Use case: Monophasic action potential detection with the module MAP30a
2 Sep 2013

Our monophasic action potential analyzer MAP30a is dedicated to detecting specific shapes in signals generated in isolated heart experiments.

The monophasic action potential (MAP) signals start with a sharp transition. To measure its maximum variation (dV/dt Max) we might increase the sampling frequency above the recommended limit of 2000 Hz.
► Does it have an impact on the detection? Is it necessary?  

MAP30a quick overview

The input signal is applied to the red input (In). The green input (Trigger) is optional and can be connected to an external detector (see MAP30a reference documentation). The module calculates general parameters characteristics for repetitive shapes (maximum, minimum, maximum of the first derivative, minimum of the first derivative, rate) and parameters specific to an action potential (resting potential, plateau, recovery marks).

MAP30a analysis at higher sampling frequencies

When the acquisition is done at a higher sampling frequency than 2000 Hz, 10000 Hz in our case,  MAPs are detected and the characteristic points are calculated with the exception of the recovery marks (Figure 1). This is due to an internal limitation of the module, which was not intended for sampling frequencies higher than 2000 Hz.

Figure 1: Detection of a MAP signal at a higher sampling frequency than recommended (MAP 10 kHz graph) and recommended (MAP 2 kHz graph).

 

A comparison was done between the dv/dt Max values obtained at the two different sampling frequencies. Mean and standard deviation, shown in Figure 2, were calculated over 20 s intervals using the AVG11a module (Arithmetic mean & filter options, median and SD calculator). The differences are insignificant for the analysis.

Figure 2: Mean and standard deviation (STD) calculated for dV/dt Max for the two sampling frequencies: 10000 Hz red line + cross and 2000 Hz blue line + cross.

 

In conclusion, if the analysis does not show the recovery marks, check the sampling frequency of the MAP channel.
For already acquired files, the sampling frequency can be reduced by inserting an interpolator (ITP10a) before the MAP30a module. Change the parameter Frequency to 2000 Hz, and then recalculate ITP10a and MAP30a.