Patent Application
20080039897
Like reference symbols in the various drawings indicate like elements.
The pressure sensing device, in some implementations, can be part a system 10 for measuring and monitoring endocardial pressure (e.g., LV pressure). An example of the overall system 10 is shown in
The system 10 also includes a physician (i.e., remote) data collection system (PDCS) 70 which can receive the data signal from the HDCS 60 via a telecommunication system 61 (e.g., the Internet). The PDCS 70 receives the data signal, evaluates the validity of the received signal and, if the received signal is deemed to be valid, displays the data, and stores the data according to a physician-defined protocol. With this information, the system 10 can enable the treating physician to monitor endocardial pressure in order to select and/or modify therapies for the patient to better treat diseases such as CHF and its underlying causes.
For example, the system 10 can be used for assessment of pressure changes (e.g., systolic, diastolic, and LV max dP/dt) in the main cardiac pumping chamber (the LV). These pressures are known to fluctuate with clinical status in CHF patients, and can provide key indicators for adjusting treatment regimens. For example, increases in end diastolic pressure, changes in the characteristics of pressure within the diastolic portion of the pressure waveform, and decreases in maximum dP/dt, or increases in minimum dP/dt together suggesting a deteriorating cardiac status. As used herein, LV max dP/dt can refer to the maximum rate of pressure development in the left ventricle. These measurements could be obtained either during clinic visits or from the patient at home, from the proposed device, and stored for physician review. The physician can then promptly adjust treatment. In addition, the system 10 can assist in management of patients when newer forms of device therapy (e.g., multiple-site pacing, ventricular assist as a bridge to recovery, or implantable drugs pumps) are being considered.
It can also be useful to automate or partially automate some level of interaction with the patient. For example, departures from prescribed limits or values for certain patient parameters can be noted automatically and brought to the attention of the physician or patient. The ability to automatically select deteriorating patients from the much larger pool of monitored patients may save a practitioner's time and improve patient care.
The system 10 can create an exception report on a daily basis to create a list of patients requiring special follow-up or care. More specifically, the system 10 can interact with the patient directly and request additional monitoring or compliance with a specific health care regime. The limits which trigger the exception report can be under the control of an attending physician.
More specifically, information received in the clinic by the PDCS 70 from the HDCS 60 can be evaluated and triaged for follow-up by a medical practitioner. Following evaluation of the information received in physician's office or clinic, the system 10 can create an exception report that lists patients to be contacted for follow-up. Patients at home can be monitored using the ITD 20 and HDCS 60 which transmit key information to the PDCS 70 for patient management to the physicians office or clinic. Information received by the PDCS 70 at the physicians office can be used to determine if the patient's status is satisfactory or whether an adjustment in diet or therapy is required in order to maintain the patient's health and to prevent worsening of status that may eventually lead to hospitalization. On a given day, only a small percentage of patients may present with a deteriorating condition and require follow-up by a health care practitioner. It therefore is advantageous to evaluate patient information automatically using an algorithm that identifies those patients that require follow-up and a potential change in therapy. Such an algorithm can identify patients that require follow-up by, for example, analyzing current data vs. preset limits determined by the physician (e.g. if LV EDP>15 mmHg, then trigger follow up), or analyzing the results of a mathematical model applied to a waveform or portion of a waveform such as the diastolic portion of the LV pressure signal.
Referring to
The TU 40 can include telemetry electronics (not visible) contained within housing 42. The TU housing 42 can protect the telemetry electronics from the harsh environment of the human body. The housing 42 can be fabricated of a suitable biocompatible material such as titanium or ceramic and can be hermetically sealed. The outer surface of the housing 42 can serve as an EGM sensing electrode. If a non-conductive material such as ceramic is used for the housing 42, conductive electrodes can be attached to the surface thereof to serve as EGM sensing electrodes. The housing 42 can be coupled to the lead 50 via a connector (not visible), and include an electrical feedthrough to facilitate connection of the telemetry electronics to the connector. The telemetry electronics disposed in the TU 40 can be the same or similar to those described in U.S. Pat. Nos. 4,846,191, 6,033,366, 6,296,615 or PCT Publication WO 00/16686, all to Brockway et al.
