The patent's assignee is
News editors obtained the following quote from the background information supplied by the inventors: "Electrical contact mapping of the heart typically involves voltage and activation mapping and is accomplished using a standard multi-polar electrode catheter, e.g., a
"An electro-anatomic activation map (such as shown in FIG. 2) is generated for the LAT and tissue voltage and those parameters are displayed on the video display as an iso-activation and an iso-voltage map. The iso-activation map is evaluated for the pattern of activation as either being centripetal or reentrant. A centripetal pattern is one having a focal area of earliest activation with waves of progressively later activation spreading out concentrically from the earliest activation site. This is compatible with a focus of electrical activity firing off rapidly and activating the rest of the chamber sequentially. The other pattern of activation, i.e., reentrant, shows a well defined region where the tissue with the earliest activation time is immediately adjacent to tissue with the latest activation time, indicating that the chamber is being activated sequentially, and continuously as a large reentrant circuit. The iso-activation map demonstrates activation emanating from one region and then sequentially spreading throughout the chamber and finally the returning to the region of earliest activation, as if inscribing a large circle of the spreading electrical wave front.
"Heretofore iso-activation maps have typically been color coded so that red indicates early activation sites, blue and purple indicates late activated sites, and orange, yellow and green indicates intermediate activation sites.
"Relying on these different patterns of the iso-activation map to differentiate these arrhythmia mechanisms so that appropriate therapy, e.g., ablation, can be applied to the patient can sometimes be misleading and can cause a lot of wasted time and energy in the effort to define the mechanism of the arrhythmia and direct the ablative therapy. The major problem is that a focal arrhythmia can mimic a reentrant arrhythmia, particularly when the focal firing tissue is in another chamber and the electrical wave fronts that travel into the chamber being mapped cause activation in the chamber of interest in a macroreentrant pattern due to anatomic/physiologic barriers that generate one-way conduction in that chamber. Thus, the iso-activation map in the chamber of interest shows the macroreentrant pattern of earliest activated tissue adjacent to latest activated tissue, while the actual arrhythmia generator is a group of cells focally firing elsewhere. Ablating across the presumed reentrant circuit in this scenario to produce a 'line of block' to interrupt the reentrant circuit isthmus and terminate the arrhythmia, will have no effect.
"There is reason to believe that the above scenario, particularly if it involves the right atrium, is not so infrequent, as in this chamber there are natural anatomic barriers that can confine the conduction of electric current to a fixed pathway, that would mimic a reentrant activation pattern, with a little help from some physiologic barriers that develop when there is associated organic heart disease that cause fibrosis which can lead to anisotropic conduction and physiologic block.
"Thus, there presently exists a need for additional methods and systems for identifying/differentiating arrhythmia sources, e.g., discriminating between focal arrhythmias and reentrant arrhythmias. Additionally, there is utility in identifying coherent, rapidly conducting pathways that may be participating in reentrant circuits and to identify damaged cardiac tissues, i.e., scar tissue, that is often the substrate for micro-reentrant circuits. The subject invention addresses those needs."
As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventor's summary information for this patent application: "One aspect of this invention is a cardiac arrhythmia discrimination system for determining the mechanism of cardiac arrhythmia in a patient. The cardiac arrhythmia discrimination system comprises a catheter and an associated processing unit. The catheter and the processing unit are arranged to measure the impedance of cardiac tissue of the patient at various selected points on the endocardial/epicardial surface of the patient's heart during a spontaneously occurring or induced arrhythmia, e.g., supraventricular tachycardia, and providing the geometric position of each of the points on the patient's heart. Each of the impedance measurements and point positions are recorded by the system. The system is arranged to determine if a point on the patient's heart exhibits low impedance (Z.sub.low), wherein Z.sub.low.ltoreq.Z.sub.min+0.1(Z.sub.max-Z.sub.min), where Z.sub.min is the minimum impedance measured and Z.sub.max is the maximum impedance measured.
