Syncope due to idiopathic paroxysmal atrioventricular block: long-term follow-up of a distinct form of atrioventricular block

Spontaneous resumption of severe infranodal conduction disturbances that followed COVID-19 vaccination

We report reversible severe infranodal conduction disturbances that followed COVID-19 vaccination in a young woman. Right and left bundle branch conduction were impaired and recovered at different times, resulting in reversible paroxysmal complete atrioventricular block.

Transient Supine-Induced Advanced Heart Block in an Octogenarian

Atrioventricular block (AVB) is a conduction disorder that can lead to significant bradyarrhythmias with resultant hemodynamic compromise and cardiogenic shock. While most cases of positional AVB that occur during erect posture are attributed to neurocardiogenic mechanisms, complete AVB occurring exclusively in the supine position is an exceedingly rare phenomenon. We present a case of an 87-year-old Caribbean Black male who presented with symptomatic supine-induced advanced heart block, which transiently resolved during standing with unremarkable comprehensive investigations and subsequently underwent successful dual-chamber permanent pacemaker implantation. The clinician should be cognizant of assessing positional vital signs with telemetric monitoring in patients presenting with idiopathic bradyarrhythmias and presyncope.

Second-degree atrioventricular block induced by electrical stimulation of transcranial motor-evoked potential: a case report

BACKGROUND

Although several complications of transcranial motor-evoked potentials (Tc-MEPs) have been reported, reports of arrhythmias during Tc-MEP are very rare.

CASE PRESENTATION

A 71-year-old woman underwent transforaminal lumbar interbody fusion under general anesthesia, with intraoperative Tc-MEP monitoring. Preoperative electrocardiography showed an incomplete right bundle branch block but no cardiovascular events in her life. After induction of anesthesia, Tc-MEP was recorded prior to the surgery. During the Tc-MEP monitoring, electrocardiography and arterial blood pressure showed a second-degree atrioventricular block, but it improved rapidly at the end of the stimulation, and the patient was hemodynamically stable. Tc-MEP was recorded seven times during surgery; the incidence of P waves without QRS complexes was significantly higher than before stimulation. The surgery was uneventful, and she was discharged eight days postoperatively without complications.

CONCLUSIONS

Our case suggests that electrical stimulation for Tc-MEP can cause arrhythmia. Electrocardiography and blood pressure must be closely monitored during Tc-MEP monitoring.

Mechanism-based therapy of non-cardiac syncope: a practical guide

The term non-cardiac syncope includes all forms of syncope, in which primary intrinsic cardiac mechanism and non-syncopal transient loss of consciousness can be ruled out. Reflex syncope and orthostatic hypotension are the most frequent aetiologies of non-cardiac syncope. As no specific therapy is effective for all types of non-cardiac syncope, identifying the underlying haemodynamic mechanism is the essential prerequisite for an effective personalized therapy and prevention of syncope recurrences. Indeed, choice of appropriate therapy and its efficacy are largely determined by the syncope mechanism rather than its aetiology and clinical presentation. The two main haemodynamic phenomena leading to non-cardiac syncope include either profound hypotension or extrinsic asystole/pronounced bradycardia, corresponding to two different haemodynamic syncope phenotypes, the hypotensive and bradycardic phenotypes. The choice of therapy-aimed at counteracting hypotension or bradycardia-depends on the given phenotype. Discontinuation of blood pressure-lowering drugs, elastic garments, and blood pressure-elevating agents such as fludrocortisone and midodrine are the most effective therapies in patients with hypotensive phenotype. Cardiac pacing, cardioneuroablation, and drugs preventing bradycardia such as theophylline are the most effective therapies in patients with bradycardic phenotype of extrinsic cause.

An Investigation of Metabolic Risk Factors and Gut Microbiota in Unexplained Syncope

BACKGROUND

The pathogenesis of many syncopal episodes remains unexplained. Intestinal dysbiosis could be involved in the pathophysiological mechanisms of syncope due to its connection with the central nervous system via the microbiota-gut-brain axis. This pilot study aimed to explore the specific cardiometabolic risk factors and gut microbiota in unexplained syncope (US), compared to other types of syncope, to assess their similarity or verify their different origins.

