Abstract:
Devices and methods for detecting inadequate tissue perfusion by measuring a parameter other than heart rate such as vascular blood pressure, intracardiac blood pressure, vascular blood flow or tissue perfusion, in addition to or as a substitute for heart rate. Such devices and methods improve the accuracy of determining when and to what degree therapy should be administered to treat inadequate tissue perfusion, such as pre-syncope, syncope, or orthostatic hypotension, particularly in the absence of abnormal cardiac function.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     The present application claims benefit under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 60/454,951, filed Mar. 12, 2003, which is incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention generally relates to devices used in the treatment of inadequate tissue perfusion. In particular, the present invention relates to devices and methods for improving the detection and analysis of episodes of inadequate tissue perfusion to enable more effective therapy. 
     In certain disease states, including, but not limited to, pre-syncope, syncope, and orthostatic hypotension, the cardiovascular system does not adequately respond to decreases in intravascular pressure. Low intravascular pressure results in under-perfusion of body tissues, particularly upper body tissues such as the brain. In a significant number of these cases, a demonstrable cardiac arrhythmia is not present but the integrated cardiovascular response is inadequate to correct the hypotensive episode. 
     Unfortunately, devices used to treat patients with this malady, such as pacemakers or infusion pumps, often do not perform adequately. These devices conventionally rely on ECG and/or electrogram as a means to effect the control of the delivery of a therapy. For example, when the patient&#39;s heart rate, as detected from ECG and/or electrogram, falls below a predetermined level, a pacemaker delivers electrical stimuli to the heart to increase the heart rate. The efficacy of this approach is limited to pathophysiologic circumstances in which reductions in tissue perfusion occur at the same time as and to the same degree as reductions in heart rate. If the pathologic drop in tissue perfusion occurs in the presence of a normal cardiac rhythm and rate, the use of ECG and/or electrogram is inadequate as means of determining when and to what degree therapy should be delivered. 
     BRIEF SUMMARY OF THE INVENTION 
     To address this problem, the present invention provides, in exemplary non-limiting embodiments, devices and methods for detecting inadequate tissue perfusion by measuring a parameter other than heart rate. For example, by measuring peripheral vascular blood pressure, intracardiac blood pressure, vascular blood flow or tissue perfusion in addition to or as a substitute for heart rate as measured by ECG or electrogram, the present invention improves the accuracy of determining when and to what degree therapy should be administered to treat inadequate tissue perfusion. The present invention also provides devices and methods to detect in real time any discrepancy between hemodynamic status and cardiac response, and to then direct interventions appropriately. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic flow chart illustrating the basic steps involved in a method of detecting and providing therapy for inadequate tissue perfusion, according to an exemplary non-limiting embodiment of the present invention. 
         FIG. 2  is a schematic illustration of a system including an implantable pressure sensing device and a pacemaker. 
         FIG. 3  is a schematic illustration of an alternative implantable pressure sensing device. 
         FIG. 4  is a schematic illustration of a pressure sensing device and a pacemaker shown implanted in a patient. 
         FIG. 5  is a schematic illustration of a flow sensing device that may be used in place of the pressure sensing device. 
         FIG. 6  is a schematic illustration of a flow sensing device and a pacemaker shown implanted in a patient. 
         FIG. 7  is a schematic illustration of a tissue perfusion monitor that may be used in place of the pressure sensing device. 
         FIG. 8  is a schematic illustration of a tissue perfusion monitor and a pacemaker shown implanted in a patient. 
         FIG. 9  is a schematic illustration of a system including an implantable pacemaker and an implantable pressure sensing device. 
         FIG. 10  is a schematic illustration of a pressure sensing device with an anchoring electrode shown implanted across a patient&#39;s atrial septal wall. 
         FIG. 11  is a schematic illustration of a pressure sensing device with an anchoring electrode shown implanted across a wall of a patient&#39;s blood vessel. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description should be read with reference to the drawings in which similar elements in different drawings are numbered the same. The drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the invention. 
     Generic Description of Methods 
     With reference to  FIG. 1 , a method  1000  of detecting and providing therapy for inadequate tissue perfusion is shown schematically. Those skilled in the art will recognize that this method  1000  is illustrative of general concepts according to an exemplary non-limiting embodiment of the present invention for detecting and providing therapy for conditions of inadequate tissue perfusion such as pre-syncope, syncope, and orthostatic hypotension. 
