Think You Might Have AF? There's an App For That

December 13, 2012

WORCHESTER, Massachusetts — Innovative researchers have developed a smartphone-based application that allows patients to detect an irregular pulse caused by atrial fibrillation [1]. Two algorithms developed for the application that analyzed signals using an iPhone 4S successfully distinguished atrial fibrillation from sinus rhythm, report investigators.

"A number of patients who are referred to us have pretty symptomatic atrial fibrillation," said lead investigator Dr David McManus (University of Massachusetts Medical School, Worchester, MA). "So they are highly motivated to keep track of their episodes. We traditionally order Holter monitors and event monitors to capture the coming-and-going episodes of atrial fibrillation. I thought there was a potential role to leverage the fact that everybody has a smartphone and to use that as a means to do a sort of physiological assay of the patient."

The results of the study are published online December 7, 2012 in Heart Rhythm.

App Uses Camera and Flash to Measure Chaos in Pulse

To heartwire , McManus explained that patients often wear Holter and event monitors for up to 30 days in order to capture an atrial-fibrillation event, but some of the paroxysmal events are so infrequent that physicians might not even bother with the monitors. A phone-based rhythm-assessment tool would have positive implications for accessibility, allowing patients to record their pulse while the event is occurring to determine whether they are in fact having an episode of atrial fibrillation.

The application works using the smartphone camera and the flash to illuminate the fingertip when it is placed on top of the camera surface. Not unlike a pulse oximeter, which uses infrared light, the flash lens works to illuminate the finger as the camera records in real time the changes in the color of the fingertip. The changes in color act as a surrogate for blood flow, and this is in turn processed by a computer program embedded within the smartphone. Two algorithms--the root mean square of successive RR differences and Shannon entropy--analyze the degree of "chaos," or the variability of the pulse waveform.

"For the purposes of this study, we had patients keep their fingertip on the camera for two minutes, but we have that down now where we've shown that even one minute is sufficient," said McManus. "So it's a quick biopsy of person's pulse that appears to be highly accurate compared with a 12-lead ECG, which is what we used in this study."

In the study, 76 adults with persistent atrial fibrillation scheduled to undergo elective cardioversion were included in the analysis. All subjects who had a preprocedure ECG placed their finger on an iPhone 4S camera for two minutes while the program ran. Following cardioversion, patients successfully converted to normal sinus rhythm again reapplied their finger to the smartphone as another recording was obtained. The algorithms had excellent sensitivity (0.962), specificity (0.975), and accuracy (0.968) for the discrimination of an irregular pulse during atrial fibrillation from sinus rhythm.

"This is really the first step, showing that when it is used in the hospital setting, where a coach was showing them how to put their finger on the phone, people could successfully use this phone to know if they were in or out of atrial fibrillation," said McManus.

Young and Old, Patients Want This

To heartwire , McManus said that patients are clamoring for such an application, particularly those with diagnosed and treated atrial fibrillation who want to be on top of how many episodes of the arrhythmia they are having. They don't want to travel to the hospital or the doctor's office every time they suspect they might be having an episode, however. "Patients want this at their fingertips," he said. "They want something quick, they wanted something that's accurate, and they want something that allows them to communicate effectively with their doctor, all the more reason for it to be a phone-based program."

The application allows users to send the results directly to their physician via email and also provides summaries of atrial-fibrillation burden over selected time periods, a useful feature for physicians to determine whether another antiarrhythmic agent might be needed. Future issues remain, however, regarding how the application will fit into traditional testing, the approval process, who pays for it, and how it will get billed. While those market-based issues remain to be worked out, McManus believes the application fills an unmet need.

"I have to say that I have done a lot of clinical studies, but I had absolutely no problem recruiting patients for this one. Universally, they all said this is really cool."