A clinical update article published in the JAMA on March 19 addressed the issue of the evaluation of heart rhythm abnormalities using portable devices *
Dr. James E. Ip, author of the note, points out that while portable devices for use by patients are potentially useful for detecting arrhythmias, physicians must understand the limitations of these devices and be prepared to analyze the data. which will be corroborated with the respective clinic of the patients.
In the article, reference is made to the KardiaTM by AliveCor®, which is an application for smartphone and smartwatch and the Apple Watch Series 4, which is a wristwatch, both capable of recording ECG tracings for 30 consecutive seconds.
Portable devices initially used accelerometers to stimulate physical activity and assess cardiac activity during sleep, but recently incorporated heart rate sensors to allow them to adapt to specific physical fitness programs and also to assess resting heart rate (as an indicator of fitness physical).
Most devices estimate heart rate using photoplethysmographic (PPG) sensors that detect changes in tissue blood volume (caused by peripheral pulses) and perform measurements using dedicated photodetectors and light-emitting diodes.
Accurate measurements depend on adequate blood flow and contact with the skin, and can be modified by patient or device movements, environmental conditions and ectopic beats.
Although most of these devices can show heart rate in real time, retrospective analysis of heart rate trends may be limited and depend on each of them and the respective application used.
Recently, Apple Watch incorporated an irregular rhythm notification function that detects irregularity based on resting PPG and can notify the user of the possible occurrence of atrial fibrillation (AF).
In addition, this device can provide notifications of tachycardia (the default is> 120 / min, but it is adjustable) and bradycardia (the default is <40 / min which is also adjustable) for 10 minutes of inactivity. Therefore, said alert parameters may not detect transient arrhythmias or induced by exercise.
Due to the limited specificity of PPG-based sensors, abnormal findings need confirmation with direct measurement of the conventional electrocardiogram (ECG).
For example, as noted, the Kardia Mobile device and the Apple Watch Series 4 can record, store and transfer single-channel ECG rhythms of 30 seconds.
Although these patient-activated intermittent ambulatory ECG monitors may be convenient to use compared to traditional ambulatory ECG monitors (eg, wired adhesive electrodes or patch-based Holter monitors, event monitors, mobile cardiac by telemetry), no they record continuously and are prone to inaccuracy due to electrical and sound interferences, movement artifacts and inadequate skin contact. A heart rate out of range (<50 or => 100 / min) also does not allow automated interpretation.
Detection and evaluation of FA
Although PPG-based sensors can detect irregularities, they may not distinguish between AF and atrial / ventricular premature beats or variable AV conduction (ie, second-degree AVB).
Apple emphasizes that “the irregular rhythm notification function is not constantly looking for the FA and should not be trusted as a continuous monitor.” Therefore, it is not intended to replace traditional methods of FA detection, but patients may receive a “talk to their doctor” message.
If an FA alert is detected, confirmation with direct ECG measurement is essential. During the concurrent use of Apple Watch and an outpatient ECG patch, 57 participants in the Apple Heart Study received an FA notification.
However, only 45 of them (79%) showed AF concordant with that recorded with the ECG patch and 11 (19%) showed “Other clinically relevant arrhythmias” (no further details were reported).
Inappropriate detections of AF may have been caused by ectopic rhythms (ie, atrial or ventricular premature beats) or variable AV conduction (ie, second-degree atrioventricular block type I or atrial flutter with variable block).
The extrasystoles, which are common, may not be clinically relevant unless they cause significant symptoms or ventricular dysfunction.
Variable AV block may also not be clinically relevant unless it causes symptoms of the resulting bradycardia.
Therefore, if other non-FA arrhythmias are detected with the ECG test, the physician should ask about symptoms related to frequent extrasystole (ie, palpitations, intolerance to exertion) or atrioventricular block (ie, presyncope, syncope) and perform a thorough examination. If there are no symptoms present, no further evaluation is necessary, but if there are symptoms such as palpitations, intolerance to exertion, presyncope or syncope, follow-up tests would be appropriate with ambulatory ECG monitoring.
If AF is confirmed with ambulatory ECG monitoring, the physician should consider the patient’s risk factors for thromboembolism (CHADS-VASc score [congestive heart failure, hypertension, age, diabetes, stroke, vascular disease]) and the risks individualized about the effects of prophylactic anticoagulation.
Additional evaluation includes evaluation of any structural heart disease (echocardiography) and consideration of the optimal frequency or rhythm control strategy, which depends on the patient’s symptoms and comorbidities.
Detection and evaluation of tachycardia
The detection of sinus tachycardia with the development of activity is expected, although a sudden acceleration of resting heart rate suggests a non-physiological tachycardia such as AF or a paroxysmal supraventricular tachycardia. Resting tachycardia may be due to anxiety, dehydration, or other underlying conditions (eg, anemia, pregnancy, infection, hyperthyroidism)
Although PPG-based sensors are reasonably accurate during regular rhythms, performance decreases during AF due to beat-to-beat pulse variations. Among patients with tachycardia during AF, only 15% of the readings of the Fitbit device and 60% of the Apple Watch readings were within a precision range of 10 beats.
If an inappropriate tachycardia is detected and it is not due to an artifact, the ECG recordings during the tachycardia and at the beginning are fundamental to determine its mechanism and guide its later handling.
In general, if the episodes are sporadic, the patient may need ambulatory monitoring with ECG. Once paroxysmal tachycardia is confirmed, an invasive electrophysiology can accurately determine the mechanism of the tachycardia and provide definitive therapy.
Detection and evaluation of bradycardia
Inadequate bradycardia can be observed with a heart rate that is very slow at rest (<40 beats / min) or that does not accelerate properly with exercise (chronotropic incompetence).
False detections of bradycardia can occur from a frequent ectopia (ventricular bigeminy). True bradycardia may be due to primary electrical disorders, such as sinus node dysfunction or atrioventricular block, or secondary to a vagal hypertonia (chronic at rest or transient during sleep apnea).
Chronotropic incompetence would not trigger a bradycardia alert when the patient is at rest, but could be triggered by a slow heart rate response during activity. Bradycardia of sinus node dysfunction or atrioventricular block is diagnosed by an ECG test.
If bradycardia is detected, the doctor should ask the patient about any correlative symptoms (ie, syncope or presyncope) because symptomatic bradycardia may justify pacemaker implantation. Pacemakers that have characteristics of frequency adaptation can improve the symptoms of chronotropic incompetence.
However, it is important to rule out the secondary causes of bradycardia, such as hypothyroidism, medications and sleep apnea, especially if bradycardia occurs only during rest.
As conclusions the author states that as they increase the use of portable devices and direct medical devices for use by the patient and the potential anomalies detected by them are brought to the attention of physicians, it is essential to carry out an adequate evaluation and perform confirmatory tests of ECG.
Understanding the possible triggers of patient notifications and concerns, as well as a careful evaluation of symptoms, are important for diagnosing arrhythmias and treating inappropriate alarms. The future development and incorporation of this technology with the practice of medicine will continue to evolve.
* Ip JE. Evaluation of Cardiac Rhythm Abnormalities From Wearable Devices. JAMA 2019 Mar 19; 321 (11): 1098-1099. doi: 10.1001 / jama.2019.1681.