Tachograms

What is a tachogram?

A tachogram is a type of time series graph used in Holter systems and other applications to graphically show the beat-to-beat intervals  (R-R intervals) (y-axis) across time or by consecutive beat numbers (x-axis). In Holter systems the tachogram often compresses many hours of data horizontally usually resulting in the interval data overlapping such that it is difficult to accurately appreciate the number of intervals at a particular time of a particular duration. Some systems permit hourly tachograms. With color-coded beat-to-beat annotation the potential exists to identify arrhythmias over time.

With this website you will be able to gain more from the tachogram because of three features:

1. A specific duration of time can be selected.
2. Three-dimensional representations of the data permit a clear delineation of beat density when the time is compressed.
3. Dynamic tachograms permit the animation of the beat-to-beat intervals with the selection of the time permitted

Creating an R-R interval tachogram

1) ECG

QRS waveforms are detected and identified with the beat-to-beat intervals determined in milliseconds.

2) DATA OUTPUT

These data are filed internally (in the Holter system) based on the point in time and the sample number (e.g. 256/sec).

3) TACHOGRAM PLOT

Time series plots can be created by exporting these data to the website herein, or if the Holter analysis system permits, using internal software. In this graph the timestamp is identified with the R-R intervals plotted and the QRS complex annotation identified by the ‘dot’ color which indicates the beat that ends the respective interval {bracketed region corresponds to ECG}.

Poincaré plots

What is a Poincaré plot?

A Poincaré plot (also referred to as a return map or Lorenz plot) is a form of geometric heart rate variability. It permits a beat-to-beat  (R-R interval) appreciation of rhythm. One beat interval (Beat-to-Beat interval on the x-axis) is plotted against the next (Beat-to-Beat +1 interval on the y-axis). An overlap of each progressive interval is graphed. These intervals are usually based on the QRS complexes and identified as R-R interval versus R-R +1 interval; however, P-P intervals could also be plotted. In fact, any data in a time series could be processed in this matter. Beat annotation (beat identification) can be indicated by color coding. Many Holter systems do not permit the intrinsic graphing of data for specified time periods (most are limited to a single hour or 24-hours). Extended or lag Poincaré plots show the relationship beyond one interval; such that R-R interval vs R-R + n interval is plotted.

With this website you will have the ability to better appreciate this type of examination because of three possibilities:

1. A specific duration of time can be selected.
2. Construction of plots with and without connecting lines.
3. Three-dimensional representations of the data permit a clear delineation of beat density when the time is compressed.
4. Dynamic Poincaré plots permit the animation of the beat-to-beat intervals with the selection of the time permitted.

Creating a Poincaré plot

To create a Poincaré plot the following steps are implemented.

1) Each beat is identified accurately and the time between beats is measured (milliseconds).

2) To begin, the first interval (R-R interval¹) between the first two beats is plotted against the next (R-R+1 interval²).

3) The interval that was ‘the next’ is then plotted against the following interval. Therefore, #1 interval versus #2 interval, then #2 interval versus #3 interval etc.

This process continues as follows until the entire selected data set has been graphed. When an interval is the ‘R-R’ it is on the x-axis and when an interval is the ‘R-R+1’ it is on the y-axis.

*indicates the beat-to-beat interval as illustrated with the electrocardiogram shown below. The value in milliseconds for each interval is shown above the electrocardiogram and labeled as RR to the left.

The table below shows the interval data that is used to construct the Poincaré plot on the x- and y- axes.

If beats are identified (e.g. sinus, ventricular, atrial, paced) they may be assigned a color to represent the beat between two intervals (RR vs RR+1). This is illustrated in the electrocardiogram above, with the QRS complexes in blue or red whereby this annotation becomes a blue dot for sinus beats and a red dot for ventricular beats on the Poincaré plot.

The completed Poincaré plot of the data in this example is shown in the graph below. Poincaré plots can reveal patterns in the beat-to-beat relationships of cardiac rhythms.

With study of this Poincaré plot, the following relationships are identified. Compare tabulated data to intervals on plot.

1. Consistent interval between couplets. (red ‘a’)
2. Following the second ventricular complex of the couplet, the interval to the next sinus beat progressively shortens. (green ‘b’)
3. The intervals preceding the first ventricular complex of a couplet progressively shortens with the shortest interval preceding a ventricular complex leading to ventricular tachycardia. (blue ‘c’)
4. Following the shortest two sinus beats ventricular tachycardia occurs. (pink ‘d’)

With dynamic (animated) Poincaré plots the true beat-to-beat relationship and patterning of cardiac rhythms becomes evident. From such studies mechanisms and triggers may be hypothesized or identified that may influence treatment (or at least provide a better understanding of cardiac arrhythmias). See video below.