Troubleshooting Pulse Sensor SEN0213 (Model: ECG, Gravity: Analog) with nRF52

Hello, community! I want to set up the SEN0213 sensor with my nRF52 device. I intend to use this sensor as a pulse sensor. I already have a driver for the ADC that was working correctly with the SEN0214 sensor. I'm using a resistive voltage divider with a division factor of 1.51 to connect the analog output from the sensor to the nRF52's ADC.
 

My issue is that when I connect the electrodes following the schematic provided in the manual, and with just two electrodes connected, the voltage at the ADC pin fluctuates around 1.09V and doesn't respond to the actual heartbeat. When I disconnect the electrodes from the body, the voltage fluctuates between 0-1.1V. What could be the problem?
 

I'm trying to set a reference voltage on the ADC corresponding to a heartbeat, and then, using a timer, calculate the time between two or three heartbeats. After that, I plan to use mathematics to calculate the pulse rate.