Surgery – Instruments – Electrical application
Reexamination Certificate
2000-08-28
2003-12-16
Peffley, Michael (Department: 3739)
Surgery
Instruments
Electrical application
C606S041000
Reexamination Certificate
active
06663622
ABSTRACT:
TECHNICAL FIELD
The invention generally relates to surgical devices and, more particularly, to surgical devices and methods for use in procedures performed on moving tissue.
BACKGROUND
Some forms of surgery involve ablation to kill tissue in an organ in order to achieve a therapeutic result. Ablation can be achieved by various techniques, including the application of radio frequency energy, lasers, cryogenic probes, and ultrasound. Thus, the term “ablation,” as used herein refers to any of a variety of methods used to kill tissue within an organ. To be successful, ablation treatment may require considerable precision. The surgeon must target a particular region, and be careful not to cause unnecessary trauma to other areas of the patient's body near the target area. Just as important, the surgeon must be confident that the procedure within the target area has been appropriately performed. For example, the surgeon may need to determine whether the tissue has been ablated to an appropriate degree. The surgery may be made more difficult if the target area is moving.
One such surgical procedure in which a surgeon may wish to ablate moving tissue is an operation to correct an abnormal heartbeat. To function efficiently, the heart atria must contract before the heart ventricles contract. As blood returns to the heart and enters the atria, blood also flows through the atrioventricular (AV) valves and partially fills the ventricles. Following an electrical excitation by the sinoatrial (SA) node, the atria contract in unison, expelling blood into the ventricles to complete ventricular filling. The ventricles then become excited and contract in unison. Ventricular contraction ejects the blood out of the heart. Blood ejected from the right ventricle enters the pulmonary arteries for oxygenation by the lungs, and blood ejected from the left ventricle enters the main aorta and is distributed to the rest of the body. If the timing of cardiac functions is impaired, such as by the atria not contracting in unison or by the ventricles contracting prematurely, then the operation of the heart is impaired.
The synchronization of heart functions is initiated by an excitation from the SA node, which is the heart's natural pacemaker. The excitation propagates along an interatrial pathway, extending from the SA node in the right atrium to the left atrium. The excitation then spreads across gap junctions throughout the atria, causing the atria to contract in unison. The excitation further travels down an internodal pathway to the AV node, which transmits the excitation to the ventricles along the bundle of His and across the myocardium via the Purkinje fibers. In an aging heart, the atria may stretch, and the conduction paths by which the excitations travel may become lengthened. As a result, the excitations have a longer distance to travel, and this may affect the timing of the heart contractions and may create an arrhythmia. The term “arrhythmia” is used to describe any variation from normal rhythm and sequence of excitation of the heart.
One form of arrhythmia is atrial fibrillation. Atrial fibrillation is characterized by chaotic and asynchronized atrial cell contractions resulting in little or no effective blood pumping into the ventricle. Ventricular contractions are not synchronized with atrial contractions, and ventricular beats may come so frequently that the heart has little time to fill with blood between beats. Atrial fibrillation may occur if conduction blocks form within the tissue of the heart, causing the electrical excitations to degenerate into flurries of circular wavelets, or “reentry circuits,” which interfere with atrial activity. Initiation or maintenance of atrial fibrillation may be facilitated if atria become enlarged. Atrial enlargement increases the time required for the electrical impulse to travel across the atria. This allows sufficient time for the cells that contracted initially to repolarize and allows the re-entry circuit to be maintained.
One surgical procedure for treating some forms of arrhythmia is to disrupt conduction paths in the heart tissue by severing the paths at selected regions of the atrial myocardium. Selective disruption of the conduction pathways permits impulses to propagate from the SA node to activate the atria and the AV node, but prevents the propagation of aberrant impulses from other anatomic sites in the atria. Severing may be accomplished, for example, by incising the full thickness of the myocardial tissue followed by closing the incision with sutures. The resultant scar permanently disrupts the conduction paths. As an alternative, permanent lesions, in which tissue is killed, can be created by ablation. The ablation process involves creating a lesion that extends from the top surface of the myocardium to the bottom surface (endocardial surface). Thus, the purpose of ablation is to create one or more lesions that sever certain paths for the excitations while keeping other paths intact. In the case of atrial fibrillation, for example, the lesions may interrupt the reentry circuit pathways while leaving other conduction pathways open. By altering the paths of conduction, the synchronization of the atrial contractions with the ventricular contractions may be restored. A plurality of lesions may be needed to achieve the desired results.
Incision through the myocardium, referred to as the “maze procedure,” requires suturing to restore the integrity of the myocardium, and exposes the patient to considerable risk and morbidity. In contrast, thermal or other forms of ablation can create effective lesions without the need for sutures or other restorative procedures. Consequently, ablation can be performed more quickly and with far less morbidity. For these reasons, ablation is becoming a preferred method for severing conduction paths. The surgical ablation procedure may be performed during open-heart surgery. In a typical open-heart surgery, the patient is placed in the supine position. The surgeon must then obtain access to the patient's heart. One procedure for obtaining access is the median stemotomy, in which the patient's chest is incised and opened. Thereafter, the surgeon may employ a rib-spreader to spread the rib cage apart, and may incise the pericardial sac to obtain access to the cardiac muscle.
For some forms of open-heart surgery, the patient is placed on cardiopulmonary bypass (CPB) and the patient's heart is arrested. CPB is preferred for many coronary procedures because the procedure is difficult to perform if the heart continues to beat. CPB, however, entails trauma to the patient with attendant side effects and risks.
In some circumstances, the patient may be treated by a procedure less invasive than the procedure described above. One such less invasive procedure may be a lateral thoracotomy. The heart may be accessed through a comparatively small opening in the chest and accessed through the ribs. In such a procedure, arrest of the patient's heart may not be feasible, and if the heart cannot be arrested, the surgery must be performed while the heart continues to beat. Other procedures for access to the heart include sternotomy, thoracoscopy, transluminal, or combinations thereof.
Once the surgeon has obtained access to the heart, ablation can be carried out with a probe that delivers ablative energy. The ablative energy may take the form of electromagnetic radiation generated by a laser or radio frequency antenna. Other techniques for achieving ablation include the application of ultrasound energy or very low temperature. For the procedure to be successful, the created lesions should sever the targeted conduction paths. Typically, the surgeon must create a lesion of a particular length to create the desired severance. The surgeon must also create a lesion of a particular depth in order to prevent the electrical impulses from crossing the lesion. In particular, when the myocardial tissue is ablated, the lesion must be transmural, i.e., the tissue must be killed in the full thickness of the myocardium
Adelman Thomas G.
Foley Frederick J.
Hoey Michael F.
Reeve Lorraine E.
Sharrow James S.
Iotek, Inc.
Peffley Michael
Shumaker & Sieffert PA
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