Abstract:
Method of determining atrial fibrillation including determining if a patient&#39;s pulse beats form an irregular pattern and only if so, indicating the presence of an irregular pulse to the patient and obtaining an electrocardiogram for determining atrial fibrillation. Initially, a pulse is detected at regular time intervals of a first appendage of the patient when motionless using a pulse detector secured to the first appendage and pulse rhythms from a succession of time intervals are detected each corresponding to a respective interval of time between successive pulse beats of a sequence of the pulse beats. Then, an electrically conductive unit is attached to a second appendage of the patient, or a wearable electrocardiogram is attached to the patient, and electrocardiograms signals are detected simultaneously with pulse rhythms while the first appendage is motionless and analyzed to determine whether, in combination, they are indicative of atrial fibrillation. If so, an indication of atrial fibrillation is provided at least to the patient.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority of U.S. provisional patent application Ser. No. 61/871,906 filed Aug. 30, 2013, incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention generally relates to a method of and an apparatus for detecting atrial fibrillation. 
         [0004]    2. Discussion of the Related Art 
         [0005]    The heart is the major muscle that functions as the primary pump for blood flow throughout the body. The heart contains two upper chambers called atria and two lower chambers called ventricles. The right atrium receives oxygen-depleted blood while the left atrium receives blood enriched with oxygen from the lungs. When the atria are full, the outlet valves within the heart open and the atria squeeze blood into the ventricles. The right ventricle then pumps oxygen-depleted blood to the lungs while the left ventricle pumps oxygen-enriched blood to all parts of the body. In this fashion, the heart functions primarily as a double sided pump. 
         [0006]    The heart&#39;s internal pacemaker, known as the sinus node, signals the start of each heart beat. This signal originates in the right atrium in the sinoatrial node and travels simultaneously to the left atrium and down to the interatrial septum to the atrioventricular node. This electrical impulse results in a “p” wave on the electrocardiogram. This cycle of electrical stimulation that occurs normally is referred to as normal sinus rhythm. The contraction of the ventricles is preceded by QRS waves on the electrocardiogram (ECG), which is the electrical activity that begins ventricular contraction. This electrical activity is also often referred to as the “R” wave. The contraction of the heart occurs after the R wave. The impulse caused by cardiac contractility is transmitted through the arteries and is detected as a pulse. This pulse beat usually occurs from about 200 msec to about 700 msec after the R wave. 
         [0007]    Many rhythm abnormalities may cause an irregular heart rhythm. Atrial fibrillation is a rhythm abnormality in which the atria do not contract normally. Instead, there is a continuously varying pattern of electrical activation of the atria resulting in a rapid highly irregular pattern of impulses reaching the atrioventricular node. The atrioventricular node acts as a filter and allows a reduced number of these impulses to reach the ventricles which results in a highly irregular heartbeat pattern. Since there is no organized electrical activity in the atrium, atrial fibrillation does not produce a p wave on the ECG. 
         [0008]    Atrial fibrillation is one of the most common arrhythmias requiring medical attention. Atrial fibrillation may be caused by a number of heart conditions, such as coronary artery disease, myocardial infarction, heart valve abnormalities, and high blood pressure. These conditions may stretch or scar the atria, thereby causing irregularities in the heart system. Atrial fibrillation may also accompany lung problems or thyroid gland disorders and is also associated with significant morbidity and possible mortality. All persons, young and old, female or male, including the visually and/or sight impaired, may experience atrial fibrillation. 
         [0009]    The most serious complication of atrial fibrillation is formation of a blood clot in the left atrium which may result in a stroke. The standard therapy used to prevent strokes in patients with risk factors for a stroke and atrial fibrillation is an anticoagulant, or blood thinner. Many people who develop atrial fibrillation, however, are unaware of their abnormal rhythm. 
         [0010]    Recommendations have been made for people at risk of developing atrial fibrillation, to check their pulse periodically. Checking the pulse manually by palpation is often difficult for some people, especially the elderly, to do reliably. Therefore, use of a device that periodically automatically assess the heart rhythm and alerts the patient to the presence of atrial fibrillation would be helpful in getting patients with atrial fibrillation to be treated earlier. This may help prevent strokes in patients who are unaware that they have atrial fibrillation. 
