Absence of Increased Systemic Vascular Resistance During Syncopal Episodes in Patients with Tilt-Positive Neurocardiogenic Syncope (original) (raw)
1999, Annals of Noninvasive Electrocardiology
Background The purpose of this study was to elucidate the mechanism of syncope in patients with neurocardiogenic syncope (NCS) by measuring hemodynamic parameters continuously during a head-up tilt (HUT) test. Methods: Twenty-three adults (mean age 22.6 t 9.8, range 15-62) participated in the study: 16 with a history of syncope suggesting NCS and 7 healthy volunteers who served as controls. The subjects underwent a 45-minute 60" tilt test. Heart rate and blood pressure were monitored continuously. The stroke volume was measured every minute by noninvasive impedance cardiography, and systemic vascular resistance was calculated from these measurements. The test was terminated when syncope occurred or after 45 minutes in an upward position. Results: Eight of the 16 patients had a positive HUT, while all control subjects had a negative HUT. Decreased stroke volume and cardiac index were observed in all subjects and subgroups in the upward position, compared to the rest position (P < 0.01). Systemic vascular resistance rose in patients with a negative HUT and all controls (P < 0.03), but did not change in the HUT-positive patients (P = 0.25), during the HUT. Systemic vascular resistance was significantly lower in the upward position in the positive HUT than in the other groups (P < 0.04), but there were no differences in the cardiac index. Conclusions: Failure to achieve an appropriate increase in systemic vascular resistance may be an important mechanism in some cases of NCS and should be taken in account when considering therapeutic options. Impedance cardiography is a noninvasive technique for the detection of this abnormal response and can be used to assess the effect of drug therapy on systemic vascular neurocardiogenic syncope; cardiographic impedance; systemic vascular resistance; tilt test; cardiac output resistance. A.N.E. 1999;4(2):121-129 Neurocardiogenic syncope (NCS) is a common disorder that accounts for 30%-50% of syncope in patients without heart disease. 1-3 It is characterized by a transient loss of consciousness accompanied by a decrease in blood pressure andlor heart rate.' The exact pathophysiology of NCS is unknown. The most commonly accepted theory is that a decrease in preload results in reduction of end-systolic volume (ESV) that activates cardioinhibitory reflexes2,3 These reflexes, in particular the Bezold-Jarisch reflex, reduce heart rate and induce va~odilatation.~-~ The head-up tilt (HUT), which mimics the circumstances in which NCS usually occurs, is the test of choice for evaluating this condition. 1s4.7-9 In previous studiesl0'l1 echocardiographic mea-This study was in partial fulfillment o f the M.D. degree requirements of Shira Pert, from the Faculty of
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