Surgery – Diagnostic testing – Structure of body-contacting electrode or electrode inserted...
Reexamination Certificate
2000-03-28
2002-04-09
Getzow, Scott M. (Department: 3762)
Surgery
Diagnostic testing
Structure of body-contacting electrode or electrode inserted...
C600S515000
Reexamination Certificate
active
06370412
ABSTRACT:
BACKGROUND OF THE INVENTION
The electrical activity generated in certain organs in the human body is intimately related to their function. Abnormalities in cardiac and brain electrical conduction processes are principal causes of morbidity and mortality in the developed world. Appropriate treatment of disorders arising from such abnormalities frequently requires a determination of their location. Such localization of the site of origin of an abnormal electrical excitation is typically achieved by painstaking mapping of the electrical activity on the inner surface of the heart or the brain from electrodes or a catheter. Often, this recording must be done while the abnormal biological electrical excitation is ongoing.
Radio frequency catheter ablation procedures have evolved in recent years to become an established treatment for patients with a variety of supraventricular [Lee, 1991; Langberg, 1993] and ventricular arrhythmias [Stevenson, 1997; Stevenson, 1998]. However, in contrast to supraventricular tachycardia ablation, which is highly successful because the atrio-ventricular node anatomy is known, ventricular tachycardia ablation remains difficult because the site of origin of the arrhythmia could be anywhere in the ventricles.
Sustained ventricular tachycardia is often a difficult arrhythmia to manage. One of the most common indications for radio frequency catheter ablation of ventricular tachycardia is arrhythmia refractory to drug therapy that results in frequent discharges from an implantable cardioverter-defibrillator. Radio frequency ablation is also indicated when the ventricular tachycardia (VT) is too slow to be detected by the implantable cardioverter-defibrillator or is incessant [Strickberger, 1997].
Selection of the appropriate target sites for ablation is usually based on a combination of anatomical and electrical criteria. The ability of the physician to deliver radio frequency energy through a catheter at the reentry site is restricted by the limitations of the current technology that is employed to guide the catheter to the appropriate ablation site. The principal limitation of the radio frequency ablation technique is the determination of the correct site for delivery of the radio frequency energy. Conventionally, this determination is achieved by painstaking mapping of the electrical activity on the inner surface of the heart from electrodes on the catheter. Often, this recording must be done while the arrhythmia is ongoing. This is a major problem, especially for those arrhythmias which compromise hemodynamic function of the patient. Many arrhythmias for this reason are not presently amenable to radio frequency ablation treatment.
The acute lesion created by radio frequency current consists of a central zone of coagulation necrosis surrounded by a zone of hemorrhage and inflammation. Arrhythmias may recur if the target tissue is in the border zone of a lesion instead of in the central area of necrosis. If the inflammation resolves without residual necrosis, arrhythmias may recur several days to several weeks after an apparently successful ablation [Langberg, 1992]. Conversely, an arrhythmia site of origin that was not initially successfully ablated may later become permanently nonfunctional if it lies within the border zone of a lesion and if microvascular injury and inflammation within this zone result in progressive necrosis [Nath, 1994]. Thus, the efficacy and long term outcome of catheter ablation depend on accurate determination of the site of origin of the arrhythmia.
Catheter ablation of sustained monomorphic ventricular tachycardia late after myocardial infarction has been challenging. These arrhythmias arise from reentry circuits that can be large and complex, with broad paths and narrow isthmuses, and that may traverse subendocardial, intramural, and epicardial regions of the myocardium [deBakker, 1991; Kaltenbrunner, 1991].
Mapping and ablation are further complicated by the frequent presence of multiple reentry circuits, giving rise to several morphologically different VTs [Wilbur, 1987; Waspel, 1985]. In some cases, different reentry circuits form in the same abnormal region. In other cases, reentry circuits form at disparate sites in the infarct area. The presence of multiple morphologies of inducible or spontaneous VT has been associated with antiarrhythmic drug inefficacy [Mitrani, 1993] and failure of surgical ablation [Miller, 1984].
Several investigators have reported series of studies of patients selected for having one predominant morphology of VT (“clinical VT”) who were treated with radio frequency catheter ablation [Morady, 1993; Kim, 1994]. It is likely that this group of patients represents less than 10% of the total population of patients with VT [Kim, 1994]. The patient must remain hemodynamically stable while the arrhythmia is induced and maintained during mapping. The mapping procedure may take many hours during which the arrhythmia must be maintained. Thus, currently radio frequency catheter ablation is generally limited to “slow” ventricular tachycardia (~130 bpm) which is most likely to be hemodynamically stable.
Ablation directed towards the “clinical tachycardia” that did not target other inducible VTs successfully abolished the “clinical VT” in 71% to 76% cases. However, during followup up to 31% of those patients with successful ablation of the “clinical VT” had arrhythmic recurrences, some of which were due to different VT morphologies from that initially targeted for ablation.
Furthermore, there are several difficulties in selecting a dominant, “clinical VT” for ablation. Often it is not possible to determine which VT is in fact the one that has occurred spontaneously. In most cases, only a limited recording of one or a few ECG leads may be available. In patients with implantable defibrillators VT is typically terminated by the device before an ECG is obtained. Even if one VT is identified as predominant, other VTs that are inducible may subsequently occur spontaneously. An alternative approach is not to consider the number of VT morphologies in determining eligibility for catheter ablation but rather to attempt ablation of all inducible VTs that are sufficiently tolerated to allow mapping [Stevenson, 1998b; Stevenson, 1997]. However, this approach requires that the patient be hemodynamically stable during the VT mapping procedure.
The use of fluoroscopy (digital bi-plane x-ray) for the guidance of the ablation catheter for the delivery of the curative radio frequency energy is common to clinical catheter ablation strategies. However, the use of fluoroscopy for these purposes may be problematic for the following reasons: (1) It may not be possible to accurately associate intracardiac electrograms with their precise location within the heart; (2) The endocardial surface is not visible using fluoroscopy, and the target sites can only be approximated by their relationship with nearby structures such as ribs and blood vessels as well as the position of other catheters; (3) Due to the limitations of two-dimensional fluoroscopy, navigation is frequently inexact, time consuming, and requires multiple views to estimate the three-dimensional location of the catheter; (4) It may not be possible to accurately return the catheter precisely to a previously mapped site; (5) It is desirable to minimize exposure of the patient and medical personnel to radiation; and (6) Most importantly, fluoroscopy cannot identify the site of origin of an arrhythmia and thus cannot be used to specifically direct a catheter to that site.
Electro-anatomic mapping systems (e.g., Carto, Biosense, Marlton, N.J.) provide an electro-anatomical map of the heart. This method of nonfluoroscopic catheter mapping is based on an activation sequence to track and localize the tip of the mapping catheter by magnetic localization in conjunction with electrical activity recorded by the catheter. This approach has been used in ventricular tachyard
Armoundas Antonis A.
Cohen Richard J.
Feldman Andrew B.
Sherman Derin A.
Choate Hall & Stewart
Gerber Monica R.
Getzow Scott M.
Massachusetts Institute of Technology
LandOfFree
Method and apparatus for guiding ablative therapy of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for guiding ablative therapy of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for guiding ablative therapy of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2846004