Indications à la stimulation cardiaque dans la syncope vasovagale [Pacing in vasovagal syncope].

This article presents a critical review of the literature about the potential benefit of cardiac pacing in patients suffering from vasovagal or neurocardiogenic syncope. The manifestation of vasovagal syncope comprises some reflex bradycardia and vasoplegia resulting in cerebral hypoperfusion that ultimately leads to a loss of consciousness. The literature reports conflicting results of the potential benefit of cardiac pacing on the prevention of recurrence of vasovagal events. A detailed analysis of the inclusion criteria of these studies permits to clarify the discrepancy. Only patients older than 50 years with prolonged sinus pause at time of syncope benefit of the implantation of a cardiac pacemaker.

Stepwise evaluation of unexplained syncope in a large ambulatory population.

BACKGROUND: Up to 60% of syncopal episodes remain unexplained. We report the results of a standardized, stepwise evaluation of patients referred to an ambulatory clinic for unexplained syncope. METHODS AND RESULTS: We studied 939 consecutive patients referred for unexplained syncope, who underwent a standardized evaluation, including history, physical examination, electrocardiogram, head-up tilt testing (HUTT), carotid sinus massage (CSM) and hyperventilation testing (HYV). Echocardiogram and stress test were performed when underlying heart disease was initially suspected. Electrophysiological study (EPS) and implantable loop recorder (ILR) were used only in patients with underlying structural heart disease or major unexplained syncope. We identified a cause of syncope in 66% of patients, including 27% vasovagal, 14% psychogenic, 6% arrhythmias, and 6% hypotension. Noninvasive testing identified 92% and invasive testing an additional 8% of the causes. HUTT yielded 38%, CSM 28%, HYV 49%, EPS 22%, and ILR 56% of diagnoses. On average, patients with arrhythmic causes were older, had a lower functional capacity, longer P-wave duration, and presented with fewer prodromes than patients with vasovagal or psychogenic syncope. CONCLUSIONS: A standardized stepwise evaluation emphasizing noninvasive tests yielded 2/3 of causes in patients referred to an ambulatory clinic for unexplained syncope. Neurally mediated and psychogenic mechanisms were behind >50% of episodes, while cardiac arrhythmias were uncommon. Sudden syncope, particularly in older patients with functional limitations or a prolonged P-wave, suggests an arrhythmic cause.

Repeated Pre-Syncope from Increased Inspired CO2 in a Background of Severe Hypoxia.

We describe a case of experimentally induced pre-syncope in a healthy young man when exposed to increased inspired CO2 in a background of hypoxia. Acute severe hypoxia (FIO2=0.10) was tolerated, but adding CO2 to the inspirate caused pre-syncope symptoms accompanied by hypotension and large reductions in both mean and diastolic middle cerebral artery velocity, while systolic flow velocity was maintained. The mismatch of cerebral perfusion pressure and vascular tone caused unique retrograde cerebral blood flow at the end of systole and a reduction in cerebral tissue oxygenation. We speculate that this occurrence of pre-syncope was due to hypoxia-induced inhibition of brain regions responsible for compensatory sympathetic activity to relative hypercapnia.

Predictive models of syncope causes in an outpatient clinic

The investigation of unexplained syncope remains a challenging clinical problem. In the present study we sought to evaluate the diagnostic value of a standardized work-up focusing on non invasive tests in patients with unexplained syncope referred to a syncope clinic, and whether certain combinations of clinical parameters are characteristic of rhythmic and reflex causes of syncope. METHODS AND RESULTS: 317 consecutive patients underwent a standardized work-up including a 12-lead ECG, physical examination, detailed history with screening for syncope-related symptoms using a structured questionnaire followed by carotid sinus massage (CSM), and head-up tilt test. Invasive testings including an electrophysiological study and implantation of a loop recorder were only performed in those with structural heart disease or traumatic syncope. Our work-up identified an etiology in 81% of the patients. Importantly, three quarters of the causes were established non invasively combining head-up tilt test, CSM and hyperventilation testing. Invasive tests yielded an additional 7% of diagnoses. Logistic analysis identified age and number of significant prodromes as the only predictive factors of rhythmic syncope. The same two factors, in addition to the duration of the ECG P-wave, were also predictive of vasovagal and psychogenic syncope. These factors, optimally combined in predictive models, showed a high negative and a modest positive predictive value. CONCLUSION: A standardized work-up focusing on non invasive tests allows to establish more than three quarters of syncope causes. Predictive models based on simple clinical parameters may help to distinguish between rhythmic and other causes of syncope

Patient with syncope and LQTS carrying a mutation in the PAS domain of the hERG1 channel.

