Abstract:
An adaptor for endovascular electrocardiography includes a member having two ends and an inner lumen such that when one of the ends is connected to a catheter and the other end is connected to a syringe, fluid from the syringe is flushed into the catheter through the inner lumen. The adaptor also includes a metal insert, disposed along the inner lumen of the member, which connects through a sealed electrical connection to the outer side of the member.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 61/213,474, filed on Jun. 12, 2009, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a endovascular device positioning. Specifically, the present invention relates to a method for positioning the tip of an endovascular device, such as a central venous catheter, in and around the heart using electrocardiogram (ECG) signals. 
     BACKGROUND OF THE INVENTION 
     The electrical conduction system of the heart creates specific electrical signals, electrical energy distributions and behaviors thereof which are indicative of specific locations in the thoracic cavity and/or of specific heart functions or conditions. When measured endovascularly, i.e., from within blood vessels or from within the heart, certain parameters of the electrical activity of the heart can be used to identify specific locations in the cardiovascular system and/or functional conditions, normal or abnormal. Moreover, by locally and accurately identifying the location and the type of condition, therapy of such conditions can be optimized and the effect of the therapy monitored in real-time. 
     Two types of clinical applications are typically addressed. The first is related to guiding endovascular devices through the cardiovascular system, while the second is related to the non-invasive or the minimally invasive remote monitoring of the electrical activity of the heart. 
     The guidance, positioning, and placement confirmation of endovascular catheters are necessary in a number of clinical applications, such as, for example:
         1. Central venous access, e.g., CVC, PICC, implantable ports;   2. Hemodialysis catheters;   3. Placement of pacemaker leads;   4. Hemodynamics monitoring catheters, e.g., Swan-Ganz and central pressure monitoring catheters; and   5. Guiding guidewires and catheters into the left heart.       

     The location of the catheter tip is very important to the patient safety, the duration and the success of the procedure. Today&#39;s golden standard for confirming the target location of the catheter tip is the chest X-ray. In addition, there are currently two types of real-time guiding products available on the market, which try to overcome the limitations of chest X-ray confirmation: electromagnetic and ECG-based. In hospitals where real-time guidance is used results have improved in terms of reducing the number of X-rays, the procedure time, and the cost of the procedure. Under real-time guidance first-time success rate has typically increased from 75%-80% to 90%-95%. In addition, in hospitals where ECG guidance is used, e.g., in Italy, Belgium, Germany, chest X-ray confirmation has been eliminated for more than 90% of the patients. Electromagnetic systems are used mostly in the United States while ECG-based systems are used mostly in Europe. Amongst other factors which determine the difference between the markets in the United States and Europe in terms of technology adoption: a) type of health care personnel allowed to perform procedures: nurses have more flexibility in the United States, b) type of devices placed: PICCs are placed more and more often in the United States, c) price sensitivity: the European market seems to be more price sensitive, and d) the current guiding devices are commercialized by specific manufacturers to work exclusively with their catheters: market penetration of the guiding systems reflects the market penetration of the catheter manufacturer. 
     It was also found that different opinions exist regarding where the target tip location should be: for example, lower third of the SVC or RA. Therefore guiding technologies should allow for discrimination of these locations. The chest X-ray, which is the current golden standard does not always allow for such discrimination requiring an accuracy of typically better than 2 cm. Also, because ECG-based systems make use of physiological information related to the heart activity, their ability to guide placement is accurate with respect to the anatomy. This is not the case with electromagnetic guiding systems which measure the distance between the catheter tip in the vasculature and an external reference placed typically on the patient&#39;s chest. Because of this aspect, ECG-based systems can be used to document the final result of the catheter placement potentially replacing the chest X-ray as the golden standard. 
     One of the most valuable diagnostic tools available, the ECG records the heart&#39;s electrical activity as waveforms. By interpreting these waveforms, one can identify rhythm disturbances, conduction abnormalities, and electrolyte imbalance. An ECG aids in diagnosing and monitoring such conditions as acute coronary syndromes and pericarditis. The heart&#39;s electrical activity produces currents that radiate through the surrounding tissue to the skin. When electrodes are attached to the skin, they sense these electrical currents and transmit them the electrocardiograph. Because the electrical currents from the heart radiate to the skin in many directions, electrodes are placed at different locations on the skin to obtain a total picture of the heart&#39;s electrical activity. The electrodes are then connected to an electrocardiograph device, or computer, and record information from different perspectives, which are called leads and planes. A lead provides a view of the heart&#39;s electrical activity between two points or poles. A plane is a cross section of the heart which provides a different view of the heart&#39;s electrical activity. Currently, the interpretation of an ECG waveform is based on identifying waveform component amplitudes, analyzing and then comparing the amplitudes with certain standards. Modifications of these amplitude components are indicative of certain conditions, e.g., the elevation of the ST segment or of certain locations in the heart, e.g., the amplitude of the P-wave. In today&#39;s practice ECG monitors are widely used to record ECG waveforms. More and more often applications are made available for automatic identification of the ECG amplitude components. In certain cases tools are available for decision making support and for automatic interpretation of ECG amplitude components with respect to underlying heart conditions. 
     Remote patient monitoring is a well established medical field. Still remote monitoring of heart conditions is not as widely accepted as it would be need and possible. One of the reasons is related to the relatively complicated way of acquiring signals related to the heart activity, in particular ECG signals. Another important limiting factor of the current remote monitoring technologies is the use of communications channels, like the telephone line, which are difficult to interface with at both the patient and the physician ends. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention advantageously provide computer-based methods for positioning the tip of an endovascular device, such as a central venous catheter, in and around the heart using electrocardiogram (ECG) signals. 
