A result after taking an EKG reading Christina Farr, CNBC

Apple and researchers from Stanford Medicine released some new results from an eight-month study of more than 400,000 participants, who had access to Apple Watches to monitor their heart rhythm for signs of a medical condition known as atrial fibrillation. The watches are not the newest version, which has an electrocardiogram built-in, but are able to detect abnormal heartbeats. The results were presented on stage this weekend at the American College of Cardiology conference in New Orleans, prompting a wide range of reactions from the cardiologists who attended. The discussion was not just limited to the Apple Watch, but about the role of consumer wearables more broadly in screening and potentially even diagnosing disease.

In interviews with CNBC, some in the medical community pointed to the high participation in the study as reason enough for optimism -- 419,000 is far higher than most medical research studies -- while others expressed concern that the Apple Watch would produce many false alarms. Most agreed that the results presented on stage were still preliminary, as the full paper has not been published in a scientific journal. Moreover, it was an observational study, and not a randomized controlled trial. (Apple is moving ahead with study of this kind that includes a control arm for the heart health features on its Apple Watch, in partnership with pharmaceutical company Johnson & Johnson.) Atrial fibrillation is an important health target for Apple, as it impacts up to 6 million people in the United States, but many of them have not been diagnosed. For some people, especially those over the age of 65, the condition can put them at a higher risk for serious health complications, including strokes.

Heart health is the focus of Apple's efforts in health care, so it's vital for the company to win over the support of cardiologists. At this stage, Apple is ahead of its rivals, including Alphabet and Samsung, in introducing novel health features to its devices. But to win over the medical community, it needs to open up a dialog about the pros and cons, and publish research in scientific journals, which is not in the DNA of a company that has historically prized secrecy. For Apple, its inaugural heart study with Stanford represents an important first step, and just one of its ongoing medical research efforts. "We're trying to be thoughtful about how we introduce this in partnership with the medical community," said Sumbul Desai, a physician and Apple's vice president of health, in an interview with CNBC. "We want to hear (from doctors) about all the positives and all the negatives."

Unpacking the results

Not all the results have been published. But the researchers shared that of the approximately 419,000 people who participated in the study, about 0.5 percent received a notification about an irregular heartbeat. Stanford Medicine's principal investigator, Mintu Turakhia, pointed to that statistic to CNBC as an "important finding," as cardiologists have expressed concern that the Watch would produce a high rate of false positives, and send hoards of young people to the doctor's office unnecessarily. That rate was higher with older users, at 3.2 percent, versus 0.16 percent in people between 22 and 39 years old. Of those who received a notification, not all of them followed the protocol by contacting the researchers to ask for an electrocardiogram patch to confirm the diagnosis. Only about 450 did so, which is roughly one in five. Medical experts shared a few theories on this. "It's possible that the folks who didn't follow through were primarily those who didn't have really bothersome symptoms," said Kumar Dharmarajan, a cardiologist and chief scientific officer at health insurance company Clover Health. Dharmarajan also made the point that the patch, which is worn on the chest, is not as enticing to wear as an Apple Watch, which might explain the drop-off. The latest version of the Apple Watch, the Series 4, does however include an electrocardiogram sensor on the device, which has been cleared by regulators to screen for atrial fibrillation. But cardiologists would still recommend a patch for patients to make a diagnosis and determine treatment.

Another result that stood out to physicians: Of the 450 people who wore the patches, atrial fibrillation was confirmed in 34 percent of cases. So the patch agreed with the Apple Watch about one-third of the time. Bimal Shah, a cardiologist who's also the chief medical officer of digital health company, called Livongo, described this as "moderately good for a screening tool, but not amazing." Christopher Granger, a professor of medicine at Duke University who participated on the steering committee for the Apple Heart Study, said the result makes more sense when compared to another data point. In a smaller group of participants that wore both a patch and the Apple Watch, the likelihood that the watch detected atrial fibrillation confirmed by the patch was 84 percent. "That's much higher," he said. "Oftentimes, atrial fibrillation occurs intermittently and might not occur for a whole week," he explained. Putting it another way, said Granger, "if I as a cardiologist knew that one of my patients with an Apple Watch who hadn't been diagnosed with atrial fibrillation had a one-third chance of having it when I put a patch on -- I would really want to know that."

'A new space'