Still referring to
The housing 32 can be adapted for implantation into a heart wall (e.g., the ventricular septum 132). By implanting the housing 32 within a heart wall, the amount of volume taken up by the electronics module adjacent to a heart wall can be reduced. For example, by implanting the electronics module in the ventricular septum 132, this can reduce the amount of volume taken up by the implantable telemetry device within a ventricle (e.g., the right ventricle when positioning the PTC 34 within the left ventricle, as shown in
The housing 32 can be adapted to allow for tissue growth from a heart wall around and/or into the housing 32 to further anchor the housing 32 into the heart wall. For example, the housing 32 can have a tissue in-growth promoting surface. In some implementations, the outside of the housing can include pores. The pores can be sized to allow tissue surrounding the housing (e.g., tissue from the ventricular septum 132) to grow into the pores and anchor the housing 32. In some implementations, the housing 32 can include a coating 37 that promotes tissue growth to anchor the housing within a heart wall (e.g., the ventricular septum).
The coating 37 can be a thin-walled cover placed over housing 32. For example, coating 37 can include a thin-walled tube or sock (closed-ended) of open cell porous polymer. Coating 37 can promote tissue ingrowth (passivation) and reduce the risk of thromboemboli formation. For example, the controlled ingrowth of tissue into the ePTFE can also allow for an easier removal of the RSA 30 from the ventricular septum 132. For example, the coating 37 can include a thin walled tube of expanded fluoropolytetrafluoroethylene (ePTFE) or a woven tube of polyethylene terephthalate, (e.g., DACRON). A number of other materials can also be suitable for use in coating 37, for example fluoropolytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), polyvinylchloride (PVC), and/or polyurethane. A number of manufacturing processes can be used to create coating 37. For example, coating 37 can be woven from a plurality of fibers. By way of a second example, coating 37 can be formed from one or more sections of shrink tubing. The shrink tubing sections can be positioned and then shrunk by the application of heat.
Referring again to
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The PTC 34 transmits pressure from the pressure measurement site (e.g., LV) to the pressure transducer 31 located inside the sensor housing 32. The PTC 34 can include a tubular structure 22 including a proximal shaft portion and a distal shaft portion, with a liquid-filled lumen 24 extending therethrough to a distal opening or port 28. The PTC 34 can optionally include one or more EGM electrodes or other physiological sensors as described in U.S. Pat. No. 6,296,615 to Brockway et al.
The proximal end of the PTC 34 is connected to the pressure transducer 31 via a nipple tube 38, thus establishing a fluid path from the pressure transducer 31 to the distal end of the PTC 34. The proximal end of the PTC 34 can include an interlocking feature to secure the PTC 34 to the nipple tube of the pressure transducer 31. For example, the nipple tube 38 can have a knurled surface, raised rings or grooves, etc., and the proximal end of the PTC 34 can include an outer clamp, a silicone band, a spring coil or a shape memory metal (e.g., shape memory NiTi) ring to provide compression onto the nipple tube 38.
A barrier 26 such as a plug and/or membrane can be disposed in the port 28 to isolate the liquid-filled lumen 24 of the PTC 34 from bodily fluids, without impeding pressure transmission therethrough. If a gel (viscoelastic) plug 26 is utilized, one to several millimeters of a gel can be positioned into the port 28 at the distal end of the PTC 34. The gel plug 26 comes into contact with blood and transfers pressure changes in the blood allowing changes in blood pressure to be transmitted through the fluid-filled lumen 24 of the PTC 34 and measured by the pressure transducer 31. The gel plug 26 can be confined in the port 28 at the tip of the PTC 34 by the cohesive and adhesive properties of the gel and the interface with catheter materials. The chemistry of the gel plug 26 can be chosen to minimize the escape of the fluid in the remainder of the PTC 34 by permeating through the gel. In some embodiments, the fluid can be fluorinated silicone oil and the gel can be dimethyl silicone gel.
The gel plug 26 can have a high penetration value in order to inject the gel plug 26 into the port 28 at the tip of PTC 34, as well as to obtain accurate measurements. Penetration value is a measure of the “softness” of the gel by assessing the penetration of a weighted cone into the gel within a specified time. Also preferably, to meet in-vivo performance requirements for measuring blood pressure, the gel 26 can be soft enough to not induce hysteresis, but not so soft that significant washout occurs. Washout can also be reduced by choosing a gel that becomes fully cross-linked and has a low solubility fraction. Furthermore, a fully cross-linked gel can be very stable, and can thereby increase the usable life of the device. In some embodiments, the gel can also include a softener (e.g., dimethyl silicone oil). The gel plug 26 can be flush with the distal end of the PTC 34 or can be recessed (e.g., 0.5 mm) to shelter the gel plug 26 from physical contact and subsequent disruption that can occur during the procedure of insertion into the heart.