     In this illustrative method  1000 , one or more indicia (X) of inadequate tissue perfusion are measured  1002  to supplement or replace heart rate (HR) measurements  1004  normally taken by ECG or electrogram. The ECG or electrogram measurement  1004  may be obtained using conventional techniques such as utilizing feedback electrodes disposed on a pacemaker implanted to treat the underlying hypotensive condition. Conventionally, the HR measurements are compared  1006  to a threshold value (Z), that may be preset, for example, by the treating physician in order to detect an incidence of hypotension. Based on this comparison, which may be manifested by an algorithm contained in the therapeutic device (e.g., pacemaker or drug infusion pump), for example, a decision or directive  1008  may be made to deliver therapy  1010  if the HR falls below the threshold value (Z). If the HR exceeds the threshold value (Z), a decision or directive  1008  may be made to not deliver therapy, but rather to continue sampling HR measurements  1004 . 
     However, because hypotension or inadequate tissue perfusion may manifest in a patient without a drop in HR, it is beneficial to measure  1002  one or more indicia (X) of hypotension or inadequate tissue perfusion. The one or more indicia (X) may be compared  1012  to a threshold value (Y), and the comparison  1012  may be made by an algorithm executed by the therapeutic device (e.g., pacemaker or drug infusion pump). Based on the comparison  1012 , a decision or directive  1014  may be made to deliver therapy  1010  if the indicia (X) falls below the threshold value (Y). If the indicia (X) exceeds the threshold value (Y), a decision or directive  1014  is made to not deliver therapy, but rather to continue taking measurements  1002  of the indicia (X). 
     The other indicia (X) may comprise, for example, peripheral vascular blood pressure, intracardiac blood pressure, vascular blood flow or tissue perfusion. Any one or a combination of these indicia (X) may be measured in addition to or as a substitute for heart rate as measured by ECG or electrogram. The indicia may be measured by a separate device or by incorporating measurement capabilities in the therapeutic device. The interpretation, analysis and decision making functions may be carried out by an algorithm executed by suitable electronics in the therapeutic device. 
     The following detailed description starts with a description of exemplary methods to measure such indicia (X), followed by a description of exemplary measurement devices for measuring the associated indicia (X). 
     Description of Vascular and Cardiac Pressure Sensing Methods 
     One of the alternative indicia (X) may comprise, without limitation, vascular or cardiac blood pressure. An example of a pressure sensing device (PSD)  10  for measuring peripheral vascular blood pressure is described with reference to  FIGS. 2 ,  3  and  4 . An example of pressure sensing device  400  for measuring intracardiac blood pressure is described with reference to  FIGS. 9 and 10 . Alternative pressure measuring devices may also be employed, such as an intravascular stent or a vascular cuff with pressure measurement capabilities. 
     In this method, heart rate data obtained by ECG and/or electrogram may be simultaneously sensed and interpreted as pressure sensor data obtained by a pressure measurement device (e.g., device  10  or  400 ) to measure pressure in an artery or within the heart. The therapeutic device (e.g., a pacemaker or drug infusion pump) may evaluate the pressure sensed by the pressure measurement device on an ongoing basis, and may create a baseline or reference pressure that is the average of the pressures measured over a designated time period (e.g., 30 seconds). If the current pressure has dropped more than a predesignated amount below the reference pressure, the therapeutic device begins to deliver stimuli (e.g., electrical pulse series from a pacemaker or a bolus of drug from an infusion pump) to the heart to increase heart rate by a predetermined (programmable) amount. If the pressure does not return to within a predesignated range of the original reference value, the therapeutic device delivers further stimuli to increase heart rate. During the delivery of therapeutic stimulus, the pressure measurement device may periodically sample blood pressure and the therapeutic device may re-evaluate the pressure relative to the reference pressure. If pressure has returned to within an acceptable range of the reference pressure, the therapeutic device may begin a sequence whereby the stimulus is decreased and heart rate is gradually returned to a normal value. If the heart rate reaches a preset upper limit, stimulus delivery may be terminated, even if the measured pressure is below the acceptable target range. 
     Those skilled in the art will recognize that the reference pressure may or may not be adjusted for barometric pressure variations. The use of a reference pressure without barometric correction (as opposed to a control algorithm that employs an absolute pressure) obviates the need to employ a barometric pressure reference for correction of the intravascular or endocardial pressure measurements. This is valuable in that the need for a barometric pressure monitor adds complexity and cost to the system and may also require patient compliance, depending on how the barometric correction were implemented. 