METHODS

We studied 86 participants with syncope, who were divided into four groups: an orthostatic syncope group (OH, n = 24), a neuromediated syncope group (NMS, n = 26), a cardiological syncope group (CS, n = 9), and an unexplained syncope group (US, n = 27). We evaluated the anthropometric, clinical, and metabolic characteristics of the four groups; the α- and β-diversity; and the differences in the abundance of the microbial taxa.

RESULTS

The US group had a lower incidence of systolic hypertension at the first visit and a lower frequency of patients with nocturnal hypertension than the CS group. Compared to the OH and NMS groups, the US group had a higher incidence of carotid plaques and greater carotid intima-media thickness, respectively. The microbiota differed significantly between the US and CS groups, but not between the US group and the OH or NMS group.

CONCLUSIONS

We observed significant differences in the gut microbiota between CS and US. Future studies are necessary to evaluate the involvement of the gut microbiota in the complex pathogenesis of syncope and whether its analysis could support the interpretation of the pathophysiological mechasnisms underlying some episodes classifiable as US.

Twenty-five years of research on syncope

Over the last 25 years, the Europace journal has greatly contributed to dissemination of research and knowledge in the field of syncope. More than 400 manuscripts have been published in the journal. They undoubtedly improved our understanding of syncope. This symptom is now clearly differentiated from other forms of transient loss of consciousness. The critical role of vasodepression and/or cardioinhibition as final mechanisms of reflex syncope is emphasized. Current diagnostic approach sharply separates between cardiac and autonomic pathways. Physiologic insights have been translated, through rigorously designed clinical trials, into non-pharmacological or pharmacological interventions and interventional therapies. The following manuscript is intended to give the reader the current state of the art of knowledge of syncope by highlighting landmark contributions of the Europace journal.

Tests for the identification of reflex syncope mechanism

INTRODUCTION

Treatment efficacy of reflex syncope is mainly related to the mechanism underlying syncope rather than its etiology or clinical presentation. The predominant mechanism underlying reflex syncope can be assigned to hypotensive or to bradycardic phenotypes.

AREAS COVERED

Methodology and diagnostic criteria of the most useful tests for the identification of hypotensive and bradycardic phenotypes are discussed. Diagnostic tests for the hypotensive phenotype include office blood pressure measurement with active standing test, home, and wearable blood pressure monitoring, 24-h ambulatory blood pressure monitoring and tilt table test. Diagnostic tests for the bradycardic phenotype include carotid sinus massage, tilt table test and prolonged ECG monitoring.

EXPERT OPINION

In reflex syncope, the documentation of bradycardia/asystole during a syncopal episode does not rule out the possibility that a preceding or parallel hypotensive reflex plays an important role. Similarly, even when a hypotensive mechanism is established, the possibility of an associated cardioinhibitory reflex should be investigated. Investigating the mechanism of reflex syncope is mandatory in patients with severe recurrent episodes, with the final aim to develop a personalized treatment strategy. Recent trials have demonstrated the benefits of personalized mechanism-based therapy, thus highlighting the importance of a comprehensive assessment of the mechanisms underlying syncope.

Syncope without prodromes is associated with excessive plasma release of adenosine at the time of syncope during head-up tilt table test

BACKGROUND

In syncopal patients without underlying structural disease, we sought to investigate the association of Adenosine Plasma Levels (ADP) with the clinical presentation of neurally mediated syncope (NMS) and the outcomes of Head-Up Tilt Table Test (HUTT) and Adenosine test (ADT).

METHODS

We studied 124 patients with different clinical types of NMS, i.e., Vasovagal (VVS, n=58), non-prodromes (NPS, n=18), or situational syncope (SS, n=48), using a standard protocol including HUTT and ADT. During HUTT, ADP was measured in the supine position, at table tilting and in syncope.

RESULTS

Baseline ADP did not differ among groups. ADP at syncope were higher in NPS (n=5) compared to VVS (n=20): 0.23 vs. 0.12 μΜ, p=0.03, and SS (n=22): 0.04 μΜ, p=0.02. In NPS, ADP increased from supine to syncope (n=5): 0.15 vs. 0.23 μΜ, p=0.04. In VVS, ADP increased only from supine to tilt position: 0.11 vs. 0.14 μΜ, p=0.02. In SS, ADP did not change during HUTT. In positive vasodepressor HUTT, ADP increased from supine to tilt position (p=0.002) and at syncope (p=0.01). In SS, 20.0% exhibited cardioinhibitory HUTT vs. 6.8% in other forms of syncope (p=0.04). In SS, 22.9% manifested positive ADT vs 6.6% in other types of syncope (p=0.012).

