taken over multiple heart cycles of the subject. A processor partitions the signals into a succession of synchronized segments, using a common annotation point as a start time for each of the segments. A typical segment uses a part of the QRS complex of the ECG signal as the start time, and the succeeding QRS complex as the end time, to define the segments.

Graphical representations of the synchronized segments are overlaid on each other on a display screen, using the common annotation point as a registration point for the segments. The overlaid segments may also be overlaid on each other so that their baselines are aligned. The segments are presented on the display screen at a respective display time corresponding to a respective start time of the segment. In addition each segment is displayed with a common initial display intensity, and the display intensity of each segment is decreased as a decaying function of time elapsed since the initial presentation of the segment on the display screen. There are thus typically a number of different signals with different intensities on the display screen.

Where points or regions of the segments overlap, the display intensities of the overlapping points are summed. The summing emphasizes the irregularly recurring waveforms in the signals, making the waveforms significantly more visible than in prior art signal displays.

Reference is now made to <FIG>, which is a schematic illustration of a waveform display system <NUM>, according to an embodiment of the present invention. System <NUM> is typically used during a medical procedure on a body organ, and in the description herein the body organ, by way of example, is assumed to comprise the heart, wherein the system is applied to display electrocardiogram (ECG) signals. Typically the system is used when the heart is undergoing atrial fibrillation, and the ECG signals may be intra-cardiac signals or signals derived from a location external to the heart, such as from a patient's skin. However, it will be understood that system <NUM> may be used for other states of the heart, including a sinus rhythm state, or for other signals, such as electroencephalograph (EEG) signals.

For clarity, except where otherwise stated, in the following description the signals displayed by system <NUM> are assumed to be ECG signals.

The description herein assumes that system <NUM> senses intra-cardiac ECG signals from a heart <NUM>, using a probe <NUM>. A distal end <NUM> of the probe is assumed to have an electrode <NUM> for sensing the signals. Typically, probe <NUM> comprises a catheter which is inserted into the body of a subject <NUM> during a cardiac procedure performed by a user <NUM> of system <NUM>. In the description herein user <NUM> is assumed to be a medical professional.

System <NUM> may be controlled by a system processor <NUM>, comprising a processing unit <NUM> communicating with an ECG module <NUM>. Module <NUM> in turn comprises a waveform display module <NUM>. Processor <NUM> may be mounted in a console <NUM>, which comprises operating controls which typically include a pointing device such as a mouse or trackball. Professional <NUM> uses the pointing device to interact with the processor, which, as described below, may be used to present results produced by system <NUM> to the professional on a display screen <NUM>.

The screen displays results of analysis and processing of ECG signals by ECG module <NUM>. Typically, the resultant ECG signals are presented on screen <NUM> in the form of a potential vs. time graph, and a schematic example <NUM> of such a graph is illustrated in <FIG>. (A more detailed graph is shown in <FIG>, described below. ) However, the resultant ECG signals may also be used by processor <NUM> to derive other results associated with the ECG signals, such as a local activation time (LAT). These results are typically presented on screen <NUM> in the form of a three-dimensional (3D) map <NUM> of the internal surface of heart <NUM>.

Processor <NUM> uses software stored in a memory of the processor to operate system <NUM>. The software may be downloaded to processor <NUM> in electronic form, over a network, for example, or it may, alternatively or additionally, be provided and/or stored on non-transitory tangible media, such as magnetic, optical, or electronic memory.

Processor <NUM> typically comprises other modules, such as a probe tracking module, a force module that measures a force on distal end <NUM>, and an ablation module that provides regulated to power to electrode <NUM>, or another electrode in the distal end. For simplicity, such modules are not shown in <FIG>. The Carto® system produced by Biosense Webster, of Diamond Bar, CA, uses such modules.

<FIG> is a schematic potential vs. time graph <NUM> of an ECG signal derived from heart <NUM>, according to an embodiment of the present invention. By way of example, graph <NUM> illustrates six QRS complexes occurring in the ECG signal, the complexes repeating at substantially regular intervals, and dividing the signal into five segments <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. A heart beating in sinus rhythm, i.e., a "normal" heart, generates ECG signals that, except for minor variations between successive QRS complexes, comprise regular repeating substantially invariant segments. However, while graph <NUM> is periodic, having repeating QRS complexes, successive segments are irregular. Thus segments <NUM>, <NUM>, and <NUM> have respective peaks <NUM>, <NUM>, and <NUM> in the segments, whereas segments <NUM> and <NUM> have no such peaks. Such an irregular yet periodic waveform is typical of signals produced during some types of atrial fibrillation.

<FIG> is a flowchart of steps performed by processor <NUM>, together with modules <NUM> and <NUM>, in implementing system <NUM>, and <FIG> shows schematic graphs illustrating some of the actions executed in the steps, according to embodiments of the present invention. <FIG> is also used to illustrate some of the actions of the flowchart steps.

In an initial step <NUM>, processor <NUM> receives a series of heart signals, such as is illustrated by graph <NUM>.

