Sudden Cardiac Death

 

• Background

  Definition

  Death due to cardiac disease occurring shortly after symptom onset (usually <1 hour), typically with loss of consciousness within seconds or minutes.

  Causes

  Overview:

  • Proximate mechanism is usually arrhythmia (VF, VT), with underlying abnormality.
  • If no cause found, referred to as sudden arrhythmic death syndrome (SADS).
  • If inherited, nearly all are autosomal dominant, except some types of CPVT.

  Cardiomyopathy:

  • Hypertrophic
  • Dilated
  • Arrhythmogenic right ventricular.
  • Noncompaction

  Electrophysiological abnormality (i.e. no structural abnormality):

  • Long QT syndrome.
  • Brugada
  • CPVT
  • WPW

  Inflammatory or infiltrative:

  • Myocarditis
  • Amyloidosis
  • Sarcoidosis
  • Cancer

  Anatomical:

  • Thoracic aortic aneurysm dissection.
  • Congenital heart disease.
  • Non-atherosclerotic coronary artery abnormality.

  Epidemiology

  • SCD accounts for 50% of all cardiac deaths (1/1,000/yr). 70% of cases are MIs (IHD) in the elderly. Other common causes in the elderly are LVF and valve disease.
  • Among young people (age <35), the annual incidence is 1/100,000. The commonest causes (in order) are premature IHD, cardiomyopathy (especially HCM and DCM), myocarditis, and arrhythmias.

• Investigations

  Postmortem diagnosis:

  • Coroner's autopsy ± molecular autopsy. May be complicated by legal issues.

  Family cascade testing if inherited SCD or SADS:

  • At least echo and ECG, and possibly 24h ECG, exercise ECG, cardiac MRI, or drug challenge.

• Long QT syndrome (LQTS)

  Pathophysiology

  Congenital long QT:

  • Autosomal dominant.
  • Prevalence 1/5000.
  • Ion channelopathy – type 1 (T1) and type 2 (T2) are reduced K+ outflow, type 3 (T3) is excess Na+ inflow – meaning that heart can't recover properly in time for next atrial depolarisation. Can then lead to VT and VF.

  Acquired long QT:

  • Electrolyte deficiencies: ↓K+,↓Mg2+,↓Ca2+.
  • CVD: MI, heart block.
  • Drugs
  • Anorexia
  • CNS disease.

  Presentation

  • Syncope, usually with pre-syncope (palpitations, angina).
  • Palpitations
  • SCD
  • Triggers: T1 emotion or exercise, T2 loud noise, T3 can happen at rest or in sleep.

  Investigations

  ECG:

  • QTc (corrected for heart rate) >470 ms (men) and >480 ms (women).
  • Torsades de pointes.
  • Notched T wave.

  U&E may show underlying cause.

  Management

  Avoid precipitants and drugs that prolong QT, including:

  • Antimicrobials: erythromycin, fluconazole
  • Psych: antipsychotics, TCAs, citalopram.
  • Class 1c and 3 antiarrhythmics.
  • Tamoxifen
  • Chloroquine
  • Sumatriptan
  • Many others.

  Treatment:

  • β-blocker for T1/2, which are rate dependant as triggered by ↑HR.
  • Implantable cardioverter defibrillator (ICD) if lots of episodes.

  These steps reduce risk of sudden cardiac death to near zero.

• Brugada syndrome

  Pathophysiology

  • Ion channelopathy (reduced Na+ inflow) which can lead to sudden VF.
  • Can be inherited (autosomal dominant) or spontaneous. Commonest identified mutation is in SCN5A.

  Presentation

  • Palpitations
  • Syncope
  • SCD, sometimes without any history of collapse/syncope.
  • Nightmares, thrashing, or agonal respiration at night.

  Diagnosis

  ECG:

  • Type 1: coved ST elevation (STE) in V1-3, with T wave inversion.
  • Type 2 – saddleback STE – and type 3 – STE <2mm – are non-diagnostic and require further testing.

  Brugada syndrome diagnosis requires ECG findings plus SCD (personal or family), VT/VF, or typical symptoms.

  Management

  Implantable cardioverter defibrillator (ICD) if symptomatic or family history of SCD. Less clear if indicated in other patients.

• Catecholaminergic polymorphic VT (CPVT)

  Pathophysiology

  • In the normal stress response, catecholamines cause increased Ca2+ release from the myocardiocyte sarcoplasmic reticulum to enhance contractility. In CPVT this release is further enhanced, potentially leading to VT, which may self-terminate or – occasionally – become sustained and fatal.
  • Due to autosomal dominant (RYR2) or recessive (CASQ2) mutation.

  Investigations

  Resting ECG is normal, while exercise ECG should reliably reproduce bidirectional or polymorphic VT.

  Management

  • β-blocker at maximal dose.
  • ICD if ongoing episodes.

• Arrhythmogenic right ventricular cardiomyopathy

  Aka arrhythmogenic right ventricular dysplasia.

  Pathophysiology and epidemiology

  • Fibro-fatty replacement of the RV myocardium leading to RV thinning and dysfunction.
  • 30% are inherited, usually autosomal dominant.
  • 1/2000 prevalence.

  Clinical features

  • Usually presents with symptomatic ventricular arrhythmias, including palpitations, syncope, and chest pain.
  • SCD may be the first presentation. Though most occur during normal daily activities, it can be exercise-induced.
  • RV failure ± LV failure may develop long-term.
  • Naxos disease is a rare, autosomal recessive form accompanied by palmoplantar keratosis and woolly hair.

  Investigations

  ECG:

  • Epsilon waves: small positive deflection at the end of QRS.
  • T wave inversion, prolonged S-wave upstroke, and QRS widening in V1-3.
  • Paroxysmal VT with LBBB morphology.

  Diagnosis is usually with echo ± cardiac MRI.

  Management

  • Avoid competitive sports.
  • β-blockers e.g. sotalol.
  • ICD if any high risk features: personal or family history of cardiac arrest, sustained VT, recurrent arrhythmias.
  • Usual HF treatment if it develops, including transplantation if severe.
  • Asymptomatic, healthy gene carriers do not require treatment.