Atrial fibrillation (AFib) is characterized by chaotic electrical signals originating in the heart’s upper chambers, the atria. This electrical disarray causes the atria to quiver instead of beating effectively, leading to an irregular and often rapid heartbeat. A pulse oximeter is a readily available, non-invasive device that measures oxygen saturation (SpO2) and the peripheral pulse rate (BPM). While not a diagnostic tool, it acts as a screening device that can display specific irregularities consistent with AFib.
How Pulse Oximeters Interpret Rhythm
A pulse oximeter determines the heart rate using photoplethysmography (PPG), which involves shining light through a tissue bed, typically a fingertip. The device then measures the changes in light absorption that occur with each surge of blood volume as the heart pumps. This pulsatile blood flow creates a wave pattern known as the plethysmographic waveform, which the device analyzes to calculate the pulse rate. For a heart beating in a regular rhythm, the resulting waveform shows predictable, uniform peaks and valleys, allowing the oximeter’s internal algorithm to calculate a stable, accurate pulse rate.
In a person experiencing AFib, the heart’s irregular rhythm translates directly into random and inconsistent arterial pulsations. Because the electrical signals are chaotic, the amount of blood ejected with each beat is highly variable. This means the pulse volume and the time between beats are also inconsistent. This irregularity disrupts the oximeter’s standard averaging algorithm, causing the device to struggle to lock onto a stable reading, which is the physical manifestation of AFib on the screen.
Visual Indicators of Atrial Fibrillation on the Device
The most immediate and common sign of AFib on a consumer pulse oximeter is the wildly fluctuating numerical pulse rate reading. Instead of settling on a stable average, the BPM number will jump erratically, for example, displaying 60, then 120, then 85, and then 100 in quick succession. This fluctuation is not always an accurate reflection of the true heart rate, but rather the device’s failed attempt to measure the chaotic, beat-to-beat variability of the peripheral pulse.
If the pulse oximeter features a plethysmograph (the small, visual waveform that scrolls across the screen), it will also display profound inconsistency. In a normal rhythm, the peaks of this wave are relatively uniform in height and evenly spaced, reflecting consistent timing and blood volume with each beat. When AFib is present, the height and distance between the peaks become highly irregular and inconsistent. This chaotic waveform reflects the variable strength and timing of the pulse volume being detected in the fingertip.
Some consumer-grade oximeters may be unable to process the level of signal instability caused by AFib. In these cases, the device may simply fail to provide a reading at all, displaying dashes, a zero, or a “N/A” error message instead of a pulse rate. Newer devices may be programmed to recognize the pattern of irregularity and display a specific icon, such as a blinking heart or an “Irregular Pulse” symbol, providing a direct visual warning.
Device Limitations and When to Seek Medical Confirmation
It is important to recognize that a pulse oximeter measures the pulse rate at the periphery, which is the physical movement of blood, and not the electrical activity of the heart. Consequently, an erratic reading on the device does not serve as a definitive diagnosis of AFib. The gold standard for diagnosing any heart rhythm disorder is an Electrocardiogram (ECG or EKG), which directly measures the heart’s electrical signals.
Many non-cardiac factors can cause a pulse oximeter to display unstable or inaccurate readings, leading to a false indication of irregularity. These factors include:
- Patient motion or shivering (known as motion artifact).
- Poor peripheral perfusion, such as cold hands or low blood pressure, which weakens the pulse signal.
- Cosmetic factors like dark nail polish.
- Darker skin pigmentation, which can interfere with the light-based technology.
If an irregular pattern is observed, a person should first ensure all external factors are corrected, such as warming the hands and remaining still, and re-test on multiple fingers. An immediate manual check of the radial pulse at the wrist can offer a simple confirmation of the perceived irregularity. If the pulse oximeter consistently shows a sustained, chaotic irregularity despite these checks, consulting a healthcare provider is the appropriate next step for definitive testing. This usually involves a diagnostic ECG or a Holter monitor, which records the heart’s electrical activity over a longer period.