Pacing in vasovagal syncope: Physiology, pacemaker sensors, and recent clinical trials-Precise patient selection and measurable benefit

Abstract

The role of pacing in vasovagal syncope (VVS) is considered from a physiological basis. Most VVS patients lose consciousness due to hypotension before severe bradycardia/asystole occurs. Patients who benefit from dual-chamber pacing typically are older with highly symptomatic, late-onset, frequent and severe syncope with short/no prodrome and documented severe cardioinhibition. Tilt testing is of value in patients with recurrent unexplained syncope to identify important hypotensive susceptibility stemming from reduced venous return and stroke volume (SV). A negative tilt test in vasovagal patients with spontaneous asystole documented by an implantable/insertable loop recorder is associated with lower syncope recurrence rates after pacemaker implantation. Pacing may be more effective if triggered by sensor detection of a parameter changing earlier in the reflex than bradycardia when SV may still be relatively preserved. In this regard, detection of right ventricular impedance offers promise. Conservatism is recommended, limiting pacing in VVS to a small subset of symptomatic older patients with clearly documented cardioinhibition and paying particular attention to the timing of loss of consciousness in relation to asystole/bradycardia. Understanding VVS physiology permits application of well-timed, appropriate pacing that yields benefit for highly symptomatic patients.

Keywords: Asystole; Cardioinhibition; Pacemaker; Vasodepression; Vasovagal syncope.

Figure 1.

Upper panel shows HR/BP during tilt. First arrow denotes tilt-up and second denotes start of bradycardia. Star denotes loss of consciousness. Lower panel also shows heart rate/blood pressure in second tilt of same patient. First arrow denotes tilt-up; second arrow denotes onset of symptoms. Fall in heart rate was steep. Pacing was triggered at heart rate 45bpm and delivered at 90ppm. With pacing, blood pressure was low (<50 mmHg systolic), but patient remained conscious while upright for ~5 min. Petersen et al. (1994). Reproduced with permission.