Surgery – Instruments – Electrical application
Reexamination Certificate
1997-11-26
2002-07-16
Dvorak, Linda C. M. (Department: 3739)
Surgery
Instruments
Electrical application
C607S101000, C606S049000
Reexamination Certificate
active
06419674
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to medical devices and, in particular, to a dilator sheath using electrical energy to separate encapsulating tissue from an implanted cardiac electrical lead.
BACKGROUND OF THE INVENTION
While cardiac electrical leads typically have a useful life of many years, over time pacemaker and defibrillator leads fail. Unfortunately, by the time they fail, they have become encapsulated by fibrotic tissue against the heart itself or the wall of the vein. Encapsulation is especially encountered in areas where a device has caused tissue injury. Encapsulation is the body's healing response to protect surrounding tissue from further injury. Scar tissue may also form due to continual device-related mechanical stresses (i.e., excessive pressure), infection, or inadequate blood supply to the site. The fibrotic tissue is tough and makes it difficult to remove the lead from the patient without causing trauma to the heart or great vessels. For example, when small diameter veins through which a pacemaker lead passes become occluded with fibrotic tissue, separating the lead from the vein can cause severe damage to the vein such as dissection or perforation.
To avoid this and other possible complications, some useless cardiac leads are simply left in the patient when the pacemaker or defibrillator is removed or replaced. However, such a practice can incur the risk of an undetected lead thrombosis or pulmonary embolism. Such a practice can also impair heart function, as multiple leads can restrict the heart valves through which they pass. Furthermore, such a lead can later become infected.
There are, of course, many other reasons why removal of a useless lead is desirable. For example, if there are too many leads positioned in a vein, the vein can become totally occluded. Multiple leads can be incompatible with one another, interfering with the pacing or defibrillating function. An inoperative lead can migrate during introduction of another adjacent lead, and mechanically induce ventricular arrhythmia. Some recalled leads include J-shaped retention wires that have been known to fracture and protrude through the insulation, causing several reported deaths. Other potentially life-threatening complications can require the removal of the lead as well. For example, removal of an infected pacemaker lead is considered mandatory in the presence of septicemia and endocarditis. Other necessary indications such as pocket infection, chronic draining sinus, and erosion can lead to significant morbidity if the lead is not removed.
Until recently, manual (or direct) traction, weighted (or sustained) traction, and open-heart surgery/thoracotomy have been the most common methods of removing useless or infected cardiac leads. Manual and weighted traction involve the risk of tearing the myocardium and are largely ineffective for leads extensively encased in fibrotic tissue. This procedure is also ineffective in patients with multiple leads when these leads become scarred together at common fibrous binding sites. The risks and trauma associated with an open surgical approach are obvious. Yet another method of transvenously extracting a cardiac lead is by the use of a grasping device, such as a forceps or basket that is positionable around the outer surface of a lead or fragments of a lead. The use of forceps or a basket for lead withdrawal is complicated by the fact that the lead should first be freed from any encapsulating material surrounding it along its path. Furthermore, tearing of the myocardium or vessels can result during attempted extraction. Many of these problems were overcome by the development of a system of tools and methods for transvenous extraction of pacemaker leads and other elongated objects such as catheters. Many of these tools and procedures were developed with the assistance of Cook Pacemaker Corp., Leechburg, Pa., as evidenced by U.S. Pat. Nos. 4,988,347; 5,013,310; 5,011,482; 4,943,289; 5,207,683; 5,507,751; 5,632,749; and corresponding foreign patents. The preferred method involves positioning a lead removal tool or “locking stylet” inside the coiled wire of the lead to engage the coil. Once the locking stylet is positioned inside the coil, reinforcement is provided and extraction forces are concentrated at the lead tip. By using a sheath to apply countertraction at the embedded tip as the lead is extracted, damage to the myocardium can be largely avoided.
Typically, the locking stylet alone does not provide the tensional force required to safely extract the lead due to excessive fibrotic or scar tissue that has encapsulated the lead against the vessel or myocardial wall. Dilator sheaths formed from plastic or metal tubes can be used to disrupt and separate the encapsulating tissue. Commonly, two coaxial dilator sheaths are positioned over the lead and advanced therealong for loosening the lead from the fibrotic tissue on the vein wall. Plastic sheaths are flexible for bending around the natural anatomical curvatures of the vascular system. A problem with the plastic dilator sheaths is that the leading edge of the dilator sheath is weak and can lose its edge and buckle onto the lead during use. As a result, the plastic dilator sheath can become damaged and unusable before the lead is loosened from the fibrotic tissue. Furthermore, the tips of the flexible plastic sheaths can deform when subjected to tough fibrotic tissue. This problem is further heightened when the sheath is bent around a vessel curve. Metal dilator sheaths provide a sharp leading edge for encountering fibrotic tissue. A problem with some metallic dilator sheaths is that they are relatively inflexible and resist bending around natural anatomical curvatures. As a result, a metallic dilator sheath can be difficult or impossible to advance toward the distal end of the pacemaker lead without injuring or obliterating the vein. Flexible metallic dilator sheaths have been developed to address the problems associated with plastic sheaths and rigid metal sheaths. While very effective for their intended use, even metal sheaths are inadequate for the toughest fibrotic tissue and calcification in a vessel. The tensile strength of the fibrous tissue increases with time. Eventually the tissue can even differentiate into cartilage or bone. Attempted separation of difficult fibrotic tissue can cause mechanical trauma to the vessel. Data show that 5.4% of all attempted lead extractions are not successful and 7.5% are only partially successful, almost entirely due to the presence of excessive scar tissue. Lead fragility is another problem and generally escalates over time when a lead has a design flaw or has been structurally compromised.
U.S. Pat. No. 5,423,806 of Dale et al. discloses a laser catheter for ablating encapsulating tissue during the extraction of pacemaker leads. Using directed high energy to burn, desiccate, or melt the tissue encapsulating the lead can reduce the length of the procedure and increase the number of leads that can be extracted. In the practiced embodiment of U.S. Pat. No. 5,423,806, optical fibers are arranged circumferentially around an open lumen through which the lead passes. One problem with this embodiment is that tissue can be readily cored and plug the internal lumen of the device, thus making forward or reverse movement of the device extremely difficult. The laser device is used in combination with a plastic outer sheath and tracks over the lead as the distal tip of the laser burns through any obstructive tissue surrounding the lead. Partly due to the difficulty in visualizing the treatment site, a significant disadvantage of this approach is the risk of burning though the vessel wall or myocardium. This is especially a problem if sufficient tension is not constantly maintained on the lead during the procedure, allowing the distal tip of the laser to angle toward the wall of the vessel or myocardium. This could pose an unacceptable risk for the large number of lead extractions that are elective procedures and do not involve life-threatening indications
Bowser Donald J.
Cook Carl A.
Goode Louis B.
Johnson William L.
Norlander Barry E.
Agnew Charles W.
Cook Vascular Incorporated
Dvorak Linda C. M.
Gibson Roy
Godlewski Richard J.
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