Study hypothesis: Dual-chamber pacemaker therapy with rate-hysteresis features is effective in preventing syncopal recurrences in patients affected by cardioinhibitory (CI) forms of reflex syncope diagnosed by means of carotid sinus massage, tilt table testing or implantable loop recorder (ILR). The outcome is measured either by the time to first syncopal recurrence or the total syncope burden.

Background Divergence of opinion exists regarding the efficacy of cardiac pacing in patients affected by different forms of reflex syncope.

Definitions.

Severe syncope is defined when:

• it is perceived by patient that it alters his/her quality of life, and
• is unpredictable because occurs without, or with very short prodromes < 10 sec (thus exposing patients to risk of trauma) or, if preceded by prodromes, syncope recurs despite appropriate therapies (CPM or drugs).

Recurrent syncopes: at least 2 episodes during the last year (including the index episode) or 3 episodes during the last 2 years (including the index episode).

Suspected (undetermined) reflex syncope: the suspicion of reflex syncope is based on a history of uncertain syncope in the absence of (i) severe structural heart disease, significant ECG abnormalities, or rhythm disturbances; (ii) orthostatic hypotension; and (iii) non-syncopal causes of transient loss of consciousness.

Study protocol

1. The eligible patients undergo firstly carotid sinus massage (according to the method of symptoms); if a diagnosis of cardioinhibitory carotid sinus syndrome (CI-CSS) is made, a pacemaker is implanted and follow-up immediately starts.
2. If the carotid sinus massage is negative or vasodepressor, the patients undergo tilt table testing (with nitroglycerin or clomipramine drug challenge); if a diagnosis of VASIS 2B form is made, a pacemaker is implanted and follow-up immediately starts.
3. If tilt table testing is negative or a form different from VASIS 2B is induced, the patients undergo ILR implantation. If a diagnosis of asystolic reflex syncope is made, a pacemaker is implanted and follow-up immediately starts.

End-points End-point of the study is syncope recurrence after pacemaker (PM) implantation. Syncope is defined as complete transient loss of consciousness. Pre-syncope is counted but it is not an end-point.

Primary end-points:

1. Comparison of the time to first syncopal recurrence in CI-CSS and CI-TTT pts with PM and in control patients with ILR.
2. Intra-patient comparison of the syncope burden in the year before and in the year following PM implant in all patients receiving a PM (CCS, TTT and ILR groups). Index syncope is not counted.

Follow-up One year after PM implantation for all enrolled patients for burden of syncope end-points Until the study end for time to first syncope recurrence end-points. Thus, the study ends one year after the enrollment of the last patient.

Study size Based on the sample size calculation the study will stop when 700 patients are enrolled.

Inclusion Criteria:

• Patients affected by severe, recurrent, certain or suspected (undetermined) reflex syncopes, aged ≥ 40 years.

Exclusion Criteria:

• Reflex syncopes due to reversible causes, e.g., vasoactive drugs, concomitant diseases, etc
• Suspected of certain cardiac syncope
• Syncope caused by orthostatic hypotension
• Non-syncopal causes of transient loss of consciousness

Patients affected by reflex syncopes