Surgery – Instruments – Electrical application
Reexamination Certificate
1999-04-06
2001-03-27
Peffley, Michael (Department: 3739)
Surgery
Instruments
Electrical application
C607S122000, C600S508000
Reexamination Certificate
active
06206874
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and method for S locating electrically active sites within a heart or other organ or internal body structure of an animal. In particular the present invention relates to an apparatus and method for locating originating sites of cardiac arrhythmias in humans.
2. Description of the Prior Art
One of the most common type of cardiac arrhythmia is 10 ventricular tachycardia (VT) which is typified by very rapid and ineffectual contractions of the heart muscle. In a majority of patients VT originates from a small (1-2 mm) lesion that is located close to the inner surface of the heart chamber. A known treatment of VT is mapping the electrical pathways of the heart, for example by recording arrival times of electrical pulses at numerous specific locations within the heart, and building up an isochronal activation map which may then be used to locate the lesion, i.e. the “active site”, from which the mapped electrical signals originate. Once located, the site is physically ablated using an ablation catheter.
One known method and apparatus for treating cardiac arrhythmias is disclosed in U.S. Pat. No. 5,391,199 (Biosense Inc.) and has means for obtaining and displaying a perspective image of the organ to be mapped, a mapping catheter having a single mapping electrode and means to locate the distal tip of the catheter by triangulation, using non-ionizing radiation. The method involves repeatedly locating the distal tip of the catheter (and hence the site of the mapping electrode), displaying the local information from the electrode is at the correct location on the perspective image and advancing the electrode to a new site. After several repetitions an activation map is created from which the active site may be deduced. An ablation catheter is advanced to this site which is then ablated. A disadvantage with this apparatus is that the mapping catheter must be repositioned several times in order to construct the map. This is time consuming and may lead to errors since the local information usually has to be collected at the same point in the cardiac cycle each time.
A further known method and apparatus for cardiac mapping is described in U.S. Pat. No. 5,465,717 (Cardiac Pathways Corporation) in which a mapping catheter is provided having a basket assembly with a number of circumferentially spaced apart, outwardly bowed, arms, on each of which is mounted a number of mapping electrodes. This enables the isochronal activation map to be rapidly constructed, in substantially one deployment of the mapping catheter and at the identical point in the cardiac cycle.
A problem with such mapping techniques is that the location of the active site can only be inferred from the map so constructed, in the same way the location of a mountain peak may be inferred from a normal isometric contour map.
This problem is mitigated in a system for locating the 25 position of an electrically active site in the heart which is described in U.S. Pat. No. 5,433,198 (Desai). The system disclosed therein has a surface ECG monitor; a cluster of electrical activity sensors for detecting the arrival of an electrical signal from a cardiac site of interest and means for estimating the location of the cardiac site by computing displacement vector. The length of this vector depends on the arrival time of the signal at each of the sensors and on a “difference” time which is an estimation of the time difference between the detection of the signal by an electrode at the point of origin of the signal and the detection of the same signal by the surface ECG monitor. Because this difference time is only an estimation, the length of the displacement vector (and hence the location of the cardiac site) is also only an estimation. As disclosed in this patent this difference time may be between typically −44 and −40 msec, the minus sign indicating that the signal is detected by the surface ECG monitor after its detection by the sensor. Using the embodiment described, this could give an error in the location of the cardiac site of ±2.5 mm, which is of the order of magnitude of the size of the site itself.
SUMMARY OF THE INVENTION
It is an object of the present invention, to provide an apparatus in which the location of an active site relative to a reference frame established by electrical activity sensors can be directly determined by triangulation without the need to create and analyze isochronal maps and without having to make an estimation of the difference time.
The above object is achieved in accordance with the invention in an apparatus for locating an electrically active site within an internal body structure having a number of electrical activity sensors respectively adapted for intracorporeal positioning proximate the internal body structure, each sensor emitting an output signal indicative of the arrival of an electrical signal from the active intracorporeal body site, and having a processor which receives the respective output signals from the activity sensors and which processes these received signals to determine, by triangulation, the location of the intracorporeal active site.
Preferably the electrical activity sensors are mounted on a catheter of a known or determinable shape. This enables the sensors to introduced into and removed from the body with a minimum of invasive surgery in order to form a known or determinable reference frame.
A number of acoustic, electromagnetic or electrical transceivers, for example ultrasonic transceivers, can be disposed along the portion of the catheter on which the sensors, are mounted in known spatial relationship with the sensors and which are operable so that their absolute or relative positions can be determined. From this determination the shape of the catheter and the location of the sensors can then be determined. Conveniently, the electrical activity sensors can be constructed to function also as the transducers and their relative location can be determined from electrical signals emitted and received between the plurality of sensors.
A method of locating catheter mounted transducers within a body which is well known is sonomicrometry and is disclosed, for example, in the above mentioned patent U.S. Pat. No. 5,391,199; in PCT Application WO 98/00060 (Siemens Elema AR); and in U.S. Pat. No. 5,515,853 (Sonometrics Corporation) the contents of all of which are incorporated herein by reference. PCT Application WO 98/00060 describes a method for locating a catheter by transmitting ultrasonic or magnetic signals between a transducer on the catheter and a number of transducers at known reference locations and then analyzing the received signals to determine the length of their transmission paths and hence the location of the catheter by triangulation. Similarly U.S. Pat. No. 5,515,853 discloses an ultrasound catheter tracking system in which the transit times of short duration ultrasound pulses are measured using clocked digital counters and the location of the tracked catheter is again determined using triangulation.
Thus by operating each transceiver of the transceivers of the present invention in turn as an emitter with the remainder of transceivers acting as receivers a signal may be emitted for receipt by all of the other transceivers. By analyzing the received signals to determine transmission path lengths the location of each emitting transceiver relative to all other transceivers can be calculated using standard triangulation methods and a relative reference frame can be established.
The above object is also achieved in accordance with the present invention in a method for locating an electrically active site within an organ, especially the heart, or other bodily structure including the steps of placing electrical activity sensors proximate with, preferably in contact with, a wall of the organ, in particular the heart, or internal bodily structure to establish a reference frame; monitoring each sensor for an output indicative of the arrival of an electrical signal
Sjoholm Gosta
Ubby Johan
Peffley Michael
Schiff & Hardin & Waite
Siemens-Elema AB
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