1
Understanding the Understanding the 1212--lead ECG, part IIlead ECG, part II
22
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
2222
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
2727
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
3030
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
3434
Common dysrhythmiasCommon dysrhythmias
3535
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
3838
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 (↓).