Abstract:
The present invention provides a new mechanical sensor approach to maneuvering catheters and other cardiac devices into blood outlets, with particular application to maneuvering cardiac devices into the coronary sinus and beyond. Additionally, the inventive sensing device provides assessment of the viability of branching veins and other potential device sites, such as within the coronary venous system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application Ser. No. 60/639,148 filed on Dec. 21, 2004, the disclosure of which is herein incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   The present invention relates generally to medical methods, apparatus and systems. More specifically, the invention relates to methods, apparatus and systems for optimizing the progression of a cardiac catheter through the coronary sinus among other venous features by monitoring blood flow. 
   Placement of cardiac leads in the distal branches of the coronary venous system, the great cardiac vein, or the coronary sinus provides new medical opportunities to place medical devices on the left ventricle with a much lower patient morbidity than direct placement within the ventricle. However, maneuvering devices into the coronary sinus can be a difficult task. 
   Deploying a pacing lead through the coronary sinus and into the distal venous system is often challenging if not impossible using standard techniques and equipment. In addition, it is often impossible to place the lead in an optimum location, for pacing or sensing cardiac electrical activity, either because there are no vessels in this region or the vasculature is too small or tortuous and therefore hard to find. 
   There are several reasons which make proper placement of the lead in these challenging locations difficult. These include difficulty in locating and maneuvering devices into the coronary sinus and beyond, partial obstruction of the vasculature, and unusually shaped bifurcations in the vasculature. 
   Prior efforts to resolve such problems included the use of stiffer guidewires, with an attended risk to the vessel walls through which the guidewire and lead are inserted. While stiffer guidewires offer additional support, they may impede advancement due to their stiffness or inability to navigate more tortuous anatomy. Leads have also been developed, such as those reported by Westlund et al (U.S. patent application Ser. No. 10/081,436 filed Feb. 20, 2002), which have sections of various stiffness, temporary locking means, and other features to expedite coronary sinus access. 
   Other approaches to improving coronary sinus access are an effort to detect and analyze electrical events to determine the electrodes&#39; position, such as reported by Yu et al (U.S. patent application Ser. No. 10/729,301 file Dec. 5, 2003). 
   Mechanical, electrical, and fluoroscopy approaches to placement of cardiac devices into the coronary sinus and beyond have been helpful, but the need remains for a practical approach to more simply maneuver devices based on immediate, real-time local sensing. Such an advancement in the medical device arts would allow an important clinical advantage and, in some cases, availability of this important clinical approach for the first time. 
   REFERENCES 
   Patent references of interest include International Patent Application US05/39535 entitled “Cardiac Motion Characterization by Strain Measurement” filed Oct. 31, 2005, incorporated herein by reference. 
   SUMMARY OF THE INVENTION 
   The present invention provides a new mechanical sensor approach to maneuvering catheters and other cardiac devices into blood outlets, with particular application to maneuvering cardiac devices into the coronary sinus and beyond. Additionally, the inventive sensing device provides assessment of the viability of branching veins and other potential device sites, such as within the coronary venous system. 
   The present invention represents an entirely novel approach to detecting the optimal approach and timing for insertion of cardiac devices into the coronary sinus using a flow sensing device. While the strain sensor embodiment exemplified below presents an effective means of carrying out the present invention, other mechanical flow sensor means can also be effectively employed in the present invention, including, but not limited to, rotameter (float in tube), propeller type, thermal dilution, hot-wire anemometer and ultrasonic flow meter. Alternate flow sensor devices can also be employed in the present invention as are well recognized by the ordinary skilled artisan. 
   In one embodiment of the present invention, the paddle configuration of the sensor with a strain gauge provides immediate report of proximity to the coronary sinus. Additionally, the clinician has real-time feedback regarding the opening and closing of the Thebesian valve, so that the device can be inserted at the optimum moment for successful cannulation. This innovation minimizes trauma to the venous walls and valve. By reducing the time of the procedure, in some cases by several fold, the inventive device lowers potential patient morbidity and mortality secondary to the procedure. 
   The difficulty in locating the coronary sinus lies in the fact that the position of the coronary sinus differs from individual to individual. Increasing this challenge is that patients with advanced heart failure have an even greater variation in their heart shapes than the range within the general population. As the heart enlarges due to heart conditions, the coronary sinus tends to move down and toward the RV, resulting in the expansion of the entire structure. 