We report the case of a woman with syncope and persistently prolonged QTc interval. Screening of congenital long QT syndrome (LQTS) genes revealed that she was a heterozygous carrier of a novel KCNH2 mutation, c.G238C. Electrophysiological and biochemical characterizations unveiled the pathogenicity of this new mutation, displaying a 2-fold reduction in protein expression and current density due to a maturation/trafficking-deficient mechanism. The patient's phenotype can be fully explained by this observation. This study illustrates the importance of performing genetic analyses and mutation characterization when there is a suspicion of congenital LQTS. Identifying mutations in the PAS domain or other domains of the hERG1 channel and understanding their effect may provide more focused and mutation-specific risk assessment in this population.

Stepwise evaluation of syncope: a prospective population-based controlled study.

BACKGROUND: Evaluation of syncope remains often unstructured. The aim of the study was to assess the effectiveness of a standardized protocol designed to improve the diagnosis of syncope. METHODS: Consecutive patients with syncope presenting to the emergency departments of two primary and tertiary care hospitals over a period of 18 months underwent a two-phase evaluation including: 1) noninvasive assessment (phase I); and 2) specialized tests (phase II), if syncope remained unexplained after phase I. During phase II, the evaluation strategy was alternately left to physicians in charge of patients (control), or guided by a standardized protocol relying on cardiac status and frequency of events (intervention). The primary outcomes were the diagnostic yield of each phase, and the impact of the intervention (phase II) measured by multivariable analysis. RESULTS: Among 1725 patients with syncope, 1579 (92%) entered phase I which permitted to establish a diagnosis in 1061 (67%) of them, including mainly reflex causes and orthostatic hypotension. Five-hundred-eighteen patients (33%) were considered as having unexplained syncope and 363 (70%) entered phase II. A cause for syncope was found in 67 (38%) of 174 patients during intervention periods, compared to 18 (9%) of 189 during control (p<0.001). Compared to control periods, intervention permitted diagnosing more cardiac (8%, vs 3%, p=0.04) and reflex syncope (25% vs 6%, p<0.001), and increased the odds of identifying a cause for syncope by a factor of 4.5 (95% CI: 2.6-8.7, p<0.001). Overall, adding the diagnostic yield obtained during phase I and phase II (intervention periods) permitted establishing the cause of syncope in 76% of patients. CONCLUSION: Application of a standardized diagnostic protocol in patients with syncope improved the likelihood of identifying a cause for this symptom. Future trials should assess the efficacy of diagnosis-specific therapy.

Pacemaker therapy in patients with neurally mediated syncope and documented asystole: Third International Study on Syncope of Uncertain Etiology (ISSUE-3): a randomized trial.

BACKGROUND: The efficacy of cardiac pacing for prevention of syncopal recurrences in patients with neurally mediated syncope is controversial. We wanted to determine whether pacing therapy reduces syncopal recurrences in patients with severe asystolic neurally mediated syncope. METHODS AND RESULTS: Double-blind, randomized placebo-controlled study conducted in 29 centers in the Third International Study on Syncope of Uncertain Etiology (ISSUE-3) trial. Patients were ≥40 years, had experienced ≥3 syncopal episodes in the previous 2 years. Initially, 511 patients, received an implantable loop recorder; 89 of these had documentation of syncope with ≥3 s asystole or ≥6 s asystole without syncope within 12 ± 10 months and met criteria for pacemaker implantation; 77 of 89 patients were randomly assigned to dual-chamber pacing with rate drop response or to sensing only. The data were analyzed on intention-to-treat principle. There was syncope recurrence during follow-up in 27 patients, 19 of whom had been assigned to pacemaker OFF and 8 to pacemaker ON. The 2-year estimated syncope recurrence rate was 57% (95% CI, 40-74) with pacemaker OFF and 25% (95% CI, 13-45) with pacemaker ON (log rank: P=0.039 at the threshold of statistical significance of 0.04). The risk of recurrence was reduced by 57% (95% CI, 4-81). Five patients had procedural complications: lead dislodgment in 4 requiring correction and subclavian vein thrombosis in 1 patient. CONCLUSIONS: Dual-chamber permanent pacing is effective in reducing recurrence of syncope in patients ≥40 years with severe asystolic neurally mediated syncope. The observed 32% absolute and 57% relative reduction in syncope recurrence support this invasive treatment for the relatively benign neurally mediated syncope. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT00359203.

