Abstract:
Miniature defibrillators and cardioverters detect abnormal heart rhythms and automatically apply electrical therapy to restore normal heart function. Therapy decisions are typically based on the time between successive beats of various chambers of the heart, such as the left atrium and left ventricle. To prevent confusing a left ventricle beat for a left atrium beat, some devices use cross-chamber blanking, a technique which disables sensing of atrial beats for a certain time period after sensing. Conventionally, these devices lack any mechanism for adjusting length of this period. Accordingly, the inventor devised a implantable device including a mechanism for adjusting this time period. This mechanism ultimately allows tailoring of the cross-chamber blanking period to fit the needs of individual patients.

Description:
TECHNICAL FIELD  
         [0001]    The present invention concerns implantable defibrillators and cardioverters and methods for ensuring accurate interval measurements in these devices.  
         BACKGROUND OF THE INVENTION  
         [0002]    Since the early 1980s, thousands of patients prone to irregular and sometimes life threatening heart rhythms have had miniature defibrillators and cardioverters implanted in their bodies. These devices detect onset of abnormal heart rhythms and automatically apply corrective electrical therapy, specifically one or more bursts of electric current, to hearts. When the bursts of electric current are properly sized and timed, they restore normal heart function without human intervention, sparing patients considerable discomfort and often saving their lives.  
           [0003]    The typical defibrillator or cardioverter includes a set of electrical leads, which extend from a sealed housing through the veinous system into the inner walls of a heart after implantation. Within the housing are a battery for supplying power, a capacitor for delivering bursts of electric current through the leads to the heart, and monitoring circuitry for monitoring the heart and determining not only when and where to apply the current bursts but also their number and magnitude. The monitoring circuitry generally includes a microprocessor and a memory that stores instructions directing the microprocessor to interpret electrical signals that naturally occur in the heart as normal or abnormal rhythms. For abnormal rhythms, the instructions, or more generally signal-processing algorithm, tell the processor what, if any, electrical therapy should be given to restore normal heart function.  
           [0004]    In general, these algorithms use the time intervals between successive heart beats, or cardiac events, as key determinants of therapy decisions. Thus, to ensure the validity of therapy decisions, it is very important to ensure accuracy of these intervals.  
           [0005]    Determining these intervals can be especially problematic in dual-chamber defibrillation and cardioversion devices, which monitor the beats of two chambers of the heart, such as the left ventricle and the left atrium. In these devices, there is a significant risk of mistaking a ventricle beat for an atrial beat, and therefore counting too many atrial beats and miscalculating some atrial intervals (the time between atrial beats). Because of this risk, many dual-chamber devices use a technique, known as cross-chamber blanking, to ensure accuracy of atrial interval measurements.  
           [0006]    Cross-chamber blanking entails using a blanking period to prevent sensing atrial beats for a certain time period after the last ventricular beat. In other words, atrial sensing is temporarily disabled after each ventricular beat to prevent mistaking the ventricular beat for an atrial beat. In conventional dual-chamber devices, the length, or duration, of the blanking period is fixed during manufacture and cannot be tailored to fit the unique needs of some patients. Accordingly, the inventors recognized a need for dual-chamber defibrillation and cardioversion devices that have programmable cross-chamber blanking periods.  
         SUMMARY OF THE INVENTION  
         [0007]    To address this and other needs, the inventor devised a dual-chamber implantable defibrillation and/or cardioversion device which includes a memory storing one or more programmable or reprogrammable settings for use as a cross-chamber blanking period. An exemplary embodiment applies one of the settings to disable atrial sensing for a period of time based on the programmed setting. Ultimately, various embodiments of the invention facilitate tailoring defibrillation and/or cardioversion devices to individual patients.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a block diagram of an exemplary medical device system  100  incorporating teachings of the present invention.  
         [0009]    [0009]FIG. 2 is a flow chart illustrating an exemplary method incorporating teachings of the present invention.  
         [0010]    [0010]FIG. 3 is an exemplary timing diagram illustrating operation of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0011]    The following detailed description, which references and incorporates FIGS. 1-3, describes and illustrates one or more specific embodiments of the invention. These embodiments, offered not to limit but only to exemplify and teach the invention, are shown and described in sufficient detail to enable those skilled in the art to practice the invention. Thus, where appropriate to avoid obscuring the invention, the description may omit certain information known to those of skill in the art.  
