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Background— The purpose of this study was to assess the effect of the serotonin reuptake inhibitor paroxetine hydrochloride (Paxil, SmithKline Beecham) on cardiovascular reflexes. We hypothesized that Paxil prevents neurally mediated syncope (NMS) by attenuating the sympathoinhibition and vagotonia associated with a vasovagal reaction. Methods and Results— In a double-blind randomized study, 25 healthy subjects with a positive response to either carotid sinus massage (CSM) or lower body negative pressure (LBNP) received Paxil (20 mg/d) or placebo for 6 weeks. Arterial baroreflex sensitivity (BRS), muscle sympathetic nerve activity (SNA), baroreflex control of SNA, blood pressure, and heart rate responses to CSM and LBNP were measured at baseline and at 6 weeks. Nineteen subjects completed the study (Paxil, n=9; placebo, n=10). In the Paxil group, BRS decreased significantly compared with baseline (15.8±4.0 ms/mm Hg versus 11.0±2.6 ms/mm Hg, P =0.05); however, all 9 subjects continued to have a positive response to LBNP with presyncope. Paxil did not attenuate the sympathoinhibition or vagotonia associated with a positive LBNP response and had no significant effect on baroreflex control of SNA. In the control group, no significant change in BRS was noted compared with baseline. Seven out of 9 subjects who had a positive LBNP response at baseline had a repeat positive LBNP response, and the subject with a positive CSM at baseline had a negative response at 6 weeks. Conclusions— Paxil decreases arterial BRS but does not prevent the presyncope associated with LBNP. The effect of Paxil on the autonomic reflexes in patients with neurally mediated syncope remains unclear.

The purpose of this study was to compare the hemodynamic and sympathetic nerve activity (SNA) responses to graded lower body negative pressure (LBNP) in healthy subjects with either a positive (n = 24, SNA in 8) or a negative (n = 18, SNA in 6) LBNP response. A positive LBNP response was defined as an abrupt drop in systolic blood pressure associated with a decrease in heart rate and/or a decrease in SNA. All positive responses were accompanied by symptoms common to pre-syncope, defined as lightheadedness, diaphoresis, tunnel vision and/or nausea. If subjects tolerated 30 minutes of LBNP, this was considered a negative response. Comparisons were made between baseline, −10 mmHg (low-level LBNP) and −60 mmHg (high-level LBNP). Baseline SNA and arterial baroreflex sensitivity were not different between the 2 groups. However, subjects with pre-syncope had a significantly attenuated SNA response during low-level LBNP (p < 0.05) compared to subjects who did not experience pre-syncope. The hemodynamic data during high-level LBNP were similar until the occurrence of pre-syncope. Pre-syncope was preceded by a significant decrease in heart rate and SNA. Our findings suggest that subjects with LBNP induced pre-syncope might have an impairment in the cardiopulmonary baroreflex gain function in the setting of a preserved arterial baroreflex gain.

Early defibrillation is the most important determinant of survival for victims of cardiac arrest due to ventricular fibrillation. The automated external defibrillator (AED) was developed as the result of the American Heart Association's Public Access Defibrillation initiative. The goal of this initiative is to place AEDs in strategic locations so that laypersons with minimal training could promptly defibrillate victims of cardiac arrest. Because of changes in design and the use of alternative waveforms for defibrillation, the modern AED is compact and portable, simple to use, and highly efficacious; in addition, it requires little maintenance. Automated external defibrillators have been used successfully by traditional and nontraditional responders as well as laypersons. In special environments, such as casinos and commercial aircraft, AEDs have performed particularly well. State and federal legislation has eased concerns about AED use by extending legal protection to AED users under Good Samaritan laws. Since the experience continues to be positive, AEDs are being used in increasingly diverse community locations, and public awareness is growing. The American Heart Association's initiative is progressing rapidly.