Picture an AA battery tumbling end over end, inside a leather football filled with salty water.
Never mind how it got there, or what's making it spin: Your goal is to figure out which way it's pointing at any instant, and whether anything is perturbing its movement, based solely on the minute changes in electrical potential detectable at the surface of the football.
How many wires would you use to take measurements? Ten? Twenty?
Markus Riemenschneider, CTO of CardioSecur in Frankfurt, says four is enough, and he'll even sell you a €99 device to do it.
But why? The question is of vital importance for some, because a tumbling battery or, more formally, a rotating electric dipole is a good model for the electrical behavior of the human heart.
Recording changes in electrical potential at the skin is a standard way of detecting and diagnosing anomalies in heart rate, rhythm and blood flow. Your cardiologist calls it taking an ECG, or electrocardiogram.
Riemenschneider's medical device, CardioSecur, has just four wires providing a reference level and measurements in three dimensions. It can provide the same results as a "12-lead" ECG (which confusingly uses just 10 wires), or even a 22-lead one taken at the doctor's office. A lead, in ECG parlance, is not a wire but a measure of the electrical activity in a particular direction across the heart, and many such measures can be deduced mathematically from measurements taken with a smaller number of wires.
A 12-lead display allows diagnosis not just of rhythm problems but also of ischemia -- heart attack.
CardioSecur allows someone with an ongoing heart problem to take their own ECG and analyze it with a smartphone app whenever they feel chest pain or discomfort. The CardioSecur Active app will compare the reading with a recording of their usual heartbeat, and recommend whether they should carry on as normal, make an appointment to see their doctor, or head straight for the emergency room. They can also transfer the reading to their doctor straight from the app.
The app is available for iOS or Android, and costs €9.95 per month, including home delivery of six sets of the disposable self-adhesive electrodes used to take the readings. Additional sets of electrodes can be ordered, costing from €1.40 per reading depending on quantity.
CardioSecur has a separate pricing plan for cardiologists, who pay more up-front for the CardioSecur but can access a Pro version of the app on iOS which displays the results as a 12-lead ECG for €9.95. Add-ons including a 22-lead display and automatic interpretation of the measurements can take the monthly price up to €39.85.
ECGs can be confusing to interpret if the placement of two electrodes is inversed -- something even professionals might do, as the color-coding of the wires is different for equipment sold in the U.S. and in Europe.
The CardioSecur app, though, automatically compensates for this and for misplacements of the electrodes of up to 5 centimeters, making it easier for patients to use, Riemenschneider said.
CardioSecur is not the only ECG device for smartphones on the market: Others include the Smartheart belt from SHL Telemedicine, which connects to a smartphone via Bluetooth, or the AliveCor, an iPhone case that has two electrodes on the back, one to be touched with each hand.
Whatever the device used, smartphone ECGs have advantages for patients as they are always present, and allow for faster analysis of measurements taken outside the doctor's office.
Many cardiologists wanting to monitor a patient's heartbeat for anomalies over a 24-hour period still expect patients to carry a dictating machine modified to make a four-track recording of the ECG on a standard microcassette at a slower than normal speed. When the patient returns the device, the recording is then transferred to a computer for analysis and interpretation.