2023 심장학: 심전도 (허혈성 및 기타)

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기타질환

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Definition of (+) deflection

Depolarization Wave

탈분극 (흥분)

Resting
- - - - - - - - - - - - - - - - - - -
+ + + + + + + + + + + + + +

- - - - - + + + + + + + + + +

Depolarization  
+ + + + - - - - - - - - - - - - - -

0 mV

0 mV

+ 1 mV

- - - - - - - - - - - - - - - - - - -

Complete Depolarization
+ + + + + + + + + + + + + +

+ 1 mV

0 mV

Repolarization Wave

재분극 (원상 복귀)

Depolarization
+ + + + + + + + + + + + + +
- - - - - - - - - - - - - - - - - - - -

- - - - - + + + + + + + + + +

     Repolarization
- - - - - - - - - - - - - - + + + +

- - - - - - - - - - - - - - - - - - -

Complete Repolarization
+ + + + + + + + + + + + + +

0 mV

0 mV

+ 1 mV

+ 1 mV

0 mV

• The ECG: a key diagnostic test for coronary heart
disease.

• Major factors on ischemic ECG findings

– (1) the duration of the ischemic process (acute vs.
evolving/chronic)

– (2) extent (transmural vs. nontransmural)

– (3) topography (anterior / inferior-posterior-lateral /
right ventricular)

– (4) other underlying abnormalities (e.g., LBBB, Wolff-
Parkinson-White syndrome, or pacemaker patterns)

• A key clinical distinction: ST-segment elevation
myocardial infarction (STEMI) vs. non-STEMI

Repolarization (ST-T Wave) Abnormalities

•The earliest and most consistent ECG finding during acute severe
ischemia d/t a current of injury mechanism.

•Normally, the ST segment : nearly isoelectric

•Ischemia: complex time-dependent effects on the electrical
properties of myocardial cells

•Severe acute ischemia

– the resting membrane potential 

– the duration of the action potential in the ischemic area 

– the rate of rise and amplitude of phase 0 

•A voltage gradient between normal and ischemic zones

– current flow between these regions

– represented on the surface ECG

– deviation of the ST segment

“diastolic” and “systolic” injury currents :
ischemic ST-segment elevations

QRS changes

• Necrosis of sufficient myocardial tissue

– R wave amplitude or Q waves

– as a result of loss of electromotive forces in the infarcted
area

• transmural myocardial infarction ≒ Q wave infarction

• subendocardial (nontransmural) infarcts ≒ non–Q
wave infarction

• Posterior or lateral infarction: loss of depolarization
forces in these regions

– reciprocally increase R wave amplitude in lead V1 ± V2

Evolution of ECG changes

•Ischemic ST-segment elevation and hyper-acute T wave

– the earliest sign of acute infarction (STEMI)

•from hours to days : evolving T wave inversion ± Q waves in the

same lead distribution

– T wave inversions can resolve after days or weeks, or persist indefinitely.

•In the days to weeks or longer following infarction, the QRS changes

can persist or begin to resolve.

– complete normalization of the ECG following Q wave infarction :

uncommon

– persistent Q waves and ST-segment elevation

– severe underlying wall motion disorder, ventricular aneurysm

Other ischemic ST-T Patterns

•Reversible transmural ischemia : coronary vasospasm - very transient ST-

segment elevation

–the classic electrocardiographic marker of Prinzmetal variant angina

•Deep T wave inversion in multiple precordial leads (e.g., V1 through V4)

–severe ischemia associated with proximal (LAD) stenosis

T Wave: Inverted
Symmetrical
Sharply pointed arrowhead

Upward convexity of ST segment

T wave inversion

Localization of infarcted area

Vectors of ECG

• Vectorcardiogram

• 12 leads ECG

Vectors of limb leads

Vectors of precordial leads

Localization of Ischemia or Infarction

more helpful in ST-segment elevation and/or hyperacute T waves

(1) 2 or more precordial leads (V1 through V6) and/or in leads I and aVL : anterior or anterolateral wall

ischemia

(2) leads V1 to V3 : anteroseptal or apical ischemia

(3) leads V4 to V6 : apical or lateral ischemia

(4) leads II, III, and aVF : inferior wall ischemia

(5) right-sided precordial leads with right ventricular ischemia

(6) Posterior wall infarction : back of the heart, leads V7 to V9

- indirectly recognized : reciprocal ST depression in leads V1 to V3

(7) STE on aVR and V1

- LM (or severe multivessel) disease (especially with diffuse prominent ST depression in other leads)

Localization of infarct area

ECG Diagnosis of BBBs and MI

• The diagnosis of Q wave infarction is not usually
impeded by the presence of RBBB

– The net effect is that the criteria for the diagnosis of a Q

wave infarct in a patient with RBBB are the same as in

patients with normal conduction

• The diagnosis of infarction in the presence of LBBB is
considerably more complicated and confusing

– LBBB alters the early and the late phases of ventricular

depolarization and produces secondary ST-T changes

– mask and/or mimic MI findings

• LBBB is often a marker of one of four underlying

conditions associated with increased risk of

cardiovascular morbidity and mortality rates: coronary

heart disease (frequently with impaired left ventricular

function), hypertensive heart disease, Ao valve disease,

and cardiomyopathy.

•New-onset (or not known to be old) LBBB in the setting of

chest pain is typically considered and treated as an STEMI.

The diagnosis of STEMI in the setting of old LBBB can be

difficult.
Hurst's The Heart, 14e CHAPTER 40: ST-SEGMENT ELEVATION MYOCARDIAL INFARCTION

Harrison's Principles of Internal Medicine, 20e Chapter 235: Electrocardiography

Non-infarction Q Waves

• Q waves simulating coronary artery disease can be

related to one (or a combination) of the following

four factors

(1) physiologic or positional variants

(2) altered ventricular conduction

(3) ventricular enlargement

(4) myocardial damage or replacement

ST-T Changes simulating ischemia

•The differential diagnosis of STEMI (or ischemia) caused by obstructive
coronary disease subtends a wide variety of diagnoses

–acute pericarditis

–acute myocarditis

–normal variants (classic early repolarization patterns)

–takotsubo (stress) cardiomyopathy

–Brugada patterns

•Acute pericarditis

–diffuse ST-segment elevation

–Reciprocal ST-segment depression is seen in lead aVR

–presence of PR-segment elevation in aVR, with reciprocal PR segment depression in

other leads

–Abnormal Q waves do not occur with acute pericarditis

–ST-segment elevation may be followed by T wave inversion after a variable period

T wave inversion

• When caused by physiologic variants, T
wave inversion is sometimes mistaken for
ischemia.

• T waves in the right precordial leads can
be slightly inverted, particularly in leads
V1 and V2.

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