ECG and PPG are two distinct methods used to measure heart activity, but they function through unique mechanisms and provide complementary information. ECG stands for electrocardiogram and detects cardiac electrical impulses produced by the heart as it beats. Electrodes are positioned on the skin to capture these signals, typically on the torso and extremities. The output signal shows the pattern and intensity of the cardiac depolarization waves that cause the heart to pump. This ensures ECG’s precision for identifying arrhythmias, heart attacks, and other electrical abnormalities in the heart.
The acronym PPG refers to photoplethysmogram and relies on optical sensing to track variations in vascular blood flow in the vessels. A PPG sensor, commonly found in fitness trackers and smartwatches, emits light—usually green or infrared into the skin and measures how much light is reflected back. During each arterial surge, the light extinction level changes slightly, permitting pulse rate approximation and occasionally identify perfusion anomalies. PPG is ideal for ongoing, contactless assessment during daily activities, but it is highly affected by physical activity, melanin content, and external conditions, which can affect its accuracy.
While ECG gives a detailed view of the heart’s cardiac conduction system, PPG is indicative of the hemodynamic response—the arterial pressure wave generated by ventricular contraction through arteries. ECG remains the clinical benchmark in healthcare facilities for evaluating cardiovascular pathology, whereas PPG serves primarily for non-clinical fitness tracker assessment and cardiac rhythm screening. Some modern devices now combine both technologies to provide more comprehensive insights, but it’s crucial to recognize that they are not interchangeable. ECG is better for diagnosing specific heart problems, while PPG helps track long-term heart rate patterns in daily routines.