The natural course of untreated sick sinus syndrome and identification of the variables predictive of unfavorable outcome

Tachy-brady syndrome: Electrophysiology and evolving principles of management

Sudden alterations in the heart rate may be associated with diverse symptoms. Sinus node dysfunction (SND), also known as sick sinus syndrome, is a sinoatrial (SA) node disorder. SND is primarily caused by the dysfunction of the pacemaker, as well as impaired impulse transmission resulting in a multitude of abnormalities in the heart rhythms, such as bradycardia-tachycardia, atrial bradyarrhythmias, and atrial tachyarrhythmias. The transition from bradycardia to tachycardia is generally referred to as "tachy-brady syndrome" (TBS). Although TBS is etiologically variable, the manifestations remain consistent throughout. Abnormal heart rhythms have the propensity to limit tissue perfusion resulting in palpitations, fatigue, lightheadedness, presyncope, and syncope. In this review, we examine the physiology of tachy-brady syndrome, the practical approach to its diagnosis and management, and the role of adenosine in treating SND.

Sinus Node Dysfunction

Sinus node dysfunction (SND) is a multifaceted disorder most prevalent in older individuals, but may also occur at an earlier age. In most cases, the SND diagnosis is ultimately established by documenting its ECG manifestations. EPS has limited utility. The treatment strategy is largely dictated by symptoms and ECG manifestations. Not infrequently, both bradycardia and tachycardia coexist in the same patients, along with other diseases common in the elderly (e.g., hypertension, coronary artery disease), thereby complicating treatment strategy. Prevention of the adverse consequences of both bradyarrhythmia and tachyarrhythmia is important to reduce susceptibility to syncope, falls, and thromboembolic complications.

EHRA expert consensus document on the management of arrhythmias in frailty syndrome, endorsed by the Heart Rhythm Society (HRS), Asia Pacific Heart Rhythm Society (APHRS), Latin America Heart Rhythm Society (LAHRS), and Cardiac Arrhythmia Society of Southern Africa (CASSA)

There is an increasing proportion of the general population surviving to old age with significant chronic disease, multi-morbidity, and disability. The prevalence of pre-frail state and frailty syndrome increases exponentially with advancing age and is associated with greater morbidity, disability, hospitalization, institutionalization, mortality, and health care resource use. Frailty represents a global problem, making early identification, evaluation, and treatment to prevent the cascade of events leading from functional decline to disability and death, one of the challenges of geriatric and general medicine. Cardiac arrhythmias are common in advancing age, chronic illness, and frailty and include a broad spectrum of rhythm and conduction abnormalities. However, no systematic studies or recommendations on the management of arrhythmias are available specifically for the elderly and frail population, and the uptake of many effective antiarrhythmic therapies in these patients remains the slowest. This European Heart Rhythm Association (EHRA) consensus document focuses on the biology of frailty, common comorbidities, and methods of assessing frailty, in respect to a specific issue of arrhythmias and conduction disease, provide evidence base advice on the management of arrhythmias in patients with frailty syndrome, and identifies knowledge gaps and directions for future research.

Sinus node dysfunction: current understanding and future directions

The sinoatrial node (SAN) is the primary pacemaker of the heart. Normal SAN function is crucial in maintaining proper cardiac rhythm and contraction. Sinus node dysfunction (SND) is due to abnormalities within the SAN, which can affect the heartbeat frequency, regularity, and the propagation of electrical pulses through the cardiac conduction system. As a result, SND often increases the risk of cardiac arrhythmias. SND is most commonly seen as a disease of the elderly given the role of degenerative fibrosis as well as other age-dependent changes in its pathogenesis. Despite the prevalence of SND, current treatment is limited to pacemaker implantation, which is associated with substantial medical costs and complications. Emerging evidence has identified various genetic abnormalities that can cause SND, shedding light on the molecular underpinnings of SND. Identification of these molecular mechanisms and pathways implicated in the pathogenesis of SND is hoped to identify novel therapeutic targets for the development of more effective therapies for this disease. In this review article, we examine the anatomy of the SAN and the pathophysiology and epidemiology of SND. We then discuss in detail the most common genetic mutations correlated with SND and provide our perspectives on future research and therapeutic opportunities in this field.

