Latent causes of Sudden Cardiac Arrest

Written By Mubasher Abbas

>90% of cases of sudden cardiac arrest are from ischemia, coronary artery disease.

Some of the other things which we should keep in mind:

  • Latent structural causes of arrest

    • Cardiac sarcoidosis

    • Coronary anomalies

    • Mitral valve prolapse

    • Myocarditis

  • Inherited arrhythmia syndromes

    • Long QT syndrome

    • Brugada syndrome

    • ARVD

    • Catecholaminergic polymorphic ventricular tachycardia (CPVT)

    • Short QT syndrome

    • Early Repolarization syndrome (ERS)

    • Short Coupled ventricular fibrillation

Catecholaminergic polymorphic ventricular tachycardia (CPVT):

Genetic condition in which disordered intracellular Ca handling results in Catecholamine-triggered episodes of malignant Ventricular arrhythmias

Pathophysiology:

  • what is normal : (cardiac myocyte depolarization > L type calcium channels with resultant influx of Ca > Calcium binds to RYR-2(ryanodine receptors) > release of Ca from Sarcoplasmic reticulum (other important proteins 1. Calsequestrin 2 CASQ-2 which binds cytosolic Calcium in sarcoplasmic reticulum > reduction in the release of the calcium from sarcoplasmic reticulum. 2. Triadin (TRDN) which anchors CASQ2 to RYR2)

  • if there is more Calcium in the cytosol > increased influx of the sodium and this will lead to depolarization of the cell after the action potential has already occurred causing delayed after depolarizations which can result in premature ventricular contraction > malignant arrhythmias.

  • increased catecholamine state will cause increased sensitivity of Ryanodine receptors leading to the increased calcium influx.

  • What if there is gain of function mutation (Autosomal dominant) of RYR2 or Loss of function mutation(Autosomal Recessive) of CASQ2 > more calcium > more chances of arrythmia (in 50-60% cases) this is the genetic abnormality

Epidemiology:

  • 10% of unexplained Sudden cardiac arrest (after exclusion of CAD or overt structural heart disease)

  • 15% of families of unexplained SCD victims are found to have CPVT

  • 30% will be diagnosed after an episode of resuscitated cardiac arrest.

  • 50% will have had syncope

Diagnosis:

  • Classic presentation: stress/exercise induced Syncope or cardiac arrest.

  • baseline EKG: normal (can have sinus bradycardia)

  • Pathognomonic feature: Exercise induced Polymophic VT - especially bidirectional VT.

  • Exercise testing is diagnostic (induction of ventricular bigeminy, couplets or VT) 97% specific. if standard exercise testing is not diagnostic Burst exercise testing protocol can be used.

  • Genetic testing is recommended once CPVT phenotype is manifested

Management:

  • Intense exercise and stress should be avoided

  • Betablockers are first line > if breakthrough symptoms > use Flecainide

  • Left cardiac sympathetic denervation despite optimization and escalation of medications.

  • AICD for secondary prevention in the sudden cardiac arrest patients.

Mubasher Abbas
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