Transcript 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).
 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/defibrillation :
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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.
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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).
Factors affecting efficacy of
cardioversion/defibrillation :
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Transthoracic impedance :
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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.
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Bissing JW, Kerber RE. Am J Cardiol 2000, 86:
587-589.
Factors affecting efficacy of
cardioversion/defibrillation :
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Configuration of electrodes :
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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.
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Oral H, Brinkman K, Pelosi F, et al. Am J Cardiol
1999, 84 : 228-230, A228.
Factors affecting efficacy of
cardioversion/defibrillation :
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Biphasic Transthoracic Shock :
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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
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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: 15951601.
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.
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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.:
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Clinical significance/implications
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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.
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Tri-phasic shock waveforms are currently
being researched.
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Huang J, Ken Knight BH, Rollins DL, et al.:
Circulation 2000, 101: 1324-1328.
What is the relevance ?
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Improved efficacy of external
cardioversion/defibrillation will improve
patient outcome (i.e. patients’ survival rates).
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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 :
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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-ofhospital arrests :
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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 :
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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.
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Conclusions of study :
Survival rate of 1.6% is low by world
standards.
 Arrest-to-call interval & Arrest-to-firstshock 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 :
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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.