Recent studies have revealed a possible link between heart rate variability (HRV) and major depressive disorder (MDD), with decreased HRV in MDD compared with healthy subjects. Corrected Q-T interval (QTc) has been suggested to represent an indirect estimate of HRV, as QTc length is inversely correlated to parasympathetic activity in healthy subjects. This retrospective study assessed the ability of QTc length in predicting response to vagus nerve stimulation (VNS) treatment in refractory depression.
We measured QTc length in 19 patients suffering from refractory depression, selected to be implanted with VNS. Correlations were calculated between baseline QTc (preimplantation) and long-term mood response.
Nineteen patients selected for VNS surgery were included in the study. Baseline 28-item Hamilton Depression Rating Scale scores were 28.5 ± 6.8 and decreased to 15.1 ± 9.5 at 12 months and 12.4 ± 10.4 at 24 months post-VNS. Among the 19 patients, 53% (10) were responders and 26% (5) were in remission at 12 months. Pretreatment QTc averaged 425.5 ± 22.0. Patients with longer baseline QTc displayed larger improvement, with a significant correlation between mood and QTc values after 12 months (r(18) = −0.526, P = 0.02) and also after 24 months of VNS therapy (r(17) = −0.573, P = 0.016).
The presented analysis showed that increased QTc in patients with MDD might be used as a baseline biomarker for depressive episodes that might respond preferentially to VNS. The link between cardiovagal activity in depression and response to VNS treatment requires further investigation in larger cohorts and randomized controlled trials.