1

Understanding the Understanding the 1212--lead ECG, part IIlead ECG, part II

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BundleBundle--branchbranch blocksblocks

Most common electrocardiogram (ECG) Most common electrocardiogram (ECG) abnormalityabnormality

Appears as a wider than normal QRS Appears as a wider than normal QRS complexcomplex

Occurs when one of the two bundle Occurs when one of the two bundle branches can’t conduct the impulsebranches can’t conduct the impulse

Most common cause: ischemic heart Most common cause: ischemic heart diseasedisease

33

Right bundleRight bundle--branch block (RBBB)branch block (RBBB)

Impulse conduction to right ventricle is Impulse conduction to right ventricle is blockedblocked

Examine lead VExamine lead V11 to to identify RBBBidentify RBBB

ECG show delayed or positive R waveECG show delayed or positive R wave

Key identifier is QRS complex wider than Key identifier is QRS complex wider than 0.12 second, with positive R wave in V0.12 second, with positive R wave in V11

44

Left bundle branch block (LBBB)Left bundle branch block (LBBB)

Electrical impulses don’t reach left Electrical impulses don’t reach left side of the heartside of the heart

QRS wider than 0.12 secondQRS wider than 0.12 second

Key to recognizing LBBB Key to recognizing LBBB is a wide downward is a wide downward S wave or rS wave in S wave or rS wave in leads Vleads V11 and Vand V22

55 66

2

77 88

99 1010

1111 1212

3

1313

What do you think?What do you think?

•Sinoatrial block, type II

•Second-degree atrioventricular (AV) block, type I

•Second-degree AV block, type II

•Nonconducted atrial premature impulse 1414

What do you think?What do you think?

•Sinoatrial block, type II

•Second-degree atrioventricular (AV) block, type I

•Second-degree AV block, type II

•Nonconducted atrial premature impulse

1515

What do you think?What do you think?

•Second-degree AV block, type IIP waves occur regularly in this tracing;

Some of them are conducted to the ventricles while others are blocked; therefore, it is second-degree AV block.

In this tracing, when the P waves are conducted, the PR intervals do not lengthen; therefore, this is second-degree AV block, type II. 1616

1717 1818

4

1919

- pauses in the middle of a regular rhythm.

- there are no extra P waves during the pauses -- an indication that this is not AV block.

- the pause is exactly twice the length of the shorter cycle, indicating regularly firing sinus impulses that fail to conduct to the atrium at times;

This is SA block. Because the pause is twice the shorter cycle, it is type II.

2020

RecognizingRecognizingmyocardial infarction (MI)myocardial infarction (MI)

Series of predictable ECG changes occur in Series of predictable ECG changes occur in MIMI

STST--segmentsegment--elevation MI elevation MI (STEMI)(STEMI)----serious type serious type of MI, associated with of MI, associated with more complications, more complications, higher risk of deathhigher risk of death

2121

Characteristic changes in AMICharacteristic changes in AMI

•• ST segment elevation over area of ST segment elevation over area of damagedamage

•• ST depression in leads opposite ST depression in leads opposite infarctioninfarction

•• Pathological Q wavesPathological Q waves•• Reduced R wavesReduced R waves•• Inverted T wavesInverted T waves

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ST elevationST elevation

R

P

Q

ST

• Occurs in the early stages

• Occurs in the leads facing the infarction

• Slight ST elevation may be normal in V1 or V2

2323

Deep Q waveDeep Q wave

R

P

Q

T

ST

• Only diagnostic change of myocardial infarction

• At least 0.04 seconds in duration

• Depth of more than 25% of ensuing R wave

2424

T wave changesT wave changes

R

P

Q

T

ST

• Late change

• Occurs as ST elevation is returning to normal

• Apparent in many leads

5

2525

Bundle branch blockBundle branch block

I II III aVR aVL aVF V1 V2 V3 V4 V5 V6I II III aVR aVL aVF V1 V2 V3 V4 V5 V6

Anterior wall MI Left bundle branch block

2626

Sequence of changes in evolving Sequence of changes in evolving AMIAMI

A day or so after onset Later changes A few months after AMI

1 minute after onset 1 hour or so after onset A few hours after onset

Q

R

P

QT

STR

P

Q

ST

P

Q

T

ST

R

P

S

T

P

QT

ST

R

P

Q

T

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Inferior wall STEMIInferior wall STEMI

Elevated ST segments in Elevated ST segments in leads II, III, and leads II, III, and aVFaVF, , which monitor the heart’s which monitor the heart’s inferior or bottom wall inferior or bottom wall

Area of the heart Area of the heart perfused perfused by the right coronary arteryby the right coronary artery

2828

Inferior infarctionInferior infarctionInferior infarction

I II III aVR aVL aVF V1 V2 V3 V4 V5 V6

Right coronary artery

2929

Septal MISeptal MI

Perfused by the left anterior Perfused by the left anterior descending (LAD) coronary arterydescending (LAD) coronary artery

STST--segment elevation seen in leads segment elevation seen in leads VV11 and Vand V22, the precordial or chest , the precordial or chest leads located on the anterior chest leads located on the anterior chest wall over the septumwall over the septum