     Description of Vascular Flow Sensing Method 
     One of the alternative indicia (X) may comprise, without limitation, vascular or cardiac blood flow. An example of a flow sensing device (FSD)  210  for measuring peripheral vascular blood flow is described with reference to  FIGS. 5 and 6 . Alternative devices for measuring blood flow may also be employed. 
     With blood flow measurements, the functional control of the stimulus delivery from the therapeutic device may be the same or similar as described with regard to blood pressure measurements. In other words, the delivery of stimulus may be triggered, maintained and/or shut-off using pre-programmed thresholds and ranges of blood flow similar to that which has been described previously for blood pressure. 
     With the flow sensing device, it may be beneficial for noise reduction purposes that the flow signal be integrated over a programmable number of complete cardiac cycles (e.g., 2 or 3 cycles). The integrated signal, referred to herein as the current flow value (CFV), may be compared to a baseline value comprising a running average of CFVs occurring over a programmed period of time. For example, CFVs that fall within a time interval (e.g., 30 second to 10 minute) prior to the current measurement may be used to create a baseline value of flow. The computed baseline value may serve as a reference value and current CFV may be compared to the reference value in a manner as described previously to detect changes in flow indicative of a need to modify heart rate with the therapeutic device. 
     Description of Tissue Perfusion Method 
     One of the alternative indicia (X) may comprise, without limitation, tissue perfusion. An example of a tissue perfusion monitor  310  (TPM) is described with reference to  FIGS. 7 and 8 . Alternative tissue perfusion measurement devices may also be utilized. 
     With tissue perfusion measurements, the functional control of the stimulus delivery from the therapeutic device may be the same or similar as described with regard to blood pressure measurements. In other words, the delivery of stimulus may be triggered, maintained and/or shut-off using pre-programmed thresholds and ranges of tissue perfusion similar to that which has been described previously for blood pressure. 
     A reference value for tissue perfusion may be obtained over a programmable period of time (e.g., 30 seconds to 10 minutes) to compute a running average. The computed running average, which may be periodically update, may serve as a reference value and current perfusion measurements may be compared to the reference value in a manner as described previously to detect changes in tissue perfusion indicative of a need to modify heart rate with the therapeutic device. 
     Description of Vascular Pressure Sensing Device 
     With reference to  FIG. 2 , an implantable pressure sensing device (PSD)  10  and an implantable therapeutic device (ITD)  60  are shown. By way of example, not limitation, the ITD  60  is shown in the form of a pacemaker. The ITD  60  may comprise other therapeutic devices that increase heart rate, such as a drug infusion pump or a pacemaker. The following disclosure is given with specific reference to pacemaker, but is understood to be equally applicable to other ITDs. 
     The PSD  10  is connected to the pacemaker  60  by an electrical lead  30 . PSD  10  measures blood pressure and generates an electrical pressure signal which is transmitted in analog or digital form to the pacemaker  60  via lead  30 . The lead  30  is preferably flexible, and may be similar to conventional pacing leads. A releasable connector  40  may be provided on the pacemaker  60  to facilitate easy connection and disconnection of the lead  30 . This provides the physician with flexibility during placement of the lead  30  and PSD  10  as well as replacement of the PSD  10  at a later time should it fail or when the battery depletes. 
     The pacemaker  60  may otherwise be substantially conventional, with the exception of suitable signal processing electronics to receive and analyze (e.g., by a suitable algorithm) the pressure signal generated by the PSD  10 . The pacemaker  60  may utilize a conventional endocardial lead  70  with a distal endocardial electrode  80  (as shown) to deliver the desired therapeutic electrical stimulus. Alternatively, subcutaneous (i.e., non-endocardial) electrodes may be used, such as those described in U.S. Patent Application Publication No. 2002/0107559 to Sanders et al., assigned to Cameron Health, the entire disclosure of which is incorporated herein by reference. 
     The PSD  10  includes a hermetically sealed housing  12  containing a pressure transducer  14  that converts fluidic pressure measurements or signals into electrical signals. The transducer  14  may be directly coupled by a plurality of wires  16  to lead  30  which transmits the electrical signals to the pacemaker  60 , which provides the necessary signal processing and power supply functions. Alternatively, as seen in  FIG. 2 , the PSD  10  may provide these functions by containing within housing  12  an electronics module  13  and battery  15  for signal processing and power functions, respectively. These features are described in more detail in U.S. Pat. No. 6,033,366, to Brockway et al., the entire disclosure of which is incorporated herein by reference. 
