sicksinus

sick sinus syndrome (SSS) / tachycardia-bradycardia syndrome

see also:

Introduction

  • SSS is a syndrome of cardiac rhythm pathologies affecting the sinoatrial node resulting in sinoatrial node pacemaker dysfunction and/or sinoatrial conduction dysfunction
  • most cases are due to acquired damage, but some are genetic familial inherited conditions which often present at an early age
  • symptomatic SSS generally requires the implantation of permanent pacemaker
  • SSS accounts for half of all permanent pacemaker placements
  • it was 1st identified in 1967 when noted after DC reversion of arrhythmias 1)
  • 1 in 600 patients with heart disease who are over age 65 have SSS, and incidence increases with age

Clinical features

  • characterized by persistent inappropriate sinus bradycardia, episodes of sinoatrial block and/or chronotropic incompetence
  • episodes of such dysfunction may cause severe reduction in cardiac output resulting in hypotension, light-headedness, syncope or sudden death due to either:
    • severe sinus bradycardia
    • sinus arrest
    • sinoatrial block
    • tachycardia-bradycardia syndrome is common (flutter, atrial fibrillation, and paroxysmal supraventricular tachycardia)

Pathophysiology

  • the pathophysiology is not just related to dysfunction of the sino-atrial node as the name suggests but may be due to impairments within:
    • cardiac neural stimuli system / autonomic influences
    • conducting system
  • the sino-atrial node
    • situated in the RA, it is the physiological pacemaker of the human heart and responsible for autonomous heart beat generation
    • the mix of ionic currents allows for the pacemaking function, and in addition its poor electrical coupling protects it from the inhibitory hyperpolarizing influence of the surrounding atrial tissue.
    • the automaticity and thus heart reate is regulated via vagal nerve parasympathetic stimulation which slows it and beta-adrenergic sympathetic stimulation which speeds it - adenosine, adrenergic, and muscarinic receptors are all present in SA nodal tissue.
    • hyperpolarization-activated cyclic nucleotide-gated (HCN) and other types of potassium ion channels are important in the automaticity of the SA node core
    • sodium channels are essential for orderly progression of action potentials from the SA node core, through its periphery, and to the surrounding atrial tissue.
    • calcium has an important role 2)

Aetiology

  • elderly
  • IHD
  • rheumatologic
  • oncologic
  • metabolic
  • infectious - myocarditis
  • structural
  • iatrogenic - radiation Rx;
  • amyloidosis
  • Lenegre’s disease
  • Lev’s disease

familial SSS

  • sinus node dysfunction and deafness syndrome (SANDD)
    • bradycardia, profound deafness, and dysfunction of atrioventricular conduction
    • CaV1.3-mediated I-caL dysfunction
  • early repolarization (ER) pattern
    • two or more continuous wall or side wall leads with a J point elevation above 0.1 mV
    • ST elevation is above 0.1 mV and exhibits concave upward or oblique type elevation
    • a polygenic inherited disease, similar to hereditary sinus bradycardia, caused by mutations in cardiomyocyte genes encoding ion channels
    • most commonly seen in young men
      • most common pathogenic genes are encoded by cardiac electrical ion channels, including calcium channels (CACNA1C, CACNB2B, and CACNA2D1), ATP-sensitive potassium channels (KCNJ8), sodium channel α subunit 5 (SCN5A) and TTN gene (cardiomyocyte gene)3)
  • sick sinus syndrome 1 (SSS1)
    • caused by compound heterozygous mutation in the SCN5A gene (600163) on chromosome 3p22 which is associated with pore-forming α-subunit of the cardiac Na+ channel which is responsible for the generation and rapid propagation of action potentials in the heart.
    • automosomal recessive
  • sick sinus syndrome 2 (SSS2)
    • caused by heterozygous mutation in the cardiac pacemaker channel gene HCN4 (605206) on chromosome 15q24
    • autosomal dominant
  • sick sinus syndrome 3 - susceptibility to sick sinus syndrome
    • influenced by variation in the MYH6 gene
    • allelic frequency of 0.38% in Icelanders
    • lifetime risk of developing SSS is 50% (cf 6% for general population)
  • atrial standstill phenotype
    • rare; certain genetic variants of Cx40 with accompanying SCN5A mutations
sicksinus.txt · Last modified: 2019/04/05 03:08 by 127.0.0.1

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