   The innovative sensing device dramatically increases access while minimizing trauma and placement time to this clinically valuable cardiac feature, which provides a minimally invasive access to the cardiac left ventricle. While in many cases the present invention will be a useful augmentation to existing positioning approaches, in certain instances, the sensing device will limit or eliminate the need for other placement devices and procedures. 
   Because of limitations to existing methods and devices, lengthy clinical efforts were typically required to gain physical access into the coronary sinus, putting patients at the attendant risk for prolonged cardiac procedures. Regrettably, such efforts often result in failure, and the valuable access to the left ventricle remains out of reach despite the effort and risk. 
   The simplified access to the coronary sinus system provided by the present invention will substantially increase the number of patients treated with left ventricular devices, during cardiac resynchronization therapy, resulting in improved clinical outcomes. Anticipating potential difficult access, many clinicians elect to entirely forgo the opportunities otherwise available with coronary sinus approach to the left ventricle. The underutilization of this otherwise valuable technique will now become more widely available. 

   
     SUMMARY OF THE DRAWINGS 
       FIG. 1  provides a diagram of the coronary sinus catheter on which is the inventive coronary sinus sensor. 
       FIG. 2A-E  provides diagrams of several embodiments of the inventive coronary sinus sensor. 
       FIG. 3A-C  provides a view of a deployable embodiment of the inventive coronary sinus sensor. 
       FIG. 4A-C  provides a view of a rounded tip triangular winged version of the inventive coronary sinus sensor. 
       FIG. 5A-C  provides a view of a diverted blood flow embodiment of the inventive coronary sinus sensor. 
       FIG. 6A-B  are charts showing data from the inventive coronary sinus sensor. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The inventive sensor provides methods, apparatus and systems for optimizing the progression of a cardiac catheter into a blood flow extruding cardiac feature, such as through the coronary sinus. 
   The difficulty with finding the coronary sinus lies in the fact that every heart is different in the spacing of anatomical features and in size and position of those features. Therefore, the position of the coronary sinus typically varies from individual to individual. The bigger challenge in cardiac feature location within a clinical setting is that people with advanced heart failure typically have a much larger variation in their heart shape than that of the general population. 
   In advanced heart failure, the heart enlarges, the coronary sinus tends to move down and toward the RV resulting in the expansion of the entire structure. The entire heart is enlarged and subsequently the location of the coronary sinus can be difficult to ascertain. 
   To date most of the work that has been done with guiding catheters for coronary sinus access has been focused on the creation of custom shaped devices that will most likely locate the coronary sinus. These custom shapes are based on the average anatomy of the heart and therefore work for many instances where the anatomy is normal. This technique also works well in instances where coronary arteries are being located, for instance when placing stents and doing angioplasty. Arteries are not blocked by valves at their openings and contrast injections can be used to find the entrance point for the catheter. The custom shapes in this environment serve two purposes: to find the artery and to keep the catheter engaged during the procedure. 
   In the case of the coronary sinus the blood flow is coming toward the catheter and therefore the use of contrast dye is difficult and of little use and would require the injection of a large amount of dye. 
     FIG. 1  provides a depiction of the heart showing the coronary sinus  103  with blood coming out from it, as well as a catheter  100  with the inventive coronary sinus sensor. This coronary sinus sensor device is nicknamed the coronary sinus sniffing device or the coronary sinus location device. 
   The coronary sinus sensor device is intended to be used in procedures where physicians are attempting to access the coronary sinus from the right atrium using a guiding catheter. This type of procedure is conducted when physicians are placing coronary sinus or venous leads for cardiac resynchronization therapy procedures. In these procedures, a third pacing lead is placed through the coronary sinus into the cardiac vein to allow pacing of the left ventricle. 
   The invention in this disclosure is a coronary sinus guide that uses a different approach to the anatomy. Rather than relying solely upon a special shape or combination of special shaped catheters to locate the coronary sinus, this invention utilizes the fact that blood is flowing out of the coronary sinus towards the catheter. By sensing this flow with some directionality, a catheter can be positioned in front of the coronary sinus to allow a guide or guide wire to be placed into the coronary sinus. 
   The invention is the use of a flow sensor, such as a sensing wing, that allows the catheter to be positioned where the flow sensing wing senses the greatest amount of flow coming from the coronary sinus. 
