Patent Application
20060122679
This patent document pertains generally to cardiac function management devices and more particularly, but not by way of limitation, to a semiconductor-gated cardiac lead and method of use.
Implantable medical devices include, among other things, cardiac function management (CFM) devices such as pacers, cardioverters, defibrillators, cardiac resynchronization therapy (CRT) devices, as well as combination devices that provide more than one of these therapy modalities to a subject. Such devices often include one or more diagnostic capabilities. Moreover, such diagnostic capabilities may be used as a basis for automatically providing therapy to the subject or for communicating diagnostic information to a physician or to the subject.
One example of a diagnostic capability is sensing intrinsic electrical heart signals. These intrinsic heart signals include depolarizations that propagate through heart tissue. The depolarizations cause heart contractions for pumping blood through the circulatory system. The intrinsic heart signals are typically sensed by an implantable medical device at implanted electrodes. The implantable medical device typically includes sense amplifier circuits and other signal processing circuits to extract useful diagnostic information from the intrinsic heart signals.
Examples of therapeutic capability include delivering pacing-level stimulations intended to evoke responsive heart contractions. By appropriately timing the delivery of such stimulations, the patient's heart rate can be adjusted to help the heart provide adequate cardiac output. Moreover, regardless of whether heart rate is adjusted, the pacing-level stimulations can be used to spatially coordinate the heart depolarizations and associated heart contractions. This can also improve cardiac output. Cardiac function management devices can also provide antitachyarrhythmia pacing, cardioversion, or defibrillation shock therapy.
When a CFM device electronics unit is implanted in a patient, for example, pectorally or abdominally, an intravascular lead with one or more conductors is typically used to make one or more electrical connections between the implanted CFM device electronics unit and the heart. Such electrical connections permit sensing of intrinsic electric heart signals, delivery of pacing-level stimulations to evoke responsive heart contractions, or to deliver defibrillation shocks to interrupt certain tachyarrhythmias. In a typical construction, one conductor goes to each electrode at the distal portion of the lead. When multiple conductors are used, they typically run side by side and are insulated from each other and also from the patient's body. There is a need for improved intravascular cardiac leads, which should be small to avoid occluding the vasculature, and which should be strong enough to resist the considerable wear resulting from the continuous flexion resulting from heart contractions.
In the drawings, which are not necessarily drawn to scale, like numerals describe substantially similar components throughout the several views. Like numerals having different letter suffixes represent different instances of substantially similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.
The following detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments, which are also referred to herein as “examples,” are described in enough detail to enable those skilled in the art to practice the invention. The embodiments may be combined, other embodiments may be utilized, or structural, logical and electrical changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents.
In this document, the terms “a” or “an” are used, as is common in patent documents, to include one or more than one. In this document, the term “or” is used to refer to a nonexclusive or, unless otherwise indicated. Furthermore, all publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as though individually incorporated by reference. In the event of inconsistent usages between this document and those documents so incorporated by reference, the usage in the incorporated reference(s) should be considered supplementary to that of this document; for irreconcilable inconsistencies, the usage in this document controls.
In the example of
Each of the electrodes 106A-D is typically individually connected to the electronics unit 102 using its own conductor extending along and within the multiconductor lead 108A. These conductors are typically insulated from each other and the surrounding tissue, such that the electrodes 106A-D are typically only in electrical communication with each other through the heart tissue and body fluid of the patient's anatomy. Using fewer conductors reduces the diameter of the lead 108. This is highly desirable because the intravascular lead then occludes less of the vessel through which it extends or the heart chamber into which it is placed. Therefore, in one example, the “dedicated bipolar” lead configuration of
When sensing intrinsic heart signals using the integrated bipolar configuration, however, the larger combined surface area of the commonly connected ring electrode 106B and distal shock electrode 106C may result in noisier sensed intrinsic heart signals. Such increased noise may result from increased sensing of myopotentials, electrical interference, or other interfering noise sources. However, the larger combined surface area of the commonly connected ring electrode 106B and distal shock electrode 106C may help reduce unintended anodal or other return electrode stimulation, such as when delivering a bipolar pacing-level stimulation pulse using the tip electrode 106A as a cathode for delivering the pacing pulse, and using as an anode the combined ring electrode 106B and distal shock electrode 106C. Such bipolar pacing pulses are typically intended to stimulate a responsive heart contraction at the cathodic tip electrode 106A. However, when the surface area of the return-path anode is too small, enough charge density can result at the anode to trigger an unintended anodic stimulation of the heart tissue. By connecting the distal shock electrode 106C in common with the anodic ring electrode 106B, a larger anodic surface area is present than when the ring electrode 106B is used alone as the anode. This reduces the areal anodic charge density, which, in turn, reduces the likelihood of producing an unintended anodic stimulation of the heart tissue.