         [0011]    There are devices available that can be used by patients to screen for atrial fibrillation. The electrocardiogram (ECG) is the gold standard for determining if a person has atrial fibrillation. However, checking the ECG is cumbersome because it requires the person to place at least two electrodes on different body locations, such as both arms, an arm and a leg or an arm and the chest, or two locations on the chest. Also ECG monitoring at home often requires a technician and then a physician to read the ECG. The cost of this approach is prohibitive for the general population at risk of atrial fibrillation. 
         [0012]    There are devices that can read the ECG automatically. However, they are easily compromised by a noisy signal, which is very common with ECG&#39;s. A noisy ECG signal can result in what is described as artifacts on the ECG signal. These artifacts can appear to be multiple R waves in an irregular pattern. These artifactual R waves will not have p waves preceding them and will, thus, result in the ECG meeting the criteria for diagnosing atrial fibrillation even though the true rhythm may be regular. 
         [0013]    The use of blood pressure monitors and smartphones which can determine the time interval between pulse beats have been described. The blood pressure monitors rely on plethysmographic signals to detect the pulse, while smartphones can use the light transmittance through the skin to detect the pulse. The blood pressure devices, in particular, are able to detect the pulse reliably with artifacts rarely affecting the pulse signal. These modalities rely on assessing the regularity of the pulse rhythm which is irregular in atrial fibrillation. However, other rhythm abnormalities, such as extra heart beats may cause an irregular heart rhythm. These extra beats often follow normal beats that have both p and R waves on the ECG. Differentiating the rhythms due to extra heartbeats from atrial fibrillation can be performed most accurately by using the ECG. 
         [0014]    Combining both the ECG recording and the pulse recording can improve the accuracy of detecting the true pulse beats. As mentioned previously, noise in either the ECG or pulse rhythm recording can result in artifacts that look like extra beats. Heart beats that occur with an adequate time interval following the previous beat to generate a pulse will always generate an R wave on the ECG and a pulse beat. Therefore, it is possible to use the pulse rhythm recording to help determine if what looks like an R wave on the ECG is due to a very premature R wave or an artifact since that electrical activity will not have a pulse beat. By deleting that electrical activity from the ECG, it is possible to generate a modified ECG that will have less electrical noise and very premature beats. This new modified ECG recording can then be analyzed for regularity. If it is regular, then the rhythm is not atrial fibrillation. If it is irregular, then the R waves on the modified ECG can be identified, and an attempt can be made to detect the preceding p waves. If the p waves are present, then the rhythm is not atrial fibrillation. If the p waves are absent, then the rhythm is atrial fibrillation. 
         [0015]    The ECG recording and the pulse rhythm recording can be most easily compared by shifting the time of the ECG by from about 200 msec to about 700 msec so that the R waves occur at a later time. When the ECG time is shifted enough to account for the delay in generating the pulse rhythm, then the ECG and pulse recordings should have R waves and pulse beats occurring simultaneously. That is the time shift that can be used to generate the new modified ECG recording. 
         [0016]    What is needed is a device that can be worn on a daily basis and can periodically take automatic pulse readings when the person is not moving so as to accurately determine if the heart rhythm is irregular. 
         [0017]    What is further needed is for that device to inform the person when the automatic pulse reading showed an irregular rhythm and a combined ECG and pulse rhythm recording needs to be taken. 
         [0018]    What is further needed is for the combined pulse and ECG recording to be analyzed to determine if atrial fibrillation is present and to inform the person of that result. 
         [0019]    Methods for determining if an ECG waveform is noisy has been described in U.S. Pat. No. 8,639,316. However, in this patent publication, the presence of noise is determined by analyzing the properties of the ECG signal such as the morphology, amplitude or frequency content of the signal. This can also be applied to other physiological signals such as blood pressure waveforms. However, there is no mention of using a combination of physiological signals to determine if the ECG signal is noisy. There is also no mention of generating a new ECG recording by using a physiological signal to modify the ECG signal and then using that modified ECG to determine if atrial fibrillation is present. 
