Swimming the Channelopathy

Drowning is one of the leading causes of accidental death in children. Some apparent drownings may be related to sudden cardiac death, in particular to unidentified channelopathies, which are known to precipitate fatal arrhythmias during swimming-related events.

The majority of cases of sudden cardiac death in children and adolescents are secondary to either hypertrophic or right ventricular cardiomyopathy with coronary artery abnormalities also prevalent, and reports have demonstrated these cardiac abnormalities on autopsy following sudden swimming-related deaths.

However, the majority of autopsies in swimming-related sudden deaths are normal suggesting causation at molecular level, in particular ion channel defects such as type 1 long-QT syndrome (LQT1) and catecholaminergic polymorphic ventricular tachycardia (CPVT).

The gene deletion in LQT1 (KCNQ1) leads to a reduction in the repolarising potassium current (IKs) and prolongation of repolarisation. This lengthens the QT interval (which may be lengthened further by facial immersion in cold water). A premature ventricular contraction (PVC) again which may be initiated by swimming occurring during the vulnerable part of repolarisation leads to establishment of polymorphic ventricular tachycardia (torsades de pointes).

The ryanodine receptor gene mutation (RyR2) in catecholaminergic polymorphic ventricular tachycardia leads to defective closure of the receptor on the surface of the sarcoplasmic reticulum during diastole. This leads to increased calcium (Ca2+) leakage from the sarcoplasmic reticulum and increased potential for delayed afterdepolarisations and subsequent ventricular tachycardia.

Some recommendations are made in an article in Archives of Disease in Childhood:

Proposed implementations to improve detection and appropriate management of apparent drownings secondary to cardiac channelopathies

  1. Improving awareness in the coronial service of the possibility of a cardiac cause for poorly explained drownings.
  2. Education of lifeguards and provision of automated defibrillators in swimming pools.
  3. Molecular autopsy for non-survivors to look for potential channelopathies.
  4. Screening for survivors and family members of non-survivors to identify those with a channelopathy.
  5. Proper counselling for those identified to have a channelopathy on family screening.

Drowning and sudden cardiac death
Arch Dis Child 2011;96:5-8