     According to one embodiment of the present invention, a computer-based method for positioning an endovascular device in or near the heart using electrocardiogram (ECG) signals is provided. This computer-based method includes receiving an endovascular ECG signal, associated with an endovascular device, including a plurality of waveforms, each waveform having at least a P-wave component, processing the endovascular ECG signal, over a plurality of predetermined time periods, to calculate a P-wave amplitude and a spectral power for each predetermined time period, determining a maximum P-wave amplitude from the plurality of P-wave amplitudes, and an associated maximum spectral power from the plurality of spectral powers, associating the maximum P-wave amplitude and the maximum spectral power with a predetermined location in or near the heart, calculating a location of the endovascular device, for each predetermined time period, based on a ratio of the P-wave amplitude to the maximum P-wave amplitude and a ratio of the spectral power to the maximum spectral power, and displaying the location of the endovascular device to a user. 
     According to a further embodiment of the present invention, the embodiment described above is adapted to simultaneously receive a skin ECG signal, associated with a skin ECG lead, including a plurality of waveforms, each waveform having at least a P-wave component, process the skin ECG signal, over the plurality of predetermined time periods, to calculate a skin P-wave amplitude and a skin spectral power for each predetermined time period, determine a maximum skin P-wave amplitude from the plurality of skin P-wave amplitudes, and an associated maximum skin spectral power from the plurality of skin spectral powers, associate the maximum skin P-wave amplitude and the maximum skin spectral power with the predetermined location in or near the heart, and calculate the location of the endovascular device, for each predetermined time period, based on a ratio of the endovascular P-wave amplitude to the maximum skin P-wave amplitude and a ratio of the endovascular spectral power to the maximum skin spectral power. 
     There has thus been outlined, rather broadly, certain embodiments of the invention in order that the detailed description thereof herein may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional embodiments of the invention that will be described below and which will form the subject matter of the claims appended hereto. 
     In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting. 
     As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram that depicts an apparatus according to an embodiment of the present invention. 
         FIGS. 2A, 2B and 2C  depict various endovascular adaptor devices. 
         FIG. 3  is a block diagram of an electronic module for acquisition and processing of endovascular electrocardiogram according to an embodiment of the present invention. 
         FIGS. 4A, 4B, 4C, and 4D  depict electrode configurations that provide optimal acquisition of endovascular electrocardiogram according to various embodiments of the present invention.  FIG. 4A  depicts a single lead configuration,  FIG. 4B  depicts a modified 3-lead configuration with monitoring and guiding capabilities,  FIG. 4C  depicts a telemetry configuration with a single grounded lead, and  FIG. 4D  depicts one use of ECG monitors for guiding endovascular devices. 
         FIG. 5  illustrates exemplary electrocardiogram signal amplitudes at different locations in the central venous system. 
         FIG. 6  illustrates exemplary electrocardiogram signal power spectra at different locations in the central venous system. 
         FIG. 7  illustrates exemplary electrocardiogram signal electrical energy distribution at different locations in the central venous system. 
         FIG. 8  depicts a graphical user interface according to an embodiment of the present invention. 
         FIG. 9  depicts a graphical user interface according to another embodiment of the present invention. 
         FIGS. 10A and 10B  depict a exemplary printouts for the information displayed by the graphical user interface, according to an embodiment of the present invention. 
         FIG. 11  is a block diagram for a computer-based method for positioning an endovascular device in or near the heart using electrocardiogram signals. 
         FIG. 12  illustrates another decision support algorithm for a computer-based method for positioning an endovascular device in or near the heart using electrocardiogram signals, according to an alternative embodiment. 
         FIG. 13  illustrates the cardiac conduction system of the heart. 
         FIG. 14  illustrates electrical signal propagation in the conduction system of the heart. 
         FIG. 15  illustrates electrical activity in the cardiovascular system due to neuronal control system. 
     
    
    
     DETAILED DESCRIPTION 
     The invention will now be described with reference to the drawing figures, in which like reference numerals refer to like parts throughout. 
     Embodiments of the present invention advantageously provide an inventive apparatus(es), computer-based data processing algorithms and methods for obtaining and using endovascular ECGs in a number of clinical applications and settings. For example, once device can be used to guide endovascular devices in and around the heart, e.g., guiding central venous access devices in the superior vena cava, right atrium, and right ventricle. Such central venous access devices may include central venous catheters (CVC), peripherally inserted central catheters (PICC), implantable ports, hemodialysis catheters, tunneled catheters and others. Other devices which may benefit from guidance with the inventive apparatus are temporary pacemaker leads placed through the central venous system. Catheters and guidewires used in left heart procedures may also benefit from the present invention by decreasing the amount of contrast and radiation required to guide these devices in position. In another example, the apparatus can be used for minimally invasive monitoring and assessing heart conditions based on its electrical activity, e.g., assessing preload in a heart cycle or monitoring ST segments and T-waves in congestive heart failure. 
     In one aspect of the invention, an apparatus is described consisting of sterile adaptors, an electronic module for signal acquisition, a computer module, software, and peripheral devices and connections. In one embodiment, the electronic module for signal acquisition can be dedicated to acquiring and processing endovascular electrical signals generated by the body (endovascular ECG), in another embodiment the electronic module can be dedicated to acquiring and processing endovascular ECGs as well as skin ECGs. 
     In one embodiment, the electronic module and the computer module can be separate modules, in another embodiment they can be integrated in the same module and enclosure, and yet in another embodiment they can communicate with each other via a wireless connection, such as Bluetooth. In one embodiment, the apparatus can contain an integrated printer, while in another embodiment the printer can be external and attached to the apparatus and the apparatus connected via network, e.g., wireless to other devices. In yet another embodiment the apparatus can be used for telemetry and for transmitting the endovascular electrograms to a remote location, e.g., via a telephone line, Internet, and/or wireless phone. Any combination of embodiments mentioned above is also possible. 