         [0020]    U.S. Pat. Appln. Publ. No. 20130060154 describes a watch-like device that is worn on the wrist and can detect pulse signals which can be used to determine if atrial fibrillation is present. However, it does not describe obtaining recordings periodically and automatically when the person is not moving. 
       BRIEF SUMMARY OF THE INVENTION 
       [0021]    The present invention provides a method and apparatus that can screen for atrial fibrillation periodically by automatically checking for a pulse irregularity when the appendage, on which the apparatus is worn or secured, is motionless. It then adds an additional step to determine if atrial fibrillation is present when the pulse rhythm is found to be irregular, by taking a combined ECG and pulse reading. In this combined reading, the presence of atrial fibrillation may be determined by (i) detecting the pulse beat intervals and the ECG signal simultaneously when at least one appendage is motionless, (ii) generating a new modified ECG recording that includes only heartbeats that are present on both the ECG and pulse rhythm recording, (iii) analyzing the modified ECG recording for regularity or irregularity, (iv) if an irregularity is found, then determining if “p” waves are present preceding the R waves on the modified ECG, (v) determining if atrial fibrillation is present by the lack of p waves, and (vi) communicating this information to the user so that a medical practitioner may be consulted by the user for further testing and/or treatment. 
         [0022]    The present invention also provides a method of and an apparatus for detecting irregular pulses and ECG rhythms during a time period and storing this information for comparison with the pulse rhythm at later time periods. The present invention may also detect patterns over multiple time periods and compare the patterns over various time periods. 
         [0023]    Pulse beats may be obtained by plethysmography such as the use of an inflatable cuff wrapped around a person&#39;s appendage, such as a wrist, which detects the pulse beats by either oscillometric or auscultatory means. The time intervals between pulse beats can be determined during cuff deflation or while the cuff is inflated at a fixed pressure. This cuff device can be incorporated into a wrist watch that can be worn on a daily basis and automatic recordings obtained periodically, such as once a day or once a week. The device would inflate the cuff only when the wrist has been stationary and motionless for a specified time period before the inflation as determined by an accelerometer within the device. The waveform generated by the device would only be analyzed if the accelerometer confirmed that no movement occurred during the measurement period. 
         [0024]    Pulse beats may also be monitored through changes in light transmitted through various body appendages. Each pulse beat changes the light transmission through a location on the appendage. The change in the light transmission corresponds to a pulse beat and the time intervals between pulse beats may be determined. This can be done with a wrist watch device that includes a light source and a light sensor on the part of the wrist watch that makes contact with the skin at the wrist. This wrist watch that can be worn on a daily basis and automatic recordings can be obtained periodically, such as once a day or once a week. The device measures light transmittance only when the wrist has been stationary and motionless for a specified time period before the measurement as determined by an accelerometer within the device. The waveform generated by the device would only be analyzed if the accelerometer confirmed that no movement occurred during the measurement period. 
         [0025]    Pulse beats may also be monitored using other plethysmographic devices, ultrasound devices that measure arterial motion with each pulse beat, ultrasound doppler devices that detect blood flow within an artery or devices that rely on localized compression of the artery to detect the presence of a pulse beat. Using any of these techniques the time intervals between pulse beats can be determined. 
         [0026]    ECG signals may be obtained by placing electrical conducting leads on the limbs, other appendages or the chest. It may also be obtained by obtaining electrical signals from conducting leads in the heart or in other locations in the chest such as in pacemakers. 
         [0027]    A monitoring method of the present invention includes communicating this information to a user such as via a screen display, a paper printout, a tone, or auditory, vibratory or other sensory communication. 
         [0028]    The invention may utilize algorithmic or heuristic techniques to determine whether the ECG and pulse beats signal the possible presence of atrial fibrillation. 
