SEATTLE – Smartphones may soon be harnessed for monitoring patients with heart failure, offering advantages such as remote assessment and early prediction of decompensation.
A recent survey suggested that 88% of physicians would like to be able to monitor measures of their patients’ health status at home, including many relevant to heart failure. "Those metrics will become more and more available" with smartphone technology, noted Dr. David E. Albert, founder and chief scientific officer of AliveCor Inc., a manufacturer of mobile monitors, including the investigational AliveCor Smartphone System.
Image Courtesy AliveCor
"With today’s smartphones, which will only get more powerful, we can evaluate cardiac rhythm, or our patients can," said Dr. David E. Albert
The device is an ECG monitor that is in clinical trials and under review by the Food and Drug Administration. A patient uses a smartphone and an app to record a clinical-quality ECG that is securely stored and processed in cloud computing-based server, and can be accessed by a physician anywhere in the world.
The device can evaluate at least three cardiac indices used in the monitoring of heart failure, according to Dr. Albert: cardiac rhythm, heart rate, and heart rate variability.
When it comes to cardiac rhythm, smartphones can be used to detect arrhythmias such as atrial fibrillation (J. Am. Coll. Cardiol. 2012;59:E726). He recounted the story of a man in Mumbai, India, experiencing asymptomatic ischemia-induced rhythm changes that were recorded with a smartphone. Physicians in Oklahoma City and Los Angeles identified the arrhythmia and notified the patient, who then went to his physician.
The ECG obtained with the smartphone has the same quality as a 12-lead ECG obtained with state-of-the-art equipment in the clinic, he said. Also, data suggest that a daily ECG is second only to implanted devices for detecting atrial fibrillation (Pacing Clin. Electrophysiol. 2007;30:458-62). "So it’s better than a 24-hour Holter, even now, and our very intermittent 7-day Holters."
Heart rate, the second index, may be a key therapeutic target in heart failure. Here, too, the smartphone-assessed heart rate is just as accurate as clinically measured heart rate, with sensitivity exceeding 99% for QRS detection (and thus R to R intervals), putting it on par with the 12-lead ECG, according to Dr. Albert.
Heart rate variability, the third index, potentially could be used as an index to guide the need for intervention before progression to decompensated heart failure.
Decompensation develops through a series of changes beginning with increasing preload and autonomic adaptation, and culminating in weight gain, symptoms, and hospitalization (Curr. Heart Fail. Rep. 2009;6:287-92). "Obviously, we want to operate on the left side of this graph, where filling and autonomic adaptation are the places we can intervene early," he noted.
Short-term heart rate variability obtained during 8 minutes of paced breathing has been shown to predict sudden cardiac death in patients having chronic heart failure (Circulation 2003;107:565-70), and smartphones can readily be used for such measurement.
The timing of events during the cardiac cycle may also be informative, according to Dr. Albert. These events can be assessed with seismocardiography, whereby vibrations in the chest are measured with an accelerometer placed on the sternum (Chest 1991;100:991-3) and can be combined with ECG data to derive the Tei index, a global measure of cardiac performance (J. Cardiol. 1995;26:135-6). Although the necessary data can be collected with a somewhat elaborate laboratory setup (J. Med. Biol. Engineer 2012;32:103-10), they can also be obtained easily with a smartphone placed on the chest.
"We can measure isovolumic contraction time, isovolumic relaxation time, and ejection time, and develop in 30 seconds not only rate, rhythm, variability, but now a modified Tei index, an index of performance, and as many papers have said, an index of preload status," he noted.
"With today’s smartphones, which will only get more powerful, we can evaluate cardiac rhythm, or our patients can. They can evaluate their cardiac rate, their heart rate variability, and probably potentially – unproven yet very interesting – their ventricular performance and their preload status, enabling that [information] to be injected into the network, enabling certainly intervention and maybe self-care," Dr. Albert concluded.
A session attendee said that this new technology "sounds very good. But we know even when [clinical devices] are used just to study time intervals, there were a lot of artifacts, and accuracy was not very easily determined. Certainly, with this kind of platform, there must be problems with accuracy and artifact in recordings."
It is still early in development of this technology, Dr. Albert acknowledged. "But understand that we have processing power that’s quite unbelievable. ... What I can tell you is that we can measure these variables; what I can’t tell you is how valuable they are going to be."