This article walks through setting up QTcH as a custom derived parameter in Ponemah v5.4. Custom Derived Parameter is a new feature in Ponemah v5.4 and is not available in previous versions of Ponemah.
Create Equations in Custom Derived Parameters (CDP) window
Open the Custom Derived Parameters Dialog by clicking on Setup>Custom Derived Parameters within a review session
- Click Add New to create a new derived parameter
- Fill out the Following fields
- Name: QTch
- Parent Algorithm: ECG
- Averaging: Mean
- Unit: msec
- Matching Type: Closest
- Create a variable for Slope by clicking on the Edit button in the Variables section
- Enter an appropriate name and default value. Note that the Headers will populate with the Groups Name (setup in the P3 Setup). In the example below, the group names were "SSAN1", "SSAN2", and "Group C".
- Build your equation by performing the following steps
- click on "ECG" under Algorithm and double click on "QT-I". You will see the variable of QT from the ECG channel in the Expression fields.
- Click on the division sign button or type in a "/" in the Expression field after [ECG:QT-I(0)].
- Double Click on "Pow" in the Functions section
- Place your cursor after the "Pow(", just preceding the comma and either type in both an opening and closing parenthesis in the expression field or Click on the "(...)" button. Ensure your cursor is after the second of the two open parenthesis "(("
- Click on "ECG" under Algorithm and double click on "RR-I".
- Click on the division sign button "/" or type in a "/" in the Expression field after [ECG:RR-I(0)].
- Enter the reference RR interval1 appropriate for the species you are correcting for
- Delete the "2" after the "," comma and either type in the variable name (case sensitive) created in Step 3, or double click on the variable in the Variables list.
- Select "Update". The formula is created and the OK button is now enabled.
Setup a RR vs QT Scatter Plot
Prior to getting the slope and intercept from the scatter plot of the RR vs QT cloud plot, it's important to note that ECG analysis, preferably using ECG PRO, needs to be completed and "Delete marks from Unmatched Cycles" is performed.
Open the Graph Setup (P3 Setup>Graph setup)
- Setup the graph type as Scatter
- Select the input for both the X and Y axes as the same ECG channel
- Set the X axis Parameter to RR-I
- Set the Y axis Parameter to QT-I. Note that in the Bin Options field, QTcH now becomes enabled.
- Set the "Width" in the Bin Options section to the appropriate Bin width for the RR intervals to be grouped in. Recommended to set to 10 msec2
- Set the "QTcH Minimum" to the appropriate minimum amount of cycles that would needs to be represented in each bin in order to be used in the calculation. Recommended to set to 250 cycles2. NOTE: This field will be grayed out if QT-I is not a parameter selected for the Y axis.
View the RR vs QT Scatterplot
- Set the logging rate (Press F8) to the appropriate logging rate that should be averaged together for the RR/QT calculations. Recommended to set to 10 sec2 or potentially larger. NOTE: if the "View Entire Dataset" icon is red (and not grayed out), click on the icon so that the entire dataset is being displayed. You may also need to auto-scale the graph page to view all the data for this step and the next few steps. This can be done by double clicking on the graph page and clicking on the "AutoScale" button
- Click on the LOG icon in the scatter plot graph and click on "Log both XY axes"
- Click on the "Toggled Binned Average Mode" icon , to enable the bin width and minimum number of cycles per bin calculations. The data points will now be represented as a 1 point average for every bin of X milliseconds (defined in Step 10), that has at least X cycles presented in each bin (defined in Step 11)
- Click on the "Linear Regression Mode" icon . A Linear regression line will be displayed.
- Click on the "Copy Linear Regression Results" Icon and select "Copy Slope To" and select the variable, created in Step 3, that was created for storing the slope of linear regression line (Beta).
- Go into the Derived Parameters dialog window (Setup>P3 setup>Channel Input Setup) to enable output of the QTcH derived parameters on the appropriate channel(s).
1. Holzgrefe, H. H., Cavero, I., Gleason, C. R., Warner, W. A., Buchanan, L. V., Gill, M. W., … Durham, S. K. (2007). Novel probabilistic method for precisely correcting the QT interval for heart rate in telemetered dogs and cynomolgus monkeys. Journal of Pharmacological and Toxicological Methods, 55(2), 159–175. https://doi.org/10.1016/j.vascn.2006.05.007
2. Holzgrefe, H. H., Cavero, I., & Gleason, C. R. (2007). Analysis of the nonclinical telemetered ECG: impact of logging rate and RR bin width in the dog and cynomolgus monkey. Journal of Pharmacological and Toxicological Methods, 56(1), 34–42. https://doi.org/10.1016/j.vascn.2006.12.002