T1 L14: Cardiac Arrhythmias

    Cards (20)

    • "Natural death within one hour of the onset of acute symptoms"?
      sudden death
    • "Sudden cardiac death"?
      Sudden death due to cardiac causes
    • Disorders leading to risks for sudden cardiac death?
      • CHD / low LVEF (left ventricular ejection fraction)
      • structural heart disease (eg cardiomyopathies)
      • primary arrhythmia
    • Broad categories of arrhythmia causes
      Electrical (primary or arrhythmogenic): ion channels and electrical issues at cellular level. Extra conduction pathways at organ level.
      Structural: Unusual shape or size of cardiac tissue that changes signal pathway. Can lead to signal delays that interfere with cardiac conduction cycle.
      Ischaemic: Hypoxia makes local heart tissue electrically unstable. Effectively changes signal pathway, leading to delays that interfere with cardiac conduction cycle.
    • Causes of primary arrhythmia
      • Unstable myocardium: often due to damaged or hypoxic tissue, eg atrial fibrillation
      • Ion channel pathologies: also called channelopathies. Eg long QT syndrome
      • Accessory conduction pathways: eg Wolff-Parkinson-White
    • Cardiomyopathy
      Pathology when heart size, shape or thickness is abnormal; excluding those due to CAD, hypertension, valve abnormalities, and heart disease present at birth
      Consequences often:
      • risk of pumping dysfunction / low output heart failure
      • conduction abnormalities (because the normal pathways of electrical conduction are altered)
    • Two types of cardiomyopathy
      • Dilated (eccentric): inner chambers enlarge, myocardium thins and stretches
      • Hypertrophic (concentric): inner LV chamber shrinks, myocardium thickens
    • Tetralogy of Fallot
      • Developmental defect
      • Four developmental defects:
      • ventricular septal defect (hole between ventricles)
      • pulmonary valve stenosis
      • Right ventricular hypertrophy
      • overriding aorta (misplaced or moved)
      • low blood oxygen saturation & cyanosis - blue baby
      • associated with a higher risk of sudden death, even after surgical correction in childhood
    • Substrate vs Trigger
      Substrate: ongoing, underlying tissue instability that increases triggers/allows for maintenance and amplification of arrhythmia
      • Electrical defect as substrate: genetic/pharmacological problems with ion channels/electrolytes
      • Structural defect as substrate: fibrosis, inflammation caused by IHD, rheumatic disease etc
      Trigger: brief event required to initiate a period of arrhythmia
      • eg extrasystole (extra beat)
    • R on T
      • ECG phenomenon
      • a type of potential trigger for arrhytmias
      • on ECG, premature QRS complex occurs during previous T wave
      • T wave is a 'vulnerable period': during repolarisation of ventricular AP, refractory period is ending
      • Resulting QRS wave is a 'premature ventricular contraction' (PVC).
    • Pacemaker
      • implanted electronic device
      • Consistently applies impulses for each heartbeat
      • mostly used for bradyarrhythmias and heart block
    • ICD - Implantable Cardioverter Defibrillator 

      • implanted electronic device. Uses large shock waves to reset entire heart
      • applies electrical impulses ONLY when ventricular dysrhythmias detected
      • protects from fast or uncontrolled rhythms
      Indications for implanting an ICD:
      • cardiac arrest due to ventricular fibrillation
      • symptomatic heart failure with low LVEF
      • cardiomyopathies
      • congenital
      • channelopathies
    • Antiarrhythmic Drugs
      • usually affect ion channel activity or sympathetic drive
      • examples:
      • Amiodarone
      • beta blockers
      • (Digoxin for AF)
      • Mostly for supraventricular arrhythmias (deriving from atria or AV node)
    • Reperfusion injury
      tissue damage caused when blood supply returns to the tissue after a period of ischaemia or hypoxia.
      (tissue damage/hypoxia leads to electrical irregularities & risk)
      • Cause: restoration of circulation results in inflammation and oxidative damage
      • Contexts: myocardium after PCI (percutaneous coronary intervention), brain tissue after ischaemic stroke
      • Preventative treatments: cooling, immunosuppression, oxygen radical scavengers
    • Syncope vs Seizures
      both may be asymptomatic so difficult to differentiate
      Syncope:
      • may be registered by Holter monitor
      • 'cumple'
      Seizure:
      • may be registered by EEG/brain imaging
      • stiffness/unusual postures, 'tip over'
    • Vasovagal vs Exertional Syncope
      Vasovagal syncope:
      • vagal increase & sympathetic decrease
      • so vasodilatation + low heart rate, resulting in sudden low cardiac output
      • triggered centrally (brain), not heart level
      • most common form; recurrent, common in young adults
      Exertional syncope:
      • benign
      • usually after exercise
    • Index case
      the initial patient in the population of an epidemiological investigation; the primary case
    • The Proband
      In medical genetics, the index case is the case of the original patient that stimulates investigation of other members of the family, usually referred to as ...?
    • Number Needed to Treat (NNT)

      Average number of patients who need to be treated to prevent one additional bad outcome.
      Statistical measurement of the impact of a medicine or therapy.
    • Penetrance (Genetic)

      the proportion of individuals carrying a particular allele of a gene and also express the trait. ie have the gene and also affected
      incomplete or reduced penetrance: some individuals will not express the trait even though they carry the allele. Many channelopathies can vary from patient to patient.