Syncope and Idiopathic (Paroxysmal) AV Block

Out of Sync: A Report of Complete Heart Block

Complete heart block is a serious cardiac conduction condition marked by the inability of electrical impulses to propagate from the atria to the ventricles. This disorder causes an absence of coordination between the upper and lower chambers of the heart, resulting in various symptoms and possible problems. Complete heart block, also known as third-degree atrioventricular block, is a more severe form of this illness compared to first and second degree. This report describes a 79-year-old man who experienced a rare presentation of complete heart block. The patient had a preexisting condition of hypertension and had been having episodes of dyspnea for the past few months. Although the patient experienced these symptoms, echocardiography did not reveal any evidence of diminished ejection fraction, indicating that the systolic function was preserved. A left cardiac catheterization procedure was conducted, which showed non-occlusive coronary artery disease. Troponin levels were within normal limits, ruling out an acute ischemic event. This finding eliminates the possibility of severe ischemia factors contributing to the patient's condition. An extensive examination of the patient's medication history showed the absence of any drugs that could have caused the total heart block. The decision was reached to proceed with the implantation of a permanent pacemaker. The pacemaker was effectively inserted, resulting in the elimination of the patient's symptoms and stabilization of his heart rhythm.

An Unusual Case of Paroxysmal Third-Degree Atrioventricular Block: Thinking Outside the Box

During the assessment of a third-degree atrioventricular (AV) block in a patient with syncope, different etiologies should be considered and evaluated. Extrinsic vagal paroxysmal AV block, extrinsic idiopathic AV block and intrinsic paroxysmal AV block are among the types of third-degree AV block in the differential diagnoses. Extrinsic vagal paroxysmal third-degree atrioventricular block (EV-AVB) is linked to parasympathetic influence on cardiac conduction and can be observed in bladder distention and urinary retention. Topical and ophthalmic beta-blockers have shown systemic effects such as bradycardia with and without syncope. We present the case of an 80-year-old male with symptomatic EV-AVB likely precipitated by bladder outlet obstruction and chronic use of an ophthalmic beta-blocker, often overlooked causes of third-degree AV block.

Adenosinergic System and Neuroendocrine Syncope: What Is the Link?

Although very common, the precise mechanisms that explain the symptomatology of neuroendocrine syncope (NES) remain poorly understood. This disease, which can be very incapacitating, manifests itself as a drop in blood pressure secondary to vasodilation and/or extreme slowing of heart rate. As studies continue, the involvement of the adenosinergic system is becoming increasingly evident. Adenosine, which is an ATP derivative, may be involved in a large number of cases. Adenosine acts on G protein-coupled receptors with seven transmembrane domains. A1 and A2A adenosine receptor dysfunction seem to be particularly implicated since the activation leads to severe bradycardia or vasodilation, respectively, two cardinal symptoms of NES. This mini-review aims to shed light on the links between dysfunction of the adenosinergic system and NHS. In particular, signal transduction pathways through the modulation of cAMP production and ion channels in relation to effects on the cardiovascular system are addressed. A better understanding of these mechanisms could guide the pharmacological development of new therapeutic approaches.

A Case of Symptomatic Paroxysmal Complete Atrioventricular Block

Paroxysmal complete atrioventricular block (PCAB) is clinically characterized by a sudden change from 1:1 atrioventricular (AV) conduction leading to complete heart block. Patients may have a vast array of symptoms, but commonly, PCAB will lead to syncope and possible sudden cardiac death. The literature currently consists of three different types of PCAB: intrinsic paroxysmal atrioventricular block, extensive vagal paroxysmal atrioventricular block, and extrinsic idiopathic paroxysmal atrioventricular block. Currently, there is no single symptom or sign that is specific to a single type of AV block. PCAB is often missed or overlooked because of its unpredictability and no evidence of conduction disease with a normal 1:1 conduction on routine electrocardiograms. Here, we present a case of a 65-year-old female who has been intermittently symptomatic for four years and was found to have PCAB.

The Role of Adenosine and Its Degradation Enzymes - Adenosinedeaminase and Adenosinekinase in Pathogenesis of Vasovagal Syncope

INTRODUCTION

Adenosine is mediator regulating physiological and pathological processes in organism. It probably plays a role in pathogenesis of vasovagal syncopes (VVS), too. Adenosine, its receptors and degradation enzymes- adenosinedeaminase (ADA) and adenosinekinase (ADK), are called the adenosinergic system.

AIM

We aimed to evaluate serum levels of adenosine, ADA and ADK in patients with tilt-induced VVS and compare them to tlit-negative controls. Secondary aim was to compare the levels between the types of VVS and correlate them with hemodynamic parameters.

SUBJECTS AND METHODS

Altogether 132 individuals were involved in this study (age 39,88±15,64 years, 51 males). All patients underwent head up tilt test (HUTT) in differential diagnosis of syncope. Blood sampling was performed before and after HUTT. Baseline and stimulated serum levels of adenosine, ADA and ADK were evaluated by ELISA method.

RESULTS

HUTT was positive in 91 patients (HUTT+), 41 individuals were negative (HUTT-). HUTT+ patients had higher baseline and stimulated adenosine levels, when compared to HUTT- population. The rise in adenosine was higher in HUTT+ group. On the other hand, the increase of ADA was significantly higher in HUTT- subjects. Among HUTT+ group, the highest adenosine was found during vasodepressoric VVS.

CONCLUSION

Adenosinergic system may play role in pathogenesis of VVS. Patients with VVS have higher adenosine levels, that may be caused by attenuated degradation. Adenosine seems to be involved predominantly in vasodepressoric type of VVS. Further research evaluating complex function of adenosinergic system in these patients is needed.

