Background: In patients in whom syncopal episodes are mainly caused by occasional drops in heart rate, Sudden Rate Drop intervention feature intends to provide high rate intervention pacing. New Vitatron Medical B.V. pacemaker system Clarity DDDR, provideS AN option FOR recognizing Sudden Rate Drop and responding by intervention pacing until it detects the recovering.
Material/Methods: In patients with carotid sinus syndrome it is possisble to provoke this situation BY sinus caroticus massage. we have implanted 10 of these devices in our center, 2 of which in patients with hypersensitive carotid sinus syndrome. in both patients, we activated sudden rate drop intervention on DDD mode pacing and applied protocol for testing the necesaary level of Suden Rate Drop Intervention Rate. Both patients gave their informed consent to be submitted to this testing. Pacemaker software assumes rate intervention level of 110 bpm. We tested our patients for rate levels of 90 and 110 bpm. Massaging the carotid sinus during 5 seconds, we provoked Suden Rate Drop Intervention 10 times, in each patient, 5 times at intervention rate of 90 and 5 times at 110bpm. Patients were unaware of the programmed intervention rate and were merely expected to report any different sensations experienced during the testing.
Results: In all 20 tests, pacemaker responded to sudden rate drop elicited by carotid sinus massage (100%), which was verified by selected event recordings. After the massage, neither of the patients registered any sensations at sudden rate drop intervention rate level of 90 bpm in a total od 10 tests (100%), while 8 out of 10 massages at 110 bpm intervention rate provoked palpitations (80%). On the grounds of this testing, we concluded that lowering of Sudden Rate Drop Intervention Rate Level from 110 BPM to 90 BPM does not affect the reliability of system reaction, but changes patient's awareness of heart beats.
Conclusions: As a final conclusion, it should be said that basic prerogatives of a pacing system: safety and efficacy with minimal energy consumption, and in this case, quality of life option that a patients practically does not feel intervention when it occurs, are all met.

Keywords: carotid sinus syndrome