     In another aspect of the invention, various configurations allow the connection of endovascular devices, such as central venous access devices, to the electronic module for signal acquisition and processing. In one embodiment, the device consists of a connecting wire with two ends and special connectors at each end. At one end, the wire can be connected to a metal or nitinol guidewire or stylet as commonly available on the market. At the other end, the wire can be safely connected to the electronic module. In another embodiment, the device includes a coated guidewire, e.g., made of nitinol or stainless steel with uncoated distal and proximal ends and cm markings. In such an embodiment, the coated guidewire is inserted endovascularly, while the connecting wire is connected to the proximal end of the coated guidewire. In another embodiment, the device includes a catheter-syringe adaptor provided with an electrical connecting wire. At one end, the electrical connecting wire is in contact with the fluid, e.g., saline flowing within the catheter-syringe adapter. At the other end the connecting wire can be connected to the electronic module. 
     In another aspect of the invention, various electrode configurations allow for the optimal acquisition of endovascular ECGs. In one embodiment, a single lead is used to provide information about the tip location of an endovascular device within the vasculature. In another embodiment a modified three lead configuration is used to provide simultaneous 3-lead monitoring of the heart activity at the same time with providing tip location information. In another embodiment a modified single lead configuration plus ground is used for telemetry and transferring information from the tip of the catheter remotely. 
     In another aspect of the invention algorithms are introduced for the analysis of the ECG waveforms and for supporting decision making based on these waveforms. These algorithms discriminate between different locations in the vasculature and assess body functions (systemic and at specific locations in the body), in particular heart functionality. In various embodiments, these algorithms use time domain analysis of waveforms: morphologic, for example shape; statistic, for example behavior. 
     In other embodiments, the algorithms use frequency domain analysis of waveforms: morphologic, for example shape; statistic, for example behavior. In further embodiments, signal energy analysis in time and frequency domains is also performed, morphologic and statistic. Fuzzy, statistical, and knowledge-based decision making are also contemplated by the present invention as decision support tools. 
     In another aspect of the invention, a user interface is provided that advantageously simplifies interpretation of data and workflow. In one, embodiment the user interface includes simplified graphics showing the location in the vasculature and in the heart of the tip of the endovascular device in use without showing any of the ECG waveforms. In another embodiment, the user interface shows, in real-time, the change in location of the tip of the endovascular device in use. 
     In another aspect of the invention, several inventive methods are presented which use the apparatus described herein in clinical applications. In one embodiment, a computer-based method is provided that guides central venous catheters (CVC, PICCs, hemodialysis, implantable ports, and others) using stylets, guidewires and saline solution to the superior vena cava, inferior vena cava, the right atrium, and the right ventricle. This method is advantageously less sensitive to patients with arrhythmias than the prior art, and represents an alternative to chest X-ray confirmation of tip location of central venous catheters in most clinical cases. In another embodiment, a computer-based method is provided that guides coated guidewires in the right and left heart. In another embodiment, a computer-based method is provided that guides the placement of temporary pacemaker leads through the central venous system. In another embodiment, a method is provided that is minimally invasive and monitors preload using depolarization and heart rhythms. In another embodiment, a method is provided that is minimally invasive and monitors arrhythmias using P-wave analysis. In another embodiment, a method is provided that is minimally invasive and monitors heart failure using ST segment and T-wave analysis. 
       FIG. 1  is a block diagram that depicts an apparatus according to an embodiment of the present invention. 
     The apparatus  100  can be attached through an adaptor ( 120 ) to a large variety of commercially available and custom designed vascular access devices ( 110 ). Examples of such devices are: central venous catheters (CVC), peripherally inserted central catheters (PICC), implantable ports, tunneled catheters, hemodialysis catheters, guiding catheters for pacemaker leads, guidewires used for coronary and other vascular interventions, guiding catheters for coronary and other vascular interventions, stylets, syringe needles, and others. If the vascular access devices is a stylet, a guidewire, or a syringe needle, its material must be sufficiently electrically conductive, e.g., stainless steel or nitinol. In such a case the hook or the alligator clip adaptor according to the present invention should be used If the vascular access devices is a catheter, than saline should be used to establish a conductive path through one of the catheter&#39;s lumens. In such a case, the syringe-catheter adaptor according to the present invention should be used. 
     The electronic module ( 130 ) receives electrical signals from the adaptor and from one or more other electrodes placed on the patient&#39;s skin ( 115 ). Alternatively, more than one adaptor can be used at the same time to connect to more than one endovascular device in order to provide different electrical signals to the electronic module. The use of skin electrodes is optional in certain device configurations. The electronic module processes the electrical signals and transmits them to a computer module ( 140 ) for further processing and other functions. In one embodiment the electronic module and the computer module can be packaged separately, and in another embodiment they can be integrated in the same package. In one embodiment, the connection between the electronic module and the computer module can be hardwired ( 131 ), and in another embodiment the connection can be wireless ( 132 ), e.g., using Bluetooth. 
     The computer module processes the signals from the electronic module applying algorithms ( 170 ) as described by the current invention. The computer module can also be connected to peripherals ( 160 ), e.g., a printer or a label printer and storage devices and provides connectivity including wireless connectivity ( 150 ) to other computers or to the internet. The storage device can be used to store a database of knowledge and information regarding the application at hand. The connectivity interface can be used to update this database remotely with newest relevant knowledge and information, e.g., new clinical cases, new findings regarding the relationship between electrograms and heart conditions. The computer module supports a graphical user interface ( 180 ) optimized for the purpose of the clinical application at hand. 
       FIGS. 2A, 2B and 2C  depict various endovascular adaptor devices. 