     FIG. 2A  shows a guiding catheter  100  with a guide wire  101  (as shown in  FIG. 3B ) inserted and a flow sensing wing  102  at the tip of the device. Arrows coming out of the coronary sinus  103  show the flow coming from the coronary sinus and deflecting the flow sensing wing. The flow sensing wing includes a strain sensing element as part of its design. Therefore, when the front of the catheter is aligned with the coronary sinus, the wing is deflected by the blood flow, indicating that the catheter is aligned with the coronary sinus. 
     FIG. 2B  provides a view of a device similar to the embodiment shown in  FIG. 2   a  with the exception that there is an opening or a side port  104 . Side port  104  allows the blood flow from the coronary sinus to enter the catheter tip and then exit behind the wing. This feature may increase the effectiveness of the wing at sensing blood flow. 
     FIG. 2C  shows an embodiment similar to those in  2   a  and in  2   b . In this configuration, catheter  100  and guide wire  101  are again provided. This view further provides flow sensing wing  102  in a different orientation. In this case, the blood flow comes into the guiding catheter  100  and flows out of the guiding catheter  100  through the side port  105  and as it flows out of the side port it deflects the wing  102 . 
     FIG. 2D  shows another embodiment of the design which includes an outer guide catheter  123  and inner guide catheter  106  with a guide wire  101 . The inner guide catheter  106  is deployed in front of the outer guide catheter  123  to protect the strain sensing wing  102  during insertion into the atrium. Strain sensing wing  102  is shown hanging off the tip of the outer guide catheter  100 , as deployed for flow sensing. In the same way, this device allows sensing of the flow from the coronary sinus. When the catheter is aligned with the coronary sinus the flow sensing wing is deflected by the flow of blood. 
     FIG. 2E  shows the use a guiding catheter  100  with a guide wire  101 . This particular device has two flow sensing wings deployed within it. The first one, the distal flow sensing wing  102  is closest to the coronary sinus. Distal flow sensing wing  102  is used to sense the coronary sinus flow. Proximal flow sensing wing  107  is farthest away from the coronary sinus. Proximal flow sensing wing  107  is used to sense other flow within the chamber, for instance flow from the inferior and superior vena cava. The blood flow comes into catheter  100  at the proximal wing  107  and exits the proximal side port  108 . In this way any flow from the inferior and superior vena cava that is sensed by the distal flow sensor wing  102  can be subtracted out so that only the flow recorded from the coronary sinus would be sensed. 
   Another use of this strain or flow sensing catheter is to allow the physician to slide the guide wire forward into the coronary sinus at the appropriate time. Referring again to  FIG. 2   a , as the physician approaches the coronary sinus  103  the flow sensing wing will sense flow coming out of the coronary sinus  103 . The flow volume amplitude will typically have a signal that is periodic in nature somewhat like a sine wave. The blood flow data will indicate when the blood flow from the coronary sinus is at a maximum and a minimum. 
   In many patients, there is a valve that covers the opening of the coronary sinus or a portion of the coronary sinus. This valve is termed the Thebesian valve. The Thebesian valve is like a skin flap which covers the opening to the coronary sinus. The Thebesian valve can make entering the coronary sinus very difficult when a physician is using a normal guiding catheter. He or she has no way of knowing when this valve is open or closed. Currently, clinicians rely on the catheter shape alone to get them in an area that is close to the valve. However, the clinician then has to relying on luck to slide the wire or the catheter into the coronary sinus at the appropriate time. 
   The present inventive system allows, for the first time, the physician to know when the blood flow is at its maximum and therefore at which point the Thebesian valve is open. If timed properly, the physician is now able to time the forward motion of the guide wire so that it enters the coronary sinus at just the time point that the flow is at the maximum, corresponding to the time point when the valve is open. This feature of the present invention will further enable physicians to access the coronary sinus more easily and more quickly in almost any clinical application regardless of the patient anatomy. 
     FIG. 3A  shows the use of a normally shaped guiding catheter  100  with a special guide wire or a flow sensing guide wire  109  that has a retractable thin membrane wing  111 . The concept embodied in this device is that the clinician slides a guide wire  109  down the guiding catheter  100 . When the guide wire  109  comes out of the tip of the device, the guide wire  109  has a tip  110  (as shown in  FIG. 3B ). When pulled backward in the guide wire  109 , tip  110  (as shown in  FIG. 3B ) deploys retractable wing  111 . 
     FIG. 3B  shows an enlarged view of guide wire  109  from  FIG. 3A  in its initial position for feeding through the catheter. In this view, the structure is shown tip  110 . Strain sensing member  112  is also shown. 