The pressure transmission fluid contained within the lumen 24 of the PTC 34 proximal of the barrier 26 can include a relatively low viscosity fluid and can be used to tune the frequency response of the PTC 34 by adjusting the viscosity of the transmission fluid. The pressure transmission fluid can include a relatively stable and heavy molecular weight fluid. The specific gravity of the transmission fluid can be low in order to minimize the effects of fluid head pressure that could result as the orientation of the PTC 34 changes relative to the sensor 31. The pressure transmission fluid can have minimal biological activity (in case of catheter or barrier failure), can have a low thermal coefficient of expansion, can be insoluble in barrier 26, can have a low specific gravity, can have a negligible rate of migration through the walls of PTC 34, and can have a low viscosity at body temperature. In some implementations, the pressure transmission fluid can incorporate end-group modifications (such as found in fluorinated silicone oil) to make the transmission fluid impermeable in the barrier material 26. In some implementations, the fluid can include a perfluorocarbon. Examples of suitable gels and transmission fluids can be found in U.S. Pat. No. 6,296,615 to Brockway et al.
Various other and specific embodiments of the PTC 34 can be found in U.S. Pat. Application No. 2005/0182330 A1 to Brockway et al. For example, the proximal and distal ends of the PTC 34 can be flared to have a larger inside diameter (ID) and outside diameter (OD), for different purposes. The distal end of the PTC 34 can be flared to provide a port 28 having a larger surface area as discussed above, and the proximal end of the PTC 34 can be flared to accommodate the nipple tube 38 and provide a compression fit thereon. The proximal flared portion can have an ID that is smaller than the nipple tube 38 to provide a compression fit that will be stable for the life of the RSA 30. The mid portion or stem of the PTC 34 can have a smaller ID/OD, with gradual transitions between the stem and the flared ends. The gradual transitions in diameter can provide gradual transitions in stiffness to thereby avoid stress concentration points, in addition to providing a more gradual funneling of the gel into the stem in the event of thermal retraction. The unitary construction of the PTC 34 can also provide a more robust and reliable construction than multiple piece constructions. Absent the gradual transitions, the PTC 34 can be more susceptible to stress concentration points, and the gel and the transmission fluid are more likely to become intermixed and can potentially dampen pressure transmission. By way of example, not limitation, the proximal flared portion can have an ID of 0.026 inches, an OD of 0.055 inches, and a length of about 7 mm. The stem (mid) portion can have an ID of 0.015 inches, and OD of 0.045 inches, and a length of about 7 mm. The distal flared portion can have an ID of 0.035 inches, an OD of 0.055 inches, and a length of about 4 to 5 mm. The proximal taper can have a length of about 0.5 mm and the distal taper can have a length of about 1.25 mm. The gel plug 26 can have a length of about 3 mm and resides in the distal flared portion. In some implementations, (e.g., where a relatively short PTC 34 is utilized) the fluid-filled lumen 24 of the PTC 34 can be completely filled with the barrier material 26 (e.g., gel). In combination with the gel plug 26, or in place thereof, a thin membrane can be disposed over the port 28.
The PTC 34 can have a length that provides adequate access across the heart wall (e.g., septum or myocardium) and into the heart chamber (e.g., LV) while being as short as possible to minimize head height effects associated with the fluid-filled lumen 24. The PTC 34 may be straight or may be curved, depending on the particular orientation of the RSA 30 relative to the heart wall and the chamber defined therein at the insertion point. The PTC 34 can have a length sufficient to allow the port 28 of the PTC 34 to reside within a chamber of the heart 100 without the heart wall tissue to propagate to overcoat the port 28. In some implementations, the PTC 34 can be between 1 cm and 2.5 cm in length (e.g., about 2 cm in length). As discussed above, coating 37 can also overlie a portion of the PTC 34 (e.g., the distal portion). In some implementations, the proximal portion of the PTC 34 can be ovennolded with silicone to provide stress relief, flex fatigue strength, and a compliance matching mechanism at the entrance to the myocardium.
