Update on external cardioversion

1
Update on external cardioversion defibrillation

• Current Opinions in Cardiology, 2001, 16 54-57

2
Background

• External cardioversion is a technique used to
  terminate arrhythmia restore sinus rhythm (e.g.
  VT, VF AF).
• 2 types asynchronous (defibrillation)
  synchronous (cardioversion).
• Emergency defibrillation in cardiac arrest
  patients is the single most important factor in
  improved survival.

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Factors affecting efficacy of cardioversion/defib
rillation

• Time from onset of arrhythmia to defibrillation
  
• The most important factor affecting efficacy of
  cardioversion/defibrillation, regardless of
  whether AF/VF.
• In VF, this not only affects efficacy, but
  survival of patient.
• International Guidelines 2000 for CPR ECC A
  Consensus on Science. Circulation 2000, 102
  1-11.
• Spearpoint KG, Mclean CP, Ziderman DA.
  Resuscitation 2000, 44 165-169.

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• Prolonged ventricular fibrillation decreases
  defibrillation success rate because of the
  release of myocardial adenosine.
• In AF, atrial remodelling decreases
  defibrillation efficacy.
• Regional variations of potassium concentrations
  in the myocardium increases defibrillation
  thresholds (i.e. the amount of energy required to
  defibrillate the heart).

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Factors affecting efficacy of cardioversion/defibr
illation

• Transthoracic impedance
• Ensuring adequate contact between the electrode
  surfaces the skin (e.g. conducting gel/adhesive
  pads).
• Exerting adequate pressure on the electrodes.
• Shaving the chest in patients undergoing elective
  cardioversion.
• Bissing JW, Kerber RE. Am J Cardiol 2000, 86
  587-589.

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Factors affecting efficacy of cardioversion/defibr
illation

• Configuration of electrodes
• Placing the cathodal pad at the apex the anodal
  pad at the Right infra-clavicular region resulted
  in a significantly lower defibrillation threshold
  than the opposite arrangement.
• Oral H, Brinkman K, Pelosi F, et al. Am J Cardiol
  1999, 84 228-230, A228.

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Factors affecting efficacy of cardioversion/defibr
illation

• Biphasic Transthoracic Shock
• Superior to monophasic shocks, for both atrial
  ventricular arrhythmias.
• Bardy and colleagues demonstrated a 130 joules
  biphasic shock wave has the same efficacy rate as
  a 200 joule monophasic shock wave in VF.
• Mittal and colleagues showed that 120J biphasic
  shock was superior in efficacy to a 200J
  monophasic shock in induced VF.
• Electrical cardioversion of AF was also improved
  with biphasic shocks.

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• White JB, Walcott GP, Wayland JL, Jr., et al.
  Ann Emerg Med 1999, 34 309-320.
• Bardy GH, Marchlinski FE, Sharma AD, et al.
  Transthoracic Investigators. Circulation 1996,
  94 2507-2514.
• Mittal S, Ayati S, Stein KM, et al. ZOLL
  Investigators. J Am. Coll Cardiol 1999, 34
  1595-1601.
• Mittal S, Ayati S, Stein KM, et al. Circulation
  2000, 101 1282-1287.

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• In laboratory canine swine models of
  defibrillation after prolonged VF, it was
  demonstrated that biphasic waveforms allowed for
  a lower defibrillation threshold shorter
  resuscitation times.
• Leng CT, Paradis NA, Calkins H, et al.
  Circulation 2000, 1012968-2974.
• Yamanouchi Y, Brewer JE, Donohoo AM, et al.
  Pacing Clin Electrophysiol 1999, 22 1481-1487.
• Scheatzle MD, Menegazzi JJ, Allen TL, et al.
  Acad Emerg Med 1999, 6 880-886.

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Clinical significance/implications

• Biphasic shocks associated with less
  post-resuscitation myocardial dysfunction in
  animals defibrillated with biphasic shocks.
• Thus, extrapolated to be safer in patients with
  cardiomyopathy those who underwent prolonged
  resuscitation, in terms of post-defibrillation
  ventricular function.
• Tang W, Weil MH, Sun S, et al. J AM Coll Cardiol
  1999, 34 815-822.

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• Tri-phasic shock waveforms are currently being
  researched.
• Huang J, Ken Knight BH, Rollins DL, et al.
  Circulation 2000, 101 1324-1328.

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What is the relevance ?

• Improved efficacy of external cardioversion/defibr
  illation will improve patient outcome (i.e.
  patients survival rates).
• Result in significant medical cost savings (e.g.
  shorter hospital stays, reduce need for other
  more expensive treatments).

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AED in treatment of out-of-hospital arrests

• Early defib. improves survival.
• Decreasing the response time of / early arrival
  of paramedics and ambulances resulted in improved
  survival rates of out-of-hospital cardiac
  arrests.
• Tanigawa K, Tanaka K, Shigematsu A. Resuscitation
  2000, 45 83-90.
• Stiell IG, Wells GA, DeMaio VJ, et al. OPALS
  Study Phase I results. Ann Emerg Med 1999, 33
  44-50.
• Stiell IG, Wells GA, Field BJ, et al. OPALS
  Study Phase II. JAMA 1999, 281 1175-1181.

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AED in treatment of out-of-hospital arrests

• Postulated that the use of AED by paramedics
  might decrease the time to first defibrillation
  in patients with cardiac arrests therefore
  improve patient survival rates.
• Survival rates remained UNCHANGED despite the
  use of AED by paramedics in Seattle Hong Kong.
• Cobb LA, Fahrenbruch CE, Wlash TR, et al. JAMA
  1999, 281 1182-1188.
• Lui JC Evaluation of the use of AED in
  out-of-hospital cardiac arrest in Hong Kong.
  Resuscitation 1999, 41 113-119.

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The Hong Kong Experience

• Dept. of Anaesthesia, CMC.
• Retrospective 6-months audit of out-of-hospital
  cardiac arrests in Hong Kong following the
  introduction of AED (1-7-95 to 31-12-95).
• Resuscitation attempted on 754 patients, but only
  744 with records a/v.
• 53.6 had a witnessed arrest.
• 8.9 received CPR by passerby.
• 80 of arrests occurred at home.
• 643 (86.4) DOA at hospital, 89 (12) died in
  hospital 12 (1.6) discharged alive.

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• Average response interval (call received to
  arrival of ambulance at scene) 6.42 mins.
• Average arrest-to-first-shock interval 23.77
  mins.
• Factors predicting survival included initial
  rhythm arrest-to-first-shock interval.

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Conclusions of study

• Survival rate of 1.6 is low by world standards.
• Arrest-to-call interval Arrest-to-first-shock
  interval must be reduced.
• Frequency of bystander CPR assistance must be
  increased.
• If these conditions are met, then beneficial
  effects from the use of AED might be seen.

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Medico-legal issue

• In USA, trend towards widely distributing / make
  a/v the use of AED (e.g. to police, air stewards,
  paramedics, OAH, etc).
• ? Law suits arising from good Samaritan acts.
• Legislative amendments to protect users of AED
  needed.

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American Heart Association

• Co-ordinating a public access to defibrillation
  program education on its use.
• Conducting a study on the effects of such a
  program on survival outcome in out-of-hospital
  arrests victims (? Better outcome than previous
  studies).
• The use of AED is included in the latest AHA
  guidelines for CPR emergency vascular care.

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The End

• Thank-you for your attention.