Multi-electrode catheter, system and method

Surgery – Diagnostic testing – Structure of body-contacting electrode or electrode inserted...

Reexamination Certificate

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C600S547000, C606S034000

Reexamination Certificate

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06546270

ABSTRACT:

FIELD OF THE INVENTION
The present invention is directed to a novel catheter, a system and a method for detecting contact of an electrode with tissue. The catheter, system and method of the invention are particularly suited for use in conjunction with intracardiac electrophysiology or electromechanical studies or in conjunction with therapeutic procedures such as cardiac ablation.
BACKGROUND OF THE INVENTION
Cardiac arrhythmias, the most common of which is ventricular tachycardia (VT), are a leading cause of death. In a majority of patients, VT originates from a 1 mm to 2 mm lesion located close to the inner surface of the heart chamber. One of the treatments for VT comprises mapping the electrical pathways of the heart to locate the lesion followed by ablation of the active site.
Commonly assigned U.S. Pat. No. 5,546,951; U.S. patent application Ser. No. 08/793,371; and PCT application WO 96/05768, which are incorporated herein in their entirety by reference, disclose methods for sensing an electrical property of heart tissue such as local activation time as a function of the precise location within the heart. The data are acquired by advancing into the heart one or more catheters that have electrical and location sensors in their distal tips. The precise three-dimensional location of the catheter tip is ascertained by the location sensor contained therein. The location sensor operates by generating signals that are responsive to its precise location within an externally generated non-ionizing field such as an electromagnetic field. Simultaneous with the acquisition of location information, electrical information is also acquired by at least one electrode contained at the catheter distal tip. Accurate sensing of location and electrical information by sensors contained in the catheter generally requires a high degree of confidence that a catheter electrode is in contact with the tissue.
In systems that use acoustic means to determine the location of mapping and ablation electrodes, it is likewise important to determine that the electrodes are in contact with the tissue to be mapped or ablated. For example, U.S. Pat. No. 5,409,000, the disclosure of which is incorporated herein in its entirety by reference, discloses the use of a catheter probe having a plurality of flexible, longitudinally extending circumferentially spaced apart arms adapted to be disposed within a chamber of a heart. Electrodes are carried by the arms and are adapted to be moved into engagement with the wall of the heart. Markers visible ultrasonically are carried by the arms for encoding the arms so that one arm can be distinguished from another. An ablation catheter having ultrasonic viewing means such as an ultrasonic sensor or transducer at its distal extremity is carried by and is slidably mounted in the catheter probe. The distal extremity of the ablation catheter is moveable into positions to view ultrasonically the markers carried by the arms of the catheter probe so that the arms can be identified and the spacing of the arms can be ascertained.
PCT application WO 99/05971, the disclosure of which is incorporated herein in its entirety by reference, discloses a system that uses one or more ultrasound reference catheters to establish a fixed, three-dimensional coordinate system within a patient's heart using principles of triangulation. The coordinate system is represented graphically in three dimensions on a video monitor and is reported to aid the clinician in guiding other medical devices, which are provided with ultrasound sensors or transducers, through the body to locations at which they are needed to perform clinical procedures. The system is reported to be useful to help a physician guide mapping catheters for measuring electrical activity and ablation catheters for ablating selected regions of cardiac tissue, to desired locations within the heart.
Methods of creating a map of the electrical activity of the heart based on these data are disclosed in commonly assigned U.S. patent application Ser. Nos. 09/122,137and 09/357,559 filed on Jul. 24, 1998 and Jul. 22, 1999, respectively, and in European Patent Application 974,936 which are also incorporated herein in their entirety by reference. In clinical settings, it is not uncommon to accumulate data at 100 or more sites within the heart to generate a detailed, comprehensive map of heart chamber electrical activity. The use of the location sensors as hereinabove described is highly useful in providing a detailed and accurate map of the heart chamber's activity.
Catheters containing position or location sensors may also be used to determine the trajectory of points on the cardiac surface. These trajectories may be used to infer mechanical motion characteristics such as the contractility of the tissue. As disclosed in U.S. Pat. No. 5,738,096 which is incorporated herein in its entirety by reference, maps depicting such motion characteristics, which may be superimposed with maps depicting local electrical information, may be constructed when the trajectory information is sampled at a sufficient number of points in the heart. Accurate maps of such motion characteristics again require confidence that the data are acquired when the catheter tip is in contact with the cardiac tissue.
The detailed maps generated as hereinabove described may serve as the basis for deciding on a therapeutic course of action, for example, tissue ablation, to alter the propagation of the heart's electrical activity and to restore normal heart rhythm. In cardiac ablation, energy, typically in the radiofrequency (RF) range, is supplied at selected points on the intracardiac surface by a catheter having an ablation electrode at its distal tip. Ablation is effected by bringing the distal tip electrode into contact with the locus of aberrant electrical activity and by initiating the delivery of RF energy through the distal tip electrode from an external RF generator in communication with the distal tip electrode. Ablation is most effectively performed when the distal tip electrode is in contact with the cardiac wall. Absence of contact or poor contact of the tip electrode with the heart wall leads to dissipation of the RF energy in the blood, as well as possible fouling of the tip electrode with the concomitant possibility of blood clot formation. Accordingly, it is important that both mapping and ablation be accompanied by methods and systems for detecting and ensuring electrode-tissue contact.
A number of references have reported methods to determine electrode-tissue contact, including U.S. Pat. Nos. 5,935,079; 5,891,095; 5,836,990; 5,836,874; 5,673,704; 5,662,108; 5,469,857; 5,447,529; 5,341,807; 5,078,714; and Canadian Patent Application 2,285,342. A number of these references, e.g., U.S. Pat. Nos. 5,935,079, 5,836,990, and 5,447,529 determine electrode-tissue contact by measuring the impedance between the tip electrode and a return electrode. As disclosed in the '529 patent, it is generally known that impedance through blood is generally lower that impedance through tissue. Accordingly, tissue contact has been detected by comparing the impedance values across a set of electrodes to pre-measured impedance values when an electrode is known to be in contact with tissue and when it is known to be in contact only with blood. A problem in using this method during intracardiac procedures is the fact that tissue and blood impedances may change during a procedure. Furthermore, the impedance through tissue also depends on the state of the tissue. For instance, impedance through infarcted tissue is known to be less than the impedance through healthy tissue.
U.S. Pat. No. 5,341,807 discloses a method of detecting contact of a catheter tip electrode with tissue. The method of the '807 patent employs a catheter having a tip electrode and a plurality of axially spaced ring electrodes mounted along the catheter surface. A test signal is applied across a pair of outer electrodes arranged along the catheter. Each outer electrode is paired with an inner electrode to de

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