Cancer Chemotherapy-Induced Sinus Bradycardia: A Narrative Review of a Forgotten Adverse Effect of Cardiotoxicity

Cardiotoxicity is a common adverse effect of anticancer drugs (ACDs), including the so-called targeted drugs, and increases morbidity and mortality in patients with cancer. Attention has focused mainly on ACD-induced heart failure, myocardial ischemia, hypertension, thromboembolism, QT prolongation, and tachyarrhythmias. Yet, although an increasing number of ACDs can produce sinus bradycardia (SB), this proarrhythmic effect remains an underappreciated complication, probably because of its low incidence and severity since most patients are asymptomatic. However, SB merits our interest because its incidence increases with the aging of the population and cancer is an age-related disease and because SB represents a risk factor for QT prolongation. Indeed, several ACDs that produce SB also prolong the QT interval. We reviewed published reports on ACD-induced SB from January 1971 to November 2020 using the PubMed and EMBASE databases. Published reports from clinical trials, case reports, and recent reviews were considered. This review describes the associations between ACDs and SB, their clinical relevance, risk factors, and possible mechanisms of onset and treatment.

Sinus Node Dysfunction

Sinus node dysfunction (SND) is a multifaceted disorder most prevalent in older individuals, but may also occur at an earlier age. In most cases, the SND diagnosis is ultimately established by documenting its ECG manifestations. EPS has limited utility. The treatment strategy is largely dictated by symptoms and ECG manifestations. Not infrequently, both bradycardia and tachycardia coexist in the same patients, along with other diseases common in the elderly (e.g., hypertension, coronary artery disease), thereby complicating treatment strategy. Prevention of the adverse consequences of both bradyarrhythmia and tachyarrhythmia is important to reduce susceptibility to syncope, falls, and thromboembolic complications.

Genetic Complexity of Sinoatrial Node Dysfunction

The pacemaker cells of the cardiac sinoatrial node (SAN) are essential for normal cardiac automaticity. Dysfunction in cardiac pacemaking results in human sinoatrial node dysfunction (SND). SND more generally occurs in the elderly population and is associated with impaired pacemaker function causing abnormal heart rhythm. Individuals with SND have a variety of symptoms including sinus bradycardia, sinus arrest, SAN block, bradycardia/tachycardia syndrome, and syncope. Importantly, individuals with SND report chronotropic incompetence in response to stress and/or exercise. SND may be genetic or secondary to systemic or cardiovascular conditions. Current management of patients with SND is limited to the relief of arrhythmia symptoms and pacemaker implantation if indicated. Lack of effective therapeutic measures that target the underlying causes of SND renders management of these patients challenging due to its progressive nature and has highlighted a critical need to improve our understanding of its underlying mechanistic basis of SND. This review focuses on current information on the genetics underlying SND, followed by future implications of this knowledge in the management of individuals with SND.

Pharmacologic Approach to Sinoatrial Node Dysfunction

The spontaneous activity of the sinoatrial node initiates the heartbeat. Sino-atrial node dysfunction (SND) and sick sinoatrial (sick sinus) syndrome are caused by the heart's inability to generate a normal sinoatrial node action potential. In clinical practice, SND is generally considered an age-related pathology, secondary to degenerative fibrosis of the heart pacemaker tissue. However, other forms of SND exist, including idiopathic primary SND, which is genetic, and forms that are secondary to cardiovascular or systemic disease. The incidence of SND in the general population is expected to increase over the next half century, boosting the need to implant electronic pacemakers. During the last two decades, our knowledge of sino-atrial node physiology and of the pathophysiological mechanisms underlying SND has advanced considerably. This review summarizes the current knowledge about SND mechanisms and discusses the possibility of introducing new pharmacologic therapies for treating SND.