CONCLUSION

The subset of NPS patients with positive HUTT, show excessive ADP release at the time of syncope. This may explain the lack of prodromes in this form of syncope. Such observations contribute to the understanding of distinct profiles of clinical forms of syncope and may differentiate the management approach accordingly.

Prevalence and Clinical Characteristics of Patients with Pause-Dependent Atrioventricular Block

Background: In patients with complete atrioventricular block (AVB), the prevalence and clinical characteristics of patients with pause-dependent AVB (PD-AVB) is not known. Our objective was to assess the prevalence of PD-AVB in a population of patients with complete (or high-grade) AVB. Methods: Twelve-lead electrocardiogram (ECG) and/or telemonitoring from patients admitted (from September 2020 to November 2021) for complete (or high-degree) AVB were prospectively collected at the University Hospital of Nice. The ECG tracings were analyzed by an electrophysiologist to determine the underlying mechanism of PD-AVB. Results: 100 patients were admitted for complete (or high-grade) AVB (men 55%; 82 ± 12 years). Arterial hypertension was present in 68% of the patients. Baseline QRS width was 117 ± 32 ms, and mean left ventricular ejection fraction was 56 ± 7%. Fourteen patients (14%) with PD-AVB were identified, and presented similar clinical characteristics in comparison with patients without PD-AVB, except for syncope (which was present in 86% versus 51% in the non-PD-AVB patients, p = 0.01). PD-AVB sequence was induced by: Premature atrial contraction (8/14), premature ventricular contraction (5/14), His extrasystole (1/14), conduction block in a branch (1/14), and atrial tachycardia termination (1/14). All patients with PD-AVB received a dual-chamber pacemaker during hospitalization. Conclusion: The prevalence of PD-AVB was 14%, and may be underestimated. PD-AVB episodes were more likely associated with syncope in comparison with patients without PD-AVB.

Is the Adenosine Test Obsolete in the Clinical Assessment of Syncope of Unknown Origin?

Syncope is a common clinical condition affecting 50% of the general population; however, its exact pathophysiology and underlying mechanisms remain elusive. The adenosine test (ADT) has been proposed as a complementary diagnostic test in the work-up of syncope of unknown origin aiming to further elucidate the underlying pathogenetic mechanism of spontaneous syncope. Although ADT has not been endorsed by the recent European Society of Cardiology guidelines on syncope management, the use of a quick, safe and non-invasive test which can contribute to an accurate diagnosis and rationalised therapy, may deserve further consideration. This review summarises the evidence on the role of ADT in the investigation and management of syncope of unknown origin and highlights future perspectives in this area. The authors also analyse the current challenges and research targets on adenosine plasma levels and its receptors due to the involvement of the adenosine pathway in the ADT response.

Theophylline in patients with syncope without prodrome, normal heart, and normal electrocardiogram: a propensity-score matched study verified by implantable cardiac monitor

AIMS

Syncope without prodromes in subjects with normal heart and normal electrocardiogram (ECG) is classified as non-classical neurally mediated syncope and is characterized by low adenosine plasma levels (APLs) and frequent asystolic syncope. We assessed the efficacy of theophylline, a non-selective adenosine receptor antagonist, in preventing syncopal events.

METHODS AND RESULTS

Participants received an implantable cardiac monitor, underwent APL measurement, and received oral theophylline at maximum tolerated dose (starting dose 300 mg b.i.d.). They were compared with a historical cohort of untreated patients with implantable cardiac monitor who had the same inclusion criteria and were balanced with the propensity score (PS) method as regard age, sex, lifetime syncopal episodes, APL, and antihypertensive drugs. Primary endpoint was time to first syncopal recurrence at 24 months. There were 76 patients in the theophylline group and 58 in the control group. Syncope recurred in 25 (33%) patients in the theophylline group and in 27 (47%) patients in the control group, with an estimated 2-year recurrence rate of 33% and 60%, respectively, and a hazard ratio of 0.53 [95% confidence interval (CI), 0.30-0.95; P = 0.034]. Most of the benefit of theophylline is derived from reduction of syncope due to asystolic atrioventricular (AV) block (hazard ratio of 0.13; 95% CI, 0.03-0.58; P = 0.008). Thirty (39%) patients discontinued theophylline after a median of 6.4 (interquartile range 1.7-13.8) months due to side effects.

