Chapter 8: Differentiating regular and irregular PPG-recordings

Introduction

In the previous chapter, we discussed the characteristics of a good-quality PPG-signal and the advantages of analyzing its first derivative. In this chapter, we will share some tips on how to interpret the PPG and the differentiation between regular and irregular PPG-recordings.

Key messages

✔️ A regular PPG-recording is characterized by a consistent pattern of beat-to-beat intervals, resulting in a smooth wave-like pattern on the PPG, a smooth curve on the tachogram, and a tight clustering of points on the Poincaré plot.

✔️ A regular rhythm with ectopic beats causes irregularities in the PPG-signal, reflected as occasional deviations in the tachogram and Poincaré plot.

✔️ Atrial fibrillation will show an irregular and erratic pattern of the PPG-signal, with no discernible pattern of beat-to-beat intervals on the tachogram and a scattered distribution of points on the Poincaré plot.

Regular rhythm

A regular sinus rhythm will be reflected in a consistent wave-like pattern of the PPG-signal, with intervals between each wave being approximately of the same length. These intervals are known as beat-to-beat intervals, and they reflect the time between consecutive heartbeats. In a regular rhythm, the intervals are consistent, with little or no variation between consecutive heartbeats.

The tachogram is a graphical representation of the beat-to-beat interval over time. A regular sinus rhythm will be reflected in a consistent pattern on the tachogram, with the beat-to-beat intervals being approximately the same length between consecutive heartbeats. This will result in a smooth curve on the tachogram with little or no variation in the height of each peak.

The Poincaré plot is a graphical representation of the correlation between successive beat-to-beat intervals. In a regular sinus rhythm, the beat-to-beat intervals are highly correlated, resulting in a tight clustering of points on the Poincaré plot.

We can conclude that a regular rhythm is characterized by a consistent pattern of beat-to-beat intervals, resulting in a smooth wave-like pattern on the PPG, a smooth curve on the tachogram, and a tight clustering of points on the Poincaré plot.

Regular rhythm with ectopic beats

A regular rhythm with ectopic beats is characterized by occasional irregular beats that originate outside of the normal electrical pathway of the heart. You can use the pattern of the PPG-signal, the shape of the tachogram and the appearance of the Poincaré plot to differentiate between a regular rhythm and a regular rhythm with ectopic beats.

A normal rhythm with ectopic beats will show occasional irregularities in the PPG-signal, such as premature or delayed peaks. This will be reflected in the tachogram as occasional deviations from the regular pattern of beat-to-beat intervals. The Poincaré plot will have a slightly irregular shape with some points deviating from the elliptical pattern.

Atrial fibrillation

On a PPG-signal, atrial fibrillation is characterized by a highly irregular and chaotic pattern of waveforms with no discernible pattern or rhythm. The intervals between beats are highly variable, with no consistent pattern of beat-to-beat intervals. The tachogram will show a highly irregular pattern of peaks and valleys, with no clear pattern of beat-to-beat intervals. The Poincaré plot will show a scattered distribution of points, with no clear clustering or pattern.