System and method for mapping cardiac activity

QRS activity duration may be indicative of cardiac tissue health. Accordingly, maps of QRS activity duration may be beneficial to practitioners. To this end, an electroanatomical mapping system can receive an electrogram signal and analyze it by transforming it into the wavelet domain, computing an energy function of the resultant scalogram, and computing QRS activity duration using the energy function. A graphical representation of the QRS activity duration can be output, for example on a three-dimensional cardiac model. Areas of diseased substrate can be identified on the output; in some aspects of the disclosure, diseased substrate corresponds to areas where the QRS activity duration exceeds a preset threshold, such as about 70 ms.

BACKGROUND

The present disclosure relates generally to electrophysiological mapping, such as may be performed in cardiac diagnostic and therapeutic procedures. In particular, the present disclosure relates to systems, apparatuses, and methods for mapping diseased cardiac substrate.

It is known to use the peak-to-peak voltage of an intracardiac electrogram to evaluate the atrial substrate of an atrial fibrillation patient in sinus rhythm. It is hypothesized, however, that QRS activity duration may also be informative when attempting to identify diseased substrate in an atrial fibrillation patient in sinus rhythm.

BRIEF SUMMARY

Disclosed herein is a method of mapping cardiac activity, including receiving an electrogram signal S(t) at a signal processor; and, using the signal processor: transforming the electrogram signal S(t) into the wavelet domain, thereby computing a scalogram G(f, t); computing an energy function L(t) of the scalogram G(f, t); and computing a QRS activity duration for the electrogram signal S(t) using the energy function L(t).

The step of transforming the electrogram signal S(t) into the wavelet domain can include applying a continuous wavelet transformation to the electrogram signal S(t) to compute the scalogram G(f, t). The continuous wavelet transformation can utilize a high time-resolution mother wavelet, such as a Paul wavelet, when a peak-to-peak voltage of the electrogram signal S(t) does not exceed a preset threshold (e.g., about 3 mV), and can utilize a high frequency-resolution mother wavelet, such as a Morlet wavelet, when the peak-to-peak voltage exceeds the preset threshold.

The step of computing an energy function L(t) of the scalogram G(f, t) can include: detecting a time Tmaxat which G(f, t) reaches a maximum; detecting a time Tdownprior to Tmaxat which G(f, t) first drops below a preset noise threshold; detecting a time Tupafter Tmaxat which G(f, t) first drops below the preset noise threshold: and computing the energy function L(t) according to an equation

L⁡(t)={max⁡(G⁡(f,t)),if⁢⁢Tdown≤t≤Tup0,elsewhere,
where f is between 0 Hz and 1000 Hz. The preset noise threshold in normalized scale can be about 0.3 when the transforming step utilizes a high time-resolution mother wavelet and about 0.45 otherwise.

The step of computing a QRS activity duration for the electrogram signal S(t) using the energy function L(t) can include: computing a pulse wave LPulse(t) having a pulse duration according to an equation

LPulse⁡(t)={1,if⁢⁢L⁡(t)>00,otherwise;
and defining the QRS activity duration for the electrogram signal S(t) to be equal to the pulse duration.

In aspects of the disclosure, the method also includes generating a graphical representation of a plurality of QRS activity durations for a plurality of electrogram signals S(t) on a three-dimensional cardiac model. Optionally, one or more areas of diseased substrate, characterized by QRS activity durations in excess of a preset threshold (e.g., about 70 ms) can be identified on the three-dimensional cardiac model.

The instant disclosure also provides a method of mapping cardiac substrate, including receiving an electrophysiology data point having an associated electrogram signal at an electroanatomical mapping system and, using the electroanatomical mapping system: transforming the electrogram signal into the wavelet domain; and computing a QRS activity duration for the electrogram signal in the wavelet domain. These steps can be repeated for a plurality of electrophysiology data points, thereby creating a QRS activity duration map, a graphical representation of which can be output on a three-dimensional cardiac model.

The step of transforming the electrogram signal into the wavelet domain can include applying a continuous wavelet transform to the electrogram signal. The continuous wavelet transform can utilize a high time-resolution mother wavelet when a peak-to-peak voltage of the electrogram signal does not exceed a preset threshold and a high frequency-resolution mother wavelet when the peak-to-peak voltage exceeds the preset threshold.

According to embodiments disclosed herein, the method also includes classifying the electrophysiology data point as a diseased substrate point if the computed QRS activity duration exceeds a preset threshold, such as about 70 ms.

