I. Cross-Reference to Related Application
Reference is made to applications Ser. Nos. 07/835,553, entitled BIPLANAR DEFLECTABLE CATHETER FOR ARRHYTHMOGENTIC TISSUE ABLATION, filed Feb. 14, 1992, now abandoned; and Ser. No. 07/840,162, entitled DEFLECTABLE LOOP ELECTRODE ARRAY MAPPING AND ABLATION CATHETER FOR CARDIAC CHAMBERS, filed Feb. 24, 1992, now abandoned of inventorship. Both of these cross-referenced applications also are directed to improved catheters.
II. Field of the Invention
The present invention is directed generally to an improved catheter for use in the field of cardiac arrhythmia ablation. More particularly, the invention is directed to the use of a rotating tip deflectable catheter system with greatly increased catheter tip maneuverability in the lateral plane, i.e., perpendicular to the catheter shaft, and especially when operating in the ventricular chambers. This allows the operator to direct the tip of the catheter in multiple directions and maneuver the catheter as close as possible to the site of the arrhythmogentic tissue to accomplish effective mapping and ablation.
III. Discussion of the Related Art
Normal cardiac pacing, in a healthy heart, is controlled by a special structure known as the sinoatrial node (SA node). This is the natural pacemaker of the heart and is a specialized tissue located within the muscle walls of the right atrium. The SA node provides impulses which dominate the inherent or natural rhythmic contractions of the heart atria and the ventricles. This dominance or control involves the transmission of ionic impulses through cardiac conduction pathways in the atria and the ventricles which cause the heart to contract and relax in an orderly sequence at a rate dictated by the SA node. This sequence ensures that blood flow to the systemic circulation or the pulmonary system will be maximized with each ventricular contraction. The SA node has its own inherent rate which can be modified by signals from the nervous system. In response to excitement, physical activity, etc., the sympathetic and parasympathetic nervous systems react to modify the rate.
A depolarization impulse begins with the SA node and spreads as an electrical wave from its location in the right atrium across to the left atrium and down toward the transition zone between the atrium and the ventricles where another node, known as the atrioventricular (A-V) node or junction, is located. This impulse conducts through the A-V node in a slower fashion and continues to a common pathway known as the Bundle of His between the right and left ventricles, then into multiple paths called right and left bundle branches, each bundle branch supplying one ventricle. These bundle branches then divide into an extensive network of finer paths of conducting tissue which spread from the inner to the outer surfaces of the heart and which are referred to as the Purkinje fibers. These fibers feed the depolarization impulse into all portions of the ventricular myocardium.
As long as this system is intact, impulses are transmitted normally and cardiac rhythm is maintained. The natural impulse or current flow in the cardiac conduction system, however, may be interrupted or altered by congenital defect, disease or injury which can cause the formation of scar tissue. When a sufficiently severe injury or a congenital defect is present in the cardiac conductive pathways or in the ventricular myocardium, the electrical impulses are not transmitted normally and rhythmic disturbances known as cardiac arrhythmias can occur. With respect to such disturbances, the term bradycardia is used to describe an abnormal slowing of the cardiac contractions and the term tachycardia is used to describe abnormally rapid heart action. While either of these conditions can endanger the life of the patient, tachycardia is the more serious, particularly in patients having underlying heart disease.
Ventricular tachycardia and other ventricular arrhythmias have been treated with a number of drugs such as lidocaine, quinidine and procainamide. In cases of excessive sympathetic nervous activity or adrenal secretion, Beta blocking drugs have been used. In cases where drug therapy has been ineffective in preventing tachyarrhythmias, certain surgical procedures have been used to ablate the arrhythmogentic tissue either from the atrium or the ventricles. This procedure involves extensive surgery in which an incision through the pericardium and heart muscle is made locate the arrhythmogentic tissue, which is then frozen or surgically removed to be replaced by scar tissue.
Because open-heart surgery is a high risk procedure which requires a prolonged period of hospitalization and recuperation, a less traumatic solution is needed. In response, catheters of various types have been devised and used for diagnosing and treating a number of cardiac abnormalities to avoid the trauma of open-heart surgery. For example, as a method for resolving atherosclerotic plaque build up, stenotic lesions are now routinely opened by the use of balloon angioplasty. In this procedure, a balloon carrying catheter is navigated through the patient's vascular system to the location of the stenosis. The balloon is inflated by fluid injected through a lumen of the catheter to apply pressure to the walls of the clogged vessel, thereby opening it.
Catheter devices have also been used to locate and ablate cardiac conduction pathways. One such device is shown in U.S. Pat. No. 4 785 815, in which a catheter tube carries at its distal end at least one electrode for sensing membrane potentials within the heart, together with a heating device for ablating at least a portion of the pathway located by the sensing device. Another thermal ablation catheter for microtransection or macrotransection of conduction pathways within the heart, which uses a resistive heating element at its distal end for highly localized treatment, is illustrated and described in U.S. Pat. No. 4 869 248. These devices are generally effective once the ablating element is properly positioned at the localized area of interest. A catheter device of the class described has also been developed which employs a single handle operated tip deflection wire. Such a device is disclosed in U.S. Pat. No. 4 960 134.
Electrophysiological catheter ablation procedures often have been hampered by the inability of the operator to maneuver the catheter tip to the precise location of the arrhythmogentic tissue. This problem is most pronounced in the ventricular chambers because of the high degree of trabeculation which forms the inner linings of the chambers. The mapping and ablation catheter tip often becomes wedged within the folds of the trabeculae. In an attempt to move the catheter, the operator must resort to applying torque to the shaft of the catheter which often leads to an abrupt dislodgment of the tip from its position to an undesirable remote location. This problem leads to prolonged and, at times, agonizing repeated attempts to maneuver and place the catheter into the appropriate location.
This is primarily a result of the limited maneuverability of the catheter tube itself. The catheter tube must have sufficient strength and stiffness to be guided through the vascular system to the vicinity of the tissue of interest. This construction does not allow the degree of flexibility at the tip of the catheter needed to perform intricate multidirectional manipulations in the highly localized areas involved. Available catheters are characterized by an inadequate control of fine movements and have tips that can be deflected only in planes parallel to the main catheter tube. They lack the ability for controlled lateral movement in planes perpendicular to that of the main catheter tube within the atria or the ventricles and to navigate the extremely rugged surfaces of the ventricular chambers inner lining (endocardium).
Most present cardiac tissue ablation procedures involve the use of radio frequency (RF) electrical current transmitted to the tissue via a catheter which is positioned as closely as possible to the arrhythmogentic site within the atria or ventricles. Radio frequency electrical current heats the tissue surrounding the catheter, creating a discrete dense lesion. In order for the patient to be cured of the arrhythmia, the lesion must be created in the area from which the arrhythmia originates. Improvement in the maneuverability of such devices could optimize precise positioning of the catheter prior to ablation.