External Cardiac Pacing Dr PG Jones MBChB, FACEM Emergency Medicine Specialist Auckland And Starship Hospitals

History 1791 Galvani –Frog experiments 1892 Duchenne –Resuscitated child (submersion ) One leg electrode, tapped chest with other

Zoll 1950’s –1st successful TCP and monitor 3cm electrode 120V AC for 2msec 1980’s –80cm 2 electrode, 40msec pulse duration  stimulation threshold x 6 –More tolerable = renewed interest FDA approval 1982

Indications Symptomatic Bradycardia –50-100% survival to discharge rates AMI with certain ECG rhythms –Mobitz type II second-degree AV block –Third-degree heart block –Bilateral BBB –Newly acquired or age-indeterminate LBBB, LBBB and LAFBa, RBBB, and LPFBa –RBBB or LBBB and first-degree AV block

Indications Asystole ? –Most studies no benefit –Benefit shown for <5min post arrest 2/5 survived neurologically normal Tachyarrythmia –57-95% termination of VT –4-24% acceleration of VT

How To Do It Inform the patient Plug in module Attach pads Set rate 70 Dial up mAmps Set mode (demand first) Start Monitor and adjust as needed

Capture Feel the pulse –mechanical capture 2nd monitor to determine electrical capture –Unless monitor blanks out skeletal muscle contraction Ultrasound

Not Capturing Paced Beat Native Beat IABP

Current mA (Unstable patient) 50-70mA (Volunteer) –90% tolerate for 15min Pain  Current / area (up to 10cm 2 )

Energy 100mA for 20msec = 0.1J (with normal TTR, 50 Ohm) Threshold for discomfort 1-2J (Skin tingling) Does not damage the myocardium

Discomfort Skeletal muscle contraction is the cause –Often the limiting factor –Attempt AP placement to minimise Left scapula and midline chest Use lowest effective current Sedation as needed CPR is safe!

Muscle Contraction

Haemodynamics Cardiac arrest and CHB –Comparable to transvenous pacing Sinus –Reduced cardiac output –No ‘atrial kick’ (atrial capture threshold too high)

References Bocka JJ eMedicine –Updated 2002 April 24, excellent summary article Bocka JJ Ann Emerg Med 1989 Dec; 18(12): Hedges JR Pacing Clin Electrophysiol 1991 Oct;14(10): Barthell E Ann Emerg Med 1988 Nov;17(11): Klumbies A Z Gesamte Inn Med 1988 Jul 1;43(13):