Unintended anodic stimulation is even a bigger problem when the two electrodes between which a pacing pulse is delivered are farther apart. For example, when the tip electrode 106A is used as the pacing cathode and the nearby ring electrode 106B is used as the pacing anode, responsive heart contractions can typically be obtained at low pacing energy levels, such that the likelihood of an unintended anodic stimulation is reduced or avoided. However, left-sided pacing (e.g., biventricular pacing) and certain other configurations may require increased pacing energy levels. In one such example, the CFM device electronics unit 102 is coupled to an intravascular lead 108B that is threaded into the right atrium 118 through the superior vena cava 120, and then into the coronary sinus 121 and one of the veins extending into the heart wall from the coronary sinus 121. This allows one or more electrodes, such as ring electrode 106E, to be positioned within one of the coronary sinus veins in association with the intrinsic electrical heart signal conduction pathways of the left ventricle 122. The ring electrode 106E can be used as a cathode for delivering a pacing stimulation. Because of the larger distance and greater amount of myocardial tissue between the cathodic ring electrode 106E and the anodic ring electrode 106B (as compared with the distance between the cathodic tip electrode 106A and the anodic ring electrode 106B), a larger pacing energy is typically delivered using the anodic ring electrode 106E in order to evoke the desired left ventricular heart contraction. This larger energy may result in anodic stimulation at the ring electrode 106B, which could interfere with the desired spatial coordination of the left and right ventricular heart contractions. Accordingly, the present inventors have recognized that for avoiding such unintended anodic stimulation, it may be desirable to commonly connect the ring electrode 106B and the distal shock electrode 106C as a larger surface area anode return path for a pacing pulse, such as when the pacing pulse is delivered at a high enough energy, for example, from the left ventricular ring electrode 106E. However, the present inventors have also recognized that at times it may be desirable to isolate the distal defibrillation shock electrode 106C from the ring electrode 106B, such as when ring electrode 106B is being used in conjunction with another electrode for bipolar sensing (e.g., between two relatively closely spaced electrodes) or unipolar sensing (e.g., sensing between two more distantly spaced electrodes) of intrinsic electrical heart signals. Further still, the present inventors have recognized that there may be opportunities for the ring electrode 106B and the distal shock coil electrode 106C to share a substantial portion of a common conductor back through the lead to the CFM device electronics unit 102, thereby allowing the diameter of the lead 108A to be reduced as compared to when individual conductors are provided.
In this example, the diodes 300A-B each have a turn-on threshold voltage that exceeds a voltage amplitude level associated with a sensed intrinsic heart depolarization. However, in this example the turn-on threshold voltage is less than a voltage amplitude level associated with a pacing-level stimulation to be delivered to evoke a responsive heart contraction. For example, typical cardiac depolarization amplitudes (e.g., QRS amplitudes associated with a ventricular depolarization and ventricular heart contraction, or P-wave amplitudes associated with an atrial depolarization and atrial heart contraction) are in the range of between about 5 millivolts and about 20 millivolts. Because of the selection of the turn-on threshold voltage value of the conductivity control device 206, the conductivity control device 206 will not conduct even when the full voltage drop of an intrinsic heart depolarization (e.g., 5-20 mV) appears between the ring electrode 106B and the distal shock coil electrode 106C. Therefore, for sensing intrinsic electrical heart depolarizations, the distal shock coil electrode 106C is electrically isolated from the ring electrode 106B by the conductivity control device 206. This avoids introducing additional far-field noise during such sensing from the additional surface area of the distal shock coil electrode 106C.
Because the turn-on threshold voltage is less than a voltage amplitude level associated with a pacing-level stimulation, the conductivity control device 206 turns on and electrically conducts between the ring electrode 106B and the distal shock coil electrode 106C during delivery of a pacing pulse. This allows the ring electrode 106B and the distal shock coil electrode 106C to be used in common as a combined larger surface area anode return path for a pacing pulse being delivered by another electrode, such as the left ventricular ring electrode 106E. This larger combined surface area anode will have a smaller charge density than the ring electrode 106B used alone, therefore anodal stimulation is much less likely to occur when the conductivity control device 206 is turned on to conduct. Because pacing voltages are typically greater than 1.0 Volts, a turn-on threshold voltage of less than 1.0 Volts can be used. In one example, the turn-on threshold voltage is between 0.5 Volts and 0.7 Volts, as is provided by using semiconductor rectification diodes 300A-B.
In an example such as that of
In the above example, the defibrillation shock coil electrodes 106C-D will also typically be used to deliver a monophasic or biphasic defibrillation shock therebetween. The defibrillation shock typically involves energies of up to about 35 Joules at voltages of up to about 780 Volts. During such a defibrillation shock, the conductivity control device 206 will turn on to provide a conduction path from the distal shock coil electrode 106C back through the ring electrode 106B and the commonly shared conductor 202 back to the CFM device electronics unit 102. The back-to-back diode configuration of
In the example of
Although the above example has emphasized using a conductivity control device 206 between a distal shock coil electrode 106C and a slightly more distal ring electrode 106B, this is merely a particularly useful example (for the reasons discussed above) that is presented to assist the reader's conceptualization. However, the conductivity control device 206 could be inserted electrically between any two cardiac electrodes to allow use of both electrodes during pacing and defibrillation, while isolating the two electrodes from each other during sensing of intrinsic electrical heart signals, as discussed above. This can be used to reduce far-field noise during sensing and to avoid unintentional stimulation at a return path electrode during pacing or resynchronization therapy when pacing-level energy stimulations are delivered.
Moreover, in the above example, if a polarity of the pacing voltage received at the distal shock coil electrode 106C is known with respect to the tip electrode 106A, then a single diode could be used in place of the back-to-back diodes shown in
Furthermore, although the above description has emphasized avoiding unwanted anodal stimulation at the return electrode, the description is presented this way merely to assist the user's conceptualization, since the tip electrode 106A is typically used as a cathode. However, the present techniques are equally applicable where the return electrode is used as a cathode in conjunction with another electrode being used as an anode. In certain such situations, it is still desirable to avoid unintentional stimulation at the return path electrode (which, in this case, is now a cathode, making such unwanted return path electrode stimulation an unintentional cathodic stimulation).
It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Also, in the following claims, the terms “including” and “comprising” are open-ended, that is, a system, device, article, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.
The Abstract of the Disclosure is provided to comply with 37 C.F.R. §1.72(b), requiring an abstract that will allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, various features may be grouped together to streamline the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter may lie in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment.