     The PSD  10  also includes a pressure transmission catheter  20 . The PTC  20  has a proximal end connected to the housing  12  and a distal end sized for insertion into a vascular lumen. The PTC  20  also includes a lumen in fluid communication with the pressure transducer contained in the housing  12 . The lumen of the PTC  20  may be filled with a viscous fluid  22 , with a distally disposed barrier  24  (e.g., gel plug or ePTFE membrane) that readily transmits pressure signals, but otherwise retains the fluid in the lumen of the PTC  20 . Further aspects of the PTC  20  are disclosed in U.S. Pat. No. 4,846,191 to Brockway et al., the entire disclosure of which is incorporated herein by reference. 
     A significant benefit of the PTC  20  for measurement of pressure in a vascular lumen is that the size of the PTC  20  may be quite small. For example, the PTC  20  may be approximately 0.5 mm–1.5 mm diameter, which is substantially smaller than the 3.5 mm diameter pressure-sensing catheter used on the Chronicle™ device. In addition to a much smaller diameter, the portion of the PTC  20  that is inserted into the artery to assure a stable placement and obtain accurate pressure measurements is only about 5 mm to 10 mm, thus allowing the PTC  20  to be relatively short. One benefit of small size is that there is a much lower surface area of the sensor exposed to the blood. The smaller the surface area (all other factors such as material properties being equal) the lesser the risk of thrombo-embolism. A further benefit of smaller size is that the risk of hematoma is reduced (a small puncture in the vessel wall is more likely to seal tightly than is a larger hole). The smaller and lighter PSD  10  is more easily inserted (a small introducer can be used that results in significantly less bleeding during insertion and the need for extended application of pressure to stop bleed after introduction is greatly reduced), and is less likely to damage the endothelial surface (because lower mass and size is less likely to cause trauma if it bumps into the vessel wall as a result of blood flow eddies and changes in patient posture). 
     The PSD  10  and/or the pacemaker  60  may optionally include ECG electrodes for measuring heart rate and other electrophysiological parameters associated with cardiac function. For example, electrodes may be incorporated on the housing of the pacemaker  60 , on the electrode lead  70  of the pacemaker  60 , on the interconnect lead  30  between the PSD  10  and pacemaker  60 , on the housing  12  of the PSD  10 , and/or on the PTC  20  of the PSD  10 . Such ECG electrodes may be electrically coupled to the signal processing circuitry of the pacemaker  60 . 
     With reference to  FIG. 3 , the PSD  10  and the pacemaker  60  are shown implanted in a patient  100 . The pacemaker  60  may be implanted in any of a number of conventional manners, such as with the lead  70  extending endocardially through the superior vena cava  112 , through the right atrium  114 , with the electrode  80  residing in the right ventricle  116  as shown. Alternatively, the electrode may reside in the right atrium  114 , the coronary sinus, etc. As mentioned before, non-endocardial electrode placement may also be used, such as subcutaneous placement. 
     The PSD  10  is implanted in the patient  100  with at least the distal end of the PTC  20  disposed in a vascular lumen, such as the subclavian artery  1118 , while the housing  12  of the PSD  10  remains outside the subject vascular lumen. The relatively small diameter and short length of the PTC  20  has minimal impact on blood flow. Arterial placement of the PTC  20  may be preferred over venous placement since the superior vena cava  112  already contains lead  70 , and additional obstructions may compromise blood flow. 
     Although the PTC  20  is shown disposed in the subclavian artery  118 , those skilled in the art will recognize that other non-endocardial or peripheral vascular sites are also possible, such as the pulmonary artery, brachial artery or the femoral artery, for example. Furthermore, although the PSD  10  provides significant benefit for detecting hypotension when used to measure pressures in non-endocardial sites (e.g., peripheral artery), the PSD  10  may also be effectively used in this application for measuring endocardial pressure in any chamber of the heart  110 . An example of this latter approach is described with reference to  FIGS. 9 and 10 . 
