Patients with reflex syncope have a higher prevalence of atrial fibrillation than general population which is predicted by the type of the tilt table test response

Introduction Reflex syncope is the result of an imbalance between the sympathetic and parasympathetic nervous system. The autonomic nervous system has been associated to some forms of atrial fibrillation (AF). Objective The aim of this study was to assess the prevalence of AF in patients with reflex syncope and a positive tilt table test and to identify the type of tilt test response in patients with AF in comparison to patients without AF. Methods We retrospectively studied consecutive patients that underwent a tilt table test at our institution between 2016 and 2019. We selected those patients with a positive test. Patients with an implanted pacemaker at the time of the tilt test and patients followed in a different institution were excluded. Previous diagnoses of AF episodes were assessed. We analysed the clinical characteristics and the tilt table test results according to previous history of AF. Results We studied 49 patients with a positive tilt test. Seven (14.3%) patients had previously diagnosed paroxysmal AF at the time of the tilt table test. Patients with AF were older, had more frequently hypertension, and the tilt test response was more frequently a vasodepressor than mixed or cardioinhibitory response (71.4% vs. 28.6%) (Table). In univariate analysis, age and hypertension were associated with AF, respectively, OR 1.08 (95% CI 1.01–1.17), p=0.034 and OR 10.80 (95% CI 1.19–98.36), p=0.035. A vasodepressor response was also associated with AF (OR 6.25, 95% CI 1.06–36.74, p=0.043). Conclusions Patients with reflex syncope and a positive tilt table test had a higher prevalence of AF than the general population. A vasodepressor response was associated with AF as were age and hypertension, demonstrating the possible impact of the autonomic nervous system and the multifactorial nature of AF. FUNDunding Acknowledgement Type of funding sources: None.

Usefulness of post-procedural heart rate response to predict syncope recurrence or positive head up tilt table testing after cardioneuroablation

Aims Previous reports have suggested that cardioneuroablation (CNA) can be effective in reducing syncopal recurrences in patients with vasovagal syncope (VVS). This study assessed the efficacy of CNA in preventing a positive response to head-up tilt testing (HUT). Methods and results This is a single-centre retrospective study reviewing prospectively collected data. Fifty-one consecutive patients with VVS were included in the study. After confirmation of >3 s asystole on HUT, all patients underwent CNA. Head-up tilt testing was repeated 1 month after CNA. The main outcome measures were recurrence of syncope episode and positive response on HUT. During a median follow-up period of 11 months (interquartile range 3–27 months), all but 3 (5.8%) of 51 patients were free of syncope. Repeated HUTs were negative in 44 (86.2%) patients. When patients with recurrent syncope were excluded, vasodepressor response was seen in three cases and cardioinhibitory response in one case, respectively. Cardioneuroablation caused significant and durable shortening of RR interval in all cases. This effect was significantly higher in patients without positive HUT responses. Conclusion This pilot study shows that CNA can effectively prevent recurrent syncopal episodes in patients with refractory VVS. Head-up tilt testing seems as a valuable diagnostic tool not only to select suitable candidates and but also to evaluate success of CNA.

Abstract 360: Effects of Different Doses of Pralidoxime Administered During Cardiopulmonary Resuscitation and the Role of Alpha-Adrenergic Receptors in its Pressor Action

Introduction: We previously reported that pralidoxime potentiated the pressor effect of epinephrine and improved restoration of spontaneous circulation (ROSC) rate and short-term survival in pigs undergoing cardiopulmonary resuscitation (CPR). We sought to explore the optimal dose of pralidoxime to be used during CPR and to evaluate the involvement of α-adrenoceptors in its pressor action. Methods: In the first substudy, 44 pigs randomly received one of three doses of pralidoxime (40, 80, or 120 mg/kg) or saline placebo during CPR. All animals were given epinephrine every 3 minutes. In the second substudy, 49 rats were divided into 7 groups. In the first 4 groups, the effects of 40 mg/kg pralidoxime on arterial pressure were determined after pretreatment with saline, guanethidine, phenoxybenzamine, or phentolamine. In the other 3 groups, the effects of 200 mg/kg pralidoxime were determined after pretreatment with saline, propranolol, or phentolamine. Results: In the first substudy, 40 mg/kg pralidoxime resulted in the highest coronary perfusion pressure (CPP) among the groups, while 120 mg/kg pralidoxime resulted in the lowest CPP (group effect P <0.001). Sustained ROSC was attained in 4 (36.4%), 11 (100%), 9 (81.8%), and 3 (27.3%) animals in the saline, 40 mg/kg, 80 mg/kg, and 120 mg/kg groups, respectively ( P <0.001). In the second substudy, 40 mg/kg pralidoxime elicited a pressor response. Phenoxybenzamine completely inhibited the pressor response, but guanethidine and phentolamine did not. The pressor response of pralidoxime was even greater after pretreatment with guanethidine or phentolamine. Two-hundred mg/kg pralidoxime produced an initial vasodepressor response followed by a delayed pressor response. Phentolamine eliminated the initial vasodepressor response and reversed it into a pressor response. Conclusions: Forty mg/kg of pralidoxime administered with epinephrine led to a significantly higher ROSC rate by improving CPP in a pig model of cardiac arrest, whereas 120 mg/kg did not improve CPP or the ROSC rate. Our findings suggest that the pressor effect of pralidoxime is unrelated to α-adrenoceptors and that its pressor effect is buffered by its vasodepressor action mediated by the inhibition of the sympathetic nervous system.

Pacing for Vasovagal Syncope

Vasovagal syncope (VVS) is due to a common autonomic reflex involving the cardiovascular system. It is associated with bradycardia (cardioinhibitory response) and/or hypotension (vasodepressor response), likely mediated by parasympathetic activation and sympathetic inhibition. While generally a situational, isolated and/or self-limited event, for some, VVS is recurrent, unpredictable and debilitating. Conservative, non-pharmacological management may help, but no specific medical therapy has been proven widely effective. Permanent pacing may have specific benefit, but its value has been debated. The temporal causative association of bradycardia with syncope in those with VVS may help identify which patient could benefit from pacing but the timing and type of pacing in lieu of blood pressure changes may be critical. The mode, rate, pacing algorithm and time to initiate dual-chamber pacing preferentially with respect to the vasovagal reflex may be important to prevent or ameliorate the faint but completely convincing data are not yet available. Based on available data, DDD pacing with the closed loop stimulation algorithm appears a viable, if not the best, alternative presently to prevent recurrent VVS episodes. While several knowledge gaps remain, permanent pacing appears to have a role in managing select patients with VVS.