Skin sympathetic nerve activity and ST-segment depression in women

Abstract

BackgroundST depression on exercise electrocardiogram (ECG) and ambulatory ECG monitoring may occur without myocardial ischemia. The mechanisms of non-ischemic ST depression remain poorly understood. ObjectiveTo test the hypothesis that the magnitudes of skin sympathetic nerve activity (SKNA) correlate negatively with the ST segment height (ST height) in ambulatory participants. MethodsWe used neuECG to measure ambulatory ST height and average SKNA (aSKNA) in 19 healthy women, 6 women with a history of Takotsubo Syndrome (TTS), and 4 women with ischemia and no obstructive coronary arteries (INOCA). ResultsBaseline average SKNA (aSKNA) was similar between healthy women, TTS, and INOCA (1.098±0.291 μV, 0.980± 0.061 μV, and 0.919 ± 0.0397 μV, respectively, p=0.22). The healthy women had only asymptomatic upsloping ST depression. All participants had a significant (p<0.05) negative correlation between ST height and aSKNA. Ischemic episodes (n=15) were identified in 2 TTS and 4 INOCA participants. The ischemic ST depression was associated with increased heart rate and elevated aSKNA compared to baseline. An analysis of SKNA burst patterns at similar heart rates revealed that SKNA total burst area was significantly higher during ischemic episodes than non-ischemic episodes (0.301±0.380 μV.s and 0.165±0.205 μV.s, p=0.023) in both the TTS and INOCA participants. ConclusionsAsymptomatic ST depression in ambulatory women is associated with elevated SKNA. Heightened aSKNA is also noted during ischemic ST depression in women with TTS and INOCA. These findings suggest that ST segment depression is a physiological response to heightened sympathetic tone but may be aggravated by myocardial ischemia.