         [0029]    Other features and advantages of the present invention will become apparent from the following detailed description of the invention with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]    For a better understanding of the present invention, reference is made to the following description and accompanying drawings, while the scope of the invention is set forth in the appended claims: 
           [0031]      FIG. 1  is shows an exemplifying, non-limiting embodiment of a wrist watch in accordance with the invention; 
           [0032]      FIG. 2  is a schematic showing the components in the housing of the wrist watch in accordance with the invention; 
           [0033]      FIG. 3  is an example of an ECG signal with noise and a simultaneous pulse beat waveform obtained from a pulse oxymeter; 
           [0034]      FIG. 4  shows the ECG time shifted so that the R waves coincide with the pulse beats and location of the R waves that would not be deleted from the new modified ECG; and 
           [0035]      FIG. 5  is a schematic similar to  FIG. 2  but including a wireless ECG device. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0036]    Referring to the accompanying drawings wherein like reference numbers refer to the same or similar elements, one embodiment of the apparatus in accordance with the invention and that may be used in a method in accordance with the invention uses pulse beats and an ECG that are detected using a wristwatch  10  which has a conductive watch band or strap  12  as shown in  FIG. 1 . The watch band or strap  12  is an example of a securing mechanism for securing a housing  40  including the electrical and mechanical components of the invention to the wrist of the patient. Other securing mechanisms may be used in the invention. 
         [0037]    The wrist watch  10  also includes a light source  14  and sensor  16  on the bottom side of watch  10 , preferably directly on or against the skin surface  18 . The light source  14  and light sensor  16  are controlled to transmit light to the skin of the wearer and receive reflected light which can be converted into a pulse in a manner known to those skilled in the art to which this invention pertains. Other pulse detector mechanisms may also be used in the invention and included in the housing of the watch  10  that is secured to the wrist of the wearer, or another appendage of the wearer. 
         [0038]    An accelerometer  20  is preferably built into the housing  40  of the watch  10 . The ECG is obtained from electrically conductive portions in wrist straps  12 ,  22  on and in skin contact with both wrists of the same person with a limb lead  24  from strap  22  connected to the housing  40  of the watch  10 . Data from the accelerometer  20  is used to determine whether the wrist to which the watch  10  is secured is sufficiently motionless or moving. In this context, motionless means that the position of the wrist is not changing. A totally still state of the appendage is desirable but practically difficult to achieve. Therefore, a threshold may be set as to the degree of permissible motion of the appendage and an indication of motion below the threshold may be considered a motionless state. 
         [0039]    Since the light source  14  and sensor  16  are operative on the underside of the watch  10 , and hence in dotted lines in  FIG. 1 , the wrist watch  10  would be able to keep track of time via a conventional time keeping and displaying mechanism  26  visible to the wearer and determine when the next automated pulse reading should be obtained. A timing mechanism to achieve this timed determination is readily configured to one skilled in the art in view of the disclosure herein. For example, pulse readings may be obtained once a day to detect if the patient has an episode of atrial fibrillation. The wrist watch  10  would automatically begin to determine if the wrist is moving when the time for the next pulse reading occurs. This movement detection is preferably performed using the accelerometer  20 , but as an alternative, another movement detection means or mechanism may be used in the invention. 
         [0040]    If the accelerometer  20  determines that the wrist is moving at that time, it will not attempt to take a pulse reading. The accelerometer  20  may be used to check for movement again a set period of time later, e.g., five minutes later, and continue to enable such movement checking until it is found that the wrist is motionless. At that time, a 30 second pulse rhythm will be obtained. If data from the accelerometer  20  confirms that no movement occurred during that 30 second reading, then the pulse rhythm obtained during the 30 second period will be analyzed to determine if the pulse rhythm is regular or irregular. If it is regular, then atrial fibrillation is not present and the watch  10  will obtain the next reading according to its programmed schedule, e.g., the following day at the same set time. 
         [0041]    If the pulse rhythm is irregular, the watch  10  will signal the person wearing the watch  10  by voice, beeping, vibration, a text, a light or on the watch screen display  26 , that an abnormal rhythm was found and an ECG needs to be taken. The mechanism that provides this is referred to as a signaling mechanism  28  and may be incorporated into the housing  40  of the watch  10 . The signaling mechanism  28  may be configured to perform one or more of these actions or responses to the determination of the irregularity of the pulse rhythm by the processor  32  in the housing  40  of the watch  10  (see  FIG. 2 ). 