Evaluating and managing bradycardia

Bradycardia is a commonly observed arrhythmia and a frequent occasion for cardiac consultation. Defined as a heart rate of less than 50-60 bpm, bradycardia can be observed as a normal phenomenon in young athletic individuals, and in patients as part of normal aging or disease (Table 1). Pathology that produces bradycardia may occur within the sinus node, atrioventricular (AV) nodal tissue, and the specialized His-Purkinje conduction system. Given the overlap of heart rate ranges with non-pathologic changes, assessment of symptoms is a critical component in the evaluation and management of bradycardia. Treatment should rarely be prescribed solely on the basis of a heart rate lower than an arbitrary cutoff or a pause above certain duration. In the 2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients with Bradycardia and Cardiac Conduction Delay (referred to hereafter as the 2018 Bradycardia Guideline), there was a significant shift in emphasis from prior guidelines that emphasized device-based implantation recommendations to a focus on evaluation and management of disease states [1,2]. In this review, we will highlight the changes in the new guideline as well as describe the key elements in evaluation and management of patients presenting with bradycardia.

Frequency and Significance of High-Degree Atrioventricular Block and Sinoatrial Node Dysfunction in Patients With Non-ST-Elevation Myocardial Infarction

Characteristics of conduction disorders after ST-elevation myocardial infarction (STEMI) have been well described. In contrast, limited data are available on the incidence, treatment trends, and prognostic impact of conduction disorders after non-ST-elevation myocardial infarction (NSTEMI). Using the National Inpatient Sample database, we compared the characteristics and outcomes of conduction disorders in patients with a primary diagnosis of STEMI versus NSTEMI between 2010 and 2014. Conduction disorders were classified into‬ high-degree AV block (HDAVB), consisting of complete AV block or Mobitz type II second-degree AV block, and sinoatrial node dysfunction (SND). We identified 135,468 STEMI patients and 281,928 NSTEMI patients. In contrast to the STEMI cohort where HDAVB was more common than SND (2.4% vs 0.5%), SND was observed more often in the NSTEMI cohort, presenting in 2,417 patients (0.9%), followed by HDAVB in 1,745 patients (0.6%). In patients who developed HDAVB, NSTEMI patients were more likely to undergo permanent pacemaker implantation than STEMI patients (30.0% vs 11.6%; p < 0.001). The rate of permanent pacemaker implantation for SND was comparable between STEMI and NSTEMI patients (33.9% vs 30.5%; p = 0.10). In the NSTEMI cohort, patients who developed HDAVB had higher in-hospital mortality than those without any major conduction disorders (16.6% vs 3.8%; p < 0.001). In conclusion, SND was more common than HDAVB in the NSTEMI cohort, in contrast to the predominance of HDAVB observed in the STEMI cohort. About one-third of patients who developed HDAVB after NSTEMI underwent pacemaker implantation, suggesting lower rates of spontaneous resolution of HDAVB, when compared with STEMI patients.

Recommendations for the use of electrophysiological study: Update 2018

The field of cardiac electrophysiology has greatly developed during the past decades. Consequently, the use of electrophysiological studies (EPSs) in clinical practice has also significantly augmented, with a progressively increasing number of certified electrophysiology centers and specialists. Since Zipes et al published the Guidelines for Clinical Intracardiac Electrophysiology and Catheter Ablation Procedures in 1995, no official document summarizing current EPS indications has been published. The current paper focuses on summarizing all relevant data of the role of EPS in patients with different types of cardiac pathologies and provides up-to-date recommendations on this topic. For this purpose, the PubMed database was screened for relevant articles in English up to December 2018 and ESC and ACC/AHA Clinical Practice Guidelines, and EHRA/HRS/APHRS position statements related to the current topic were analyzed. Current recommendations for the use of EPS in clinical practice are discussed and presented in 17 distinct cardiac pathologies. A short rationale, evidence, and indications are provided for each cardiac disease/group of diseases. In conclusion, because of its capability to establish a diagnosis in patients with a variety of cardiac pathologies, the EPS remains a useful tool in the evaluation of patients with cardiac arrhythmias and conduction disorders and is capable of establishing indications for cardiac device implantation and guide catheter ablation procedures.

