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

1. 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 > 30 days duration was 5.5% at < 200 J, 35% at 200 J and 56% at 360J • In atrial flutter, an initial 100 J shock work in 68% • In Af of > 30 days duration, shock of < 200 J had a 6.1% probability of success , this fell to 2.2% with a duration of > 180 days • AF > 180 days, initial use of a 360 J shock was associated with eventual use of less electrical energy than initial shock of ≦100 J

2. 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 1988;223:53-9 • 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

3. 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

4. DC countershock vs Myocardial damage • Animal study • Myocardial injury from transthoracic defibrillation countershock--- Warner ED et al. Arch Pathol 1975;99:55-9 • 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

5. Cardiac damage produced by direct current countershock to the heart. ---- Doherty PW et al.Am J Cardiol 1979;43:225-32 • 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

6. Therapeutic indices for transchest defibrillator shocks: effective, damage and lethal electrical doses---- Babbs CF et al. Am Heart J 1980;99:734-8 • 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

7. Direct current cardioversion dose not cause cardiac damage: evidence from cardiac troponin T estimation ---RaoAC et al. Heart 1998;80:229-30 • 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.

8. Plasma levels of troponin T after electrical cardioversion of atrial fibrillation and flutter--- Neumayr G et al. Am J Cardiol 1997;10:1367-9 • 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

9. 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

10. Electrical Cardioversion (2) • Monophasic waveform shock • damped sinusoidal • truncated exponential • biphasic waveform shock • low energy internal cardioversion