       FIG. 2A  illustrates adaptors that can be made of an isolated conductive wire ( 255 ) made of copper or stainless steel having two ends: one end connected to a vascular access device ( 255 ), the other end connected to the electronic module ( 250 ). The end that connects to the vascular access devices includes a connector that may have several configurations. In one embodiment, the connector is a J-clip connector ( 230 ) with a spring for isolation purposes when the J tip is not extended. In another embodiment, the connector is an isolated alligator clip ( 220 ). In another embodiment, the connector is catheter-syringe adapter ( 210 ). One end of the catheter-syringe adapter ( 211 ) can connect to the catheter luer. The other end can connect ( 215 ) to a syringe. A metal insert ( 214 ), e.g., a metal ring is located inside the body of the adaptor, comes in contact with the saline solution as it flows from the syringe towards the catheter lumen. The metal insert is connected through the adapter wall to a wire ( 212 ) which in turn is connected to the connector ( 250 ). In one embodiment the connector ( 250 ) is secured through external isolation ( 241 ) and plugs into a secure plug in the electronic module. In another embodiment the connector ( 250 ) has an optimized nipple shape ( 242 ) allowing for an easy and safe connection of a standard ECG cable connector. 
       FIG. 2B  illustrates a new guidewire ( 260 ) which allows for collecting electrical information only at its distal end ( 261 ). The guidewire made of electrically conductive materials with good enough conductivity, e.g., stainless steel or nitinol. The guidewire is coated with an electrically isolating coating like conformal parylene coating over its entire length except at the distal end and at the proximal end. The catheter has length markings printed on it ( 262 ). The distal end which is an a-traumatic tip, either as a J-tip or in any other a-traumatic embodiment is not coated and it allows for electrical contact with the blood. The proximal end is not coated ( 263 ) and allows connectors like the ones in  FIG. 2  ( 220  or  230 ) to be electrically connected to the guidewire. 
       FIG. 2C  illustrates another embodiment of a catheter-syringe adaptor. A plastic piece ( 270 ) consists of a shaped end ( 271 ) which can fit into a standard catheter luer or into it lumen. The shape and the material allow for a good contact between the end ( 271 ) and the inner wall of the luer or lumen such that fluid can flow without leakage and no air is introduced into the lumen in the process. The other end of the piece ( 272 ) is a luer type connector which can fit any standard syringe. The body of the adaptor or inner chamber ( 273 ) adapts the diameter of the luer ( 272 ) to the size of the inner catheter lumen ( 271 ) and provides for a connection of an electrically conductive element in the inner chamber to a wire connected to the outside of the chamber through a perforation in the chamber wall ( 274 ). The connection through the chamber wall is waterproof. When saline is injected through the adaptor, the connection ( 274 ) creates a waterproof conductive path between the saline and an outside wire. The adaptor ( 290 ) is a plastic piece which interfaces two sizes of diameters ( 291 ) and ( 292 ). In one embodiment the end ( 271 ) of the adaptor ( 270 ) fits into the lumen end ( 291 ) of adaptor ( 290 ) and the other end ( 292 ) of adaptor ( 290 ) fits into the lumen of a catheter used to place implantable ports. 
       FIG. 3  is a block diagram of an electronic module ( 300 ) for acquisition and processing of endovascular electrocardiogram according to an embodiment of the present invention. 
     The patient connector interface ( 310 ) allows for connecting electrical leads to the patient ( 305 ). Any combination of skin electrodes and/or electrical connections to endovascular devices using the adaptors discussed above can be used. In one embodiment, the amplifier ( 320 ) is a four stage amplifier with variable gain, which can amplify electrical signals coming though the patient cable, for example, typical of electrocardiographic values. The analog-to-digital converter ( 330 ) converts the signals in digital format readable by the micro-processor ( 340 ). Any number and configurations of microprocessors, microcontrollers, digital signal processors can be used to implement the micro-processing function ( 345 ). 
     In one embodiment, a microcontroller is responsible for controlling the serial communication with a computer module ( 390 ) via the serial interface ( 370 ) or via the wireless interface ( 380 ) and a digital signal processor (DSP) is responsible for implementing one or several of the inventive algorithms described herein. Alternatively, a single processor ( 346 ) can be used for both communication and processing. 
     The micro-processor ( 340 ) also receives commands from the computer module ( 390 ) and controls different elements of the electronic module, e.g., the amplifier ( 320 ) accordingly. The patient isolation block ( 350 ) decouples electrically the power ( 360 ) and the serial communication channel ( 370 ) from the patient interface ( 310 ) in order to ensure patient protection to electrical shock. In one embodiment the isolation block ( 350 ) can consists of a transformer and/or couplers, e.g. optical couplers. 
       FIGS. 4A, 4B, 4C, and 4D  depict electrode configurations that provide optimal acquisition of endovascular electrocardiogram according to various embodiments of the present invention. 
       FIG. 4A  depicts a single lead configuration with a reference electrode ( 410 ), for example attached to the patient&#39;s skin over the right arm and with the other electrode attached through an adaptor to an endovascular device ( 415 ). The reference electrode attached to the skin over the right arm is presented in this configuration for illustration purposes only. Other locations of the reference electrode are possible depending on the type of ECG required. The reference electrode over the right arm together with the tip of the endovascular device used with the adaptor can be similar to lead II of a standard ECG. In this case the ECGs obtained from the superior vena cava ( 401 ) and inferior vena cava ( 402 ) can be optimized. The reference electrode can be attached to the skin in any other location in order to simulate other leads of the standard ECG. The reference electrode can be also connected to adaptors attached to other endovascular devices in order to obtain more local information from within the patient&#39;s heart ( 400 ). 
