Initial energy setting, outcome and efficacy in direct current cardioversion of atrial fibrillation and flutter

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Initial energy setting, outcome and efficacy in
direct current cardioversion of atrial
fibrillation and flutter

• The probability of success on the first shock in
  AF of gt 30 days duration was 5.5 at lt 200 J, 35
  at 200 J and 56 at 360J
• In atrial flutter, an initial 100 J shock work in
  68
• In Af of gt 30 days duration, shock of lt 200 J had
  a 6.1 probability of success , this fell to 2.2
  with a duration of gt 180 days
• AF gt 180 days, initial use of a 360 J shock was
  associated with eventual use of less electrical
  energy than initial shock of ?100 J

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ACC/AHA/ESC Practice Guidlines

• An initial shock of 100 J is often to low, and an
  initial energy of 200 J or greater is recommended
  for electrical CV of AF
• Chronic atrial fibrillation. Long-term results of
  direct current conversion--- Lundstrom T et al.
  Acta Med Scand 198822353-9
• primary success rate as measured 3 days after CV
  in 100 consecutive subjects was 86 increase to
  94 when procedure was repeated during treatment
  with quinidine or disopyramide

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• 23 remained in SR after 1 year and 16 after 2
  years
• in relapsed pts, repeated CV with antiarrhythmic
  medication resulted in SR in 40 and 33 after 1
  and 2 years
• relapsed again, a third CV resulted in SR in 54
  at 1 year and 41 at 2 year

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DC countershock vs Myocardial damage

• Animal study
• Myocardial injury from transthoracic
  defibrillation countershock--- Warner ED et al.
  Arch Pathol 19759955-9
• DC shock in 66 dogs, 400 watt-seconds, animal
  were killed from 3 to 14 days after receiving the
  discharges, myocardial necrosis was produced in
  most of the animals

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• Cardiac damage produced by direct current
  countershock to the heart. ---- Doherty PW
• et al.Am J Cardiol 197943225-32
• DC shock over a dose range of 10-90 watt-seconds,
  applied directly to the heart in 26 dogs
• The threshold for significant injury was
  approximately 30 watt-seconds

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Therapeutic indices for transchest defibrillator
shocks effective, damage and lethal electrical
doses---- Babbs CF et al. Am Heart J 198099734-8

• In terms of delivered energy the ED50, TD50, LD
  50 were 1.5 30, and 470 joules/Kg
• TD50 median toxic or damage-inducing dose, ED50
  median effective or defibrillating dose, LD50
  median lethal dose
• a reasonable margin of safety for damped sine
  wave defibrillator shock in dogs

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Direct current cardioversion dose not cause
cardiac damage evidence from cardiac troponin T
estimation ---RaoAC et al. Heart 199880229-30

• Cardiac troponin T and CK were estimated 20-28
  hours after DC cardioversion in 51 Pts who
  received DC shocks for elective CV of chronic
  AF/AFL
• Although CK was raised in 44 patients, cardiac
  troponin T was undetectable in all Pts.

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Plasma levels of troponin T after electrical
cardioversion of atrial fibrillation and
flutter--- Neumayr G et al. Am J Cardiol
1997101367-9

• Measure plasma levels of troponin T after
  electrical CV in 33 AF/AFL patients
• unchanged normal levels of troponin T indicate
  that significant myocardial cell injury by shocks
  in the usual dosage in unlikely to occur

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Electrical Cardioversion (1)

• Successful CV of AF depends on the nature of the
  underlying heart disease and the current density
  delivered to the atrial myocardium
• The latter depends on the voltage of the
  defibrillator capacitor , the output waveform,
  the size and position of the electrode paddles,
  and transthoracic impedance

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Electrical Cardioversion (2)

• Monophasic waveform shock
• damped sinusoidal
• truncated exponential
• biphasic waveform shock
• low energy internal cardioversion

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