Understanding the Understanding the 12-lead ECG, part II12-lead ECG, part II

By Guy Goldich, RN, CCRN, MSNBy Guy Goldich, RN, CCRN, MSN

Nursing2006,Nursing2006, December December

Online: Online: http://www.nursing2006.com

© 2006 Lippincott Williams & Wilkins© 2006 Lippincott Williams & Wilkins

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Bundle-branchBundle-branch 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 diseaseMost common cause: ischemic heart disease

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

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

Examine lead VExamine lead V11 to identify to identify RBBBRBBB

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

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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 is Key to recognizing LBBB is a wide downward S a wide downward S wave or rS wave in leads wave or rS wave in leads VV11 and V and V22

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RecognizingRecognizingmyocardial infarction (MI)myocardial infarction (MI)

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

ST-segment-elevation MI ST-segment-elevation MI (STEMI)--serious type of (STEMI)--serious type of MI, associated with more MI, associated with more complications, higher risk complications, higher risk of deathof death

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Inferior wall STEMIInferior wall STEMI

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

Area of the heart perfused Area of the heart perfused

by the right coronary arteryby the right coronary artery

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Septal MISeptal MI

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

ST-segment elevation seen in leads ST-segment elevation seen in leads VV11 and V and 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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Anterior-wall STEMIAnterior-wall 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 V and V44

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Lateral-wall STEMILateral-wall 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 frontal Monitored by precordial (chest) and frontal (limb) leads(limb) leads

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

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Leads and the heartLeads and the heart

MIs can affect a single heart wall or MIs can affect a single heart wall or more than one areamore than one area

ST-segment elevations appear in the ST-segment elevations appear in the leads monitoring all of the involved leads monitoring all of the involved areasareas

Areas involved are reflected by the Areas involved are reflected by the MI descriptive nameMI descriptive name

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Tissue damage after MITissue damage after MI

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Common dysrhythmiasCommon dysrhythmias

Always treat the patient, not the Always treat the patient, not the rhythmrhythm

Assess your patientAssess your patient

Document level of consciousness, Document level of consciousness, vital signs, chest pain, shortness of vital signs, chest pain, shortness of breath and any other signs and breath and any other signs and symptomssymptoms

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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 sinoatrial (SA) node to disease causing sinoatrial (SA) node to malfunctionmalfunction

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

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Sinus bradycardiaSinus bradycardia

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

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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 beta-blocker if cause unknownMay need beta-blocker if cause unknown

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Atrial fibrillation (AF)Atrial fibrillation (AF)

Common dysrhythmiaCommon dysrhythmia

Irregular heart rhythm with no meaningful P Irregular heart rhythm with no meaningful P waveswaves

Atrial kick lost, atrias quiver due to depolarization Atrial kick lost, atrias 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

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Causes of AFCauses of AF

• Atrial enlargement due to Atrial enlargement due to COPDCOPD

• Other lung diseases Other lung diseases

• Thyroid disease Thyroid disease

• Acute MI Acute MI

• Ischemic heart disease Ischemic heart disease

• Stress Stress

• FatigueFatigue

• AlcoholAlcohol

• CaffeineCaffeine

• CigarettesCigarettes

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About AFAbout AF

Two hallmarks of AF:Two hallmarks of AF:• irregularly irregular rhythmirregularly irregular rhythm• f wavesf waves

If patient unstable or symptomatic: If patient unstable or symptomatic: administer oxygen and obtain I.V. accessadminister oxygen and obtain I.V. access

All patients with AF lasting longer than 48 All patients with AF lasting longer than 48 hours are at increased risk for thrombushours are at increased risk for thrombus

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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 His-Purkinje ventricle instead of His-Purkinje systemsystem

QRS greater than 0.12 QRS greater than 0.12 secondsecond

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Causes of PVCsCauses of PVCs

Heart failureHeart failure

Electrolyte imbalancesElectrolyte imbalances

CaffeineCaffeine

HypoxiaHypoxia

Mitral valve prolapseMitral valve prolapse

Thyroid diseaseThyroid disease

Acute MIAcute MI

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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, pulseless, Patient may be unconscious, pulseless, apneic--initiate CPRapneic--initiate CPR

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