         [0012]    [0012]FIG. 1 shows an exemplary medical device system  100  which includes a device programmer  110  and an implantable dual-chamber defibrillation and/or cardioversion device  120  in accord with teachings of the present invention. Device programmer  110 , which generally communicates programming information, such as one or more cross-chamber blanking settings, to defibrillator  120 , includes a user interface  112 , microcontroller or processor  114 , a memory  116 , and a wireless transceiver  118 .  
         [0013]    User interface  112 , which includes a keyboard and graphical-user interface (not shown) generated by processor  114 , facilitates selection of one or more cross-chamber settings or insertion of one or more manual settings, during a refractory programming mode. Memory  116  stores, among other things, a number of cross-chamber blanking settings  116   a , for example a set of times ranging from 30-200 milliseconds in 10-millisecond increments or a set of temporal indices which can be used to determine duration of a blanking period. Settings  116   a  are displayed for user selection by user interface  112  during the programming mode.  
         [0014]    In the exemplary embodiment, determination of appropriate blanking period settings or times follows an iterative procedure of visually analyzing electrogram data to determine whether a particular cross-chamber blanking period is either too long or too short, programming a new blanking period, and then visually analyzing updated electrogram data. The selected or manually inserted settings can then be communicated alone or in combination with other programmable parameters into implantable device  120 .  
         [0015]    Implantable dual-chamber device  120  includes a wireless transceiver  130  monitoring system  140 , a lead system  150 , a therapy system  160 , a power system  170 , and an interconnective bus  180 . Wireless transceiver  130  communicates with wireless transceiver  118  of device programmer  110 . Monitoring system  140  includes a processor or microcontroller  142  and a memory  144 . Memory  144  includes one or more software modules  144   a  which store one or more computer instructions in accord with the present invention. Additionally, memory  144  includes one or more parameter storage portions  144   b  which store one or more programmed cross-chamber blanking settings in accord with the present invention.  
         [0016]    Some embodiments of the invention replace software modules  144   a  with one or more hardware or firmware modules. In the exemplary embodiment, processor  142  is a ZiLOG™ Z80 microprocessor (with a math coprocessor). However, the invention is not limited to any particular microprocessor, microcontroller, or memory.  
         [0017]    Lead system  150 , in the exemplary embodiment, includes one or more electrically conductive leads—for example, atrial, ventricular, or defibrillation leads—suitable for insertion into a heart. One or more of these are suitable for sensing electrical signals from a portion of the heart and one or more are suitable for transmitting therapeutic doses of electrical energy. Lead system  120  also includes associated sensing and signal-conditioning electronics, such as atrial or ventricular sense amplifiers and/or analog-to-digital converters, as known or will be known in the art.  
         [0018]    In some embodiments, lead system  150  supports ventricular epicardial rate sensing, atrial endocardial bipolar pacing and sensing, ventricular endocardial bipolar pacing and sensing, epicardial patches, and Endotak® Series and ancillary leads. In some embodiments, lead system  120  also supports two or more pacing regimens, including DDD pacing. Also, some embodiments use a housing for device  100  as an optional defibrillation electrode. The invention, however, is not limited in terms of lead or electrode types, lead or electrode configurations, sensing electronics, or signal-conditioning electronics.  
         [0019]    Therapy system  160  includes one or more capacitors and other circuitry (not shown) for delivering or transmitting electrical energy in measured doses through lead system  150  to a heart or other living tissue (not shown). In the exemplary embodiment, therapy system  160  includes aluminum electrolytic or polymer-based capacitors. However, other embodiments use one or more other devices for administering non-electrical therapeutic agents, such as pharmaceuticals, to a heart. Thus, the invention is not limited to any particular type of therapy system.  
         [0020]    In general operation, lead system  150  senses atrial or ventricular electrical activity and provides data representative of this activity to monitoring system  140 . Monitoring system  140 , specifically processor  142 , processes this data according to instructions of software module  144   a  of memory  144 . If appropriate, processor  142  then directs or causes therapy system  160  to deliver one or more measured doses of electrical energy or other therapeutic agents through lead system  150  to a heart.  