Syncope: Electrocardiographic and Clinical Correlation

Syncope is a frequent condition, owing to a transient global cerebral hypoperfusion, that may depend on a reduction of vascular total peripheral resistance and/or cardiac output. Cardiac syncope doubled the risk of death from any cause and increased the risk of nonfatal and fatal cardiovascular events. Arrhythmias are the most common cardiac causes of syncope. Both bradyarrhythmias and tachyarrhythmias may predispose to syncope. The first line evaluation relies on clinical history, physical examination, active standing test, 12-lead echocardiogram. The diagnostic yield of electrophysiological study in detecting the cause of syncope depends highly on the pretest probability.

Electrophysiological Testing for the Investigation of Bradycardias

In this article we review the role of electrophysiological testing in patients presenting with bradycardia due to sinus node or atrioventricular node disease. In sinus bradycardia the role of electrophysiology studies is not established. In AV conduction disturbances, an electrophysiology study may be necessary both for the establishment of atrioventricular block as the main cause of symptoms, and for identification of the anatomic site of block that may dictate the potential need of permanent pacing.

Clinical evaluation and risk stratification in patients with syncope

Syncope accounts for approximately 1 % of visits to emergency departments. The first diagnostic step is to rule out nonsyncopal conditions as a cause of the transient loss of consciousness. Next, the basic clinical evaluation should identify patients at high risk for potentially life-threatening events. These patients should be admitted and monitored until a diagnosis is made and definitive treatment can be offered. Guided by the basic evaluation findings, specific tests should be performed to prove or rule out the suspected diagnosis. In low-risk patients, this should preferably be done in an outpatient setting. To date, there is no consensus on a structured algorithm for the evaluation of patients with syncope. Therefore, it seems beneficial to formulate an algorithm based on the current guidelines for the management of syncope for use in the clinical setting.

Clinical laboratory testing: what is the role of tilt-table testing, active standing test, carotid massage, electrophysiological testing and ATP test in the syncope evaluation?

The first step in the diagnostic evaluation of patients with suspected syncope begins with an "initial evaluation" consisting of careful history taking, physical examination including orthostatic blood pressure measurement and electrocardiogram. However, even in expert centers the diagnostic yield of this "initial evaluation" is only approximately 50%. In the remaining cases in which a satisfactory diagnosis is either unknown or uncertain after initial assessment, additional clinical testing is needed. This article reviews the role of some of the more commonly used additional diagnostic tests, including: tilt-table testing, the active standing test, carotid sinus massage, electrophysiological testing, and the adenosine triphosphate (ATP) test. The role of angiography, exercise testing and imaging is noted briefly. Other clinical laboratory investigations, such as ambulatory ECG monitoring, are examined in other papers in this issue. In brief, clinical laboratory tests, carefully interpreted, may be useful in the evaluation of the basis of suspected syncope. However, these tests should be selected carefully and performed based on the pre-test probability inferred from the initial examination, and the less invasive tests should be used first.

Bradyarrhythmias in the elderly

Over the next decade, there will be a dramatic increase in the number of elderly people in the United States and in most parts of the world. With this increase, there will be an accompanying increase in patients with sinus node dysfunction and atrioventricular block; therefore, it will be essential for health care personnel to have a basic knowledge of bradyarrhythmias and the considerations required for managing these rhythms in elderly patients. In particular, comprehensive assessment before decisions on medical and device-based management is critical and must take into account social issues and the presence of comorbid conditions.

Sinus node dysfunction: recognition and treatment

Sinus node dysfunction (SND) refers to a wide range of abnormalities involving sinus node and atrial impulse generation and propagation. SND occurs at any age and is commonly encountered in clinical practice. Clinicians must be able to accurately diagnose this syndrome, which can present from asymptomatic bradycardia to atrial standstill.

Can we predict outcomes in atrial fibrillation?