CONCLUSION

Theophylline was effective in preventing recurrences in patients with syncope without prodromes, normal heart, and normal ECG. The benefit was greater in patients with syncope due to asystolic AV block.

CLINICALTRIALS.GOV IDENTIFIER

NCT03803215.

Effects of Pacemaker Implantation on Sudden Cardiac Death Rate and Quality of Life in Atrial Fibrillation Patients With Ventricular Pauses

Ventricular arrest is a rare arrhythmic disease in the clinic; 35% to 55% of cases are associated with atrial fibrillation (AF). It is well known that ventricular arrest for ≥3 seconds can lead to brain symptoms such as dizziness and even syncope, but it is not clear whether ventricular pauses (≥3 seconds) with AF will lead to sudden cardiac death. If the implantation of a pacemaker can improve the quality of life of patients with permanent AF with ventricular arrest and whether it has a long-term protective effect on sudden cardiac death. To this end, we conducted a prospective follow-up observation study, which was conducted through telephone interviews and clinical hospital observation to obtain information on the quality of life, survival rate, and other details. The results show that for patients with permanent AF with ventricular arrest, pacemaker implantation cannot reduce sudden cardiac death, cardiovascular events, and stroke nor can it improve the cumulative survival rate. Fortunately, the implantation of pacemakers can improve the quality of life of patients.

Plasma adenosine and neurally mediated syncope: ready for clinical use

Either central or peripheral baroreceptor reflex abnormalities and/or alterations in neurohumoral mechanisms play a pivotal role in the genesis of neurally mediated syncope. Thus, improving our knowledge of the biochemical mechanisms underlying specific forms of neurally mediated syncope (more properly termed 'neurohumoral syncope') might allow the development of new therapies that are effective in this specific subgroup. A low-adenosine phenotype of neurohumoral syncope has recently been identified. Patients who suffer syncope without prodromes and have a normal heart display a purinergic profile which is the opposite of that observed in vasovagal syncope patients and is characterized by very low-adenosine plasma level values, low expression of A2A receptors and the predominance of the TC variant in the single nucleotide c.1364 C>T polymorphism of the A2A receptor gene. The typical mechanism of syncope is an idiopathic paroxysmal atrioventricular block or sinus bradycardia, most often followed by sinus arrest. Since patients with low plasma adenosine levels are highly susceptible to endogenous adenosine, chronic treatment of these patients with theophylline, a non-selective adenosine receptor antagonist, is expected to prevent syncopal recurrences. This hypothesis is supported by results from series of cases and from observational controlled studies.

Recommendations for tilt table testing and other provocative cardiovascular autonomic tests in conditions that may cause transient loss of consciousness : Consensus statement of the European Federation of Autonomic Societies (EFAS) endorsed by the American Autonomic Society (AAS) and the European Academy of Neurology (EAN)

An expert committee was formed to reach consensus on the use of tilt table testing (TTT) in the diagnosis of disorders that may cause transient loss of consciousness (TLOC) and to outline when other provocative cardiovascular autonomic tests are needed. While TTT adds to history taking, it cannot be a substitute for it. An abnormal TTT result is most meaningful if the provoked event is recognised by patients or eyewitnesses as similar to spontaneous events. The minimum requirements to perform TTT are a tilt table, a continuous beat-to-beat blood pressure monitor, at least one ECG lead, protocols for the indications stated below and trained staff. This basic equipment lends itself to the performance of (1) additional provocation tests, such as the active standing test, carotid sinus massage and autonomic function tests; (2) additional measurements, such as video, EEG, transcranial Doppler, NIRS, end-tidal CO2 or neuro-endocrine tests; and (3) tailor-made provocation procedures in those with a specific and consistent trigger of TLOC. TTT and other provocative cardiovascular autonomic tests are indicated if the initial evaluation does not yield a definite or highly likely diagnosis, but raises a suspicion of (1) reflex syncope, (2) the three forms of orthostatic hypotension (OH), i.e. initial, classic and delayed OH, as well as delayed orthostatic blood pressure recovery, (3) postural orthostatic tachycardia syndrome or (4) psychogenic pseudosyncope. A therapeutic indication for TTT is to teach patients with reflex syncope and OH to recognise hypotensive symptoms and to perform physical counter manoeuvres.

