Today, the U.S. Patent and Trademark Office published a patent application from Apple that reveals a possible new wearable device beyond Apple Watch that could be in the works that has the capability of recording electrocardiographic signals, and more particularly to detecting and correcting for inversions in electrocardiographic measurements caused by wearing the device on varying locations on the human body.
About Apple's Patent
Popular computing devices can be used for performing a wide variety of tasks, from the simple to the most complex. As an example, some portable computing devices can have electrocardiographic functionality with various kinds or types of electrodes configured to be worn or attached to identify locations on the human body for the purpose of making measurements of the electrical activity of the human heart.
A portable computing device can be fashioned into a wearable accessory that can be worn on the body. Examples of a wearable device can include a watch, a ring, a pendant, a brooch, a wrist-band or wrist band, a pendant, a bracelet, etc.
A wearable device can be affixed to a limb of the human body such as a wrist or ankle, as an example. The wearable device can be worn on the left or right wrist, or even on the right or left ankle. Since electrocardiographic measurements can depend on the electrode's relative position to the heart being measured, and since the electrodes can be affixed to the wearable device, changing the device's location from right to left, or wrist to ankle, can have an impact on the acquired electrocardiographic measurements. As an example, wearing the device on the left wrist vs. wearing the device on the right wrist can produce electrocardiographic measurements that are inverted relative to one another.
Apple invention relates to a wearable device that can determine the wearing limb of the device, and if the device is being worn in such a way as to produce inverted electrocardiographic readings. It can then correct the inverted readings in order to produce electrocardiographic measurements that are consistent for a given pair of limbs of the user.
In one example, the wearable device can detect lead inversion by first assessing whether the P-wave of a given electrocardiographic measurement has a negative amplitude, and if the P-wave is found to be negative, the device can determine if the magnitude of the R-wave is smaller than the maximum of the magnitudes of the S-wave and the Q-wave. If both of the conditions are true, the device can determine that the electrocardiographic reading is inverted and correct for the inversion.
In another example, the device can be put through an enrollment procedure in which electrocardiographic measurements are taken with the device being worn at known locations on the body. Once the enrollment procedure is completed, when the device is being used, any electrocardiographic results obtained can be compared against the measurements taken during the enrollment phase, and the location of the device on the body can be determined.
Apple's patent FIG. 4 noted above illustrates an exemplary wearable device capable of recording an electrocardiographic measurement. Wearable device #400 can be worn by a user on the wrist (as pictured) or the ankle/leg of the user, or any other part of the human body.
The wearable device can be configured to have three electrocardiographic electrodes #401, #402, and #403. In the example of FIG. 4, electrode #402 can act as the positive electrode for the purpose of measuring the potential difference from electrode #401, which can act as the negative electrode.
The potentials at electrode #401 and #402 can be measured with respect to the ground electrode #403. Also, in the example of FIG. 4, the positive electrode #402 and the ground electrode #403 can be positioned such that they are in direct contact with the wrist (i.e., on the underside of the wearable device 400), while electrode #401 can be positioned such that it is not in contact with any portion of the user's body as illustrated.
In order to take an electrocardiographic measurement, the user can place a part of his or her body, such as a finger, on the open electrode (i.e., electrode 401) that is not already in contact with the user's body. For instance, the user can place his or her finger on electrode #401, or can place electrode #401 in contact with either ankle. Once electrode #401 has made contact with a portion of the user's body, an electrocardiographic measurement that measures the potential difference between the portion of the body in contact with electrode #402 and the portion of the body in contact with electrode #401 can be acquired.
Apple's patent FIG. 6 noted below illustrates an exemplary placement of a wearable device on the user and FIG. 9 illustrates another exemplary method for detecting lead inversion of an electrocardiographic measurement.
Apple's patent FIG. 8 illustrates additional electrocardiographic lead configurations. . If the wearable device could be worn on any wrist or any leg of the user's body, then non-standard electrocardiographic leads can be defined between the right leg and other limbs, thereby expanding Einthoven's triangle.
Apple's patent FIG. 10 illustrates various enrollment phase lead configurations. As illustrated at #1002, as part of the enrollment phase, the device can be worn in the Lead I configuration with the device on the left wrist and the negative electrode making contact with a finger of the right wrist. After the measurement has been obtained in the Lead I configuration, the device can prompt the user to wear the device in the Lead II configuration with the device being worn on the left leg and a finger of the right arm making contact with the negative electrode of the device, as illustrated at #1004.
After the measurement has been obtained in the Lead II configuration, the device can prompt the user to wear the device in the Lead V configuration with the device being worn on the right leg and one of the fingers of the left arm making contact with the negative electrode, as illustrated at #1006.
At the end of the enrollment phase, the device can have stored six different measurements, one for each lead. A processor in the device can then calculate the positions of the QRS complexes (or R waves) and can compute an average template for each of the 6 leads by overlapping and averaging the recorded beats in synchrony with the R waves. A time scaling can be applied to normalize each template lead to a given heart rate such as 60 bpm (beats per minute) using the same principles used in QT interval correction known in the art. A normalization in amplitude can also be applied. The 6 templates are stored for use in the subsequent test (detection) phases.
Apple patent application 20160228025 was filed in Q2 2016. The patent lists Sorin Dusan, Senior DSP Engineer, Lead at Apple. Dusan also worked at Dolby Laboratories and Director of Research at MCT Inc. / NASA Ames Research Center. Considering that this is a patent application, the timing of such a product to market is unknown at this time.
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