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

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 that benefit from dual-chamber pacing are typically 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. A negative tilt-test in vasovagal patients with spontaneous asystole documented by 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 stroke volume may still be relatively preserved. In this regard, detection of right ventricular impedance offers promise. In conclusion, conservatism is recommended limiting pacing in VVS to a small subset of symptomatic older patients with clearly documented cardioinhibition paying particular attention to the timing of loss of consciousness in relation to asystole/bradycardia. Understanding VVS physiology permits application of well-timed and appropriate pacing that yields benefit for highly symptomatic patients