Adenosine and neurohumoral syncope

Either central or peripheral baroreceptor reflex abnormalities and/or alterations in neurohumoral mechanisms play a pivotal role in the genesis of neurally mediated syncope. Thus, improving our knowledge of the biochemical mechanisms underlying specific forms of neurally mediated syncope (more properly termed 'neurohumoral syncope') might allow the development of new therapies that are effective in this specific subgroup. A low-adenosine phenotype of neurohumoral syncope has recently been identified. Patients who suffer syncope without prodromes and have a normal heart display a purinergic profile which is the opposite of that observed in vasovagal syncope patients and is characterized by very lowadenosine plasma level values, low expression of A2A receptors and the predominance of the TC variant in the single nucleotide c.1364 C>T polymorphism of the A2A receptor gene. The typical mechanism of syncope is an idiopathic paroxysmal atrioventricular block or sinus bradycardia, most often followed by sinus arrest. Since patients with low plasma adenosine levels are highly susceptible to endogenous adenosine, chronic treatment of these patients with theophylline, a non-selective adenosine receptor antagonist, is expected to prevent syncopal recurrences. This hypothesis is supported by results from series of cases and from two controlled studies.

Recommendations for tilt table testing and other provocative cardiovascular autonomic tests in conditions that may cause transient loss of consciousness : Consensus statement of the European Federation of Autonomic Societies (EFAS) endorsed by the American Autonomic Society (AAS) and the European Academy of Neurology (EAN)

An expert committee was formed to reach consensus on the use of Tilt Table Testing (TTT) in the diagnosis of disorders that may cause transient loss of consciousness (TLOC) and to outline when other provocative cardiovascular autonomic tests are needed. While TTT adds to history taking, it cannot be a substitute for it. An abnormal TTT result is most meaningful if the provoked event is recognised by patients or eyewitnesses as similar to spontaneous ones. The minimum requirements to perform TTT are a tilt table, a continuous beat-to-beat blood pressure monitor, at least one ECG lead, protocols for the indications stated below and trained staff. This basic equipment lends itself to perform (1) additional provocation tests, such as the active standing test carotid sinus massage and autonomic function tests; (2) additional measurements, such as video, EEG, transcranial Doppler, NIRS, end-tidal CO₂ or neuro-endocrine tests; (3) tailor-made provocation procedures in those with a specific and consistent trigger of TLOC. TTT and other provocative cardiovascular autonomic tests are indicated if the initial evaluation does not yield a definite or highly likely diagnosis, but raises a suspicion of (1) reflex syncope, (2) the three forms of orthostatic hypotension (OH), i.e. initial, classic and delayed OH, as well as delayed orthostatic blood pressure recovery, (3) postural orthostatic tachycardia syndrome or (4) psychogenic pseudosyncope. A therapeutic indication for TTT is to teach patients with reflex syncope and OH to recognise hypotensive symptoms and to perform physical counter manoeuvres.

Neurologic complications of brady-arrhythmias

Brady-arrhythmias are responsible for both overt as well as subtle neurologic signs and symptoms, from the seemingly benign and nonspecific symptoms associated with presyncope, to sudden focal neurologic deficits. A brief background on nodal and infra-nodal brady-arrhythmias is provided, followed by extensive discussion regarding neurologic complications of brady-arrhythmias. The multiple mechanisms of and associations between Brady-arrhythmias and transient ischemic attacks and ischemic stroke are discussed. Controversial associations between brady-arrhythmias and neurologic disease are discussed as well, such as potential roles of brady-arrhythmias in cognitive impairment and sequelae of chronotropic incompetence; and the contribution of brady-arrhythmias to syncope and associated injuries to the nervous system. The chapter is written to stand on its own, with guidance toward other pertinent sections of this text where appropriate for further reading.

