![]() ![]() Our understanding of cardiac electrophysiology has significantly advanced with the use of pre-clinical animal models, which are amenable to pharmacological, physical or genetic manipulation for studying the consequences of ion channel abnormalities ( 16– 19), and have provided insight for translational application ( 14, 20– 25). A related condition, Bayes syndrome, involves inter-atrial block associated with AF ( 5– 15). Tachycardia complicates approximately 50% of SSS cases ( 2– 4). The association between sick sinus syndrome (SSS) and atrial fibrillation (AF) has been recognized for more than 5 decades since 1968 ( 1) with the first description of tachycardia-bradycardia syndrome (TBS) reported 5 years later ( 2). The aim of this article is to review the different ion channels involved in TBS, examine the three-way relationship between ion channel dysfunction, tachycardia and bradycardia in TBS and to consider its current and future therapies. Alternatives to electronic pacemakers are gene-based bio-artificial sinoatrial node and cell-based bio-artificial pacemakers, which are promising techniques whose long-term safety and efficacy need to be established. The mainstay treatment option for SSS is pacemaker implantation, an effective approach, but has disadvantages such as infection, limited battery life, dislodgement of leads and catheters to be permanently implanted in situ. Dysfunction of ion channels responsible for initiation or conduction of cardiac action potentials may underlie both bradycardia and tachycardia bradycardia can also increase the risk of tachycardia, and vice versa. Techniques such as genetic screening and molecular diagnostics together with the use of pre-clinical models have elucidated the electrophysiological mechanisms of this condition. ![]() Tachycardia-bradycardia syndrome (TBS) is a complication of SSS characterized by alternating tachycardia and bradycardia. Symptoms associated with sick sinus syndrome may be aggravated by digoxin, verapamil, beta-blockers, sympatholytic agents such as clonidine and methyldopa, and anti-arrhythmic agents.Sick sinus syndrome (SSS) encompasses a group of disorders whereby the heart is unable to perform its pacemaker function, due to genetic and acquired causes.Other: digestive disturbances, dizziness, errors in judgment, facial flushing, fatigue, oliguria.Cardiovascular system: angina, arterial thromboemboli, cerebrovascular accident, congestive heart failure (dyspnoea), palpitations.Central nervous system: dementia, irritability, lethargy, light-headedness, confusion, memory loss, nocturnal wakefulness, syncope.Presentation may be with fatigue, dizziness, palpitations, and syncope or presyncope.Patients are often asymptomatic, or have subtle or nonspecific symptoms, such as fatigue.At least 50% of people with sick sinus syndrome develop alternating bradycardia and tachycardia, also known as tachy-brady syndrome.Abnormalities in sick sinus syndrome include episodes of sinus bradycardia, sinus arrest or exit block, combinations of sinoatrial and atrioventricular nodal conduction disturbances, and atrial tachyarrhythmias.The average age of a person with sick sinus syndrome is 68 years and it develops in 1 in 600 patients with cardiac disease aged over 65 years. Sick sinus syndrome is most common in the elderly, but can occur in all ages. Paediatric causes include congenital abnormalities and sinoatrial nodal artery deficiency. Sleep apnoea may be a contributing factor by causing reduced cardiac oxygenation. Drugs - eg, digoxin, calcium-channel blockers, beta-blockers, sympatholytic agents, anti-arrhythmic drugs.Hyperkalaemia, hypoxia, hypothermia, hypothyroidism, hyperthyroidism.Cardiomyopathies: ischaemia, myocardial infarction, myocarditis, pericarditis, rheumatic heart disease, surgical injury, arteritis.Friedreich's ataxia, muscular dystrophy.Familial sinoatrial node disorders: autosomal and recessive forms.Collagen vascular disease: amyloidosis, haemochromatosis, fatty replacement, sarcoidosis.Idiopathic degeneration of the sinus node is the most common cause of sick sinus syndrome.An intrinsic disease of the sinus node:. ![]()
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