In a partition step <NUM>, the processor partitions the series into a succession of segments, using a selected annotation point as a fiducial start time for each of the segments. Typically, the annotation point is derived from the signal received by electrode <NUM>. Alternatively, the annotation point is derived from another ECG signal, which may be acquired by another electrode on the catheter, or alternatively as a body surface signal from a body surface electrode. By way of example, the selected annotation points for the segments of graph <NUM> are assumed to be the peak of the QRS complex, and each segment is assumed to terminate at the next successive QRS complex. The succession of segments <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, after they have been partitioned, is illustrated in <FIG>.

In a synchronization step <NUM>, the succession of segments is synchronized to the selected annotation point. The synchronization is illustrated in <FIG> by the peaks of the initial QRS complex of each segment being located on a vertical line <NUM>.

In a display step <NUM> graphs of the successive synchronized segments are presented on display screen <NUM>, the segments being aligned and overlaid with each other according to the selected annotation point. In some embodiments professional <NUM> selects the signal (different possible signals are described above in step <NUM>) to be used for the selected annotation point, typically by preliminary observation of sets of overlaid segments, so as to determine the signal giving the most stable synchronization. Typically the alignment also includes aligning an estimated baseline of each segment. Each segment is first presented with an initial display intensity at a display time corresponding to the start time of the segment.

After initial presentation, the display intensity of each segment is allowed to decay, according to a predetermined decay function of a time elapsed since the initial presentation. A typical decay function reduces the intensity linearly by <NUM>% for the time period between adjacent segments, so that after seven time periods, the display intensity is zero, i.e., the segment is not displayed. However, any other convenient function may be used for the reduced intensity.

<FIG> illustrates the different display intensities of the five segments of graph <NUM>, according to the presentation times of the segments shown in <FIG>. Thus, in <FIG>, the most recent segment is segment <NUM>, and the elapsed time from presentation of each of the segments, compared to the presentation time for segment <NUM>, increases monotonically through segments <NUM>, <NUM>, <NUM>, and <NUM>, so that segment <NUM> has the largest elapsed time. For clarity, <FIG> shows the different segments as being separated vertically. Since the elapsed times for the respective segments <NUM>, <NUM>, <NUM>, and <NUM> increases, the display intensities of the segments decreases. By way of example, assuming the linear intensity reduction of <NUM>% described above, and an intensity if <NUM> (measured in arbitrary units) for segment <NUM>, segments <NUM>, <NUM>, <NUM>, and <NUM> have respective intensities of <NUM>, <NUM>, <NUM>, and <NUM>.

<FIG> illustrates the different segments as they are overlaid on display screen <NUM>, according to an embodiment of the present invention. As the segments are overlaid, processor <NUM> sums the intensities of overlapping points of the graph. The summing enhances the visibility of regions of the graphs that repeat on an irregular basis. Thus, as illustrated, in overlaid segments <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> peaks <NUM>, <NUM>, and <NUM> overlap, so that the intensity of the overlapped points is increased compared to the intensity of non-overlapped sections of the graphs. As shown in <FIG>, peaks <NUM>, <NUM>, and <NUM> have respective intensities <NUM>, <NUM>, and <NUM>, so that the overlapped peaks have a nominal intensity of <NUM>. <FIG> illustrates the overlapped peaks as having an intensity on screen <NUM> of <NUM>.

The embodiments described above have assumed that each segment is assigned an intensity according to the time elapsed on the display screen since its first presentment on the screen, and that where the segments overlap the intensities are summed. In an alternative embodiment of the present invention, rather than the intensity summation being applied to complete segments, the intensity summation is only applied to a portion of each of the segments. Typically, the portion to which the summation applies is selected by professional <NUM>.

For example, the professional may choose that the summation is only applied to the central <NUM>% of each segment. This type of limitation allows system <NUM> to only enhance, by increasing their intensity, selected sections of the segments that are of interest to the professional, while not enhancing other sections, such as the start QRS complex and/or the end QRS complex, of the segments.

In a further alternative embodiment, rather than summing the intensities where segments overlap, e.g., where two or more segments have portions occupying the same pixels on screen <NUM>, the intensities may be configured to be summed if two or more segments have portions occupying pixels that are close to each other. The degree of closeness may be selected by professional <NUM>, and may be, for example where portions are within a selected number, for example <NUM>, of pixels of each other. Allowing this type of summation provides the professional with the ability to sum sections that are of interest, even if there are slight variations, typically due to noise, between the sections of interest. The result of the summation may be presented on screen <NUM> as one or more pixels, with the summed intensity, at a mean location of the pixels that are close to each other.

Claim 1:
A method for display, comprising using a processor (<NUM>) to perform the steps of:
acquiring an electrical signal from a heart of a subject over multiple heart cycles;
partitioning the signal into a succession of synchronized segments (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) having respective start times at a selected annotation point in the heart cycles;
overlaying respective graphical representations of the synchronized segments (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) in the succession on a display screen (<NUM>), such that each segment (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) is first presented on the display screen (<NUM>) with an initial display intensity at a respective display time corresponding to a respective start time of the segment (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>), wherein overlaying the respective graphical representations comprises either: summing the display intensity of the synchronized segments (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) at overlapping points of the synchronized segments, or summing the display intensity of the synchronized segments (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) at points of the synchronized segments (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) within two pixels of the display screen from each other; and
gradually decreasing a display intensity of each segment (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) overlaid on the display screen (<NUM>) as a decaying function of a time elapsed since the respective display time.