Susan Straka

Simultaneous noninvasive recording of skin sympathetic nerve activity and electrocardiogram

BACKGROUND Sympathetic nerve activity is important to cardiac arrhythmogenesis. OBJECTIVE The purpose of this study was to develop a method for simultaneous noninvasive recording of skin sympathetic nerve activity (SKNA) and electrocardiogram (ECG) using conventional ECG electrodes. This method (neuECG) can be used to adequately estimate sympathetic tone. METHODS We recorded neuECG signals from the skin of 56 human subjects. The signals were low-pass filtered to show the ECG and high-pass filtered to show nerve activity. Protocol 1 included 12 healthy volunteers who underwent cold water pressor test and Valsalva maneuver. Protocol 2 included 19 inpatients with epilepsy but without known heart diseases monitored for 24 hours. Protocol 3 included 22 patients admitted with electrical storm and monitored for 39.0 ± 28.2 hours. Protocol 4 included 3 patients who underwent bilateral stellate ganglion blockade with lidocaine injection. RESULTS In patients without heart diseases, spontaneous nerve discharges were frequently observed at baseline and were associated with heart rate acceleration. SKNA recorded from chest leads (V1-V6) during cold water pressor test and Valsalva maneuver (protocol 1) was invariably higher than during baseline and recovery periods (P < .001). In protocol 2, the average SKNA correlated with heart rate acceleration (r = 0.73 ± 0.14, P < .05) and shortening of QT interval (P < .001). Among 146 spontaneous ventricular tachycardia episodes recorded in 9 patients of protocol 3, 106 episodes (73%) were preceded by SKNA within 30 seconds of onset. Protocol 4 showed that bilateral stellate ganglia blockade by lidocaine inhibited SKNA. CONCLUSION SKNA is detectable using conventional ECG electrodes in humans and may be useful in estimating sympathetic tone.

Small Conductance Calcium-Activated Potassium Current Is Important in Transmural Repolarization of Failing Human Ventricles

Background—The transmural distribution of apamin-sensitive small conductance Ca2+-activated K+ (SK) current (IKAS) in failing human ventricles remains unclear. Methods and Results—We optically mapped left ventricular wedge preparations from 12 failing native hearts and 2 rejected cardiac allografts explanted during transplant surgery. We determined transmural action potential duration (APD) before and after 100 nmol/L apamin administration in all wedges and after sequential administration of apamin, chromanol, and E4031 in 4 wedges. Apamin prolonged APD from 363 ms (95% confidence interval [CI], 341–385) to 409 (95% CI, 385–434; P<0.001) in all hearts, and reduced the transmural conduction velocity from 36 cm/s (95% CI, 30–42) to 32 cm/s (95% CI, 27–37; P=0.001) in 12 native failing hearts at 1000 ms pacing cycle length (PCL). The percent APD prolongation is negatively correlated with baseline APD and positively correlated with PCL. Only 1 wedge had M-cell islands. The percentages of APD prolongation in the last 4 hearts at 2000 ms PCL after apamin, chromanol, and E4031 were 9.1% (95% CI, 3.9–14.2), 17.3% (95% CI, 3.1–31.5), and 35.9% (95% CI, 15.7–56.1), respectively. Immunohistochemical staining of subtype 2 of SK protein showed increased expression in intercalated discs of myocytes. Conclusions—SK current is important in the transmural repolarization in failing human ventricles. The magnitude of IKAS is positively correlated with the PCL, but negatively correlated with APD when PCL is fixed. There is abundant subtype 2 of SK protein in the intercalated discs of myocytes.

Crescendo Skin Sympathetic Nerve Activity and Ventricular Arrhythmia

We recently reported a new method (neuECG) to simultaneously record electrocardiogram (ECG) and skin sympathetic nerve activity (SKNA) in humans [(1)][1]. There was a significant association between SKNA and paroxysmal atrial tachyarrhythmias [(2)][2]. While our preliminary study showed that

Simultaneous recordings of intrinsic cardiac nerve activity and skin sympathetic nerve activity from human patients during the postoperative period

BACKGROUND Intrinsic cardiac nerve activity (ICNA) and skin nerve activity (SKNA) are both associated with cardiac arrhythmias in dogs. OBJECTIVE The purpose of this study was to test the hypothesis that ICNA and SKNA correlate with postoperative cardiac arrhythmias in humans. METHODS Eleven patients (mean age 60 ± 13 years; 4 women) were enrolled in this study. Electrical signals were simultaneously recorded from electrocardiogram (ECG) patch electrodes on the chest wall and from 2 temporary pacing wires placed during open heart surgery on the left atrial epicardial fat pad. The signals were filtered to display SKNA and ICNA. Premature atrial contractions (PACs) and premature ventricular contractions were determined manually. The SKNA and ICNA of the first 300 minutes of each patient were calculated minute by minute to determine baseline average amplitudes of nerve activities and to determine their correlation with arrhythmia burden. RESULTS We processed 1365 ± 973 minutes of recording per patient. Low-amplitude SKNA and ICNA were present at all time, while the burst discharges were observed much less frequently. Both SKNA and burst ICNA were significantly associated with the onset of PACs and premature ventricular contractions. Baseline average ICNA (aICNA), but not average SKNA, had a significant association with PAC burden. The correlation coefficient (r) between aICNA and PAC burden was 0.78 (P < .01). A patient with the greatest aICNA developed postoperative atrial fibrillation. CONCLUSION ICNA and SKNA can be recorded from human patients in the postoperative period. The baseline magnitude of ICNA correlates with PAC burden and development of postoperative atrial fibrillation.