Smartphone Heart Rate-Monitoring App Can Accurately Assess Ulnar Artery Patency

Using an iPhone with a commercially available heart rate-monitoring app may allow physicians to better assess the patency of a patient’s radial and ulnar arteries compared with a modified Allen test, which is widely used clinically, a proof-of-concept study shows.

The tested approach essentially turns the iPhone camera into a plethysmograph. The camera is placed on a patient’s index finger and the app (Instant Heart Rate; Azumio) begins recording the heart rate. As in standard plethysmography (a Barbeau test), the clinician performing the test occludes both the ulnar and radial arteries and then releases the ulnar artery, monitoring the displayed waveform over the next 2 minutes to assess patency.

Against Doppler ultrasonography as the standard, the smartphone approach was more accurate in assessing ulnar patency than was a modified Allen test (91.8% vs 81.7%; P = 0.002), driven by greater specificity, lead author Pietro Di Santo, MD (University of Ottawa Heart Institute, Canada), and colleagues report in a study published online April 3, 2018, ahead of print in CMAJ. It performed comparably versus conventional plethysmography.

The utility of performing an assessment of ulnar artery patency prior to transradial procedures has been questioned in recent years, senior author Benjamin Hibbert, MD, PhD (University of Ottawa Heart Institute), pointed out to TCTMD.

“In terms of using it to select patients for transradial access, I don’t think it’s necessary,” he said, adding that he’s abandoned the practice. “That being said, lots of people still use it as a diagnostic test and so I think if you’re going to use the modified Allen test, then maybe using an application such as this will yield better results.”

Commenting for TCTMD, Jordan Safirstein, MD (Morristown Medical Center, NJ), called this approach “a really cool, novel, neat concept” similar to using a wireless pulse oximeter that transmits a waveform via Bluetooth to a smartphone.

Though limited by the fact that it was performed at a single center, he said, the study was rigorous and “showed that you could use the phone to do some cool things, even if it’s not necessarily intended for that purpose, and sort of open new doors to say . . . maybe we can do some things that we haven’t necessarily thought of before.”

That said, Safirstein was uncertain about using this approach in practice. “They sort of confirmed that it actually is a decent assessment, it’s a decent waveform, the waveform does correlate, but I still would be a little bit hesitant to use an iPhone app that’s not designated for that specific purpose to assess a patient’s patency.”

Easy to Use

Hibbert said his group initiated this study because they had started using the app clinically as part of their assessment of arterial patency and wanted to perform a rigorous evaluation of the practice compared with the modified Allen test, the clinical standard at the time.

Thus began the single-center CAPITAL iRADIAL study, which randomized 438 patients undergoing planned cardiac catheterization to undergo initial assessments with the smartphone approach—using an Apple iPhone 4S—or the modified Allen test. All patients then underwent conventional plethysmography followed by Doppler ultrasonography of the radial and ulnar arteries.

Only 10 patients (six in the smartphone group and four in the control group) had an absence of ulnar flow confirmed by Doppler ultrasonography, and the increased accuracy of the smartphone approach for identifying ulnar artery occlusion relative to the modified Allen test was mainly driven by a reduction in false-positive results (6.8% vs 16.9%), the authors report.

Hibbert said that he expected the modified Allen test to perform poorly but was surprised by the performance of the smartphone approach. “We thought we might have a little bit more difficulty using the application simply because it wasn’t designed to do this, but it performed very, very well,” he said. “The thing that I found most surprising about this is how easy it is to integrate into your daily clinical practice.”

Although he no longer performs preprocedural patency assessments, Hibbert said he still uses the app to monitor for radial artery occlusion after transradial procedures.

The Future of Mobile Health Technology

Hibbert said this study “is just proof of concept that you can use mobile health technology like this to improve what we’re doing at the bedside.”

In the future, he said his team will work on improving the app to boost diagnostic accuracy and on finding a clinical niche for the technology, which could be for monitoring complications or selecting patients for bypass surgery (in whom radial artery grafts could be used). He added that point-of-care diagnostics using mobile health technology could potentially be used for other purposes as well, like monitoring for microvascular dysfunction or diagnosing PAD.

“I think there’s a whole host of clinical problems and clinical applications where we’ll be able to develop point-of-care testing using smartphone applications that are low cost, [are] available at the bedside, and can improve our diagnostic yield just using tools that we all carry in our pocket,” Hibbert said.

Safirstein also touted the potential of mobile health technologies moving forward, saying that “it’s clear that [with] these phones and these devices and the advent of Bluetooth technology I think that we will have more portable and easier assessments of vessels. I look forward to the time when we have a Bluetooth-enabled small ultrasound probe that we just have as part of every cath lab set up.”

He bemoaned the fact that smartphones are now ubiquitous in many aspects of daily life but that healthcare has not kept up with the trend. “This is sort of just the beginning of people recognizing there’s a need to use smartphones for healthcare,” he said. “Everybody recognizes that need. We use them for everything else in our lives and to not use them for healthcare, what a wasted opportunity for us. And I think we’ll see [progress] in the next coming years.”

Hibbert pointed out that as new technologies come out, it’s important for rigorous evaluations to be done to develop an evidence base to support their use because oftentimes the data lag behind introduction into the real world. “This should be the standard assessment that should be done with these tools before they get used in clinical applications,” he said.

Indeed, Kumanan Wilson, MD (Ottawa Hospital Research Institute), adds in an accompanying editorial, “The study’s authors should be congratulated for conducting a rigorous evaluation of the application of their technology, because most mHealth applications do not undergo any evaluation.”

“Referred to as a new industrial revolution, the impact of digital technologies will be both disruptive and transformative,” Wilson says. “The continued maturation of technologies, such as artificial intelligence, virtual reality and blockchain, will further expand the possibilities for mHealth in both diagnosis and treatment in healthcare. It is incumbent upon the healthcare profession to address proactively the many challenges mHealth presents to best maximize its benefits.”

Note: One of the study co-authors, Roxana Mehran, MD, is a faculty member of the Cardiovascular Research Foundation, the publisher of TCTMD.