     To determine if the patient is experiencing hypotension, the signal processing circuitry of the pacemaker  60  evaluates the pressure signal generated by the PSD  10 , either alone or in combination with an ECG signal. Signal processing circuitry known to those skilled in the art may be used to detect hypotension as a trigger for stimulus. A function (e.g., algorithm) for both the pressure and ECG signals may be used to indicate the likelihood that a hypotensive episode requiring stimulus is occurring in the patient  100 . 
     Description of Vascular Flow Sensing Device 
     With reference to  FIGS. 5 and 6 , a flow sensing device (FSD)  200  may be used in place of the PSD  10  described with reference to  FIGS. 2 ,  3  and  4 . In this alternative embodiment, the FSD  200  measures blood flow rate and generates an electrical flow signal which is transmitted in analog or digital form to the pacemaker  60  via lead  30 . The flow measurement signal is indicative of inadequate tissue perfusion and the need to deliver stimulus with pacemaker  60 . 
     FSD  200  includes a transducer cuff assembly  210  and an electronics assembly  220 . Cuff assembly  210  includes a housing  212  sized and shaped to fit around a blood vessel, such as subclavian artery  118 . Cuff housing  212  may be formed of a flexible polymer or rubber such as silicone rubber. Alternatively, cuff housing  212  may be formed of a more rigid moldable biocompatible polymer, for example, and may available in different sizes to accommodate vessels of different diameters. An example of a suitable cuff design is disclosed in U.S. Patent Application Publication No. 2002/0072731 to Doten et al., the entire disclosure of which is incorporated by reference. 
     A plurality of transducers  214  are disposed in the housing  212  at diametrically opposite positions so as to direct ultrasound at the vessel at a 45 degree angle, for example, to facilitate flow measurement within the vascular lumen. The transducers  214  may be ultrasonic transducers, for example, and blood flow may be measured by continuous wave Doppler, pulsed Doppler, or transit time techniques, for example. Other flow measurement techniques such as thermal dilution may be used as well. The transducers  214  of the cuff assembly  210  may be connected to a separate electronics assembly  220  by lead  218 . Electronics assembly  220  includes a hermetically sealed housing  222  containing a suitable signal processing circuit  224  and battery power source  226 . An example of a suitable transducer arrangement and electronics assembly is described in U.S. Pat. No. 5,865,749 to Doten et al., the entire disclosure of which is incorporated herein by reference. 
     It may be beneficial to employ a pulsed Doppler technique to allow for flow to be measured using very low power by positioning a single Doppler flow crystal on the outer surface of the artery or vein. Such Doppler flow “cuffs” are available commercially from Crystal Biotech (Hopkinton, Mass.) and by Prof. Craig Hartley (Baylor School of Medicine, Houston, Tex.). Such a cuff could be located on many different arteries and veins located under the skin or within the body, but the subclavian artery or vein would be a good choice. Optionally, the Doppler flow crystal may be incorporated into the pacing lead  70 , or into a flexible lead designed specifically for that purpose, such as those commercially available from Millar Instruments (Houston, Tex.). Such a lead may plug directly into the header of the pacemaker via a connector similar to an IS1 connector. 
     Description of Tissue Perfusion Monitor 
     With reference to  FIGS. 7 and 8 , a tissue perfusion monitor (TPM)  310  may be used in place of the PSD  10  described previously. In this alternative embodiment, the TPM  310  measures blood perfusion in bodily tissue and generates a blood perfusion signal which is transmitted in analog or digital form to the pacemaker  60  via lead  30 . The degree of tissue perfusion as measured by TPM  310  may be used in a manner similar to how hemodynamic measurements can be used to provide a more effective therapy, either alone or in combination with other information such as ECG and pressure. 
     The TPM  310  may utilize, for example, laser Doppler techniques to measure blood perfusion in tissue. The laser Doppler flow sensor reflects laser light off bodily tissue and the return signal is indicative of the movement of blood through capillaries contained in the tissue. The sensor may be incorporated into the therapeutic device  60  (e.g., implantable housing or electrode lead) or may comprise a separate device  310  as shown. The sensor may be located in an area where changes in tissue perfusion would not be induced by everyday activities such as pressure applied to an area of the skin. In order to maintain current drain of the sensor at a sufficient low level, it may be beneficial to duty cycle the sensor such that it takes measurements at regular intervals, between which the current drain of the electronics is reduced to a minimum. 
