Sympathetic skin response and RR interval variation in patients with cardiac syndrome X

Sympathetic skin response (SSR) and R-R interval variation (RRIV) are noninvasive electrophysiological tests used in the assessment of sympathetic and parasympathetic nervous system function, respectively. Cardiac syndrome X (CSX) is usually diagnosed in the presence of typical angina pectoris, a positive response to exercise testing, and normal-appearing coronary angiograms without spasm induced by hyperventilation or ergonovine. Alterations of autonomic nervous system control of cardiac function have been described in CSX. The aim of the study was to investigate autonomic nervous system function in patients with CSX. Nine patients with CSX (2 men, 7 women) and healthy controls (11 men, 19 women) were included in the study. SSRs were recorded from palm of hands by stimulation of the median nerve. RRIV recordings were taken from precordium during both rest position (R%) and deep inspiration of 6 times per minute (D%). In addition D% - R% and D%/R% values were calculated. SSR amplitude of CSX was lower than in controls (3.64 +/-4.78 vs 6.36 +/-3.4 mV, p = 0.017). There was no difference between groups for SSR latency values (CSX: 1,366 +/-99; controls: 1,383 +/-85 msec). Also, R% (CSX: 13.04 +/-6.3; controls: 12.92 +/-3.91) and D% (CSX: 16.63 +/-8.88; controls: 21.43 +/-7.3) values were similar in the 2 groups. However, D% - R% (CSX: 3.59 +/-10.11; controls: 8.51 +/-7.01) and D%/R% (CSX: 1.45 +/-0.93; controls: 1.78 +/-0.69) values were slightly lower in patients with CSX but were not statistically significant. A linear correlation was found between SSR amplitude and D%/R% (r = 0.336, p = 0.036). The authors conclude that, among patients with CSX, there are alterations of autonomic nervous control of skin as well as of other organs (ie, heart). SSR and RRIV testing can be done easily in the neurophysiology laboratory to assess the sympathetic and parasympathetic system, respectively.