         [0042]    Once notified that an ECG needs to be taken, the person should then take a conductive wrist strap  22  that is incorporated in the wristwatch band  12  and pull it off the watch band  12  and place it on the other wrist (as shown in  FIG. 1 ). The wrist strap  22  will have a wire or lead  24  that is in place connecting it to the housing of the watch  10 , i.e., to the electronic componentry in the housing of the watch  10  (schematically shown in  FIG. 2 ). A connector  42 , e.g., an elastic cord, is optionally provided to connect the wrist strap  40  to the housing  40 . Once the second wrist strap  22  is in place, the conductive wristwatch band  12  and the other wrist strap  22  become two leads for the ECG. The wristwatch band  12  is positioned to have continuous contact with the skin surface  20  on the wrist and the watch  10 , i.e., processor  32  therein, can detect that the second wrist strap  22  has made contact with the skin surface  30  since an ECG signal will then be generated. 
         [0043]    At that point, data from the accelerometer  20  will be used to determine if the wrist watch  10  is motionless. If it is not, then the wrist watch  10  will signal to the person to stop moving both arms and to relax. If data from the accelerometer  20  provides a determination that there is no movement, then the ECG and the pulse rhythm will be recorded simultaneously for 30 seconds. This recording may be stored in a memory  34  of the housing of the watch  10  (see  FIG. 2 ). 
         [0044]    Once the ECG and pulse signals are obtained, the processor  32  in the wristwatch  10  will analyze the two signals (see  FIG. 2 ). The pulse rhythm recording will be used to help the processor  32  determine if what looks like an R wave on the ECG is due to a very premature R wave or an artifact. Electrical activity on the ECG that does not have a pulse beat associated with it will be deleted (through processing performed by the processor  32  upon execution of appropriate software being executed by the processor  32 ). By deleting that electrical activity from the ECG, the processor  32  is configured to generate a modified ECG that will have less electrical noise and very premature beats. 
         [0045]    This new modified ECG recording can then be analyzed by the processor  32  for regularity using algorithms or other processing techniques. If it is regular, then the rhythm is not atrial fibrillation and the person will be informed by voice, by a green light or by the watch screen that the rhythm is normal, via the signaling mechanism  28 , and the next automatic reading will be performed as scheduled. If it is irregular, then the R waves on the modified ECG can be identified by the processor  32 , and an attempt can be made to detect the preceding p waves. If the p waves are present, then the rhythm is not atrial fibrillation and the person will be informed that the rhythm is normal, again by means of the signaling mechanism  28 . If the p waves are absent, then the rhythm is atrial fibrillation and the person will be informed that he has atrial fibrillation via the signaling mechanism  28  and should seek the advice of a physician. After the person acknowledges that he has received this message by pressing a button  38  on the watch  10 , then the watch  10  will take the next reading as scheduled. If no acknowledgement is made, then the watch  10  will continue to show that atrial fibrillation was detected. 
         [0046]    The processor  32  can store the time of each pulse beat, the intervals between pulse beats and other information in the memory  34  (see  FIG. 2 ). The memory  34  may include RAM or other device memory or include a hard disc, a floppy disk or other memory devices. The processor  32  may comprise a microprocessor, and applications specific integrated circuit (ASIC), a programmable logic array (FLA) or reduced instruction set chip (RISC). 
         [0047]    Instead of incorporating the ECG determination and analysis unit in the processor  32 , the ECG device may be a separate ECG recorder with a signal output that can be connected to the wrist watch processor  32  (see ECG device  36  in dotted lines in  FIG. 2 ). The wrist watch  10  may also have one lead incorporated into other accessories on the device such that it can be strapped onto the limbs or chest of the patient. The ECG device  36  may thus be a wearable electrocardiogram device configured to be attached to the limbs or the chest of the patient and provides an electrocardiogram signal to the processor  32  via an electrical lead (in dotted lines in  FIG. 2 ). 
