Skin Sympathetic Nerve Activity and the Short-Term QT Interval Variability in Patients With Electrical Storm

Abstract

Background: Skin sympathetic nerve activity (SKNA) and QT interval variability are known to be associated with ventricular arrhythmias. However, the relationship between the two remains unclear. Objective: The aim was to test the hypothesis that SKNA bursts are associated with greater short-term variability of the QT interval (STVQT) in patients with electrical storm (ES) or coronary heart disease without arrhythmias (CHD) than in healthy volunteers (HV). Methods: We simultaneously recorded the ECG and SKNA during sinus rhythm in patients with ES (N = 10) and CHD (N = 8) and during cold-water pressor test in HV (N = 12). The QT and QTc intervals were manually marked and calculated within the ECG. The STVQT was calculated and compared to episodes of SKNA burst and non-bursting activity. Results: The SKNA burst threshold for ES and HV was 1.06 ± 1.07 and 1.88 ± 1.09 μV, respectively (p = 0.011). During SKNA baseline and burst, the QT/QTc intervals and STVQT for ES and CHD were significantly higher than those of the HV. In all subjects, SKNA bursts were associated with an increased STVQT (from 6.43 ± 2.99 to 9.40 ± 5.12 ms, p = 0.002 for ES; from 9.48 ± 4.40 to 12.8 ± 5.26 ms, p = 0.016 for CHD; and from 3.81 ± 0.73 to 4.49 ± 1.24 ms, p = 0.016 for HV). The magnitude of increased STVQT in ES (3.33 ± 3.06 ms) and CHD (3.34 ± 2.34 ms) was both higher than that of the HV (0.68 ± 0.84 ms, p = 0.047 and p = 0.020). Conclusion: Compared to non-bursting activity, SKNA bursts were associated with a larger increase in the QTc interval and STVQT in patients with heart disease than in HV.

Keywords: QT interval and corrected QT interval; QT interval variability; electrical storm; sudden cardiac death; sympathetic nerve activity.

Figure 1

Manual marking of the QT interval using the tangent method in a healthy volunteer performing the cold-water pressor test (CPT). The vertical dotted lines mark the onset of QRS complexes and the end of T waves. The T wave ends when it crosses the isoelectric segments between T and P waves (dashed red line segments). The measured QT interval of each beat is also shown in the figure.

Figure 2

Representative examples of determining skin sympathetic nerve activity (SKNA) burst activity in healthy volunteers (A) and ES group (B). The SKNA was the averaged SKNA amplitude of 30 consecutive beats. The distribution of SKNA values resulted in two Gaussian distributions. The burst threshold, indicated by a red dotted line, was calculated as the mean representing the lower distribution plus three times the SD. (A) The threshold value was 1.40 μV for one healthy volunteer. (B) The threshold value was 1.03 μV for one patient with ES. (C) Summary threshold data of the three groups. The threshold for a SKNA burst in the ES group was lower than that of control group.

Figure 3

The correlation of SKNA to the QT/QTc interval and short-term variability of the QT interval (STVQT) for healthy volunteers and ES group. Tracings show the ECG, SKNA, average SKNA (aSKNA), QT interval, QTc interval, and STVQT. (A) In a healthy volunteer who underwent CPT, the increase in aSKNA correlated to a change in the QT/QTc interval and was associated with an increase in the STVQT. (B) In a patient with ES, the aSKNA burst (red star) was associated with an oscillation of the QT/QTc interval and a significantly increased STVQT. Interestingly, the STVQT of the patient with ES increased dramatically even when the aSKNA increased slightly (red arrows did not reach the burst threshold), which may indicate that the vulnerability of STVQT may be influenced by aSKNA in ES patients. (C) The example of a SKNA burst and its timing relation to the QT interval and STVQT in an ES patient. The QT interval (ms) of each beat is shown above the ECG tracing. The mean aSKNA at baseline was 0.866. The aSKNA at the red arrow is 0.947. The aSKNA threshold (blue arrow) is 1.025.

Figure 4

The heart rate (A), QT interval (B), QTc interval (C), STVQT (D), and their differences between SKNA baseline (non-bursting activity) and SKNA burst in healthy volunteers and ES group and coronary artery disease (CHD) group. At SKNA baseline and SKNA burst, the QT interval, QTc interval, and STVQT in ES group (red) and CHD group (green) are significantly higher than those of healthy volunteers (black). Although with higher STVQT at baseline, the STVQT difference between the SKNA burst and baseline in the ES group and CHD group was significantly higher than that in healthy volunteers.