New insights in diagnostics and therapies in syncope: a novel approach to non-cardiac syncope

This article aims to give advice on how to identify and manage patients with syncope who are at risk of severe outcomes, that is, at risk of trauma, potentially life-threatening episodes or frequent recurrences reducing quality of life. The first step of syncope diagnostic assessment is to identify patients with cardiac syncope, and once established, these patients must receive the adequate mechanism-specific treatment. If cardiac syncope is unlikely, reflex (neurally mediated) syncope and orthostatic hypotension are the most frequent causes of transient loss of consciousness. For these presentations, efficacy of therapy is largely determined by the mechanism of syncope rather than its aetiology or clinical features. The identified mechanism of syncope should be carefully assessed and assigned either to hypotensive or bradycardic phenotype, which will determine the choice of therapy (counteracting hypotension or counteracting bradycardia). The results of recent trials indicate that 'mechanism-specific therapy' is highly effective in preventing recurrences. Established mechanism-specific treatment strategies include withdrawal of hypotensive drugs, applying fludrocortisone and midodrine for the hypotensive phenotype and cardiac pacing in the bradycardic phenotype.

Aetiologies and temporal trends of atrioventricular block in young patients: a 20-year nationwide study

Aims

To describe aetiologies and temporal trends in young patients with atrioventricular block (AVB).

Methods and results

We identified all patients in Denmark, receiving their first pacemaker because of AVB before the age of 50 years between 1996 and 2015. Medical records were reviewed and clinical information and diagnostic work-up results were obtained to evaluate the aetiology. We used Poisson regression testing for temporal trends. One thousand and twenty-seven patients were identified, median age at time of implantation was 38 (interquartile range 25–45) years, 584 (56.9%) were male. The aetiologies were complications to cardiac surgery [n = 157 (15.3%)], congenital AVB [n = 93 (9.0%)], cardioinhibitory reflex [n = 52 (5.0%)], congenital heart disease [n = 43 (4.2%)], complication to radiofrequency ablation [n = 35 (3.4%)], cardiomyopathy [n = 31 (3.0%)], endocarditis [n = 18 (1.7%)], muscular dystrophy [n = 14 (1.4%)], ischaemic heart disease [n = 14 (1.4%)], sarcoidosis [n = 11 (1.1%)], borreliosis [n = 9 (0.9%)], hereditary [n = 6 (0.6%)], side-effect to antiarrhythmics [n = 6 (0.6%)], planned His-ablation [n = 5 (0.5%)], complication to alcohol septal ablation [n = 5 (0.5%)], and other known aetiologies [n = 11 (1.1%)]. The aetiology remained unknown in 517 (50.3%) cases. While the number of patients with unknown aetiology increased during the study period (P < 0.001), we observed no significant change in the number of patients with identified aetiology (P = 0.35).

Conclusion

In a nationwide cohort, the aetiology of AVB was identified in only half the patients younger than 50 years referred for first-time pacemaker implantation. The number of patients with unknown aetiology increased during the study period. These findings indicate need for better insight into aetiologies of AVB and improved diagnostic work-up guidelines.

Pacing Therapies for Vasovagal Syncope

Vasovagal Syncope (VVS) is mediated by a cardiac autonomic reflex with resultant bradycardia and hypotension, precipitating syncope. While benign and mostly well controlled, recurrent VVS can be debilitating and warrants intervention. Non-pharmacological management of VVS have had variable success. In patients with recurrent cardioinhibitory VVS, permanent pacing can be effective. The utility of pacing to preempt the syncopal depends on the prominent temporal role of bradycardia during the vasovagal reflex. Current guidelines recommend pacing as a therapy to consider in older patients with recurrent VVS. Although younger patients can benefit, one should be cautious given the long-term risk of complications. Available data appears to favor a dual chamber pacemaker with closed loop stimulation algorithm to prevent recurrent cardioinhibitory VVS. Several aspects, including mechanistic understanding of VVS and appropriate patient selection, remain unclear, and require further study.

