Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical energy applicator
Reexamination Certificate
2001-07-31
2004-11-23
Peffley, Michael (Department: 3739)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical energy applicator
C606S033000, C607S101000
Reexamination Certificate
active
06823218
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates generally to ablation catheter systems that use electromagnetic energy in the microwave frequency range to ablate internal bodily tissues. More particularly, the present invention relates to a monopole tip for a catheter that enables distal fire capabilities while enabling a relatively even electromagnetic field to be created at the sides of the monopole tip to facilitate the ablation of cardiac tissue.
2. Description of the Related Art
Catheter ablation is a therapy that is becoming more widely used for the treatment of medical problems such as cardiac arrhythmias, cardiac disrhythmias, and tachycardia. Most presently approved ablation catheter systems utilize radio frequency (RF) energy as the ablating energy source. However, RF energy has several limitations which include the rapid dissipation of energy in surface tissues. This rapid dissipation of energy often results in shallow “burns,” as well as a failure to access deeper arrhythmic tissues. As such, catheters which utilize electromagnetic energy in the microwave frequency range as the ablation energy source are currently being developed. Microwave frequency energy has long been recognized as an effective energy source for heating biological tissues and has seen use in such hyperthermia applications as cancer treatment and the preheating of blood prior to infusions. Catheters which utilize microwave energy have been observed to be capable of generating substantially larger lesions than those generated by RF catheters, which greatly simplifies the actual ablation procedures. Some catheter systems which utilize microwave energy are described in the U.S. Pat. No. 4,641,649 to Walinsky; U.S. Pat. No. 5,246,438 to Langberg; U.S. Pat. No. 5,405,346 to Grundy, et al.; and U.S. Pat. No. 5,314,466 to Stern, et al., each of which is incorporated herein by reference in its entirety.
Cardiac arrhythmias, which may be treated using catheter ablation, are generally circuits, known as “reentry circuits,” which form within the chambers of the heart. As is known to those skilled in the art, reentry circuits are abnormal electrical pathways that may form in various areas of the heart. For example, reentry circuits may form around veins and/or arteries which lead away from and to the heart. Cardiac arrhythmias may occur in any area of the heart where reentry circuits are formed.
The catheters used for treatment of cardiac arrhythmias, disrhythmias, and tachycardia may have a variety of different antenna configurations to create electromagnetic fields used in ablation. Some catheters have antennas that essentially protrude from the distal ends of the catheters. In other words, some catheters have antennas which form the distal tips of the catheters. A monopole antenna is typically configured to form the distal tip of a catheter.
FIG. 1
a
is a diagrammatic representation of a distal end of a catheter with a monopole antenna at its tip. A distal end
102
of a catheter has a monopole antenna
108
at its tip. As shown, monopole antenna
108
has a rounded shape, and is coupled to a center conductor
112
of a co-axial transmission line
116
. Typically, monopole antenna
108
is formed from a metallic material. Distal end
102
of the catheter may also include electrodes
120
, which may be used for mapping processes, that may be coupled to processing equipment (not shown) using ECG wires
122
.
Monopole antenna
108
is often arranged to be used in ablating tissue. Center conductor
112
transmits energy, e.g., electromagnetic energy, to monopole antenna
108
to allow an electromagnetic field to be formed with respect to monopole antenna.
FIG. 1
b
is a diagrammatic representation of a monopole antenna, i.e., monopole antenna
108
of
FIG. 1
a, shown with electromagnetic field lines. Electromagnetic field lines
130
generally radiate from monopole antenna
108
in a substantially ellipsoidal pattern. Hence, near sides
134
, “hot spots”
138
of electromagnetic energy are typically formed. Hot spots
138
are generally associated with the highest amounts of electromagnetic energy radiated by monopole antenna
108
. The existence of hot spots
138
causes certain portions of a myocardium of heart, for example, such as those that are substantially contacted by a hot spot to be ablated more than other portions.
When an ablation procedure is performed using monopole antenna
108
, the depth of cuts formed may not be uniform, since electromagnetic field lines
130
are not uniform. That is, the shape, or profile, of electromagnetic field lines
130
are such that when ablation is performed, the depth associated with the ablation may not be even. The lack of even depth in an ablation procedure may cause the ablation, e.g., an ablation in the myocardium of a heart, to be unsuccessful, as all of the cardiac tissue may not be effectively ablated. Hence, the ablation procedure may have to be repeated, which is both time-consuming and inefficient.
Therefore, what is needed is a monopole antenna structure for use with an ablation catheter that efficiently allows tissue to be ablated. More specifically, what is desired is a monopole antenna structure that is capable of producing a relatively field, e.g., electromagnetic field, a deep lesion, and a microwave power deposition at the tip of a catheter, i.e., a tip-firing catheter.
SUMMARY OF THE INVENTION
The present invention relates generally to an ablation catheter with a monopole antenna that is arranged to provide an electric field that is able to produce a deep lesion, e.g., in the myocardium or a heart, and has a tip-firing capability. According to one aspect of the present invention, an ablation catheter includes an elongated flexible tubular member that is adapted to be inserted into the body of a patient, and a transmission line that is disposed within the tubular member. The transmission line has a distal end and a proximal end which is arranged to be connected to an electromagnetic energy source. The catheter also includes a monopole antenna with tip section and a body section that includes a distal end and a proximal end. The tip section and the body section are arranged to produce a relatively uniform electric field around the monopole antenna which is sufficiently strong to cause deep tissue ablation. The proximal end of the body section of the monopole antenna is arranged to be electrically coupled to the transmission line.
In one embodiment, the transmission line is a coaxial cable, which has a center conductor and an outer conductor. In such an embodiment, the proximal end of the monopole antenna is arranged to be electrically coupled to the center conductor. In another embodiment, the body section of the monopole antenna is tapered such that the diameter at the proximal end of the body section of the monopole antenna is smaller than the diameter at the distal end of the body section of the monopole antenna.
According to another aspect of the present invention, an antenna structure arranged to be used in an ablation catheter has a longitudinal axis, and includes a body section with a first end and a second end, a tip section, and a transition section. The body section is sized such that the axial cross-sectional area about the longitudinal axis of the second end is smaller than the axial cross-sectional area about the longitudinal axis of the first end. The second end is arranged to be electrically coupled to a transmission line, and the body section is shaped to allow a relatively uniform electric field to be formed with respect to the antenna structure.
The tip section has a proximal portion that has an axial cross-sectional area about the longitudinal axis which is greater than or approximately equal to the axial cross-sectional area of the first end, and the transition section is disposed between the proximal portion and the first end.
In one embodiment, the first end has a diameter that is greater than the diameter of the second end, and the proximal portion has a diameter that is greater than or e
AFX Inc.
Fenwick & West LLP
Peffley Michael
LandOfFree
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