Currently, a 45-minute ultrasound scan is required to provide detailed information about heart health. Researchers have discovered a method by which a smartphone camera can noninvasively provide the same information.
By simply holding a smartphone to a patient's neck for a minute or two, the technique can infer the left ventricular ejection fraction (LVEF) of the heart by measuring the amount that the carotid artery displaces the skin of the neck as blood pumps through it. LVEF represents the amount of blood in the heart that is pumped out with each beat. In a normal heart, this LVEF ranges from 50 to 70 percent. When the heart is weaker, less of the total amount of blood in the heart is pumped out with each beat, and the LVEF value is lower. LVEF is a key measure of heart health — one upon which physicians base diagnostic and therapeutic decisions.
To test the smartphone app, clinical trials were conducted with 72 volunteers between the ages of 20 and 92 at an outpatient magnetic resonance imaging (MRI) facility. MRI is the gold standard in measuring LVEF, but is seldom used clinically due to its high cost and limited availability. LVEF is most commonly measured using an ultrasound machine during a procedure known as echocardiography; however, LVEF requires a trained technician, an expensive ultrasound machine, and up to 45 minutes of a patient's time.
The measurements made by the smartphone during trials had a margin of error of ±19.1 percent, compared with those done in an MRI. By way of comparison, the margin of error for echocardiography is around ±20 percent.
The app works because the walls of arteries are almost completely elastic — they expand and contract with each beat of the heart. That expanding and contracting can be measured and described as a waveform that encodes information about the heart. For the study, the team used an iPhone 5, but any smartphone with a camera will work. The technique could be developed to diagnose heart valve diseases like aortic stenosis, and coronary artery blockages.