sudden cardiac death Flashcards
what is sudden death?
- natural, rapid, unexpected
- not trauma, toxicity or poison
- not due to chronic illness
- natural death within one hour of the onset of acute symptoms
what are the causes of sudden death?
- heart and/or its vessels
- noncardiac vessels
- pulmonary system (PE)
- central nervous system
what causes sudden cardiac death?
sudden death due to cardiovascular/coronary vessel causes
what are the direct causes of sudden cardiac death?
- coronary obstruction: infarct, embolism
- arrhythmia/dysrhythmia
what are the disorders leading to risks for sudden cardiac death?
- CHD/low LVEF
- structural heart disease
- primary arrhythmia
what is the definition of a cardiac arrest?
a sudden stop in effective blood circulation due to the failure of the heart to contract effectively or at all
what is an acute myocardial infarction?
when blood flow to some heart muscle is impaired. Usually the heart continues pumping but less effectively
what is the definition of heart failure?
when the circulation is substandard, but the heart is still pumping sufficient blood to sustain life
what is arrhythmia/dysrhythmia?
a variation in the normal beating pattern of rhythm of the heart
what are the 3 broad categories of arrhythmia causes?
- electrical
- structural
- ischaemic
how do the electrical causes link to arrhythmia?
- ion channels and electrical issues at cellular level
- extra conduction pathways at the organ level
how do the structural causes link to arrhythmia?
- unusual shape or size of cardiac tissue that changes signal pathway
- can lead to signal delays that interfere with cardiac conduction cycle
how do the ischaemic causes link to arrhythmia?
- hypoxia makes local heart tissue electrically unstable
- effectively changes signal pathway, leading to delays that interfere with cardiac conduction cycle
what are the causes of primary arrhythmia?
- unstable myocardium: often due to damaged or hypoxic tissue
- ion channel pathologies: long QT syndrome
- accessory conduction pathways
what is cardiomyopathy?
- pathology when heart size, shape or thickness is abnormal
- this excludes heart disease due to coronary artery disease, hypertension, abnormalities of the heart valves, and heart disease present at the time of birth
what are the consequences of cardiomyopathy?
- risk of pumping dysfunction or low output heart failure
- conduction abnormalities because the normal pathways or electrical conduction are altered
what are the 2 types of cardiomyopathy?
- dilated (eccentric)
- hypertrophic (concentric)
what is associated with tetralogy of fallot?
a developmental defect associated with high risk of sudden death even after surgical correction in childhood
what is trigger?
brief event required to initiate a period of arrhythmia
what is substrate?
- ongoing, underlying tissue instability that increases triggers or allows for maintenance and amplification or dysrhythmia.
- it can be and electrical or structural defect
what is R on T (ECG phenomenon)?
- a type of potential trigger for arrhythmias
- on the ECG, when a premature QRS complex occurs during the previous T wave
- the T wave is a ‘vulnerable period’ during depolarisation of ventricular AP, refractory period is ending
- resulting QRS wave is a premature ventricular contraction
what is a pacemaker?
- implanted electronic device that had electrodes that can stimulate the heart
- consistently applies impulses for each heart beat
what is a pacemaker used for?
bradyarrhythmias and heart block
what is an implantable cardioverter defibrillator?
- implanted electronic device that has electrodes that can stimulate the heart
how does an implantable cardioverter defibrillator work?
- applies electrical impulses ONLY when ventricular dysrhythmias detected
- protects from fast or uncontrolled rhythms
what are the indications for implanting an ICD?
- cardiac arrest due to ventricular fibrillation
- symptomatic heart failure with low LVEF
- cardiomyopathies
- congential
- channelopathies
how do antiarrhythmic drugs work?
usually affect ion channel activity or sympathetic drive
what is reperfusion injury?
tissue damage caused when blood supply returns to the tissue after a period of ischemia or hypoxia
what causes reperfusion injury?
the restoration of circulation results in inflammation and oxidative damage
what are the preventative treatments for reperfusion injury?
- cooling
- immunosuppression
- oxygen radical scavengers
what are the difference between syncope and seizures?