Also disclosed herein is an electroanatomical mapping system, including a wavelet transformation processor configured to: receive an electrophysiology data point having an associated electrogram signal; transform the electrogram signal into the wavelet domain; and compute a QRS activity duration for the electrogram signal in the wavelet domain, as well as a mapping processor configured to generate a QRS activity map from a plurality of QRS activity durations computed by the wavelet transformation processor. The mapping processor can also be configured to output a graphical representation of the QRS activity map on a three-dimensional cardiac model.

DETAILED DESCRIPTION

The instant disclosure provides systems, apparatuses, and methods for the creation of electrophysiology maps (e.g., electrocardiographic maps) that provide information regarding cardiac activity. Certain embodiments of the disclosure will be explained with reference to the use of bipolar electrograms to create electrophysiology maps, and in particular to create maps of QRS duration. The teachings herein can be applied to good advantage in evaluating the atrial substrate during sinus rhythm in atrial fibrillation patients, and can facilitate identification of diseased substrate.

For purposes of illustration, aspects of the disclosure will be described in detail herein in the context of a cardiac mapping procedure carried out using an electrophysiology mapping system (e.g., using an electroanatomical mapping system such as the EnSite Precision™ cardiac mapping system from Abbott Laboratories).

FIG. 1shows a schematic diagram of an exemplary electroanatomical mapping system8for conducting cardiac electrophysiology studies by navigating a cardiac catheter and measuring electrical activity occurring in a heart10of a patient11and three-dimensionally mapping the electrical activity and/or information related to or representative of the electrical activity so measured. System8can be used, for example, to create an anatomical model of the patient's heart10using one or more electrodes. System8can also be used to measure electrophysiology data at a plurality of points along a cardiac surface and store the measured data in association with location information for each measurement point at which the electrophysiology data was measured, for example to create a diagnostic data map of the patient's heart10.

As one of ordinary skill in the art will recognize, and as will be further described below, system8determines the location, and in some aspects the orientation, of objects, typically within a three-dimensional space, and expresses those locations as position information determined relative to at least one reference.

For simplicity of illustration, the patient11is depicted schematically as an oval. In the embodiment shown inFIG. 1, three sets of surface electrodes (e.g., patch electrodes) are shown applied to a surface of the patient11, defining three generally orthogonal axes, referred to herein as an x-axis, a y-axis, and a z-axis. In other embodiments the electrodes could be positioned in other arrangements, for example multiple electrodes on a particular body surface. As a further alternative, the electrodes do not need to be on the body surface, but could be positioned internally to the body.

InFIG. 1, the x-axis surface electrodes12,14are applied to the patient along a first axis, such as on the lateral sides of the thorax region of the patient (e.g., applied to the patient's skin underneath each arm) and may be referred to as the Left and Right electrodes. The y-axis electrodes18,19are applied to the patient along a second axis generally orthogonal to the x-axis, such as along the inner thigh and neck regions of the patient, and may be referred to as the Left Leg and Neck electrodes. The z-axis electrodes16,22are applied along a third axis generally orthogonal to both the x-axis and the y-axis, such as along the sternum and spine of the patient in the thorax region, and may be referred to as the Chest and Back electrodes. The heart10lies between these pairs of surface electrodes12/14,18/19, and16/22.

An additional surface reference electrode (e.g., a “belly patch”)21provides a reference and/or ground electrode for the system8. The belly patch electrode21may be an alternative to a fixed intra-cardiac electrode31, described in further detail below. It should also be appreciated that, in addition, the patient11may have most or all of the conventional electrocardiogram (“ECG” or “EKG”) system leads in place. In certain embodiments, for example, a standard set of 12 ECG leads may be utilized for sensing electrocardiograms on the patient's heart10. This ECG information is available to the system8(e.g., it can be provided as input to computer system20). Insofar as ECG leads are well understood, and for the sake of clarity in the figures, only a single lead6and its connection to computer20is illustrated inFIG. 1.

A representative catheter13having at least one electrode17is also shown. This representative catheter electrode17is referred to as the “roving electrode,” “moving electrode,” or “measurement electrode” throughout the specification. Typically, multiple electrodes17on catheter13, or on multiple such catheters, will be used. In one embodiment, for example, the system8may comprise sixty-four electrodes on twelve catheters disposed within the heart and/or vasculature of the patient. In other embodiments, system8may utilize a single catheter that includes multiple (e.g., eight) splines, each of which in turn includes multiple (e.g., eight) electrodes.

