Autonomic modulation of repolarization instability in patients with heart failure prone to ventricular tachycardia

Abstract

QT variability (QTV) signifies repolarization lability, and increased QTV is a risk predictor for sudden cardiac death. The aim of the present study was to investigate the role of autonomic nervous system activity on QTV. This study was performed in 29 subjects: 10 heart failure (HF) patients with spontaneous ventricular tachycardia [HFVT(+)], 10 HF patients without spontaneous VT [HFVT(-)], and 9 subjects with structurally normal hearts (HNorm). The beat-to-beat QT interval was measured on 3-min records of surface ECGs at baseline and during interventions (atrial pacing and esmolol, isoprenaline, and atropine infusion). Variability in QT intervals was expressed as the SD of all QT intervals (SDQT). The ratio of the SDQT to SD of RR intervals (SDRR) was calculated as an index of QTV normalized to heart rate variability. There was a trend toward a higher baseline SDQT-to-SDRR ratio in the HFVT(+) group compared with the HFVT(-) and HNorm groups (P = 0.09). SDQT increased significantly in the HFVT(+) and HFVT(-) groups compared with the HNorm group during fixed-rate atrial pacing (P = 0.008). Compared with baseline, isoprenaline infusion increased SDQT in HNorm subjects (P = 0.02) but not in HF patients. SDQT remained elevated in the HFVT(+) group relative to the HNorm group despite acute β-adrenoceptor blockade with esmolol (P = 0.02). In conclusion, patients with HF and spontaneous VT have larger fluctuations in beat-to-beat QT intervals. This appears to be a genuine effect that is not solely a consequence of heart rate variation. The effect of acute autonomic nervous system modulation on QTV appears to be limited in HF patients.

Entropy Analysis of RR and QT Interval Variability during Orthostatic and Mental Stress in Healthy Subjects

“…Closer inspection of the baseline data points towards a statistical outlier with a value of SDQT that is four times higher than in the other recordings. Increased QTV during sympathetic activation is in line with several previous reports [2,5,8].…”

“…In healthy subjects sympathetic activation via orthostatic provocation or pharmacological β-adrenoceptor stimulation was shown to increase QTV [2], while the relationship between sympathetic activity and QTV during rest is less clear. In patients with cardiovascular (co-)morbidities the relationship between sympathetic activity and QTV has been insufficiently explored [3][4][5][6].…”

Autonomic Modulation in Patients with Heart Failure Increases Beat-to-Beat Variability of Ventricular Action Potential Duration

“…Enhanced sympathetic activity by tilt table testing in heart failure patients is associated with an increased QTV although the increase may be impaired in comparison to normal subjects (Desai et al, 2004; Piccirillo et al, 2006). Heart failure patients with a history of ventricular tachycardia (VT) show higher baseline values of QTV compared to those without VT and compared to normal subjects (Nayyar et al, 2013). In the latter study Isoprenaline increased QTV in normal subjects but not in the heart failure-VT group, highlighting the limited autonomic modulation of QTV in heart failure patients (Nayyar et al, 2013).…”

“…Heart failure patients with a history of ventricular tachycardia (VT) show higher baseline values of QTV compared to those without VT and compared to normal subjects (Nayyar et al, 2013). In the latter study Isoprenaline increased QTV in normal subjects but not in the heart failure-VT group, highlighting the limited autonomic modulation of QTV in heart failure patients (Nayyar et al, 2013). …”

A Time-Varying Nonparametric Methodology for Assessing Changes in QT Variability Unrelated to Heart Rate Variability

“…A methodology that provides non-invasive assessment of intrinsic VRD by measuring QTV unrelated to heart rate variability may find applications in arrhythmic risk stratification [1], [9], [13], [48] as well as in the noninvasive assessment of sympathetic ventricular activity [19], [49]. For instance, correlations between QTV and a direct measure of sympathetic activity were observed in patients with hypertension [50], while patients with heart failure and spontaneous ventricular tachycardia have higher QTV than control [51]. Passive tilt is an established model to study the autonomic modulation of cardiac activity, since it induces a shift of the sympathovagal balance toward sympathetic predominance [49], [52].…”