Cardioneuroablation in the Management of Vasovagal Syncope, Sinus Node Dysfunction and Functional Atrioventricular Block: Patient Selection Based on Supporting Evidence

The problem with the regulation of the autonomic nervous system or paroxysmal reflex vagal activation episodes may have an important role in the pathophysiology of vasovagal syncope (VVS), sinus bradycardia or periods of sinus arrest, and variable-degree atrioventricular block (AVB). Because existence of structural heart disease tends to shift the vagosympathetic balance towards a sympathetic predominance, vagally-mediated bradyarrhythmias (VMB) usually occurs in young individuals with structurally normal hearts. However, similar reflex problems may be observed in the elderly people and even those with structural heart disease. Modification of the efferent arm of autonomic nervous system by ablation of main ganglionated plexi (GPs) is called as cardioneuroablation (CNA) and seems as a promising treatment option for appropriately selected patients with VMB. This review outlines the process of patient selection for CNA on the basis of supporting evidence.

Reflex Atrioventricular Block

Reflex atrioventricular block is well-recorded although it is considered rare. Recent data suggests that it is less rare than has been supposed. It has been shown to occur in both vasovagal and carotid sinus reflexes. It has to be distinguished from paroxysmal atrioventricular block due to ventricular conduction tissue disease. Low chronic adenosine levels combined with adenosine release may mimic reflex atrioventricular block. Explanations of the mechanism of these phenomena have been lacking until the recent past. The relevance of reflex atrioventricular block to clinical decision-making is as a possible indication for pacing the heart with consideration given to the vasodepressor component of the reflex.

What is the mechanism of paroxysmal atrioventricular block in a patient with recurrent syncope?

Paroxysmal atrioventricular (AV) block is characterized by sudden appearance of complete heart block with no escape rhythm. Three types have been described having different mechanisms namely, vagally mediated, intrinsic, and idiopathic. A rare case scenario is being described with the occurrence of paroxysmal AV block of all three types in the same patient.

Novel Therapeutic Options in the Management of Reflex Syncope

BACKGROUND

Syncope is a symptom associated with a wide range of pathological conditions, ranging from benign to life threatening. The most frequent is the reflex syncope that may be challenging to treat because of the complex and partially unknown pathophysiological mechanism that has to be addressed by the chosen therapy.

AREAS OF UNCERTAINTY

Head-up tilt testing is so far the only clinical test able to reproduce reflex syncope, but its diagnostic yield has been recently redefined. A new mechanism such as adenosine-sensitive syncope and idiopathic atrioventricular block have been recently described, and the appropriate therapy is not yet established. There is uncertainty on the efficacy of theophylline and on the use of cardiac pacing in these patients.

DATA SOURCES

Clinical trial published data and position paper from the main expert groups on fludrocortisone, midodrine, etilefrine, beta-blockers, and cardiac pacing as useful therapies for patients affected by reflex syncope.

THERAPEUTIC ADVANCES

Theophylline proved in observational trials to be efficient in preventing reflex syncope recurrences in patients with documented spontaneous paroxysmal conduction disorders comparable to cardiac pacing in a subgroup of patients. Reboxetine and sibutramine may elicit a significant pressor and tachycardic effect able to delay the onset of symptoms during head-up tilt testing. Droxidopa has short-term effects on improving the symptoms because of orthostatic hypotension. Cardiac pacing is effective in preventing reflex syncope recurrences with best results when the indication for pacemaker implantation was based on the documentation of bradycardia or asystole during the spontaneous event by a cardiac monitor. External compression using elastic bandage or compressive stockings is able to prevent the decrease in blood pressure in patients with orthostatic hypotension.

CONCLUSIONS

The optimal management of the complex diagnostic and therapeutic options can be achieved following a standardized and evidence-based approach to the patient with syncope.

Efficacy of theophylline in patients with syncope without prodromes with normal heart and normal ECG

BACKGROUND

Patients affected by syncope without or with very short (≤5 s) prodrome with normal heart and normal ECG have been seen to present low plasma adenosine levels. We investigated whether chronic treatment of these patients with theophylline, a non-selective adenosine receptor antagonist, results in clinical benefit.

METHODS

In a consecutive case-series of 16 patients (mean age 47 ± 25 years, 9 females) who had ECG documentation of asystolic syncope, we compared the incidence of syncopal recurrence during a period without and a period with tailored theophylline therapy.

