mechanisms of death

And when i'm a man - Wayne Chisnall 1998

A conceptual difficulty when learning about the forensic pathology of trauma, and sudden or unexpected death, is 'why did the individual die when they did?'.

Medical students - and pathology trainees - are taught what the relevant signs, symptoms and pathological findings are in diseases and conditions, but rarely are they taught about the pathophysiological disturbances that accompany potentially fatal diseases/ conditions. When dealing with traumatic events, such pathophysiological disturbances are also neglected, in favour of identifying the anatomic/ pathologic abnormality that can be seen - either by the 'naked eye' or under the microscope.

The most comprehensive resource for reviewing such 'mechanisms of death' can be found in 'Spitz and Fisher's Medicolegal Investigation of Death', and the following notes are adapted from this source.

The principle mechanisms of interest are those having an adverse effect on the heart, the brain, or both.

[Adams VI, Flomenbaum MA, Hirsch CS. Mechanisms of death. Chapter 9 In: Spitz and Fisher's Medicolegal Investigation of Death, 4th Edition (2006), Spitz WU (Ed), Charles C Thomas, Springfield, Illinois, USA]

electrical disturbances of heart and central nervous system

• electrical irritability
  • seizures
  • ventricular arrhythmias
• electrical depression
  • heart - bradycardia degenerates to idioventricular complexes without effective pumping activity (Pulseless Electrical Activity) e.g. following hypoxia
  • brain - respiratory arrest e.g. following cerebral hypoxia or central nervous system 'respiratory depressants' (e.g. morphine and alcohol etc)

exogenous electrical disturbances

Electric chair - Andy Warhol

Source: Mindy Nierenberg

Electrocution

• Alternating Current (AC) passing through the heart during the vulnerable repolarisation phase can precipitate Ventricular Fibrillation (VF)
• AC/ Direct Current (DC) can provoke tetany if the current is high enough
• Return of sinus rhythm is possible following removal of DC source
• The effect of 'electrocution' on the brain is poorly described in the literature

Electrocution (from 30 ways to die of electrocution)

Electrocution and public safety campaigns

Accidental electrocution

Source: 'Dumb ways to die' - Metro Trains Melbourne public safety campaign 2012

conversion of impact mechanical energy to electrical energy

A proportion of impact (mechanical) kinetic energy is converted in the body to electrical energy.

• in the heart, conversion of impact mechanical energy - from a blow to the precordium - can lead to 'cardiac concussion' ('commotio cordis'), and result in VF or asystole
• in the central nervous system, transmission of mechanical energy can lead to respiratory paralysis or autonomic-medicated asystole

non-impact pressure gradients in vital areas

• Subarachnoid haemorrhage (SAH) can lead to:
  • brainstem/ hypothalamic tamponade leading to autonomic-mediated ventricular arrhythmias;
  • cerebral blood vessel vasospasm leading to autonomic-mediated arrhythmias;
  • brainstem tamponade leading to respiratory arrest
• Cerebral herniation can cause failure of medularry respiratory centres and loss of vasomotor centre abnormalities
• Compression of the heart by a pericardial fluid accumulation (cardiac tamponade as a consequence of, for example, a rapidly accumulating haemopericardium) interferes with cardiac chamber filling and reduces cardiac output. Central blood flow decreases and the heart becomes hypoxic, leading to bradycardia and PEA.

exogenous chemical interference with electrochemical cellular communication

• CNS excitation (leading to seizures) - e.g. cocaine, theophylline, isoniazid
• CNS depression (leading to 'reduced level of consciousness', 'failure to protect the airways', 'aspiration pneumonitis/ pneumonia' etc) - e.g. heroin/ morphine, alcohol
• CNS depression with or without cardiac arrhythmia - e.g. cocaine, anti-arrhythmics, tricyclic antidepressants, phenothiazines
• Direct cardiac 'irritant' - e.g. alcohol
• interference with neuromuscular/ synaptic signal transmission - e.g. curare-induced hypoxia due to diaphragmatic paralysis

thermal physiological disturbance

• elevated temperature (hyperthermia)
  • environmental heat exposure - heat stroke and dehydration leading to arrhythmias, seizures
  • 'malignant' hyperthermia - cocaine, amphetamines/ MDMA (ecstasy), neuroleptic malignant syndrome, excited delerium
• reduced temperature (hypothermia) - depressed cardiac conduction, ectopic beats and VF

microscopy in multiple organ failure following hyperthermia

'Hyperacute heart muscle cell injury' (contraction band necrosis/ myofibril degeneration)