The foregoing embodiments are merely exemplary, however, and any number of electrodes and/or catheters may be used. For example, in some embodiments, a high density mapping catheter, such as the Ensite™ Array™ non-contact mapping catheter of Abbott Laboratories, can be utilized.

Likewise, it should be understood that catheter13(or multiple such catheters) are typically introduced into the heart and/or vasculature of the patient via one or more introducers and using familiar procedures. For purposes of this disclosure, a segment of an exemplary catheter13is shown inFIG. 2. InFIG. 2, catheter13extends into the left ventricle50of the patient's heart10through a transseptal sheath35. The use of a transseptal approach to the left ventricle is well known and will be familiar to those of ordinary skill in the art, and need not be further described herein. Of course, catheter13can also be introduced into the heart in any other suitable manner.

Catheter13includes electrode17on its distal tip, as well as a plurality of additional measurement electrodes52,54,56spaced along its length in the illustrated embodiment. Typically, the spacing between adjacent electrodes will be known, though it should be understood that the electrodes may not be evenly spaced along catheter13or of equal size to each other. Since each of these electrodes17,52,54,56lies within the patient, location data may be collected simultaneously for each of the electrodes by system8.

Similarly, each of electrodes17,52,54, and56can be used to gather electrophysiological data from the cardiac surface (e.g., surface electrograms). The ordinarily skilled artisan will be familiar with various modalities for the acquisition and processing of electrophysiology data points (including, for example, both contact and non-contact electrophysiological mapping), such that further discussion thereof is not necessary to the understanding of the techniques disclosed herein. Likewise, various techniques familiar in the art can be used to generate a graphical representation of a cardiac geometry and/or of cardiac electrical activity from the plurality of electrophysiology data points. Moreover, insofar as the ordinarily skilled artisan will appreciate how to create electrophysiology maps from electrophysiology data points, the aspects thereof will only be described herein to the extent necessary to understand the present disclosure.

Returning now toFIG. 1, in some embodiments, an optional fixed reference electrode31(e.g., attached to a wall of the heart10) is shown on a second catheter29. For calibration purposes, this electrode31may be stationary (e.g., attached to or near the wall of the heart) or disposed in a fixed spatial relationship with the roving electrodes (e.g., electrodes17), and thus may be referred to as a “navigational reference” or “local reference.” The fixed reference electrode31may be used in addition or alternatively to the surface reference electrode21described above. In many instances, a coronary sinus electrode or other fixed electrode in the heart10can be used as a reference for measuring voltages and displacements; that is, as described below, fixed reference electrode31may define the origin of a coordinate system.

Each surface electrode is coupled to a multiplex switch24, and the pairs of surface electrodes are selected by software running on a computer20, which couples the surface electrodes to a signal generator25. Alternately, switch24may be eliminated and multiple (e.g., three) instances of signal generator25may be provided, one for each measurement axis (that is, each surface electrode pairing).

The computer20may comprise, for example, a conventional general-purpose computer, a special-purpose computer, a distributed computer, or any other type of computer. The computer20may comprise one or more processors28, such as a single central processing unit (“CPU”), or a plurality of processing units, commonly referred to as a parallel processing environment, which may execute instructions to practice the various aspects described herein.

Generally, three nominally orthogonal electric fields are generated by a series of driven and sensed electric dipoles (e.g., surface electrode pairs12/14,18/19, and16/22) in order to realize catheter navigation in a biological conductor. Alternatively, these orthogonal fields can be decomposed and any pairs of surface electrodes can be driven as dipoles to provide effective electrode triangulation. Likewise, the electrodes12,14,18,19,16, and22(or any number of electrodes) could be positioned in any other effective arrangement for driving a current to or sensing a current from an electrode in the heart. For example, multiple electrodes could be placed on the back, sides, and/or belly of patient11. Additionally, such non-orthogonal methodologies add to the flexibility of the system. For any desired axis, the potentials measured across the roving electrodes resulting from a predetermined set of drive (source-sink) configurations may be combined algebraically to yield the same effective potential as would be obtained by simply driving a uniform current along the orthogonal axes.

Thus, any two of the surface electrodes12,14,16,18,19,22may be selected as a dipole source and drain with respect to a ground reference, such as belly patch21, while the unexcited electrodes measure voltage with respect to the ground reference. The roving electrodes17placed in the heart10are exposed to the field from a current pulse and are measured with respect to ground, such as belly patch21. In practice the catheters within the heart10may contain more or fewer electrodes than the sixteen shown, and each electrode potential may be measured. As previously noted, at least one electrode may be fixed to the interior surface of the heart to form a fixed reference electrode31, which is also measured with respect to ground, such as belly patch21, and which may be defined as the origin of the coordinate system relative to which system8measures positions. Data sets from each of the surface electrodes, the internal electrodes, and the virtual electrodes may all be used to determine the location of the roving electrodes17within heart10.

