Is heart rate recovery index a predictive factor for cardioinhibitory syncope?

Background: Cardioinhibitory syncope is related with excessive bradycardia or asystole due to parasympathetic response.

Aim: We investigated whether patients with cardioinhibitory syncope have higher heart rate recovery index (HRRi) considered as a parasympathetic system activation in exercise stress testing (EST) than in those with other neurogenic syncope forms.

Methods: A total of 262 patients who had neurogenic syncope documented by head-up tilt test (HUTT) and 199 healthy control individuals were examined. A maximal EST was applied to all patients after the HUTT. The HRRi was obtained by subtracting the heart rate that was measured at the first (HRRi-1), second (HRRi-2), and third minute (HRRi-3) of the recovery period from the maximal heart rate that was measured during the test.

Results: Eighty patients had cardioinhibitory syncope, 118 patients had vasodepressor syncope, and 64 patients had mixed-type syncope. The HRRi-1 was higher in patients with syncope (43.3 ± 7.7) compared to the control group (34.5 ± 4.8; p < 0.001). Post hoc analysis showed that among the syncope groups, there was no difference between patients with vasodepressor syncope (42.2 ± 7.6) and those with mixed type syncope (40.7 ± 4.1) in terms of HRRi-1 (p = 0.420). However, patients with cardioinhibitory syncope (47 ± 8.7) had a higher HRRi-1 than vasodepressor and mixed-type syncope groups (p < 0.05). The threshold value of the HRRi-1, which can be used for the prediction of cardioinhibitory syncope development, was determined to be 41 with 75% sensitivity and 72% specificity.

Conclusions: The HRRi-1 was higher in patients with cardioinhibitory syncope compared to the controls. The HRRi-1 has the predictive feature of differentiating cardioinhibitory syncope from other syncope types.