(H&E staining)

(PTAH staining)

Renal tubular casts in a setting of acute renal failure

(H&E staining)

Extensive liver necrosis

(H&E staining - low power)

(H&E staining - higher power)

obstruction or diversion of central blood circulation

• diversion of blood volume
  • exsanguination (in general, rapid loss of 1/3rd of the blood volume results in shock whilst rapid loss of 1/2 is fatal due to inability to perfuse the coronary circulation)
  • acute neurogenic shock (disordered agonal autonomic function results in a redistribution of circulating blood volume to the musculoskeletal system, e.g. following concussive blunt force head injury or an injury between the IIIrd ventricle in the brain and the mid-cervical spinal cord)
  • anaphylactic shock (fluid shifts from plasma to the extracellular compartment following histamine release due to mast cell activation and degranulation)
• obstruction of blood volume (inadequate supply of blood to the lungs to be oxygenated leads to cardiac hypoxia, bradycardia and asystole)
  • cardiac tamponade
  • cardiac thromboembolism
  • pulmonary thromboembolism
  • cardiac air embolism
  • severe external compression of the heart

anaphylaxis - one minute med school tutorial

obstruction of arterial blood supply to the heart or CNS

• to the heart (leading to coronary insufficiency, regional cardiac ischaemia and arrhythmias):
  • occlusive coronary artery atherosclerosis
  • coronary artery thrombosis
  • air embolism (e.g. SCUBA diving, open heart surgery, sharp force injury to neck veins etc)
  • fat embolism (e.g. blunt force trauma with skeletal injury)
• to the brain (leading to 'stroke' or brainstem ischaemia and sudden death) - similar causes to those above in the heart/ coronary circulation
• external compression of blood vessels in the neck
  • reduced flow through the carotid arteries can lead to sudden death (arrhythmia) or 'stroke'
  • reduced flow through internal jugular veins can lead to congestion and hyperaemia of the brainstem and cerebellum

Arteries in the neck

Source: Gray's Anatomy via Wikipedia

mechanical interference with respiration

• pressure to the neck - tongue pushed into the oropharynx occluding the upper airways
• occlusion of the mouth/ nose ('suffocation')
• obstruction of upper airways due to the position of the head on the neck (i.e. bent forwards) in a setting of intoxication, concussion or neurological disease ('positional asphyxiation')
• compression of the chest preventing adequate ventilation movements (e.g. 'traumatic asphyxiation', 'pressing')
• occlusion of the airways from within e.g. by food or foreign bodies in intoxicated - or otherwise neurologically compromised - individuals
• pneumothorax leading to pulmonary vascular 'shunts' and hypoxaemia
• 'flail chest' following blunt force chest trauma, causing paradoxical inward chest movements on inspiration and leading to hypoxaemia
• chemical aspiration pneumonitis leading to hypoxaemia/ intra-pulmonary 'shunts'

chemical interference with oxygen metabolism

SCUBA diver

Source: Wikipedia

• as a consequence of a reduced level of oxygen in the inspired air mixture
  • high altitude pilots
  • SCUBA divers with rusty oxygen tanks
  • SCUBA divers - or anaesthetised patients - given the 'wrong gas mixture'
• in confined spaces (e.g. caves and storage tanks etc)
  • reduced oxygen partial pressures following oxygen displacement from the confined space by carbon dioxide or gaseous products, for example
• as a consequence of breathing in an oxygen poor medium e.g. drowning
• breathing in carbon monoxide (irreversibly binds to haemoglobin) or cyanide (poisons the mitochondrial cytochromes)

Wrinkling of the skin of the hand following recovery of body from water (Johann Ludwig Caspar 1864)

Source: National Library of Medicine

shock

• Inadequate tissue perfusion manifested by arterial hypotension as a consequence of:
  • sepsis (capillaries become 'leaky' and fluids used in resuscitation leave the circulating blood volume to enter the extracellular compartment; myocardial perfusion is reduced and hypoxia leads to arrhythmias)
  • post cardiac arrest/ generalised hypoxaemia can also lead to shock

public safety campaign animation 'Dumb ways to die' (Metro Trains Melbourne 2012)

murder in comtemporary society - Cluedo boardgame

Cluedo weapons (1949)

Source: The art of murder

Taser conducted electrical weapons

mortality statistics - England and Wales 2009

see the full-size version of this infographic at the Guardian DataBlog (and the Office for National Statistics Statistical Bulletin)

complexity in forensic pathology and medicine on Pinterest

American male death statistics: infographic

see the full-sized version of this at Dan Read Interaction Design