       FIG. 4B  depicts a modified 3-lead configuration, with monitoring and guiding capabilities, with 4 electrodes. Three (3) electrodes correspond to the standard ECG electrodes: right arm (RA,  420 ), left arm (LA,  425 ), and left leg (LL,  430 ) used as reference. The fourth electrode is attached through an adapter to the endovascular device (C,  435 ). In this configuration, the electronic module and the algorithm perform two functions simultaneously: the three standard electrodes (RA, LL, and LL) perform a monitoring function of the heart, while the C electrode ( 435 ) allow for recording the ECG at the tip of device. 
       FIG. 4C  depicts a telemetry configuration with a single grounded lead, including the configuration illustrated in  FIG. 4A  and a ground reference ( 450 ). This configuration can be used to transmit ECGs remotely through a telemetry system configuration. 
       FIG. 4D  depicts one use of ECG monitors for guiding endovascular devices. A standard ECG monitor is used having standard inputs RA ( 465 ), LA ( 460 ), and LL ( 470 ). LA ( 460 ) is connected to the left arm and LL ( 470 ) to the left leg of the patient. The RA input ( 465 ) is connected to a switch which can be used be the clinician to switch the RA input ( 465 ) between the RA electrode and the catheter (C) electrode  475 . Thus either monitoring or guiding of catheter placement can be achieved alternatively. 
       FIG. 5  illustrates exemplary electrocardiogram signal amplitudes at different locations in the central venous system. 
     The heart ( 504 ), right atrium ( 501 ), superior vena cava (SVC) ( 502 ), and the inferior vena cava (IVC) ( 503 ) are illustrated. Location A is in the upper SVC, location B is in the lower third of the SVC, location C is at the caval-artial junction, location D is in the right atrium, and location E is in the upper inferior vena cava. 
     Graph  510  illustrates an ECG waveform as a function of time at recorded at location A. The absolute amplitude of the waveforms is recorded on an amplitude scale ( 590 ). In the case of an endovascular ECG, the standard elements of the electrocardiogram are illustrated: the P-wave ( 560 ), the R-wave ( 570 ), and the T-wave ( 580 ). The amplitudes and shape at location A recorded with a lead configuration as in  FIG. 4D  are similar to an electrocardiogram recoded at the skin level with the same electrode configuration. 
     Graph  520  illustrates an endovascular ECG depicted at location B. The amplitude at this location is higher than the one at location A but the overall shapes of the waveform are similar at location A and B. 
     Graph  530  illustrates an endovascular ECG depicted at location C. At location C at the caval-atrial junction, the amplitude of the waveform is yet higher than the one at location B and the P-wave has dramatically changed becoming higher than the R-wave. This waveform is an indication of the proximity of the sino-atrial node. 
     Graph  540  illustrates an endovascular ECG depicted at location D. At location D in the right atrium, the amplitudes are similar to location C but the P-wave changes polarity becoming bi-polar. This is an indication that the measurement of the ECG occurs beyond the sino-atrial node. 
     Graph  550  illustrates an endovascular ECG depicted at location E. At location E in the inferior vena cava, the waveform is similar to the one at location A in terms of amplitude except the P-wave has reverse polarity. The differences in the ECG waveforms at different locations are used by the algorithms introduced herein to discriminate between the corresponding locations and to assess heart and blood vessel functionality. 
       FIG. 6  illustrates exemplary electrocardiogram signal power spectra at different locations in the central venous system, using a spectral scale ( 690 ). 
     The heart ( 604 ), right atrium ( 601 ), superior vena cava (SVC) ( 602 ), and the inferior vena cava (IVC) ( 603 ) are illustrated. Graph  610  illustrates an endovascular ECG spectrum depicted at location A. At location A, the spectrum ( 610 ) has the appearance of a single central frequency or single band ( 660 ) and with a frequency distribution spectral power and energy similar to those at skin level. 
     Graph  620  illustrates an endovascular ECG spectrum depicted at location B. At location B the frequency distribution has two major bands and a higher energy and spectral power than the one at location A. 
     Graph  630  illustrates an endovascular ECG spectrum at location C. At location C, there are multiple (3-4) major frequencies or principal spectral components distributed over a wider range of frequencies ( 670 ). This spectral distribution is indicative of the energy distribution around the sino-atrial node. The spectral power and signal energy have increased compared to location B. 
     Graph  640  illustrates an endovascular ECG spectrum depicted at location D. At location D the spectrum is wider and more broadband indicative of the electrical activity of the right atrium. 
     Graph  650  illustrates an endovascular ECG spectrum depicted at location E. The frequency spectrum at location E is similar to the one at location A. The differences in the spectral waveforms at different locations are used by the algorithms introduced herein to discriminate between the corresponding locations and to assess heart and blood vessel functionality. 
       FIG. 7  illustrates exemplary electrocardiogram signal electrical energy distribution at different locations in the central venous system. The heart ( 704 ), right atrium ( 701 ), superior vena cava (SVC) ( 702 ), and the inferior vena cava (IVC) ( 703 ) are illustrated. Graphs ( 710 ,  720 ,  730 ,  740 ,  750 ) depict the energy distribution at different locations (A, B, C, D and E, respectively) and the changes in time are used by the algorithms introduced herein to discriminate between the corresponding locations and to assess heart and blood vessel functionality. 
       FIG. 8  depicts a graphical user interface according to an embodiment of the present invention. 
     Window ( 810 ) presents the ECG waveform in real-time as it is acquired by the electronic module using the attached electrode configuration. Window ( 820 ) is a reference window and shows a frozen waveform used to compare with the current window. In one embodiment, the reference waveform in window ( 820 ) can be obtained through the electrodes connected to the electronic module at a reference location of the catheter and/or using a reference configuration of the skin electrodes. For example, such a reference waveform can be the ECG recorded using an adaptor according to the present invention connected to an endovascular device placed at the caval-atrial junction. In a different embodiment, the reference waveform in window  820  can be a typical waveform at a certain location in the vasculature or of a certain heart condition as it is recorded in a database of waveforms and as it is stored in the storage medium of the computer system. If the electrode configuration allows for simultaneous heart monitoring and recording of electrograms using an endovascular device, window ( 830 ) shows one of the standard ECG leads for heart monitoring, while window ( 810 ) shows the ECG at the tip of the endovascular devices when connected to an adaptor, such as the ones discussed above. 