     FIG. 3C  shows the guide wire  109  in the position with the wing  111  deployed. In this view, the guide wire tip  110  is pulled backwards towards the rest of the guide wire  109  in the direction of the arrow. In turn, guide wire  109  deploys thin membrane wing  111 . Thin membrane wing  111  is surrounded by, for instance, two pieces of wire that form the desired shape. 
     FIG. 3C  further shows the guide wire wing  111  and its shape. The guide wire wing  111  also has a strain sensing member (strain gauge)  112  attached. In this manner, when the guide wire  109  is deflected by flow, because of the wing  111 , the strain sensing member  112  senses strain. This strain data is transmitted back as an indication that the catheter  100  is aligned with the coronary sinus, as shown in  FIG. 3A . 
     FIGS. 4A and 4B  show the catheter  100  approaching the coronary sinus  103 . The inventive method embodiment is conveyed in these figures.  FIG. 4A  shows that as the catheter  100  approaches the coronary sinus  103 , the flow wing  102  senses a little bit of the flow and therefore the deflection will be minimal. In  FIG. 4   b , as the catheter  100  becomes more aligned with the coronary sinus  103 , the flow sensing wing  102  will deflect more. This greater deflection as conveyed to the clinician from data received from strain gauges  112  is used as an indication that the catheter is well aligned with the coronary sinus  103 . 
     FIG. 4C  shows one embodiment of a wing design with a strain gauge  112  attached to the wing  102  design. In this embodiment, a large surface area is created by providing a paddle-like wing design. The blood flow from the coronary sinus deflects the strain sensor as a result of the wing design. The thinner area of the paddle on which strain gauge  112  is positioned is most likely to bend from that coronary sinus blood flow. 
   Referring to  FIGS. 5A ,  5 B, and  5 C, these figures illustrate an additional design feature of the present invention for directing blood flow to optimize blood flow sensing. The feature is a catheter that is shaped in a manner that assists in the direction of blood flow. 
     FIG. 5A  shows an embodiment of the blood flow directing feature of the invention where the bottom lip  113  of the outer guide catheter  100  is extended so that the catheter  100  will catch and direct more of the blood flow towards the sensing wing  112 . This blood directing feature can be fabricated by providing an angled cut on the tubing. Alternately, a tongue may be placed in the tip of the catheter which would scoop or direct blood into the guide catheter and direct it towards the flow sensing wing  112 . Other device features to accomplish blood flow direction will be apparent to the skilled artisan. 
     FIG. 5B  shows an embodiment similar to that shown in  FIG. 5A  it with the side port  105  to allow blood to come in and go out of the catheter once it passes the flow sensing wing.  FIG. 5C  shows again the flow being directed into the catheter  100  and towards the flow sensing wing  112 . The blood flow will then come out of the catheter  100  just beyond the wing  112  arrows showing blood flow have been added for clarity. 
   The above described embodiments of the present invention, as well as those apparent to the skilled artisan, can be employed with a number of different types of strain sensing devices. With the present invention, how the strain is measured, or how the flow is measured is not critical. Rather, it is enough that measured flow is used to detect and locate the coronary sinus. Typical strain gauges could be used, such as a piezoelectric device, fiber optics, semi conductor strain gauges, and the like. An example providing such strain gauges is found in the provisional patent applications “Cardiac Motion Characterization by Strain Measurement” filed Dec. 17, 2004 by some of the present inventors, 60/638,247, hereby incorporated by reference in its entirety. 
   It is also important to note that with this particular device it may be valuable to include a pressure sensor at the tip of the device as well as the strain sensing device. The two devices in combination can be used to help begin the of the coronary sinus location process by measuring the local pressure within the right atrium. This pressure signal could also be used as a timing mechanism to time the introduction of a wire into the coronary sinus once it has been located by the coronary sinus location device of this invention. 
   Example 1 
   A prototype device similar to those show in  FIG. 2A  was constructed. In a water bath, a laminar flow of water was introduced from a tube to simulate flow from the coronary sinus. A periodic, moderate pulse in that liquid flow was provided. The prototype device was that directed in varying degrees towards this flow, simulating a catheter approaching the coronary sinus. 
   When the sensor was directed towards, but somewhat obliquely towards the coronary sinus flow, the pressure sensor provide a moderate pressure sensor reaction, such as shown in  FIG. 4A . As the simulated catheter more closely approached the fluid flow, the pressure sensor reaction was considerably increased, such as seen in  FIG. 4B . The data obtained during this prototype experiment is provided in  FIGS. 6A&amp;B .