The measured voltages may be used by system8to determine the location in three-dimensional space of the electrodes inside the heart, such as roving electrodes17relative to a reference location, such as reference electrode31. That is, the voltages measured at reference electrode31may be used to define the origin of a coordinate system, while the voltages measured at roving electrodes17may be used to express the location of roving electrodes17relative to the origin. In some embodiments, the coordinate system is a three-dimensional (x, y, z) Cartesian coordinate system, although other coordinate systems, such as polar, spherical, and cylindrical coordinate systems, are contemplated.

As should be clear from the foregoing discussion, the data used to determine the location of the electrode(s) within the heart is measured while the surface electrode pairs impress an electric field on the heart. The electrode data may also be used to create a respiration compensation value used to improve the raw location data for the electrode locations as described, for example, in U.S. Pat. No. 7,263,397, which is hereby incorporated herein by reference in its entirety. The electrode data may also be used to compensate for changes in the impedance of the body of the patient as described, for example, in U.S. Pat. No. 7,885,707, which is also incorporated herein by reference in its entirety.

Therefore, in one representative embodiment, system8first selects a set of surface electrodes and then drives them with current pulses. While the current pulses are being delivered, electrical activity, such as the voltages measured with at least one of the remaining surface electrodes and in vivo electrodes, is measured and stored. Compensation for artifacts, such as respiration and/or impedance shifting, may be performed as indicated above.

In some embodiments, system8is the EnSite™ Velocity™ or EnSite Precision™ cardiac mapping and visualization system of Abbott Laboratories. Other localization systems, however, may be used in connection with the present teachings, including for example the RHYTHMIA HDX™ mapping system of Boston Scientific Corporation, the CARTO navigation and location system of Biosense Webster, Inc., the AURORA® system of Northern Digital Inc., Sterotaxis' NIOBE® Magnetic Navigation System, as well as MediGuide™ Technology from Abbott Laboratories.

The localization and mapping systems described in the following patents (all of which are hereby incorporated by reference in their entireties) can also be used with the present invention: U.S. Pat. Nos. 6,990,370; 6,978,168; 6,947,785; 6,939,309; 6,728,562; 6,640,119; 5,983,126; and 5,697,377.

Aspects of the disclosure relate to mapping QRS duration. In particular, when mapping within and around an atrial substrate in an atrial fibrillation patient, intracardiac bipolar electrograms can take one of several forms: a single component QRS activity lasting for a short duration, shown as trace300ainFIG. 3A; a single component QRS activity lasting for a long duration, shown as trace300binFIG. 3B; or a multiple component (that is, fractionated) QRS activity lasting for a long duration, shown as trace300cinFIG. 3C.

For purposes of this disclosure, “short duration” QRS activity indicates fast wave conduction within the underlying tissue, which can be presumed to be healthy. On the other hand, “long duration” QRS activity indicates slow wave conduction or block within the underlying tissue, and thus can be presumed to be diseased. Suitable quantitative distinctions between “short duration” and “long duration” QRS activity are described in greater detail below.

Accordingly, system8can also include a QRS detection module58. QRS detection module58can be used, inter alia, to measure QRS duration, as discussed in detail below. In turn, the long duration signals, whether single component or multiple component, may be indicative of diseased substrate, allowing a practitioner to identify additional potential therapy (e.g., ablation) targets.

One exemplary method of mapping QRS duration according to the present teachings will be explained with reference to the flowchart400of representative steps presented asFIG. 4. In some embodiments, for example, flowchart400may represent several exemplary steps that can be carried out by electroanatomical mapping system8ofFIG. 1(e.g., by processor28and/or QRS detection module58). It should be understood that the representative steps described below can be either hardware- or software-implemented. For the sake of explanation, the term “signal processor” is used herein to describe both hardware- and software-based implementations of the teachings herein.

In block402, system8receives an electrogram signal, denoted S(t), for example in connection with the collection of an electrophysiology data point by catheter13. According to aspects of the disclosure, the electrogram signal S(t) is a bipolar signal, such as signal300a,300b, or300c.

