Saturday, December 29, 2012

Autonomic Conflict and Cardiac Arrhythmias



‘Autonomic conflict’: a different way to die during cold water immersion?.
Authors: Michael Shattock, Michael Tipton

I had the pleasure of seeing this research presented at the World Conference on Drowning Prevention in 2011, and I think it stands as a great example of the role that applied clinical science can play on improving our understanding of drowning.  Dr Tipton has provided a wealth of knowledge and research to the field, especially involving cold water submersion.  This paper highlights the topic of "Autonomic Conflict" and its proposed role in sudden cardiac death in drowning.

Study focus: "In this review we describe a cardiac arrhtymogenic response that we believe may account for some immersion deaths but, due to its nature, largely goes unnoticed or detected.  We have termed the trigger for this response 'autonomic conflict'."

Autonomic Conflict
  • Cold shock response: thermorecptor mediated, tachycardia, gasp, hyperventilation, vasoconstriction
  • Diving response: cardiac vagal response, bradycardia
     
  • Contrary to classic belief of a "Yin/Yang" relationship between sympathetic and parasympathetic responses, with one being "on" while the other is "off", the authors argue the idea that the effect of both responses being "on" and "conflicting" at the same time leads with rhythm instability.
While the primary response much individuals experience is rapid heart rate due to cold shock response, other events like breath holding can cause autonomic conflict.  This is supported by studies cited in which young.healthy participants displayed higher incidence of arrhythmias during cold water submersion with breath holding.

There is also a section in the paper on abnormal QT interval response that I am still trying to wrap my head around, more to come on that.

All in all, this is a fairly complex paper that takes more focused attention than usual to get through, but it offers evidence for an interesting phenomena that likely plays an important role in drowning deaths.  Cheers to Drs Shattock and  Tipton for their continued groundbreaking work.

Source:
Shattock M, Tipton M.‘Autonomic conflict’: a different way to die during cold water immersion?.  J Physiol. 2012; 14: 3219-3230.