     As seen in  FIG. 7 , the TPM  310  includes a hermetically sealed housing  312  containing a source of coherent light (e.g., laser)  316  and one or more photodetectors  318  with associated collecting lenses  314  which interface with the tissue to be monitored. For purposes of the clinical applications discussed herein, any well vascularized tissue may be monitored at a convenient in-vivo site such as adjacent the pacemaker  60  as shown in  FIG. 8 . The photodetectors  318  are connected to suitable signal processing circuitry  322  powered by battery  320 . Examples of suitable laser Doppler componentry may be found in U.S. Pat. No. 6,259,936 to Boggett et al. and European Patent Application No. 0282210A1 to Fujii. 
     A benefit of the TPM  310  is that it does not require insertion into an artery or cardiac chamber. Another benefit is that the TPM  310  may be incorporated as an integral part of the pacemaker  60 , with the lenses extending through the housing and the light emitter/detector and electronics disposed inside the housing, thus eliminating the need for additional leads. This would have particular benefit for use with subcutaneously implanted defibrillators, since it is an objective of such devices to eliminate the use of any leads. 
     Description of Intracardiac Pressure Sensing Device 
     With reference to  FIGS. 9 and 10 , a combined pressure sensing and electrode device (PSED)  400  is shown. The PSED  400  generally includes a PSD  10  as described previously, in addition to an anchoring electrode  410 , which facilitates both as a stimulus electrode for pacing purposes, and as an anchor to hold the PSD  10  to the atrial septal wall  115 , for example, with the PTC  20  extending across the septal wall  115  and into the left atrium  117 . The PSED  400  in conjunction with the pacemaker  60  allows for both the delivery of therapeutic stimulus (e.g., pacing) via electrode  410  to the intra-atrial septum  115  and the measurement of pressure in the left atrium  117  for feedback and triggering purposes, for example. 
     Those skilled in the art will recognize that the PSED  400  may be positioned such that the PSD  10  resides inside or outside the heart and the distal end of the PTC  20  resides in any desired chamber of the heart  110 . For example, the PTC  20  may be positioned across the left ventricular lateral wall such that the distal end of the PTC  20  is disposed in the left ventricle and the PSD  10  is mounted to the epicardial surface of the left ventricular lateral wall. As an alternative, the PTC  20  may be positioned across the right ventricular lateral wall such that the distal end of the PTC  20  is disposed in the right ventricle and the PSD  10  is mounted to the epicardial surface of the right ventricular lateral wall. As a further alternative, the PTC  20  may be positioned across the atrial septal wall or the ventricular septal wall such that the distal end of the PTC  20  is disposed in the left or right atrium or the left or right ventricle, respectively, with the PSD mounted to the opposite side of the septal wall. 
     The PSED  400  may be implanted as shown in  FIG. 10  by using conventional atrial pacing procedure to position the PSED  400  in the right atrium  114 . The PTC  20  may be disposed across the atrial septal wall  115  by using trans-septal approach similar to that which is used to deliver electrophysiology catheters in the left atrium  1117 . For example, using fluoroscopic visualization, a guide wire or needle may be used to puncture the septal wall  115 , and radiopaque dye may be injected to confirm complete puncture and placement. A dilator and sheath may be advanced over the guide wire to access the left atrium  117 . The PSED  400  may then be advanced through the sheath and/or along the guide wire (with the use of a guide wire lumen on the side of the PSED  400 ), until the PTC  20  extends across the punctured septum  115 . The PSED  400  may then be rotated (for a corkscrew-type anchor) or pushed (for a barb-type anchor) to secure the PSED  400  to the septal wall  115 . 
     In this alternative embodiment, the PSED  400  measures blood pressure in the left atrium and generates an electrical pressure signal which is transmitted in analog or digital form to the pacemaker  60  via lead  30 . 
     From the foregoing, it will be apparent to those skilled in the art that the present invention provides, in exemplary no-limiting embodiments, implantable devices that measure vascular pressure, vascular blood flow, tissue perfusion, and/or intracardial pressure, and provide feedback directly to a therapeutic device to improve detection and treatment of inadequate tissue perfusion. For instance,  FIG. 11  shows a sensor  500  which includes a transducer  514  and a catheter  520 , wherein the catheter  520  extends through a wall  530  and inside a lumen of the blood vessel  540  and the transducer  514  resides outside the blood vessel  540 . Further, those skilled in the art will recognize that the present invention may be manifested in a variety of forms other than the specific embodiments described and contemplated herein. Accordingly, departures in form and detail may be made without departing from the scope and spirit of the present invention as described in the appended claims.