The present invention relates to denervation, and more particularly to a system and method for performing denervation using a cooled microwave catheter introduced into a neighboring body lumen such as an artery.
Medical research has revealed that a number of problematic human conditions can be treated by damaging certain nerves or groups of nerves, which is generally referred to as denervation. One example of a denervation procedure that has been found to produce beneficial effects is renal denervation. It has been demonstrated in many subjects that surgical renal denervation by renal artery transection and re-anastomosis is effective in reducing noradrenaline content in the kidney and favorably impacts blood pressure in resistant hypertension patients. This has led to less invasive, percutaneous approaches that use RF energy to create focal ablation lesions in each renal artery. These approaches have been demonstrated clinically to be an improvement over surgical renal denervation but they still have several drawbacks. Existing RF based approaches will damage the intima and media of the artery. In some approaches, several lesions must be created in each renal artery, such as up to six lesions in each renal artery for a total of twelve lesions per patient, and due to the intimal and medial damage, must be created with some longitudinal separation to avoid damage to the artery that could lead to aneurism or possible rupture. If created individually, each lesion takes about two minutes to create and is performed under fluoroscopic guidance. It is relatively easy to identify where the ablation device is positioned along the length of the artery, but it is significantly more difficult to know where the ablation device is positioned within the circumference of the artery. Accordingly, considerable variability is expected in the extent of the circumference for which the nerves have been ablated. Additionally, there is an opportunity to shorten procedure time. Devices are now emerging that create multiple ablations simultaneously but they still damage the intima and media.
Renal nerves do not merely travel parallel to the renal artery but, rather, twist around it. The discrete lesions must not be created at the same location along the length of the artery to completely block the renal nerve activity as that would result in unacceptable weakening of the artery and likely aneurism and possible rupture. It is therefore impossible to eliminate all nerve pathways by the discrete lesions.
Lesions created by an RF device damage the entire thickness of the artery, including the intima, media, and adventitia. Even with the translation described above, angiographic images of the renal artery following an RF ablation procedure demonstrate a lumpy appearance that is indicative of undesirable cellular and mechanical changes in the wall of the artery. Although this lumpy appearance has been reported to resolve, there have been anecdotal reports of aneurism. The present devices do not protect the media of the artery except possibly by passive cooling due to arterial blood flow.
Further, and of greater concern is that the damage to the artery intima creates a site for atherosclerosis to form over time and it is anticipated that significant sequelae or late effects will manifest 5 or more years from the date of treatment. There is no long term data on any of the percutaneous approaches so this limitation is not generally apparent today.
Another limitation of existing RF based devices that damage the media is that patients who may fail treatment are not candidates for retreatment. This is because there is unacceptable risk to creating an overlapping thermal injury to the media a second time.
Accordingly, there is a need for a percutaneous, transluminal device that addresses these limitations and can provide a complete circumferential thermal injury to consistently and completely destroy the problematic renal nerves without damaging the intima or media of the artery.
It has also been demonstrated that denervation of the nerve trunks running along the outside of the bronchus will “disconnect” airway smooth muscle and mucus producing glands from the central nervous system, resulting in relaxation of the airway smooth muscle and a reduction in mucus production. Accordingly, airway obstruction due to disease such as COPD and asthma is reduced. The present invention has the advantage of protecting the intervening bronchial tissue and not requiring the energy emitter to be electrically in contact with the tissue. An additional advantage is the potential for a shortened procedure time and easier procedure.
Cooled RF devices have been disclosed (US2012/0016363A1) that also seek to accomplish this. However, the RF electrode must be in electrical contact with tissue for this approach to work. This requires a more complex device to accomplish the necessary cooling and heating is dependent upon tissue impedance which varies dramatically between smooth muscle, cartilage and fat. In contrast, microwave heating is accomplished by a travelling electromagnetic field so that the antenna need not be in contact with tissue. A more simple balloon structure is appropriate and the field will travel through tissue of differing dielectric constants and effectively heat the target nerve bundle. In concert with cooling accomplished with good heat transfer from a simple thin walled balloon, the result is a temperature field that protects the mucosa, smooth muscle, glandular tissue and cartilage of the bronchus but controllably thermally ablates the targeted nerve bundle.
Accordingly, there is a need for a simple percutaneous, transluminal device that addresses these limitations and can provide a controlled thermal injury to consistently and completely destroy the problematic pulmonary nerves without damaging the mucosa, muscle or cartilage of the bronchus.