         [0048]    Referring now to  FIG. 5 , the wrist watch  10  may also communicate wirelessly with a separate ECG device  46  that may have leads  50 ,  52  placed upon the person&#39;s limbs or chest or is worn by the person. The wireless communication may be with radio waves using Bluetooth, near field communication technology or other data communication technologies. One embodiment using wireless technology would include the ECG device  46  that is separate and apart from the housing  40  of the wrist watch  10 , and which would incorporate a wireless signal transmission and/or reception unit  48 , and two or more electrically conductive leads  50 ,  52  that are adapted to be secured or otherwise attached at a respective location to the person for which the ECG is to be taken, specifically in contact with skin of the person. The ECG device  46  may thus be configured as a wearable electrocardiogram device attachable to the limbs or chest of the patient with the leads  50 ,  52  extending therefrom to be positioned in contact with skin of the patient. The housing  40  of the wrist watch  10  is then also provided with a wireless signal transmission and/or reception unit  44  and configured to issue commands to be wirelessly transmitted to the ECG device  46  to cause the ECG device  46  to obtain an electrocardiogram signal via the leads  50 ,  52  and output an ECG which is then transmitted to the wrist watch  10  via the wireless signal transmission and/or reception units  44 ,  48 . An example of a wearable electrocardiogram device  36  that may be used in the invention is a T-shirt manufactured by HealthWatch of Tel Aviv, Israel. 
         [0049]    In either case, the processor  32  determines from the pulse beats and ECG if the results suggest atrial fibrillation or not. Programming of the processor  32  to perform this determination is readily ascertainable by those skilled in the art in view of the disclosure herein. The processor  32  can then deliver the results to a printer, a display, a vibration generator, and/or an auditory generator, etc. (signaling mechanism  28 ) which may include an indication that the pulse beat pattern is regular, irregular, in possible atrial fibrillation, or that a physician should be contacted. Other information, such as the pulse rate, may also be displayed. 
         [0050]      FIG. 3  shows an exemplifying ECG signal, the top signal, simultaneous with a pulse waveform, the bottom signal. The diagonal lines extending between the ECG signal and the pulse waveform show the R wave with the resulting pulse beat generated by the cardiac contraction caused by the R wave. ECG waveforms that do not have a resulting pulse beat are due to electrical noise. The noise stops after the third R wave. In this example of a recording, the ECG signal shows noise artifact that cannot easily be differentiated from the real R waves. 
         [0051]      FIG. 4  shows an exemplifying ECG signal, the top signal, time shifted so that pulse beats, the middle signal, coincide with R waves. The noise artifact on the ECG signal can then be ignored since they do not coincide with the pulse beats. Combined heart rhythm recording, the lower signal, shows which wave would not be deleted from the new modified ECG generated by the processor  32  in the manner described above, i.e., the new ECG recording can be generated at each time point where both R wave and pulse beats occur simultaneously. If this heart rhythm recording were regular, then the rhythm would be determined not to be atrial fibrillation. However, since this heart rhythm recording is irregular, further analysis of the modified ECG is needed to determine the presence or absence of p waves. The R waves are analyzed by the processor  32  to determine if there are p waves that preceded them. Since p waves are noted before the R waves on this tracing, the rhythm would be called not atrial fibrillation. 
         [0052]    Advantageously, the invention provides a method and apparatus that easily detect the presence of atrial fibrillation, and differentiates atrial fibrillation from non-atrial fibrillation rhythms including normal and other abnormal rhythms. 
         [0053]    A still further advantage is that the invention provides relatively simple, non-invasive monitoring for long term at home or other location outside of a physician&#39;s office. Nevertheless, the use of the invention may occur at a physician&#39;s office or hospital or at any location where long term heart monitoring is desired. 
         [0054]    Additional information about heart monitoring and processing of heart signals is disclosed in U.S. Pat. Nos. 6,519,490, 7,020,514, 7,680,532 and 7,706,868, to the same inventor. The disclosures of all of these patents are incorporated by reference herein. Also, the techniques disclosed in these patents may be used in combination with or as modifications to the techniques disclosed herein, and such are also considered to be inventions 
         [0055]    Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses may become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by this specific disclosure herein, but only by the appended claims.