Chapter 10 - 12 lead Interpretation - Part 2

BASE HOSPITAL GROUPONTARIO

Chapter 10 for 12 Lead Training

-12 Lead Interpretation – Part 2-

Ontario Base Hospital GroupEducation Subcommittee

2008

TIME IS MUSCLE

OBHG Education Subcommittee

12 Lead Interpretation – Part 2

REVIEWERS/CONTRIBUTORS

Neil Freckleton, AEMCA, ACPHamilton Base Hospital

Jim Scott, AEMCA, PCPSault Area Hospital

Ed Ouston, AEMCA, ACPOttawa Base Hospital

Laura McCleary, AEMCA, ACPSOCPC

Tim Dodd, AEMCA, ACPHamilton Base Hospital

Dr. Rick Verbeek, Medical DirectorSOCPC2008 Ontario Base Hospital Group

AUTHOR

Greg Soto, BEd, BA, ACPNiagara Base Hospital


Chapter 10 - Objectives

Recognize ST-depression and relate to the ACS patient

Recognize Reciprocal Changes (RCs) and relate to the significance of STEMI

Recognized Q-waves and relate to the ACS patient

Discuss the evolution of an AMIExplain the reasons why a normal ECG

does not rule out AMI


Epicardial Coronary Artery

Lateral Wall of LV

Positive Electrode

Septum

Left Ventricular

Cavity

Inferior Wall of LV

Ischemia

Thrombus forming


Ischemia

Inadequate oxygen to tissue

Subendocardial

Represented by ST depression or T-wave inversion

May or may not result in infarct


ST depression


T-wave Inversion


Evolution of AMI

• Hyperacute T WaveHyperacute T Wave


Evolution of AMI

• AcuteAcute


Evolution of AMI

• AcuteAcute


Evolution of AMI

• Age undeterminedAge undetermined


Hyper-acute T-waves

Earliest ECG sign of AMI

Tall and peaked w/in minutes of blood flow interruption

Differential Dx:hyperkalemia BERLVH


Why hyper-acute T-wave are important to recognize


AMI Recognition

A “normal” 12-lead ECG

DOES NOT rule out AMINot all AMI have STE (approx. 50%)Early AMI may have no STE but may

evolve over timeNon STEMI AMI have non specific but

abnormal ECGs


Why can’t AMI be ruled out?

PHECG has high specificity for STEMI = 97%*

Meaning = when PHECG shows STEMI it almost always turns out to be an AMI.


PHECG has only moderate sensitivity for AMI = 68%

Meaning - when PHECG does not show STEMI only 68% of time does it turn out to NOT be an AMI. (over 30% of AMI patients do not have STE on PHECG)

CAN’T RULE OUT AMI WITH NO STE on 12 LEAD ECG

Source: Ioannides JA et al. Accuracy & clinical effect of out-of-hospital ECG in the diagnosis of acute cardiac ischemia: a meta-analysis. Annals of Emergency Medicine 2001;37.

Why can’t AMI be ruled out?


Practice


Practice


Practice


QRS

Q wavesPhysiologic Q waves

< .04 sec (40ms)

Pathologic Q waves>.04 sec (40 ms)


Q-wave & Infarct

represent irreversible necrosis – death of tissue

may develop early (1st hour) but usually 8-12 hours post-AMI

may persist permanently but some resolve regardless of reperfusion

not all AMIs produce Q-waves


QRS

Q wave


QS Complex


Common Q-waves

“age undetermined”Likely old septal MI ↑ index of suspicion not

a bad idea

Q-wave associated with an AMI = necrosis has likely begun

↑ ↑ severity/seriousnessseverity/seriousness


Sample ECGs with Q-waves

Find them……….


Septal – V1 to V3

(? – II, III, aVF )


Lateral - aVL


aVL, V1 – V5


Reciprocal Changes


Reciprocal Changes

Occur in larger MIAble to “see” the MI on the opposite side

because it is larger

RC’s make the STE more likely to be due to AMIDon’t have to have RC’s but they make

the diagnosis easier


Reciprocal Changes


Reciprocal Changes


Reciprocal Changes

II, III, aVFII, III, aVF I, aVL, V leadsI, aVL, V leads


Reciprocal Changes

Inferior

Anterior = Septal, Anterior and Lateral walls


Practice


Practice


AMI Recognition


AMI Recognition

Imitators of infarctBBB LVHVentricular beatsPericarditisEarly RepolarizationOthers


Summary

AMI recognitionKnow what you are looking for

> 1mm of ST elevation in limb leads> 2mm of ST elevation in chest

leadsTwo contiguous leads

Know where you are lookingPositive electrode as an “eye”Memorize lead locations


Summary

Reciprocal ChangesNot necessary to presume

infarctionStrong confirming evidence

when present


Summary

ST segment elevation is presumptive evidence for AMI

Other conditions may also cause ST elevation


Summary

NEVER FORGET:

A normal 12-Lead ECG DOES NOT rule out AMI


QUESTIONS?


Well Done!

Education Subcommittee

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Chapter 10 - 12 lead Interpretation - Part 2