Rafael Ortega, MDRafael Ortega, MD

Boston University Medical CenterBoston University Medical Center

External External PacemakersPacemakers

From the TrenchesFrom the Trenches

70-year-old woman70-year-old woman

Returns to OR for expanding neck Returns to OR for expanding neck hematomahematoma

Cardiac arrest after intubationCardiac arrest after intubation

ManagementManagement

OBJECTIVES OBJECTIVES

Review External Pacemakers (EP)Review External Pacemakers (EP)

Summarize EP historical evolutionSummarize EP historical evolution

Clarify EP indicationsClarify EP indications

Explain the Philips/Agilent HeartStart UnitExplain the Philips/Agilent HeartStart Unit

External Pacemaker

Manual Defibrillator

Automatic Defibrillator

3 in 1 Biphasic Unit 3 in 1 Biphasic Unit

QuestionQuestion

What is “Biphasic”?What is “Biphasic”?

A Few Words on “Biphasic”A Few Words on “Biphasic”

Biphasic energy is delivered in two directions Biphasic energy is delivered in two directions

Require less energy for defibrillationRequire less energy for defibrillation

Less myocardial injury and myocardial Less myocardial injury and myocardial dysfunctiondysfunction

150 J should be used for defibrillating 150 J should be used for defibrillating ventricular fibrillation (in adults) ventricular fibrillation (in adults)

Waveform ComparisonWaveform Comparison

MonophasicMonophasic

BiphasicBiphasic

Indications for EPIndications for EP

Temporizing measure in patients with Temporizing measure in patients with symptomatic bradycardiasymptomatic bradycardia

Little benefit in pulseless situationsLittle benefit in pulseless situations

May be useful for overdrive-pacing in May be useful for overdrive-pacing in certain tachycardias. certain tachycardias.

Early History Early History

1791: Galvani electrically stimulates dead frog’s 1791: Galvani electrically stimulates dead frog’s heart heart

1872: Duchenne resuscitates child tapping 1872: Duchenne resuscitates child tapping precordium with an electrodeprecordium with an electrode

1932: Hyman designs external pulse generator: 1932: Hyman designs external pulse generator: ""artificial cardiac pacemakerartificial cardiac pacemaker““

1952: Zoll uses simultaneous precordial and 1952: Zoll uses simultaneous precordial and transesophageal electrodes for pacing transesophageal electrodes for pacing

46 Years later 46 Years later

HesselvikHesselvik JF. JF. OrtegaOrtega RA. RA. Simultaneous transesophageal Simultaneous transesophageal atrial pacing and transesophageal echocardiography in atrial pacing and transesophageal echocardiography in cardiac surgical patients.cardiac surgical patients. Journal of Cardiothoracic & Journal of Cardiothoracic & Vascular Anesthesia. 12(3):281-3, 1998 Jun.Vascular Anesthesia. 12(3):281-3, 1998 Jun.

Who was Dr. Zoll?Who was Dr. Zoll?

A Boston nativeA Boston native Harvard Medical SchoolHarvard Medical School Internship BI Hospital Internship BI Hospital

In 1939 joins a research In 1939 joins a research group at BI group at BI

WW-ll on Dwight Harken's WW-ll on Dwight Harken's surgical teamsurgical team Paul Zoll

Professor Emeritus

HMS

Transvenous Pacing Transvenous Pacing EffectEffect

Temporary and permanent implantable Temporary and permanent implantable transvenous pacemakers (late 1950’s) transvenous pacemakers (late 1950’s) superseded the use of external models.superseded the use of external models.

But, these took time to insertBut, these took time to insert

There was still a need for external pacingThere was still a need for external pacing

1981: A New Era1981: A New Era

Zoll patents and introduces a transcutaneous Zoll patents and introduces a transcutaneous external pacemakerexternal pacemaker

Longer pulse duration and larger electrode Longer pulse duration and larger electrode surface surface

Reduced current required for capture and Reduced current required for capture and increased comfort for the patient increased comfort for the patient

New model could be applied much more rapidly New model could be applied much more rapidly

Pulse Duration and CurrentPulse Duration and Current Early models used short (1-2 msec) impulses Early models used short (1-2 msec) impulses

resembling the action potential of skeletal musclesresembling the action potential of skeletal muscles

Zoll increased duration to 4 msec with a 3-fold Zoll increased duration to 4 msec with a 3-fold reduction in threshold reduction in threshold

Stimulation 20% over threshold stimulates only the Stimulation 20% over threshold stimulates only the ventricles. ventricles.

External pacing requires 30-100 times greater External pacing requires 30-100 times greater current than transvenous pacing current than transvenous pacing

QuestionQuestion

What is the effect of EP What is the effect of EP

on on

hemodynamics?hemodynamics?

Hemodynamics Hemodynamics EP can simultaneously stimulate all 4 heart chambers EP can simultaneously stimulate all 4 heart chambers

(in dogs)(in dogs) Madsen echo demonstrated that atrial stimulation was Madsen echo demonstrated that atrial stimulation was

retrograde without opening the mitral valve.retrograde without opening the mitral valve. Atrial-pacing threshold in humans is much higher than Atrial-pacing threshold in humans is much higher than

for ventriclesfor ventricles

Net result: loss of the “atrial kick”Net result: loss of the “atrial kick”

Cardiac output is reducedCardiac output is reduced

Reducing DiscomfortReducing Discomfort

Not a problem under GANot a problem under GA

If awake, place electrodes in the midline If awake, place electrodes in the midline chest and just below the left scapulachest and just below the left scapula

Considered sedationConsidered sedation

QuestionQuestion

Can you perform CPR Can you perform CPR

and and

use EP at the same time?use EP at the same time?

EP During CPREP During CPR

CPR can be performed with EP pads in CPR can be performed with EP pads in place. place.

No electrical hazard to the person No electrical hazard to the person performing CPRperforming CPR

However, turning the unit off during CPR However, turning the unit off during CPR is advisable. is advisable.

No Heart DamageNo Heart Damage

No enzymatic, EKG, or microscopic No enzymatic, EKG, or microscopic evidence of myocardial damage has evidence of myocardial damage has been found after pacing (dogs and been found after pacing (dogs and humans) for as long as 60 minutes humans) for as long as 60 minutes

Low risk of triggering ventricular Low risk of triggering ventricular fibrillationfibrillation

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