To facilitate a discussion of the implantation process, it is helpful to define and label some of the anatomical features of the heart 100 shown in
The right atrium 108 receives oxygen deprived blood returning from the venous vasculature through the superior vena cava 116 and inferior vena cava 118. The right atrium 108 pumps blood into the right ventricle 104 through tricuspid valve 122. The right ventricle 104 pumps blood through the pulmonary valve and into the pulmonary artery which carries the blood to the lungs. After receiving oxygen in the lungs, the blood is returned to the left atrium 106 through the pulmonary veins. The left atrium 106 pumps oxygenated blood through the mitral valve and into the left ventricle 102. The oxygenated blood in the left ventricle 102 is then pumped through the aortic valve, into the aorta, and throughout the body via the arterial vasculature.
Referring to
The RSA 30 can be implanted by a number of techniques. For example, the RSA 30 can be implanted by an assembled introducing apparatus 80, including an introducer 82, a sheath 84 positioned within the introducer 82, and a needle 86 positioned within the sheath 84.
The introducing apparatus 80 can be guided to the RV 104 by a guidance scheme. For example, fluoroscopy can be used to help guide the introducing apparatus 80. The use of pressure measurements at the distal tip of the introducing apparatus can also help determine the location of the distal tip of the introducing apparatus 80 by monitoring the pressure changes (e.g., the RV 104, the ventricular septum 132). By monitoring changes in pressure at the tip of the introducing apparatus 80, the location of the tip can be determined. The use of fluoroscopy can further assist in determining the positioning of the tip of the introducing apparatus 80. The monitoring of pressure changes at the distal tip of the introducing apparatus 80 can also allow a user to confirm a location of a distal tip of the needle while extending the needle through the ventricular septum into the left ventricle during initial registration.
Furthermore, by monitoring the pressure changes detected by the RSA 30 during implantation, the location of the RSA 30 can be confirmed while inserting the RSA 30 through the interior of the sheath into the ventricular septum. Furthermore, pressure changes can also help to measure the width of the ventricular septum 132 and insure proper placement of the RSA 30 within the ventricular septum 132. For example, as the RSA 30 is introduced through the passage from the RV 104 into the LV 102, the PTC 34 can detect a pressure change of about 50 to 100 mmHg. This pressure change can indicate that port 28 of the PTC 34 is positioned within the LV 102. Fluoroscopy and device marking can also be used to confirm the depth and placement of the RSA within the ventricular septum 132.
The needle 86 can be a modified Brockenbrough needle. The needle 86 can have a smaller diameter than the housing 32 of the electronics module 33. The passage formed by the needle 86 can have a diameter smaller than the housing 32. Accordingly, the insertion of the RSA 30 though the passage can further stretch the passage and result in the final dilatation of the passage. By sizing the needle 86 to produce a passage having a smaller diameter than the housing 32, the implantation of the housing within the ventricular septum 132 can ensure a frictional anchoring of the housing 32 within the passage of the ventricular septum 132. Once the PTC 34 resides in the LV 102 and the housing 32 is frictionally anchored in the ventricular septum 132, the sheath 84 and the introducer 82 can be removed without dislodging the RSA 30.
The RSA 30 can also allow for easier removal of the RSA 30 from within the ventricular septum 132. The presence of the coating, e.g., ePTFE, on the outside of the housing 32 can allow for a controlled ingrowth of tissue such that the tissue surrounding the RSA 30 still allows for removal of the RSA 30 without causing significant damage to the ventricular septum 132. Furthermore, the shape of the RSA 30 can allow for the RSA 30 to slip out of the passage formed through the ventricular septum 132. Furthermore, in some implementations, the RSA 30 can be free of anchoring devices that would prevent the RSA 30 from being able to slip out of the passage, such as spikes that would lock the RSA 30 into the ventricular septum 132 or self-expanding portions that would expand in the left ventricle (LV) to lock the RSA 30 into the heart. The use of spikes or self-expanding portions could require the use of invasive heart surgery to remove the RSA 30 from the heart.
The entire disclosure of all patents and patent applications mentioned in this document are hereby incorporated by reference herein.
A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of this disclosure. For example, the electrical lead 50 can, in some implementations, be connected directly to a device outside of the body rather than to an internally implanted telemetry unit (TU) 40. Accordingly, other embodiments are within the scope of the following claims.
The present application claims the benefit of U.S. Provisional Patent Application No. 60/837,352, filed Aug. 10, 2006, the entire disclosure of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60837352 | Aug 2006 | US |
