Surgery – Diagnostic testing – Structure of body-contacting electrode or electrode inserted...
Reexamination Certificate
2001-04-18
2003-06-03
Schaetzle, Kennedy (Department: 3762)
Surgery
Diagnostic testing
Structure of body-contacting electrode or electrode inserted...
C600S393000, C600S424000
Reexamination Certificate
active
06574492
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to medical electrophysiology systems, and specifically to invasive medical probes that may be used to map the electrical activity of the heart.
BACKGROUND OF THE INVENTION
Cardiac catheters comprising electrophysiological sensors are known for mapping the electrical activity of the heart. Typically the time-varying electrical potentials in the endocardium are sensed and recorded as a function of position inside the heart, and then used to map the local electrogram or local activation time. Activation time differs from point to point in the endocardium due to the time required for conduction of electrical impulses through the heart muscle. The direction of this electrical conduction at any point in the heart is conventionally represented by an activation vector, which is normal to an isoelectric activation front, both of which may be derived from a map of activation time. The rate of propagation of the activation front through any point in the endocardium may be represented as a velocity vector.
Mapping the activation front and conduction fields aids the physician in identifying and diagnosing abnormalities, such as ventricular and atrial tachycardia and ventricular and atrial fibrillation, that result from areas of impaired electrical propagation in the heart tissue. Localized defects in the heart's conduction of activation signals may be identified by observing phenomena such as multiple activation fronts, abnormal concentrations of activation vectors, or changes in the velocity vector or deviation of the vector from normal values. Furthermore, there may be no electrical propagation at all within defective portions of the heart muscle that have ceased to function, due to local infarction, for example. Once a defect is located by such mapping, it may be ablated (if it is functioning abnormally) or otherwise treated so as to restore the normal function of the heart insofar as is possible.
Mapping of the electrical activation time in the heart muscle requires that the location of the sensor within the heart be known at the time of each measurement. Such mapping may be performed using a single movable electrode sensor inside the heart, which sensor measures activation time relative to a fixed external reference electrode. This technique, however, gives maps of low resolution and relatively poor accuracy, limited by the accuracy of determination of the position of the electrode at the time of each measurement. The natural movement of the heart makes it very difficult to maintain an accurate reading of the position of the moving electrode from beat to beat. Mapping of electrical activation time using a single electrode is, furthermore, a lengthy procedure, which must generally be performed under fluoroscopic imaging, thereby exposing the patient to undesirable ionizing radiation. Further, in an arrhythmic heart, activation times at a single location may change between consecutive beats.
Because of these drawbacks of single-electrode mapping, a number of inventors have taught the use of multiple electrodes to measure electrical potentials simultaneously at different locations in the endocardium, thereby allowing activation time to be mapped more rapidly and conveniently, as described, for example, in PCT patent publication WO 95/05773, whose disclosure is incorporated herein by reference. In this case, the positions of all the electrode sensors must be determined at the time of measurement, typically by means of fluoroscopic or ultrasonic imaging. These methods of position determination, however, are complicated, inconvenient and relatively inaccurate, therefore limiting the accuracy of mapping.
Alternatively, U.S. Pat. Nos. 5,471,982 and 5,465,717, whose disclosures are incorporated herein by reference, teach the use of an electrode basket, which is inserted into a chamber of the heart and then expanded so that a plurality of electrodes are simultaneously brought into contact with multiple points on the endocardium. The relative electrical activation times at all the electrodes may then be measured simultaneously and used to detect and localize abnormalities. The basket is of limited usefulness in creating high-resolution maps of the electrical activation vector, however, because it cannot easily be repositioned once it is expanded inside the heart, and furthermore, determining the absolute positions of the electrodes requires the use of fluoroscopy or other painstaking and undesirable imaging methods. Further, the basket catheter does not contract with the heart, so the electrodes in the basket catheter cannot maintain contact with the same portion of the myocardium for the entire cycle, and the electrodes may not return to the same position relative to the myocardium for each cycle.
U.S. Pat. No. 5,487,391, to Panescu, for example, describes a multiple electrode probe for deployment inside the heart. Signals received from the multiple electrodes are used for deriving the propagation velocity of depolarization events. This patent makes no provision, however, for independently determining the positions of the electrodes relative to an external or heart-fixed frame of reference, and the velocity is derived relative to the probe, rather than to the heart itself.
Detecting the position in space of a single electrophysiology mapping electrode is described, inter alia, in PCT patent application number PCT/US95/01103, filed Jan. 24, 1995, U.S. provisional application 60/009,769, filed Jan. 11, 1996, U.S. patent application Ser. No. 08/595,365, filed Feb. 1, 1996, both titled “Cardiac Electromechanics”, and U.S. Pat. No. 5,391,199, issued Feb. 21, 1995, the disclosures of all of which are incorporated herein by reference.
U.S. Pat. No. 5,450,846, whose disclosure is incorporated herein by reference, describes a catheter, which may be easily repositioned inside the heart, comprising an ablator at its distal tip and pairs of non-contacting sensing electrodes arrayed around the outside of the catheter near the distal end. Each electrode senses local electrogram signals generated in the endocardium in a small area near the side of the catheter that it faces. Differences in the activation times in the signals sensed by the pairs of electrodes are used to estimate the direction of the activation vector in the vicinity of the catheter, so as to guide the operator in positioning the ablator. However, use of this device in high-resolution mapping of activation vectors is not practical either, because of the difficulty of determining the absolute position of the catheter tip, which must be performed by imaging methods, and because of the inferior accuracy of the non-contact electrogram measurement.
PCT publication WO/ 95/10226 describes a catheter that includes a ring at its distal end, designed to bear against the circumference of a valve of the heart. The ring comprises electrodes, which measure electrical activity in the valve tissue. When abnormal electrical activity is detected in the valve tissue adjacent to one of the electrodes, an electrical current is applied through the electrode so as to ablate the tissue at the site of the abnormal activity. The invention provides no means for determination of the position of the ring and electrodes, however, other than methods of imaging known in the art, and is therefore not useful for mapping electrical activity, nor is it useful in areas of the heart other than the valves.
U.S. Pat. No. 5,555,883, to Avitall, the disclosure of which is incorporated herein by reference, describes a catheter with a loop shaped mapping and ablation system. There is no provision, in this patent, for determining the position of individual electrodes relative to the heart surface being mapped/ablated.
SUMMARY OF THE INVENTION
It is an object of the present invention to allow simultaneous measurement of physiological signals by multiple sensors inside a human body, while simultaneously providing accurate measurement of at least the relative locations of all the sensors.
In one aspect of the invention, th
Bahar Boaz
Ben-Haim Shlomo
Greenberg Ilan
Biosense Inc.
Capezzuto Louis J.
Schaetzle Kennedy
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