Atrial fibrillation (AF) is the most common arrhythmia encountered by generalists and cardiologists alike. Much of the attendant morbidity from AF arises from systemic embolic complications which are effectively reduced with utilization of anti-platelet and/or anticoagulant therapy. The systemic embolic complications of AF and the medical therapy to attenuate these risks are very well established. Through the course of this review, we aim to highlight the complex relationship between AF and other, "non-embolic" outcomes. The presence of AF has been demonstrated to be associated with a 1.5 to 2-fold increase in mortality across numerous observational cohorts. Still further, AF frequently coexists with heart failure, whether as a causative factor or a consequence of underlying structural heart disease or neurohumoral derangement, where its presence is associated with worse clinical outcomes. Whether AF is an independent risk factor for acute coronary syndromes (ACS) remains controversial, though its occurrence in patients with ACS has been shown to be associated with adverse outcomes both in observational cohorts as well as clinical trial populations. Individuals with AF have a 1.5 to 3-fold increase in the rate of hospitalization and are at elevated risk for other arrhythmic disorders including both bradyarrhythmias as well as tachyarrhythmias. AF leads to considerable morbidity and mortality for patients and exacts a tremendous financial toll on the healthcare system-estimated to range from $6.0 to $26.0 billion. Given the current demographic transition in developed countries, the prevalence of AF will continue to increase and the need for refined approaches to risk stratification and pharmacotherapeutic interventions to attenuate the burden on patients will only become more important.

Electrophysiological features in patients with sinus node dysfunction and vasovagal syncope

INTRODUCTION

Syncope is a common presentation of sinus node dysfunction (SND). Some patients who receive a permanent pacemaker due to SND do not benefit from it and further diagnostic workup leads to the diagnosis of vasovagal syncope (VVS). The aim of the study was to identify electrophysiological criteria that can be used for identification of patients with SND and concurrent VVS.

MATERIAL AND METHODS

Transoesophageal atrial pacing (TAP) was performed in 100 patients divided into four groups depending on symptoms and TAP results. Standard electrophysiological parameters of sinus node function and their variability were obtained in the basal state and after pharmacological autonomic blockade (AB).

RESULTS

Patients with concurrent SND and VVS had a greater variability of sinoatrial conduction time assessed by Strauss' method than patients without incidents of syncope (83.2 ±53.9 vs. 34.1 ±19.6, 47.8 ±33.6 and 32.1 ±22.99). Apart from abnormal sinus node recovery time and second pause, patients with SND had bigger basal state variability of these parameters. In patients with SND and concurrent vasovagal syncope the variability of sinus node recovery time (SNRT), corrected SNRT (cSNRT) and second pause (IIP) decreased after autonomic blockade.

CONCLUSIONS

Patients with concurrent SND and VVS have distinct electrophysiological features - greater sinoatrial conduction time (SACT) variability and the decrease of SNRT, cSNRT and IIP variability after AB. However, further studies in larger study groups are needed to validate our findings. Transoesophageal atrial pacing is a useful procedure in patients with syncope, especially when the coexistence of more than one cardiac cause is suspected.

[Significance of diagnostic methods in the work-up of syncope]

After the initial evaluation including detailed history, physical examination, electrocardiogram, and orthostatic blood pressure measurements, risk stratification should follow, if the cause of syncope is still unclear in order to define the acuteness and extensiveness of the further diagnostic evaluation. The documentation of arrhythmia during syncope is the gold standard for diagnosis of arrhythmic syncope. The implantable loop recorder should be integrated early in the diagnostic work-up. In patients >40 years with otherwise unexplained syncope, carotid sinus massage is recommended. In suspected reflex-mediated syncope, the tilt test is able to confirm the diagnosis and gives information about the underlying pathomechanisms, while electrophysiological studies have still a proven indication in patients with previous myocardial infarction and preserved left ventricular function. The adenosine triphophate test has no clinical relevance in the diagnostics of syncope. Echocardiography plays an important role in the risk stratification by diagnosing structural cardiac disease. In patients experiencing syncope associated with exertion, exercise stress testing is indicated. Finally, a coronary angiogram should be performed, if ischemia triggered syncope is suspected. A routinely performed neurological evaluation is not recommended.