Update on external cardioversion defibrillation Current Opinions in

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). n 2 types : asynchronous (defibrillation) & synchronous (cardioversion). n Emergency defibrillation in cardiac arrest patients is the single most important factor in improved survival. n

Factors affecting efficacy of cardioversion/defibrillation : n n n 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: 111. Spearpoint KG, Mclean CP, Ziderman DA.

n n n 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 : n Transthoracic impedance : n 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. n n n Bissing JW, Kerber RE. Am J Cardiol 2000, 86: 587 -589.

Factors affecting efficacy of cardioversion/defibrillation : n Configuration of electrodes : n 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. n Oral H, Brinkman K, Pelosi F, et al. Am J Cardiol 1999, 84 : 228 -230, A 228.

Factors affecting efficacy of cardioversion/defibrillation : n Biphasic Transthoracic Shock : n 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 120 J biphasic shock was superior in efficacy to a 200 J monophasic shock in induced VF. Electrical cardioversion of AF was also improved n n n

n n 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: 15951601. Mittal S, Ayati S, Stein KM, et al. : Circulation 2000, 101: 1282 -1287.

n 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. n 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. : n n

Clinical significance/implications n n n Biphasic shocks associated with less postresuscitation 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 postdefibrillation ventricular function. Tang W, Weil MH, Sun S, et al. : J AM Coll Cardiol 1999, 34: 815 -822.

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

What is the relevance ? n Improved efficacy of external cardioversion/defibrillation will improve patient outcome (i. e. patients’ survival rates). n Result in significant medical cost savings (e. g. shorter hospital stays, reduce need for other more expensive treatments).

AED in treatment of out-ofhospital arrests : n n n 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, De. Maio 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-ofhospital arrests : n n 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-ofhospital cardiac arrest in Hong Kong. Resuscitation 1999, 41: 113 -119.

The Hong Kong Experience : n n n n 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. n Average arrest-to-first-shock interval = 23. 77 mins. n Factors predicting survival included initial rhythm & arrest-to-first-shock interval. n

Conclusions of study : Survival rate of 1. 6% is low by world standards. n Arrest-to-call interval & Arrest-to-firstshock interval must be reduced. n Frequency of bystander CPR assistance must be increased. n If these conditions are met, then beneficial effects from the use of AED might be seen. n

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…). n ? Law suits arising from “good Samaritan” acts. n Legislative amendments to protect users of AED needed. n

American Heart Association : n n n 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.