Apple Watch Pulse Warnings Fairly Accurate

NEW ORLEANS — Optical pulse monitoring by the Apple Watch may be fairly accurate in identifying heart rhythm problems, like atrial fibrillation (Afib), researchers reported here.

Among people whose watch alerted them of an abnormal pulse, ECG patch monitoring confirmed Afib for 34% overall, and 34.8% of those ages ≥65, the prospective, open-label, single arm Apple Heart Study showed.

For the 450 patients wearing the ECG patch and watch simultaneously, the positive predictive value (PPV) was 0.71 (97.5% 0.69-0.74) for the irregular tachogram, while the PPV was 0.84 (95% CI 0.76-0.92) for irregular pulse notifications, reported Marco Perez, MD, of Stanford University School of Medicine in California, and colleagues at the American College of Cardiology (ACC) annual meeting.

Of the overall cohort, 0.52% received an initial irregular pulse notification, Perez added.

Optical sensors, such as those found on smart watches including the Apple Watch, passively measure heart rate by detecting pulse waveform. Detection of pulse irregularity may be beneficial in identifying Afib, noted co-author Mintu Turakhia, MD, also of Stanford.

This process can be used to create a tachogram, which is a plot of time intervals between pulses. Apple created an algorithm that samples tachograms when the user is still. A tachogram that shows irregularity will then initiate a cascade of more frequent monitoring. If the subsequent tachograms are normal, then it goes back to normal. However, if five out of six are irregular over a 48-hour period than this event is flagged for irregular rhythm notification, Turakhia stated.

“Of note, the algorithm and the study do not use the ECG watch feature found in newer watches,” he said.

Study Details

The investigators evaluated 419,297 people with a mean age of about 41. Of the participants, 42% were women, 12% were Hispanic, and 8% were African American.

Inclusion criteria included residing in the U.S, ages ≥22 years, and having a compatible watch series and iPhone. Exclusion criteria were current use of anticoagulation, or a diagnosis of atrial flutter or Afib.

Only 2,161 participants received an initial irregular pulse notification during an 8-month monitoring period. Of those participants, 450 participants received ECG patches.

The CHA2DS2-VASc score were ≥2 for 13% of the overall cohort, 33% of participants who received a notification, and 38% of participants who received an ECG patch.

After downloading the app, a number of procedures were done, including verification of eligibility, self-reporting of baseline characteristics, self-reporting of outcomes, consent, and enrollment.

The algorithm would then be activated on the watch. If an irregular rhythm were identified, the participant was prompted to initiate a study visit. The first study visit connected participants to a telehealth doctor, who would do an assessment. If there were no indications of urgent or emergent symptoms, then the participant would receive an ECG patch by mail to wear as ambulatory ECG monitor for up to 7 days.

After returning the patch by mail, the data was adjudicated according to protocol, and then there was a second study visit. The investigators did not prescribe treatment, but they reviewed the recommendations and assessed for safety. Participants received copies of their study and ECG reports.

The researchers also collected 90-day survey information on participants, who received a notification and end-of-study data on the overall cohort.

The survey data showed that of the participants that received notification, 15% of the patients admitted they had Afib before the study, and 57% contacted a provider outside of the study. Of the participants seeking care outside of the study, 36% needed additional testing, 28% started a new treatment, and 33% were referred to a specialist.

There were 1,038 adverse events in the overall cohort. Only 16 of the events were related to the app and were primarily related to anxiety, Perez noted. All events related to the app were non-serious and 14 were expected.

“This study does have several limitations. We had higher than anticipated drop offs after the notification. There were fewer ECG patches than we had planned,” Perez said. “This was a virtual study design, which allowed us to do this study very quickly and very pragmatically. However, we had to rely on the self-assessment of enrollment criteria and outcomes.”

Disruptive Tech?

The study results may be useful in further clinical assessment “after notification, when taking into consideration things like the history, physical examination, and other clinical observations. We need rigorous investigation of this technology and its potential use in the clinical setting,” Perez said. “We believe the Apple Heart Study provides a solid foundation upon which further research into digital health can be conducted.”

This is a disruptive technology that expands on what clinicians already do with ambulatory recordings and management, said ACC discussant Matthew Martinez, MD, of Lehigh Valley Health Network, in Pennsylvania, at a press conference. “I think patient engagement, being a self-champion and taking initiative, is going to lead to better outcomes. If we can engage the patient — and this is one of the ways we do it, — I view it as a real positive,” he said. “I think there’s value in just the detection, but there’s risk.”

Martinez explained that the risk can be summarized with the word “over” — overload of information, overdiagnosis, overtreatment, and over-anxiety. Though the study does show feasibility overall, “it is way too early for me to say this is a replacement for ambulatory ECG, but this is certainly a tool that I have in my tool box.”

He added that, from a clinical perspective, a notification suggested a signal for early detection of possible Afib, which gives the opportunity for screening, and serves as a signal of high suspicion that warrants further attention.

Jeanne Poole, MD, of University of Washington in Seattle, pointed out that research is ongoing on the use of anticoagulation in patients with Afib who are asymptomatic. She said the trial “has the possibility to lead a lot of patients potentially to being treated unnecessarily or prematurely or flooding doctors’ offices and cardiologists’ offices with a lot of young people, since the majority of the people who enrolled in this trial were young people.”

Perez pointed out that the portion of trial participants, ages 22-39, who received notifications was “very, very small” at 0.16%. The researchers also acknowledged that they did not reach their target enrollment of 500,000 participants, of which they hoped 75,000 would be ages ≥65.

Perez noted that “there are also other things that atrial fibrillation is associated with [such as] cardiomyopathy, heart failure. So finding atrial fibrillation, for example, in the young population might be important because if they really do have atrial fibrillation, maybe they don’t need anticoagulation, but maybe there is something else that’s going.”

“I think that taking all of this into context, knowing that in the older population if you identify somebody with the risk factors and who now has Afib, there may be a benefit here,” he stated. “But…I think there’s a lot more research that we need to know in order to decide whether or not this population being detected with new technologies benefits from things like anticoagulation.”

last updated 03.16.2019