When I was a cardiology fellow back in the 1980s, I learned about a variety of early tools for evaluating heart health that had been displaced by the modern standards of electrocardiography (ECG, or EKG for the Deutschephiles) and echocardiography. One such technique – ballistocardiography – stuck with me, and may be making a comeback.
Ballistocardiography is based on the observation that the mechanical action of the heart leads to subtle but reproducible movement of the whole body. It is the old “every action has an equal and opposite reaction” maxim in, well, action. We literally shudder a little bit each time the heart ejects blood. Back in the day, researchers compared patterns of that shudder to detect and quantify disorders of cardiac output. As someone who had studied biomedical engineering in college, I thought it was pretty cool that you could non-invasively estimate cardiac output by measuring how much somebody bounced up and down with each heartbeat, even though it had been eclipsed by more accurate and easier to use technology.
By the way, you can easily measure the effect yourself, if you have an analog bathroom scale. Just stand on it as still as you can, and you will notice the needle deflects slightly with each heart beat – as the blood goes “up” out of your heart, your body goes “down” and your weight appears to increase momentarily. More elaborate ways to measure and quantify the effect are, of course, available on YouTube.
Well, imagine my surprise when a similar principle of using movement of the whole body as a non-invasive cardiac diagnostic tool was reported in a recent issue of Circulation. In this case, the authors took advantage of the accelerometers built into contemporary smartphones. By placing a smartphone on the chest of a supine subject, they were able to record body motion without electrodes or other sensors, and then use the pattern of that motion to accurately distinguish the regular steady beating of normal sinus rhythm from the irregularity of atrial fibrillation (AF). They conclude, “smartphone mechanocardiography reliably detects AF without additional hardware and provides a new easy-to-use and accessible concept for AF screening.”
I still think that is pretty cool. What do you think?