![]() The prognosis of individuals with sick sinus syndrome or atrioventricular block is variable and difficult to predict because it may depend on the presence and severity of comorbidities (such as ischaemic heart disease) and the underlying cause of the conduction defect.Ģ.6 The prevalence of sick sinus syndrome is thought to be about 0.03% of the whole population, and increases with age. Although partial atrioventricular block is usually asymptomatic, it carries a high risk of progression to complete block.Ģ.5 The diagnosis of sick sinus syndrome and atrioventricular block is based on the correlation of symptoms with electrocardiographic findings (electrocardiogram and ambulatory ECG or Holter monitoring). Atrioventricular block may be intermittent or permanent, and it can progress from minimal asymptomatic conduction delay to the ventricles (first‑degree), to partial (second‑degree) atrioventricular block, or complete (third‑degree) atrioventricular block, in which there is no conduction between the atria and ventricles. The AV node captures waves of depolarisation from the atria, which are then transferred to the ventricles via the bundles of His and the Purkinje system (branches of the conducting system). This may be caused by conduction defects at the AV node (situated between the atria and ventricles), bundle of His and/or bundle branches. Sick sinus syndrome is characterised by impaired impulse formation, which is often the result of chronic fibrotic degeneration or calcification of the sinus node and/or the surrounding atrial tissues.Ģ.4 Atrioventricular block is a failure in the conduction of electrical impulses from the atria to the ventricles. Common pathological conditions that cause bradycardia are sick sinus syndrome, atrioventricular block or a combination of the two.Ģ.3 Sick sinus syndrome is an irreversible dysfunction of the sinus node, a small area of the right atrium in which a small group of cells spontaneously depolarise and act as the heart's natural pacemaker. Dysrhythmias may be fast (tachyrhythmias) or slow (bradyrhythmias), and regular or irregular.Ģ.2 Symptoms of bradycardia include faints, falls, dizziness and confusion (manifestations of hypotension), palpitations, fatigue on exertion, difficulty with breathing (dyspnoea) and chest pain. 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.2.1 Abnormal heart rhythms (dysrhythmias) are caused by disturbances in electrical impulse generation or by abnormal conduction between chambers of the heart – principally within the sinus node, atrioventricular (AV) node and the His–Purkinje network.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. ![]()
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