In block404, the electrogram signal S(t) is transformed into the wavelet domain, which computes a scalogram G(f, t). More specifically, the scalogram G(f, t) can be computed for a preset window, referred to as a “Roving Activation Interval” (“RAI”) about a reference time point Trefcorresponding to a trigger event (e.g., the signal from an EKG lead). The width of the RAI can be user-defined; in embodiments, the RAI is between about 100 ms and about 300 ms wide. Scalograms500a,500b, and500c, respectively corresponding to electrogram signals300a,300b, and300c, are shown inFIGS. 5A-5C.

In embodiments of the disclosure, block404applies a continues wavelet transform to the electrogram signal S(t). The mother wavelet used in the wavelet transform can be a high time-resolution mother wavelet, such as a Paul wavelet, or a high frequency-resolution mother wavelet such as a Morlet wavelet, both of which will be familiar to those of ordinary skill in the art. In particular, it is desirable to use a high time-resolution mother wavelet when a peak-to-peak voltage of electrogram signal S(t)300a,300b,300cdoes not exceed a preset threshold (e.g., about 3 mV, or another suitable, user-defined threshold value) and to use a high frequency-resolution mother wavelet otherwise.

Other mother wavelets can be employed without departing from the scope of the instant teachings. Likewise, the teachings herein can be applied using discrete, rather than continuous, wavelet transforms.

QRS activity duration for electrogram signal S(t)300a,300b,300cis determined in the wavelet domain. Thus, according to aspects of the disclosure, an energy function L(t) of the scalogram G(f, t) is computed in block406.

In some embodiments of the disclosure, the energy function L(t) is computed by detecting a time, Tmax, at which G(f, t) reaches a maximum; searching backwards in time from Tmaxto detect a time, Tdown, at which G(f, t) first drops below a preset noise threshold ET; and searching forwards in time from Tmaxto detect a time, Tup, at which G(f, t) first drops below ET. Referring toFIGS. 5A-5C, Tmaxpoints502a,502b, and502care shown in scalograms500a,500b, and500c, respectively. L(t) can then be computed according to an equation

L⁡(t)={max⁡(G⁡(f,t)),if⁢⁢Tdown≤t≤Tup0,elsewhere,
where f is between about 0 Hz and about 1000 Hz. The preset noise threshold in normalized scale can be user-defined, and can vary depending on the mother wavelet used. For instance, for a high time-resolution mother wavelet, ETcan be about 0.3, and can be about 0.45 otherwise. Illustrating the foregoing,FIGS. 5A-5Cdepict energy functions504a,504b, and504ccorresponding to scalograms500a,500b, and500c.

In block408, system8computes the QRS duration in the wavelet domain, such as from the energy function L(t). For instance, in aspects of the disclosure, system8computes the QRS duration by converting L(t) into a pulse wave LPulse(t), where

LPulse⁡(t)={1,if⁢⁢L⁡(t)>00,otherwise.
The QRS duration can then be defined as the duration of the pulse wave LPulse(t).

Steps402,404,406, and408can be repeated for a plurality of electrogram signals S(t), thereby creating a QRS activity duration map. In block410, the QRS activity duration map can be output, for example on a three-dimensional cardiac model.FIG. 6is a representative QRS activity duration map on a three-dimensional cardiac model600.

Optionally, the QRS activity duration map can also be used to identify one or more areas of diseased substrate. In particular, areas of the heart having a QRS activity duration in excess of a preset threshold can be classified as diseased. For instance, areas of the heart having a QRS activity duration in excess of about 70 ms can be classified as scar or diseased tissue; areas of the heart having a QRS activity duration between about 50 ms and about 70 ms can be classified as border zone, and areas of the heart having a QRS activity duration less than about 50 ms can be classified as healthy. Of course, it should be understood that these values can vary with the geometry of catheter13(e.g., interelectrode spacing), and thus can be user-defined.

Although several embodiments have been described above with a certain degree of particularity, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this invention.

For example, the teachings herein can be applied in real time (e.g., during an electrophysiology study/as electrophysiology data points are collected) or during post-processing (e.g., to electrophysiology data points collected during an electrophysiology study performed at an earlier time).

All directional references (e.g., upper, lower, upward, downward, left, right, leftward, rightward, top, bottom, above, below, vertical, horizontal, clockwise, and counterclockwise) are only used for identification purposes to aid the reader's understanding of the present invention, and do not create limitations, particularly as to the position, orientation, or use of the invention. Joinder references (e.g., attached, coupled, connected, and the like) are to be construed broadly and may include intermediate members between a connection of elements and relative movement between elements. As such, joinder references do not necessarily infer that two elements are directly connected and in fixed relation to each other.