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AnteriorAnterior--wall STEMIwall STEMI

Directly to the left of the septal areaDirectly to the left of the septal area

Also perfused by the LADAlso perfused by the LAD

Most muscular, powerful Most muscular, powerful pumping wall of the heart, pumping wall of the heart, responsible for large responsible for large proportion of cardiac outputproportion of cardiac output

ST elevation seen in VST elevation seen in V33 and Vand V44

6

3131

Anterior infarctionAnterior infarctionAnterior infarction

I II III aVR aVL aVF V1 V2 V3 V4 V5 V6

Left coronary artery

3232

LateralLateral--wall STEMIwall STEMI

Perfused by the circumflex arteryPerfused by the circumflex artery

Muscular, contributes significantly to the Muscular, contributes significantly to the heart’s pumping abilityheart’s pumping ability

Monitored by precordial (chest) and Monitored by precordial (chest) and frontal (limb) leadsfrontal (limb) leads

STST--segment elevation will appear in segment elevation will appear in leads I, aVL, Vleads I, aVL, V55, V, V66

3333

Lateral infarctionLateral infarctionLateral infarction

I II III aVR aVL aVF V1 V2 V3 V4 V5 V6

Left circumflexcoronary artery

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Common dysrhythmiasCommon dysrhythmias

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Sinus bradycardiaSinus bradycardia

Sinus rhythm slower than 60 beats per Sinus rhythm slower than 60 beats per minuteminute

Commonly caused by ischemic heart Commonly caused by ischemic heart disease causing disease causing sinoatrialsinoatrial (SA) node to (SA) node to malfunctionmalfunction

Also seen in MI, some medications (such Also seen in MI, some medications (such as betaas beta--blockers), and wellblockers), and well--conditioned conditioned athletesathletes

3636

Sinus bradycardiaSinus bradycardia

Signs and symptoms: hypotension, Signs and symptoms: hypotension, lethargy, fatigue, chest pain, lethargy, fatigue, chest pain, difficulty breathingdifficulty breathing

7

3737

Sinus tachycardiaSinus tachycardia

Sinus rhythm faster than 100 beats per Sinus rhythm faster than 100 beats per minuteminute

Related to physiologic cause: fever, Related to physiologic cause: fever, infection, pain, physical exertion, anxiety, infection, pain, physical exertion, anxiety, shock, hypoxiashock, hypoxia

May need betaMay need beta--blocker if cause unknownblocker if cause unknown

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3939

Atrial fibrillation (AF)Atrial fibrillation (AF)

Common dysrhythmiaCommon dysrhythmia

Irregular heart rhythm with no meaningful Irregular heart rhythm with no meaningful P wavesP waves

Atrial kick lost, Atrial kick lost, atriasatrias quiver due to depolarization quiver due to depolarization of atrial cellsof atrial cells

Causes irregular ventricular rate, 40 to 180 beats Causes irregular ventricular rate, 40 to 180 beats per minuteper minute

4040

4141 4242

Premature ventricular Premature ventricular contractions (PVCs)contractions (PVCs)

Wide abnormal premature QRS Wide abnormal premature QRS complex complex

Due to conduction through the Due to conduction through the ventricle instead of Hisventricle instead of His--Purkinje Purkinje systemsystem

QRS greater than QRS greater than 0.12 second0.12 second

8

4343

Ventricular tachycardia (VT)Ventricular tachycardia (VT)

Rapid rate, 100 to 250 beats per minuteRapid rate, 100 to 250 beats per minute

Wide, bizarre, QRS complex followed by Wide, bizarre, QRS complex followed by large T wavelarge T wave

Patient may be unconscious, Patient may be unconscious, pulselesspulseless, , apneicapneic----initiate CPRinitiate CPR

If patient awake, treat as medical If patient awake, treat as medical emergencyemergency 4444

4545 4646

4747 4848

9

4949 5050

5151 5252

5353 5454

10

5555 5656

5757

Shortened QT interval (short/absent ST segment)

Hypercalcemia

5858

5959 6060

Digitalis Digitalis

Scooping of ST segmentShortening of QT intervalLow amplitude of T waveElongation of PR intervalHigh amplitude of U wave

11

6161

Atrial tachycardia with AV blockAtrial tachycardia with AV blockDigitalis poisoningDigitalis poisoning

AF with accelerated junctional rhythm

6262

11stst degree AV Blockdegree AV Block

Digitalis poisoningDigitalis poisoning

Mobitz I

6363

Digitalis poisoningDigitalis poisoningBidirectionalBidirectional VTVT

Ventricular bigeminy

6464

6565

TricyclicTricyclic antidepressants (TAD) antidepressants (TAD)

Sinus tachycardia with a prolonged QRS interval

Rightward axis

Tall R wave in lead aVR

Markedly abnormal repolarization changes suggests TAD poisoning6666

HYPOTHERMIAHYPOTHERMIA

Sinus bradycardia with first-degree AV block is evident.

The downstroke of each QRS complex is slurred and is typical of a J (Osborne) wave (↓).