Because QT interval calculations are dramatically affected by heart rate, correcting for this is necessary in order to accurately assess any QT interval changes (for example, those induced by a study drug). Ponemah calculates QTc using the equation: QTC=QT +β(HR-60), where β is the correction factor used to account for heart rate. This value is the slope of the linear regression line between QT and HR (or RR). It must be calculated for each individual animal, then entered into Ponemah’s ECG analysis attribute module. For more information on this method of correction, see King et al., 2006.
Poneamh v5.4 or greater can calculate this within Ponemah using Custom Derived Parameters
- Perform template analysis in Ponemah.
- Set the logging rate to desired rate (1 epoch/30 seconds). Note: you may want to change this logging rate based on what the literature says is best for the species.
- Save Marks Section after completion of the calculations in Ponemah.
- Open the Ponemah Excel Output in Microsoft Excel.
- Remove any unnecessary sheets – eg the data reduction, group tabs, and sheets for any animals not being analyzed.
- Remove Nans displayed as 1E16 values (value: 9999900414574590) by performing a find and replace. Replace all instances with a blank cell. If you click Options under the find and replace menu, you can do this for the entire workbook at once.
- Now delete any rows with blank values (e.g. sections with bad data marks). To do this, highlight the heart rate column. Click on Find & Select > Go To Specials > Blank Cells, then Right Click on a blank cell and select delete entire row.
- Repeat this step for the QT column.
- In an empty cell in the formula =LINEST(QT values, HR values). (This formula takes the form LINEST(y values, x values)). This value will be negative; if it is positive then check to make sure your x and y values are in the correct order. If you get an error, check to make sure that you don’t have any empty cells in the columns of interest.
- Repeat this process for each animal included in the analysis.
- In Ponemah, enter the slope calculated in step 9 in the QTcK IACF field with the subject’s attribute analysis dialog (shown in screenshot below).