Update on external cardioversion defibrillation
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Update on external cardioversion & defibrillation :. Current Opinions in Cardiology, 2001, 16 : 54-57. Background : . External cardioversion is a technique used to terminate arrhythmia & restore sinus rhythm (e.g. : VT, VF & AF).

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Update on external cardioversion & defibrillation :

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


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.


Factors affecting efficacy of cardioversion/defibrillation :

  • 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.


  • 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).


Factors affecting efficacy of cardioversion/defibrillation :

  • 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.


Factors affecting efficacy of cardioversion/defibrillation :

  • 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.


Factors affecting efficacy of cardioversion/defibrillation :

  • 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.


  • 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.


  • 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, 101:2968-2974.

  • 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.


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.


  • Tri-phasic shock waveforms are currently being researched.

  • Huang J, Ken Knight BH, Rollins DL, et al.: Circulation 2000, 101: 1324-1328.


What is the relevance ?

  • Improved efficacy of external cardioversion/defibrillation 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).


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.


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.


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.


  • 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.


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.


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.


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.


The End

Thank-you for your attention.


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