         [0021]    More precisely, FIG. 2 shows a flow chart  200 , illustrating an exemplary method at least partly embodied within software modules  144   a  and executed by processor  142 . Flow chart  200  includes blocks  202 - 224 , which are executed serially in the exemplary embodiment. However, other embodiments of the invention may execute two or more blocks in parallel using multiple processors or a single processor organized as two or more virtual machines or subprocessors. Moreover, still other embodiments implement the blocks as two or more specific interconnected hardware modules with related control and data signals communicated between and through the modules. Thus, the exemplary process flow is instructive to software, hardware, and firmware implementations.  
         [0022]    In process block  202 , device  120  is programmed using device programmer  110 . In the exemplary embodiment, this entails wireless transceiver  130  receiving one or more cross-chamber blanking settings via wireless transceiver  118  of device programmer  110 . The one or more settings take any desired value or form, for example, one or more time values ranging from 30-200 milliseconds or one or more temporal indices which are used as a basis for determining time values. In any event, upon receipt of the one or more settings, processor  142  stores them in portion  144   b  of memory  144 . At completion of this and any other programming procedures related to operational criteria for device  120 , execution of the exemplary method proceeds to block  220 .  
         [0023]    In block  220 , which assumes normal post-programming operation, processor  142  retrieves one or more of the programmed cross-chamber blanking settings from portion  144   b  of memory  144 . In the exemplary embodiment, this entails retrieving one time value, for example, 45, 65, or 85 milliseconds, for use as the cross-chamber blanking period and then computing a corresponding noise window based on the difference between a preset refractory period value (also stored in memory portion  144   b ), such as 86 milliseconds, and the retrieved cross-chamber blanking period. In other words, the exemplary embodiment implements a refractory period having two parts, the cross-chamber blanking part and the noise window part, with the duration of the noise window contingent on the cross-chamber blanking period. However, other embodiments implement refractory periods with more or less than two parts and/or without noise windows.  
         [0024]    After retrieving the cross-chamber blanking setting, processor  146  registers a ventricular event sensed through lead system  150 , as indicated in block  222 . In the exemplary embodiment, this entails recording a marker in memory  144  along with appropriate timing indicia, before proceeding to block  224 . The marker can represent either a sensed ventricular signal or a ventricular pacing signal.  
         [0025]    In block  224 , processor  142  invokes cross-chamber blanking to prevent sensing of further atrial events via lead system  150  for the duration of the cross-chamber blanking period. In the exemplary embodiment, this entails electronically disabling an appropriate portion of lead system  150  for the duration of the cross-chamber blanking period. However, other embodiments ignore or discard data from the appropriate portion of lead system  150  for the duration of the blanking period. After termination of the blanking period, sensing resumes.  
         [0026]    [0026]FIG. 3 shows an exemplary timing diagram  300  which illustrates function of the cross-chamber blanking interval. Specifically, diagram  300  includes a horizontal time axis  302 , a ventricular event marker  304 , and a refractory period  306  having a programmable cross-chamber-blanking portion  306   a  and noise-window portion  306   b . Ventricular event marker  304  represents a ventricular event sensed at block  224  in FIG. 2. Refractory period  306  represents the result of retrieving a programmed cross-chamber-blanking setting from memory portion  144   b , which defines where blanking period  306   a  ends and noise window  306   b  begins. This point is shown as broken line segment  306   c  in the Figure. Atrial sensing is blanked during blanking period  306   a . Thus, apparent atrial events such as  308  are either not sensed because of atrial sensing electronics are disabled or are ignored. Events occurring within noise window  306   b  are assumed to be noise and are thus similarly ignored.  
       Conclusion  
       [0027]    In furtherance of the art, the inventors have presented an implantable dual-chamber defibrillator and/or cardioverter which includes programmable cross-chamber blanking. Unlike conventional dual-chamber devices, those in accord with the present invention allow physicians or other medically trained personnel to tailor the cross-chamber blanking period to fit the needs of individual patients.  
         [0028]    The embodiments described above are intended only to illustrate and teach one or more ways of practicing or implementing the present invention, not to restrict its breadth or scope. The actual scope of the invention, which embraces all ways of practicing or implementing the teachings of the invention, is defined only by the following claims and their equivalents.