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Update on external cardioversion & defibrillation :

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 :

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  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.

  3. 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.

  4. 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).

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

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

  12. 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).

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. The End Thank-you for your attention.

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