Pacing in neurocardiogenic/vasovagal syncope.

Pacing for neurocardiogenic or vasovagal syncope (VVS) has been practised for five decades, but the 1986 advent of tilt testing provided a means of diagnosis frequently revealing, in the early days, asystole caused by VVS. This was the basis for pacing these patients and the first studies created enthusiasm followed by randomised controlled trials, which were imperfectly designed, "confirming" benefit. When better trial design was employed, there was no obvious benefit. However, some cardiologists had seen patients experience a huge positive difference with pacing, so they set out to identify them. Two studies using ECG loop recorders to document heart rhythm during spontaneous attacks allowed better patient selection for pacing and appeared to achieve the aim. Further, it was noted in the second study, a randomised controlled trial (RCT) with good design, that tilt testing added a further dimension to the identification of the patient who would benefit. Thus, loop recorders are used to show asystole in spontaneous attacks and when tilt testing is negative, implying a lesser vasodepressor component, the patient will have the best outcome. From the available evidence, pacing should be dual-chamber in older patients (>40 years) with severe symptoms and in whom standard measures have demonstrably failed. The method of triggering pacing and its timing of introduction have not yet been resolved. Today's method is rate-hysteresis but there is another sensed event as an alternative: right ventricular impedance, which is now in RCT with substantial pilot evidence in its favour.