Cardiac outcome measures such as heart rate, arrhythmia, and interbeat intervals are essential indicators of cardiorespiratory diseases. At the same time, heart rate variability (HRV) provides a non-invasive way to study the autonomic nervous system (ANS) and detect a change in a patient's physiologic state.
ECG: Wearable electrode sensors are used to measure the heart's electrical activity during each cardiac cycle. The heart's high-resolution voltage is plotted against time to create an electrocardiogram (ECG) and identify heart rhythm abnormalities. The accuracy and complexity of cardiac outcomes derived from ECG technology mainly depend on the number and placement of electrodes. Wearable ECG technology can be implemented in shirt, patch, and strap form factors and range from single to 12-lead.
PPG: PPG sensors provide an alternative form factor to measure pulse rate as a surrogate for heart rate and HRV measures at rest. PPG may also be used to assess decompensation via derived SpO2. Wearable PPG sensors may include the wrist, ring, patch worn form factors, and more standard finger clip sensors that can be used for spot checks and short recording durations.