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 – 80cm2 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

• 65-100mA (Unstable patient)

• 50-70mA (Volunteer)– 90% tolerate for 15min

• Pain Current / area (up to 10cm2)

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 http://www.emedicine.com/emerg/topic699.htm

– Updated 2002 April 24, excellent summary article

• Bocka JJ Ann Emerg Med 1989 Dec; 18(12):1280-6

• Hedges JR Pacing Clin Electrophysiol 1991 Oct;14(10):1473-8

• Barthell E Ann Emerg Med 1988 Nov;17(11):1221-6• Klumbies A Z Gesamte Inn Med 1988 Jul 1;43(13):348-52.