Stepwise evaluation of unexplained syncope in a large ambulatory population

La syncope est un symptôme clinique fréquent mais son origine demeure indéterminée jusque dans 60% des cas de patients admis dans un centre d'urgences. Le développement de consultations spécialisées de la syncope a considérablement modifié l'évaluation des patients avec une syncope inexpliquée en les orientant vers des stratégies d'investigations non-invasives, tels que le tilt-test, le massage du sinus carotidien et le test ^hyperventilation. Cependant, il existe peu de données dans 10 la littérature concernant dans la performance diagnostique réelle de ces tests fonctionnels.Notre travail de recherche porte sur l'analyse des données des 939 premiers patients adressés à la consultation ambulatoire de la syncope du CHUV pour l'investigation d'une syncope d'origine indéterminée. L'objectif de notre travail de thèse est 1) d'évaluer la performance diagnostique de l'algorithme de prise en charge standardisé et de ses différents tests pratiqués dans le cadre de notre 15 consultation et 2) de déterminer les caractéristiques cliniques communes des patients avec un diagnostic final de syncope d'origine rythmique ou vaso-vagale.Notre travail de thèse démontre qu'un algorithme de prise en charge standardisé basé sur des tests non-invasifs permet de déterminer 2/3 des causes de syncope initialement d'origine indéterminée. Par ailleurs, notre travail montre que des étiologies bénignes, telles que la syncope d'origine vaso- 20 vagale ou psychogène, représentent la moitié des causes syncopales alors que les arythmies cardiaques demeurent peu fréquentes. Finalement, notre travail démontre que l'absence de symptomatologie prodromique, en particulier chez les patients âgés avec une limitation fonctionnelle ou un allongement de la durée de l'onde Ρ à l'électrocardiogramme, suggère une syncope d'origine rythmique. Ce travail de thèse contribuera à optimaliser notre algorithme de prise 25 en charge standardisée de la syncope d'origine indéterminée et ouvre de nouvelles perspectives de recherche dans le développement de modèles basés sur des facteurs cliniques permettant de prédire les principales causes syncopales.

Ictal bradycardia and asystole: an uncommon cause of syncope.

We report on two patients with recurrent syncope secondary to ictal bradyarrhythmias, triggered by partial epileptic seizures with atypical, stereotyped auras. Ictal bradyarrhythmias are potentially lethal, and likely originate from the involvement of limbic autonomic regions. The appropriate treatment is double-headed, including an antiepileptic drug and the implantation of a pacemaker.

Death caused by cardioinhibitory reflex cardiac arrest--a systematic review of cases.

Forensic pathologists often refer to the cardioinhibitory reflex cardiac arrest (CiRCA) following short neck trauma as a mechanism of death. We sought via a systematic review of the literature to identify circumstances under which carotid bifurcation stimulation could lead to death. Two independent reviewers selected case studies or reports from Medline, ISI Web of Knowledge, and Embase. Circumstances and contributory factors were extracted for each case. From the available data, authors independently assessed whether CiRCA was highly probable (no alternative explanation possible), probable (alternative explanation possible), or unlikely (alternative explanation highly probable). A narrative approach was used to define circumstances in which CiRCA remained possible. From the 48 published cases evoking CiRCA as a possible cause of death between 1881 and 2009, 28 were most likely to result of other mechanism of death (i.e., cerebral hypoxia due to carotid compression, mechanical asphyxia, myocardial infarction). CiRCA remained possible for 20 cases (including five based on anecdotal evidence only) with only one case with no alternative explanation other than CiRCA. Our findings support the presumption that reflex cardiac arrhythmia due to carotid bifurcation stimulation cannot provoke death alone. Actual state of knowledge suggests CiRCA might be contributory to death in the presence of drug abuse and/or cardiac pathology, often associated with physical and/or mental excitation.