"The system is also arranged to discard from its impedance measurements any points associated with tissue voltage of less than 0.5 mV indicating poor contact of the catheter to the cardiac tissue, as well as any points that are too internal to the anatomic shell (e.g., >1 mm internal to a 15 degree spherical arc of curvature with a radius of 1.5-2 cm inscribed by a local group of measured points on the heart chamber shell) or points with far-field low amplitude electrograms, and evaluates the remaining points of measured impedance to determine if there is an area of approximately 3.4.+-.2 cm.sup.2 or 2.4.+-.1.8% of the atrial surface area having plural Z.sub.low points therein.
"In accordance with another aspect of this invention the system includes a video display coupled to the processing unit and which is arranged to produce an iso-impedance map of the cardiac tissue. The iso-impedance map is colored to represent differing impedances measured by the catheter to enable a user of the system to visually analyze the color pattern of the iso-impedance map to differentiate a focal arrhythmia caused by a group of cells focally firing, from a reentrant arrhythmia caused by a macroreentrant circuit.
"In accordance with another aspect of this invention there is provided a method determining the mechanism of cardiac arrhythmia in a patient. The method entails measuring impedance of cardiac tissue of the patient at various selected points on the patient's heart using a catheter during spontaneously occurring or induced arrhythmia. Measurements of impedances at points associated with tissue voltage of less than 0.5 mV or poor contact of the catheter to the cardiac tissue are discarded as are impedance measurements from mapping points that are too internal to the anatomic shell or points with far-field low amplitude electrograms. The remaining points of measured impedance are evaluated to determine if there is an area of approximately 3.4+2 cm.sup.2 or 2.4.+-.1.8% of the atrial surface area having plural low impedance (Z.sub.low) points therein, where Z.sub.low.ltoreq.Z.sub.min+0.1(Z.sub.max-Z.sub.min)and where Z.sub.min is the minimum impedance measured and Z.sub.max is the maximum impedance measured, wherein the existence of said area of said plural low impedance (Z.sub.low) points therein indicates a focal arrhythmia caused by a circumscribed region of focal firing and wherein the absence of said area of said plural low impedance (Z.sub.low) points therein indicates a reentrant arrhythmia caused by a macroreentrant circuit.
"The measurements may be displayed in the form of an iso-impedance map, which may appear on a video display to facilitate appropriate therapy, e.g., ablation.
DESCRIPTION OF THE DRAWING
"The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
"FIG. 1 is an illustration including a block diagram of one exemplary system for measuring the impedance of cardiac tissue and providing an iso-impedance map thereof to enable the user of the system to determine if the patient's arrhythmia is the result of reentrant activation or focal activation;
"FIG. 2 is an exemplary prior art anterior-posterior view iso-activation map of the right atrium of a patient exhibiting a focal arrhythmia; the successful ablation site correlates with the region of earliest activation as indicated by the red coloration.
"FIG. 3 is an exemplary iso-impedance map of the patient of FIG. 2, with the iso-impedance map of the right atrium being in a shallow left anterior oblique projection slightly different from the view of FIG. 2, but produced using the method and system of this invention and showing a focal activation pattern as evidenced by the contiguous low impedance area or
"FIGS. 4A is an exemplary right anterior oblique iso-impedance map of the right atrium of another patient produced using the method and system of this invention and showing the patient undergoing a macroreentrant based arrhythmia, i.e., isthmus dependent atrial flutter; as evidenced by the uniform impedance pattern with no
"FIG. 4B is another exemplary iso-impedance map of the right atrium of the patient of FIG. 4A, with this view being a left anterior oblique caudal view showing a macroreentrant impedance map pattern, i.e., uniform impedance with no
"FIG. 5 is an exemplary left anterior oblique view iso-impedance map of the right atrium in the patient of FIGS. 4A and 4B produced using the method and system of this invention during an induced focal atrial tachycardia that occurred the same day and showing a contiguous low impedance area superior-laterally indicative of the focal-based arrhythmia."
For additional information on this patent application, see: Greenspan, Allan M. Cardio Mapping System and Method for Cardio Mapping. Filed
Keywords for this news article include: Therapy, Cardiology, Tachycardia, Heart Disease, Cardiovascular, Cardiac Arrhythmias,
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