The Longer the Block, the Harder You Fall: Extrinsic Idiopathic Atrioventricular Block Masquerading as Seizures

History and physical examination are the diagnostic cornerstones of transient loss of consciousness (TLOC). However, details can be scarce and examination unrevealing, thus making the diagnosis elusive. In a case of convulsive TLOC, the initial diagnosis was incorrect, but a fortuitously captured event on telemetry yielded the diagnosis: extrinsic idiopathic atrioventricular block. (Level of Difficulty: Beginner.)

Catheter Ablation of Atrioventricular Block: From Diagnosis to Selection of Proper Treatment

A 39-year-old man presented with recurrent syncope. A 12-lead electrocardiogram and a 24-h Holter recording demonstrated atypical persistent Mobitz type I and high-degree atrioventricular block, respectively. The functional nature of the atrioventricular block was confirmed by atropine challenge, exercise testing, and electrophysiological study. The patient was successfully treated with a cardioneuroablation procedure. (Level of Difficulty: Intermediate.).

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.

Adenosine and the Cardiovascular System: The Good and the Bad

Adenosine is a nucleoside that impacts the cardiovascular system via the activation of its membrane receptors, named A₁R, A_2AR, A_2BR and A₃R. Adenosine is released during hypoxia, ischemia, beta-adrenergic stimulation or inflammation and impacts heart rhythm and produces strong vasodilation in the systemic, coronary or pulmonary vascular system. This review summarizes the main role of adenosine on the cardiovascular system in several diseases and conditions. Adenosine release participates directly in the pathophysiology of atrial fibrillation and neurohumoral syncope. Adenosine has a key role in the adaptive response in pulmonary hypertension and heart failure, with the most relevant effects being slowing of heart rhythm, coronary vasodilation and decreasing blood pressure. In other conditions, such as altitude or apnea-induced hypoxia, obstructive sleep apnea, or systemic hypertension, the adenosinergic system activation appears in a context of an adaptive response. Due to its short half-life, adenosine allows very rapid adaptation of the cardiovascular system. Finally, the effects of adenosine on the cardiovascular system are sometimes beneficial and other times harmful. Future research should aim to develop modulating agents of adenosine receptors to slow down or conversely amplify the adenosinergic response according to the occurrence of different pathologic conditions.

Step-by-Step Cardioneuroablation Approach in Two Patients with Functional Atrioventricular Block

Parasympathetic overactivity may cause functional atrioventricular block episodes and necessitate pacemaker implantation in symptomatic cases and those refractory to conventional therapies. In these patients, if it can be clearly demonstrated that there is no structural damage in the conduction system, elimination of the vagal activity based on radiofrequency catheter ablation of main ganglionated plexi around the heart, which is called as cardioneuroablation, might be a rational approach. In this review article, we try to discuss patient selection and procedural steps suitable for cardioneuroablation based on two patients with functional atrioventricular block.

Potential usage of cardioneuroablation in vagally mediated functional atrioventricular block

An increase in parasympathetic tone may be the main cause of some transient or permanent atrioventricular block cases. Some of these patients, defined as vagally mediated functional atrioventricular block, may be severely symptomatic and refractory to conventional therapies and may necessitate cardiac pacing. Cardioneuroablation is a relatively new strategy for management of patients with excessive vagal activation based on radiofrequency catheter ablation of main ganglionated plexi around the heart. Present review was dedicated to discuss potential usage of cardioneuroablation in patients with vagally mediated functional atrioventricular block.

ELectrophysiological mechanisms underlying the Inhibitory CArdiac syncope without asystolic significant pause: Therapeutic and prognostic implications. The ELICA randomized trial

BACKGROUND

The aim of this study was to investigate syncope recurrence in patients with a 2A cardioinhibitory response to the head up tilt testing (HUT).

METHODS

In this study, we enrolled 72 consecutive patients affected by syncope with cardioinhibitory response without asystolic significant pause to HUT (2A type). In these patients, we randomly performed electrophysiological study (ES). In case of sino-atrial node, atrio-ventricular node dysfunction, and sustained arrhythmias induction, the ES resulted positive. ES was positive in 9 patients (group A), then treated by catheter ablation, and/or by devices implants. Otherwise, ES resulted negative (group B), and these patients did not receive an interventional treatment. However, after ES, we evaluated syncope recurrence during 360 days follow-up.

RESULTS

There was a lower statistical significant syncope recurrence at follow-up, comparing group A to group B of patients [n of events 9 (40.9%) vs 8 (57.1%), P < .05]. At multivariate analysis, ES result was the only factor predicting syncope recurrence at follow-up (hazard ratio = 27.63, 95% confidence interval = 1.02-54.24, P < .005).

CONCLUSION

The positivity to ES study, and successful interventional therapies may reduce the burden of syncope recurrence at 360 days follow-up in 2A HUT subjects.Clinical trial number: NCT02861274.

Syncope and paroxysmal atrioventricular block

Current literature reveals three types of paroxysmal atrioventricular block (AVB) that can cause syncope: Intrinsic paroxysmal atrioventricular block is due to an intrinsic disease of the AV conduction system; this type of "cardiac syncope" is also called Stokes-Adams attack; Extrinsic vagal paroxysmal atrioventricular block is linked to the effect of the parasympathetic nervous system on cardiac conduction and is one of the mechanisms involved in "reflex syncope." Extrinsic idiopathic paroxysmal atrioventricular block is associated with low levels of endogenous adenosine and is supposed to be one of the mechanisms involved in "low-adenosine syncope." These three types of paroxysmal AVB present different clinical and electrocardiographic features. Additionally, the efficacy of cardiac pacing and theophylline therapy to prevent syncopal recurrences is also different for these three types of AVB.