     The icon ( 870 ) is a representation of the heart, and the locations A through E ( 875 ) illustrate different locations in the heart and vascular system which can be discriminated by analyzing endovascular ECGs in accordance with the methods disclosed herein. As a location in the vasculature is identified by the algorithms, the corresponding place and letter on the icon ( 875 ) becomes highlighted or in some other way is made visible to the user. The bars ( 884 ), ( 885 ), and ( 886 ) show signal energy levels. The “E” bar ( 885 ) presents the amount of electrical energy computed from the ECG frequency spectrum at the current location of the tip of the endovascular device. The “R” bar ( 884 ) presents the amount of electrical energy computed from the ECG frequency spectrum at a reference location. The “M” bar ( 886 ) presents amount of electrical energy computed from the ECG frequency spectrum using the monitoring ECG signal from the skin electrodes. The window ( 840 ) depicts monitoring information, e.g., heart rate. Patient information (name, date of procedure and others) are shown in window ( 850 ). Window ( 860 ) contains system control elements like buttons and status information, e.g., scale, scroll speed, system parameters and system diagnostics. 
       FIG. 9  depicts a graphical user interface according to another embodiment of the present invention. 
     The icon ( 920 ) is a representation of the heart and the locations A through E ( 930 ) illustrate different locations in the heart and vascular system which can be discriminated by analyzing endovascular ECGs. As a location in the vasculature is identified by the algorithms, the corresponding place and letter on the icon ( 930 ) becomes highlighted or in some other way is made visible to the user. The bars ( 940 ), ( 950 ), and ( 960 ) show signal energy levels. The “E” bar ( 940 ) depicts the amount of electrical energy computed from the ECG frequency spectrum at the current location of the tip of the endovascular device. The “R” bar ( 950 ) shows the amount of electrical energy computed from the ECG frequency spectrum at a reference location. The “M” bar ( 960 ) shows amount of electrical energy computed from the ECG frequency spectrum using the monitoring ECG signal coming from the skin electrodes. The button “Print” ( 960 ) allows the user to print the information documenting the case on a printer, for example on a label printer for quick attachment to the patient&#39;s chart. 
       FIGS. 10A and 10B  depict a exemplary printouts for the information displayed by the graphical user interface, according to an embodiment of the present invention. 
       FIG. 10A  illustrates a printout ( 1000 ) for the case of a catheter tip placement procedure in the lower third of the SVC. The field  1010  depicts the heart icon whereby the letter “B” corresponding to the lower third of the superior vena cava (SVC) is highlighted ( 1040 ). Field  1030  depicts the reference ECG waveform recorded at the tip of the catheter at the caval-atrial junction in the proximity of the sino-atrial node. Field  1020  depicts the ECG waveform at the tip of the catheter in the position in which it was placed at the end of the procedure. For  FIG. 10A , this location is in the lower third of the SVC and the ECG waveform corresponds to this location. The patient name ( 1001 ) and the date of procedure ( 1002 ) are also printed. 
       FIG. 10B  depicts a similar printout ( 1050 ) except that the final position at the end of the procedure is at the caval-atrial junction at location C ( 1090 ) on the heart icon ( 1060 ). The “SA Node” field depicts the reference ECG waveform ( 1080 ), and the “Final Position” field ( 1070 ) shows that the catheter was placed with the tip at the sino-atrial node: the ECG waveform in final location is similar or even identical with the one in the reference location at the sino-atrial node (SA Node). It is known that the proximity of the SA Node indicates a location at the caval-atrial junction. These locations are sometimes considered identical by some clinicians. 
       FIG. 11  is a block diagram for a computer-based method ( 1100 ) for positioning an endovascular device in or near the heart using electrocardiogram signals. 
     The algorithms are applied to the input signal ( 1102 )(ECG) acquired by the adaptor to the endovascular devices and, optionally, through skin electrodes as well. The Error Detection Block ( 1105 ) detects at least three types of error conditions/exceptions, such as, for example, when a defibrillator has been applied to the patient, when a pacemaker is firing excitation pulses and/or when a lead/electrode is off. These errors/exceptions may be handled differently, and the user may be informed about the presence of an exception and the way of handling the exception ( 1110 ). 
     The Pre-Processing block ( 1115 ) may amplify the signal, reduce noise, eliminate artifacts, etc. In one embodiment, rescaling the signal to the display range occurs under user control and is not automatic, as with most currently available ECG monitors. Thus, changes in the amplitude of the ECGs are easily noticed. A high-pass filter corrects the baseline and reduces such artifacts as respiratory artifact. Wideband noise suppression may be achieved using a selective filter, e.g., a wavelet transform. Electromagnetic interference with other equipment and the power grid may be suppressed by a notch filter (narrow band filter) centered at 60 Hz or 50 Hz to accommodate domestic or international power supplies. High frequency noise may be suppressed with a low-pass filter, which, in one embodiment, is implemented with variable length averaging, such as, for example, a running window corresponding to a heart cycle, an averaging of the ECG over several consecutive heart cycles, etc. The Adaptive Filtering block ( 1120 ) optimizes the filter coefficients by minimizing an error signal. 
