recognizable in the case of an egm endocardial the collected signal is a complex signal which is spread over time this signal shows a phase of fast increase of the potential with a duration of approximately 10 ms followed by a phase of slow decrease spreading over approximately 30 ms that decrease phase has a slightly uneven profile in the case when an evoked endocardial signal is actually present as illustrated by the full line and a less uneven profile in reverse case as illustrated by the dashed line the discrimination between those two profiles will allow to determine whether or not the capture has been performed that is to say whether the pacing pulse has been effective or not that discrimination is done by analyzing the endocardial atrial signal s over the duration of a sensing window or u201c listening window u201d f of a fixed duration of 40 ms for example or parameterable i e programmable duration e g in the range of from 10 to 150 ms following an atrial pacing pulse stima the period referred to as u201c microblanking u201d immediately following the delivery of the pacing pulse and during which the amplifier is switched off during a few tens of microseconds so as to avoid any load of sensing circuits is not taken into account here based upon the collected atrial endocardial signal s t the device determines the second derivative s u2033 t d 2 s dt 2 that second derivative is easy to calculate based upon.