- can be difficult to differentiate from a patient’s description
- both may have no symptoms
- syncope may be registered by Holter monitor
- seizure may be registered by EEG
- seizures tend to be associated with stiffness and unusual postures/movements
- syncope patients ‘crumple’ and seizure patients tip over
what is vasovagal syncope?
vagal increase and symp decrease leading to vasodilation and low heart rate
what is exertional syncope?
- neurocardiogenic origin
- benign
what is the index case?
- the initial patient in the population of an epidemiological investigation
- the case of the original patient that stimulates investigation of other members of the family
what is penetrance?
the proportion of individuals carrying a particular variant (or allele) of a gene (the genotype) that also express an associated trait (the phenotype)
what happens with 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
- an individual disease can have different phenotypes
- most phenotypes of polygenic, especially in genes for ‘risk’
what are the mechanisms of arrhythmia?
- substrate for arrhythmia: structural or electrical
- ectopic activity: early after depolarisation, short coupling interval, delayed after depolarisation
- re-entry
- wave break
what are the clinical scenarios with sudden cardiac death?
- ischaemic heart disease
- structural heart disease
- arrhythmic SCD
what are the key characteristics of ischaemic heart disease?
- acute ischaemia
- ventricular remodelling
- scar formation
- myocardial fibrosis
- coupling
- dilatation
- poor function
what are the key characteristics of dilatated cardiomyopathy?
- accounts for 10% of SCD
- non-ischaemic dilatation of ventricle
- causes: idiopathic, viral, alcohol, drugs (chemotherapy), autoimmune
what is the pathophysiology of structural heart disease?
- subendocardial myocardial fibrosis
- neurohormonal activation
- increased sympathetic tone
- electrode disturbances
- leads to: ectopy, re-entry, VT/VF
what are the key characteristics of hypertrophic cardiomyopathy?
- most common cause of SCD in young athletes
- autosomal dominant, incomplete penetrance
- mutation of cardiac muscle sarcomere genes
- > 45 mutations identified
- most commonly beta-myosin or troponin-T
- asymmetrical septal hypertrophy
- systolic anterior motion of mitral valve
- LV outflow tract obstruction
what are the symptoms of hypertrophic cardiomyopathy?
- may be asymptomatic
- exertional chest pain/dyspnoea
- exteriontal syncope
- palpitations
- mechanism of SCD unclear
what is ARVC?
arrhythmogenic RV cardiomyopathy
what happens with ARVC?
- replacement of RV myocardium with fibro-fatty tissue
- RV hypertrophy and dilatation
- VT/VF due to re-entry around interstitial fibrosis
what are the symptoms of ARVC?
- often asymptomatic
- exertional syncope of SCD
- atrial arrhythmia common
- epsilon wave of ECG
what are the other structural SCD?
- aortic stenosis
- mitral stenosis
- mitral valve prolapse
- congenital heart disease: anomalous coronary arteries, ebstein’s abnormally, complex
what are the key characteristics of primary arrhythmia?
- non-ischaemic
- structurally normal heart
- syndromes include: long QT, wolff-parkinson-white, brugada, primary VT/VF
what is Wolff-Parkinson-White?
- accessory pathway from atria to ventricle
- atrial arrhythmia
- ventricular pre-excitation
- VT/VF
- often clues on resting ECG
what is Brugada?
- channelopathy
- most commonly SCN5A
- affects fast-type sodium channels
- reduces conduction velocities
- particularly affects RVOT
- prone to VT arising from RVOT
how do you treat sudden cardiac death?
- identify at-risk groups
- preventative treatment
- treat underlying cause
- avoid precipitants
- anti-arrhythmic medication
- implantable defibrillators
- family screening where appropriate
how do you select the patients for ICD?
- survivors of cardiac arrest (not MI)
- VT with haemodynamic compromise
- high risk groups: coronary disease, poor LV function +/- large scar, broad QRS complex on ECG
- some HCM/long QT/Brugada/ARVC
- congenital heart disease
what are the indications in HCM?
- survived cardiac arrest
- one or more of: VF or spontaneous sustained VT, unexplained syncope, LV wall thickness more than 30mm, spontaneous NSVT, abnormal exercise BP, family history of premature sudden death