     The Time-Domain Pattern Recognition block ( 1130 ) identifies elements of the ECG waveform, their relationship(s) and their behavior(s) in time. An important aspect of the time-domain pattern recognition algorithm in block  1130 , as well as of the Frequency Domain Patter Recognition block  1140 , is data history. The ECGs are analyzed in real time for certain elements, and, for other elements, a data buffer with an appropriate buffer length is maintained in the memory of the electronic and/or computer modules in order to allow for historic data analysis and prediction based on this analysis. In one embodiment, the data history buffer is several seconds long allowing for the ECG signal corresponding to several heartbeats to be saved in the buffer. A double buffering technique allows the waveform in one buffer to be processed while the second buffer continues to store signals. Thus no signal data are lost while the waveform in one buffer is processed. After data processing on one buffer is completed, the results are sent to the Decision Support Algorithms ( 1150 ) and the two buffers switch roles. The length of the buffer accommodates the time duration of data processing in order to ensure that no data are lost. A similar double buffering technique is also applied to the data subject to Frequency Domain Pattern Recognition block ( 1140 ). 
     In the case of an endovascular ECG, elements of interest may include, but are not limited to, one or more of the following:
         1. The P, Q, R, S, T, and U waves, their peaks, amplitudes and duration;   2. The duration of the P-R, S-T, and T-P segments/intervals;   3. The elevation of the S-T segment;   4. The variances of the P-P and R-R intervals;   5. The variance of the S-T and of the R-T intervals, etc.;   6. The peak-to-peak values of the P-wave and of the QRS complex;   7. The ratio of the P-wave and R-wave amplitudes and the ratio of the P-wave and QRS complex peak-to-peak amplitudes;   8. The polarity of the P-wave: single positive, single negative, or bipolarity;   9. The derivative of the P-wave, QRS-complex, and T-wave;   10. Temporal average of the R-R interval and the heart beat;   11. Maximum value of the P-wave amplitude/peak and of the P-wave peak-to-peak amplitude over a certain period of time;   12. Maximum value of the R-wave amplitude/peak and of the ORS complex peak-to-peak amplitude over a certain period of time.       

     Several techniques may be used to derive the information listed above from the ECG waveforms, including, but not limited to, one or more of the following:
         1. “Peak detection”;   2. Computation of first derivatives;   3. Running averages along the signal in one heartbeat and along multiple heartbeats;   4. Adaptive thresholding;   5. Auto-correlation.       

     The Fast Fourier Transform in block ( 1125 ) performs a Fast Fourier Transform on a number of ECG samples stored in a buffer of a certain length, e.g., 256, 512, 1024, 2048 or more data samples. The Fourier Transform transforms the waveform from the time domain into the frequency domain. 
     The Frequency-Domain Pattern Recognition block ( 1140 ) illustrates various aspects of pattern recognition performed on the ECGs in the frequency domain, including, but not limited to, one or more of the following:
         1. Principal components analysis, i.e., determination of the most significant elements of the frequency spectrum (similarly to determining the morphological elements of the electrograms, e.g., certain waves and segments in time domain);   2. Data compression in order to reduce the amount of computation based on the principal components;   3. Determination of the number and morphology of the principal components, in particular determination if the spectrum has only one, two or multiple main frequencies (frequency bands);   4. Calculation of the spectral power and of the signal energy from the frequency spectrum;   5. Running average along the frequency dimension over a single spectrum in order to reduce wideband noise;   6. Running average along several spectra in order to filter out artifacts;   7. Determination of additional morphological elements of the spectrum, e.g., the maximum frequency, the energy contained in the maximum frequency, the frequency histogram, i.e., what frequencies contain how much energy, the frequency of the highest significant maximum energy peak, etc.;   8. Calculation of behavior and averages over time of the principal components and other parameters determined from the spectral distribution, e.g., determining the maximum value of the signal energy and of the spectral power over a certain period of time;   9. Determine/estimate certain heart conditions based on the spectral analysis. This determination/estimation is also performed in more detailed in the decision support blocks  1150  and  1250 .       

     Several decision support algorithms use the information provided by the time domain pattern recognition and frequency-domain pattern recognition algorithms. In one embodiment, block ( 1150 ) supports placing an endovascular device in either the lower third of the SVC or at the caval-atrial junction. 
     In particular, block  1150  is based on the concept of first reaching the caval-atrial junction during catheter placement. At the caval-atrial junction or near the sino-atrial node the P-wave and other electrical parameters reach a maximum value. At the caval-atrial junction the P-wave is unipolar. After reaching the sino-atrial node at the caval-atrial junction, i.e., the maximum value of the P-peak amplitude and spectral power, the catheter is pulled back several centimeters until the P-wave decreases to half the amplitude reached at the caval-atrial junction. At the location where the P-wave has decreased to half the amplitude as the caval-atrial junction, the catheter is considered to be in the lower third of the superior vena cava. The P-wave peak amplitude or peak-to-peak amplitude, as well as the spectral power, is used to map the location in the vasculature to the ECG waveform. 
     More particularly, after receiving an endovascular ECG signal associated with an endovascular device, the signal is processed, over a plurality of predetermined time periods, to calculate a P-wave amplitude and a spectral power for each predetermined time period. A maximum P-wave amplitude is then determined from the plurality of P-wave amplitudes, as well as an associated maximum spectral power from the plurality of spectral powers. The location at which these maximum values are determined is associated with a predetermined location in or near the heart, such as the cava-atrial junction. The location of the endovascular device is then calculated, for each predetermined time period, based on a ratio of the P-wave amplitude to the maximum P-wave amplitude and a ratio of the spectral power to the maximum spectral power, and the location of the endovascular device is then displayed to the user. Additionally, the polarity of the P-wave and the R-wave amplitude may also be used to determine the location of the endovascular device. 
     A single criterion or a combination of such criteria can be used to support decision making. In one embodiment, T1, T2, and T3 may be empirically established thresholds which are different for each patient, and the algorithm can use an adaptive loop to adjust the thresholds based on the current measurements. In another embodiment, these thresholds are predetermined. 