RESULTS

During a median of 60 months before ECG documentation of the index episode, the patients had a median of 2 syncopes per year. During the 6 months of the study phase without therapy, the patients had a median of 2.6 syncopes per year, p = 0.63. During the 23 months of the study phase with theophylline, the patients had a median of 0.4 syncopes per year, p = 0.005 vs history and p = 0.005 vs no therapy. In the 13 patients who had an implantable loop recorder during both study phases, the incidence of asystolic episodes > 3 s decreased from 9.6 per year to 1.1 per year, p = 0.0007. During theophylline treatment, syncope recurred in 1/5 (20%) patients who had an idiopathic atrioventricular block as the index event versus 9/11 (81%) patients who had a sinus arrest, p = 0.005.

CONCLUSION

Theophylline is effective in reducing syncopal burden in patients with syncope without prodromes with normal heart and normal ECG. Its efficacy is greater in those with idiopathic atrioventricular block.

Fluoxetine oral treatment discloses 5-HT1D receptor as vagoinhibitor of the cardiac cholinergic neurotransmission in rat

Although depression and cardiovascular diseases are related, the role of antidepressants such as fluoxetine (increasing serotonin levels) within cardiac regulation remains unclear. We aimed to determine whether fluoxetine modifies the pharmacological profile of serotonergic influence on vagal cardiac outflow. Rats were treated with fluoxetine (10 mg/kg per day; p.o.) for 14 days or equivalent volumes of drinking water (control group); then, they were pithed and prepared for vagal stimulation. Bradycardic responses were obtained by electrical stimulation of the vagal fibers (3, 6, and 9 Hz) or i.v. acetylcholine (ACh; 1, 5, and 10 μg/kg). The i.v. administration of 5-hydroxytryptamine (5-HT; 10 and 50 μg/kg) inhibited the vagally induced bradycardia. 5-CT (5-HT1/7 agonist) and L-694,247 (5-HT1D agonist) mimicked the serotonin inhibitory effect while α-methyl-5-HT (5-HT2 agonist) was devoid of any action. SB269970 (5-HT7 antagonist) did not abolish 5-CT inhibitory action on the electrically induced bradycardia. Pretreatment with LY310762 (5-HT1D antagonist) blocked the effects induced by L-694,247 and 5-CT. 5-HT and 5-CT failed to modify the bradycardia induced by exogenous ACh. Our outcomes suggest that fluoxetine treatment modifies 5-HT modulation on heart parasympathetic neurotransmission in rats, evoking inhibition of the bradycardia via prejunctional 5-HT1D in pithed rats.

Prognostic significance of noncardiac syncope in the general population: A systematic review and meta-analysis

INTRODUCTION

Cardiac syncope heralds significantly higher mortality compared with syncope due to noncardiac causes or unknown etiology, commonly considered a benign event. A few epidemiologic studies have examined the outcome of noncardiac/unexplained syncope comparing individuals with and without syncope, but with controversial results. We performed a systematic review and meta-analysis to clarify whether history of noncardiac/unexplained syncope is associated with increased all-cause mortality in the general population.

METHODS AND RESULTS

Our systematic review of the literature published between January 1, 1966, and March 31, 2018 sought prospective, observational, cohort studies reporting summary-level outcome data about all-cause mortality in subjects with history of noncardiac/unexplained syncope compared with syncope-free participants. Adjusted hazard ratios were pooled through inverse variance random-effect meta-analysis to compute the summary effect size. Meta-regression models were performed to explore the effect of age, cardiovascular risk factors, or other potential confounders on the measured effect size. We identified four studies including 287 382 individuals (51.6% men; age, 64 ± 12 years): 38 843 with history of noncardiac/unexplained syncope and 248 539 without history of syncope. The average follow-up was 4.4 years. History of noncardiac/unexplained syncope was associated with higher all-cause mortality (pooled adjusted hazard ratio = 1.13; 95% confidence interval, 1.05 to 1.23). Meta-regression analysis showed a stronger positive relationship proportional to aging and increasing prevalence of diabetes and hypertension.

CONCLUSIONS

This study-level meta-analysis showed that among older, diabetic and/or hypertensive individuals, history of noncardiac/unexplained syncope, even in the absence of an obvious cardiac etiology, is associated with higher all-cause mortality.

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.