     In alternative embodiments, the ratio between the P-peak/P amplitude or the P-wave peak-to-peak amplitude to the R-peak/R amplitude or to the QRS complex peak-to-peak amplitude can also be used to establish location relative to the sino-atrial node. In one embodiment the P-peak/amplitude must be approximately half of the R-peak/amplitude and the P-wave must be unipolar for the location to correspond to the lower third of the SVC. In another embodiment, the P-wave peak-to-peak must be half of the QRS peak-to-peak amplitude and the P-wave must be unipolar for the location to correspond to the lower third of the SVC. 
     As discussed above, the results of the decision support algorithms block  1150  may be presented to the user, for example, by high lightening the appropriate location on the heart icon corresponding to the type of ECG identified by the system ( 1160 ). 
     The decision support algorithm block  1250 , depicted in  FIG. 12 , is based on comparing the P-wave, R-wave and P-wave spectral power at the current locations with the values of these parameters determined from the skin electrocardiograms in an equivalent lead, e.g., lead II. Thresholds T1 through T6 are empirical values subject to adaptive adjustments relative to each patient. Each of the criteria or a combination of criteria shown in  FIG. 12  can be used. 
     Other decision algorithms can also be used, in particular related to the level of electrical energy as calculated from the ECG spectrum. In the case of placing endovascular devices, one criterion may be that, at the location corresponding to the lower third of the SVC, the average electrical energy calculated from the endovascular ECG is twice as high as the average electrical energy calculated from the endovascular ECG at skin level or from a skin ECG in a corresponding lead, e.g., lead II. 
       FIG. 13  illustrates the cardiac conduction system of the heart, while  FIG. 14  illustrates electrical signal propagation in the conduction system of the heart. 
     These figures illustrate the conductive mechanism of the heart, which explains why the electrical energy distribution within the heart as measured is indicative of specific locations within the heart. Accordingly, local electrical signals, behaviors and energy concentrations can be measured and locations within the heart and blood vessel can be determined more accurately; local heart conditions can also be described more accurately. 
     The conduction system of the heart begins with the heart&#39;s dominant pacemaker, the sino-atrial node ( 1310 ). The intrinsic rate of the SA node is 60 to 100 beats/minute. When an impulse leaves the SA node, it travels through the atria along the Bachmann&#39;s bundle ( 1350 ) and the inter-nodal pathways, on its way to the atro-ventricular (AV) node ( 1320 ) and ventricles. After the impulse passes through the AV node, it travels to the ventricles, first down to the bundle of His ( 1330 ) then along the bundle branches and finally down to the Purkinje fibers ( 1340 ). Pacemaker cells in the junctional tissue and Purkinje fibers on the ventricles normally remain dormant because they receive impulses from the SA node. They initiate an impulse only they do not receive one from the SA node. The intrinsic rate of the AV junction is 40 to 60 beats/minute, the intrinsic rate of the ventricles 20 to 40 beats/minute. The different propagation speeds of the electrical impulses are shown in  FIG. 14 . From the SA node ( 1410 ) the impulses propagate through the atrial muscle ( 1420 ) and through the ventricular muscle ( 1460 ) at app. 0.5 ms, through the bundle branches ( 1440 ) and ( 1450 ) at app. 2 msec, through the Purkinje fibers ( 1470 ) at app 4 m/s and through the AV node ( 1430 ) at app. 0.05 m/s. 
     The electrical signals and the electrical energy distribution are advantageously used to identify the proximity of the sino-atrial node and right atrial electrical activity even in the cases of arrhythmia, i.e., in the absence of a coherent P-wave measured by standard skin electrocardiogram. While in some cases of arrhythmia random electrical signal generated in the right atrium is not coherent enough to propagate through the body to the skin, the electrical energy is still present in the right atrium and can be detected by local endovascular measurements as a non-coherent P-wave, i.e., as significant electrical activity in the P-segment of the ECG waveform. Energy measurements are also less sensitive to some local abnormalities in impulse conduction: altered automaticity (arrhythmias), retrograde conduction of impulses, reentry abnormalities. 
     The electrical signals and the electrical energy distribution are also advantageously used to quantify heart functionality, e.g., preload which is related to the depolarization and extension of the heart muscle. 
     The electrical signals and the electrical energy distribution are also advantageously used to guide guidewires and guiding catheters through the aorta into the left heart. This method is useful in simplifying the access to the left atrium and to the coronary arteries and in reducing the amount of contrast and radiation needed to guide endovascular devices to those locations. In a different application, the inventive apparatus can also be used to guide catheters, e.g. Swan-Ganz through the right ventricle into the pulmonary artery. Other endovascular devices can be guided and be used to measure endovascular electrical activity in other locations of the cardiovascular system which are identifiable by the cardiograms measured with the new apparatus introduced in the present invention. 
       FIG. 15  illustrates electrical activity in the cardiovascular system due to neuronal control system. Several paths of conduction are related to the mechanism of control of heart ( 1530 ) and blood vessel ( 1520 ) activity: receptors ( 1510 ), e.g., pressure receptors transmit information related to the state of the blood vessels and to the state of the heart to the nervous system through the Medullary centers ( 1500 ). The hypothalamus ( 1540 ) and the higher centers ( 1550 ) are involved in processing and reacting to the information received from the sensors/receptors. In turn they send impulses ( 1560 ) back to blood vessels and the heart. By measuring electrical activity related to the control system, information regarding heart conditions can be obtained which could not have been obtained previously. 
     The many features and advantages of the invention are apparent from the detailed specification, and, thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and, accordingly, all suitable modifications and equivalents may be resorted to that fall within the scope of the invention.