Understanding the 12-lead ECG, part II By Guy Goldich, RN, CCRN, MSN Nursing2006, December Online: © 2006 Lippincott Williams & Wilkins

2 Bundle-branch blocks Most common electrocardiogram (ECG) abnormality Most common electrocardiogram (ECG) abnormality Appears as a wider than normal QRS complex Appears as a wider than normal QRS complex Occurs when one of the two bundle branches can’t conduct the impulse Occurs when one of the two bundle branches can’t conduct the impulse Most common cause: ischemic heart disease Most common cause: ischemic heart disease

3 Right bundle-branch block (RBBB) Impulse conduction to right ventricle is blocked Impulse conduction to right ventricle is blocked Examine lead V 1 to identify RBBB Examine lead V 1 to identify RBBB ECG show delayed or positive R wave ECG show delayed or positive R wave Key identifier is QRS complex wider than 0.12 second, with positive R wave in V 1 Key identifier is QRS complex wider than 0.12 second, with positive R wave in V 1

4 Left bundle branch block (LBBB) Electrical impulses don’t reach left side of the heart Electrical impulses don’t reach left side of the heart QRS wider than 0.12 second QRS wider than 0.12 second Key to recognizing LBBB is a wide downward S wave or rS wave in leads V 1 and V 2 Key to recognizing LBBB is a wide downward S wave or rS wave in leads V 1 and V 2

5 Recognizing myocardial infarction (MI) Series of predictable ECG changes occur in MI Series of predictable ECG changes occur in MI ST-segment-elevation MI (STEMI)--serious type of MI, associated with more complications, higher risk of death ST-segment-elevation MI (STEMI)--serious type of MI, associated with more complications, higher risk of death

6 Inferior wall STEMI Elevated ST segments in leads II, III, and aVF, which monitor the heart’s inferior or bottom wall Elevated ST segments in leads II, III, and aVF, which monitor the heart’s inferior or bottom wall Area of the heart perfused by the right coronary artery Area of the heart perfused by the right coronary artery

7 Septal MI Perfused by the left anterior descending (LAD) coronary artery Perfused by the left anterior descending (LAD) coronary artery ST-segment elevation seen in leads V 1 and V 2, the precordial or chest leads located on the anterior chest wall over the septum ST-segment elevation seen in leads V 1 and V 2, the precordial or chest leads located on the anterior chest wall over the septum

8 Anterior-wall STEMI Directly to the left of the septal area Directly to the left of the septal area Also perfused by the LAD Also perfused by the LAD Most muscular, powerful pumping wall of the heart, responsible for large proportion of cardiac output Most muscular, powerful pumping wall of the heart, responsible for large proportion of cardiac output ST elevation seen in V 3 and V 4 ST elevation seen in V 3 and V 4

9 Lateral-wall STEMI Perfused by the circumflex artery Perfused by the circumflex artery Muscular, contributes significantly to the heart’s pumping ability Muscular, contributes significantly to the heart’s pumping ability Monitored by precordial (chest) and frontal (limb) leads Monitored by precordial (chest) and frontal (limb) leads ST-segment elevation will appear in leads I, aVL, V 5, V 6 ST-segment elevation will appear in leads I, aVL, V 5, V 6

10 Leads and the heart MIs can affect a single heart wall or more than one area MIs can affect a single heart wall or more than one area ST-segment elevations appear in the leads monitoring all of the involved areas ST-segment elevations appear in the leads monitoring all of the involved areas Areas involved are reflected by the MI descriptive name Areas involved are reflected by the MI descriptive name

11 Tissue damage after MI

12 Common dysrhythmias Always treat the patient, not the rhythm Always treat the patient, not the rhythm Assess your patient Assess your patient Document level of consciousness, vital signs, chest pain, shortness of breath and any other signs and symptoms Document level of consciousness, vital signs, chest pain, shortness of breath and any other signs and symptoms

13 Sinus bradycardia Sinus rhythm slower than 60 beats per minute Sinus rhythm slower than 60 beats per minute Commonly caused by ischemic heart disease causing sinoatrial (SA) node to malfunction Commonly caused by ischemic heart disease causing sinoatrial (SA) node to malfunction Also seen in MI, some medications (such as beta-blockers), and well-conditioned athletes Also seen in MI, some medications (such as beta-blockers), and well-conditioned athletes

14 Sinus bradycardia Signs and symptoms: hypotension, lethargy, fatigue, chest pain, difficulty breathing Signs and symptoms: hypotension, lethargy, fatigue, chest pain, difficulty breathing

15 Sinus tachycardia Sinus rhythm faster than 100 beats per minute Sinus rhythm faster than 100 beats per minute Related to physiologic cause: fever, infection, pain, physical exertion, anxiety, shock, hypoxia Related to physiologic cause: fever, infection, pain, physical exertion, anxiety, shock, hypoxia May need beta-blocker if cause unknown May need beta-blocker if cause unknown

16 Atrial fibrillation (AF) Common dysrhythmia Common dysrhythmia Irregular heart rhythm with no meaningful P waves Irregular heart rhythm with no meaningful P waves Atrial kick lost, atrias quiver due to depolarization of atrial cells Atrial kick lost, atrias quiver due to depolarization of atrial cells Causes irregular ventricular rate, 40 to 180 beats per minute Causes irregular ventricular rate, 40 to 180 beats per minute

17 Causes of AF Atrial enlargement due to COPD Atrial enlargement due to COPD Other lung diseases Other lung diseases Thyroid disease Thyroid disease Acute MI Acute MI Ischemic heart disease Ischemic heart disease Stress Stress Fatigue Fatigue Alcohol Alcohol Caffeine Caffeine Cigarettes Cigarettes

18 About AF Two hallmarks of AF: Two hallmarks of AF: irregularly irregular rhythmirregularly irregular rhythm f wavesf waves If patient unstable or symptomatic: administer oxygen and obtain I.V. access If patient unstable or symptomatic: administer oxygen and obtain I.V. access All patients with AF lasting longer than 48 hours are at increased risk for thrombus All patients with AF lasting longer than 48 hours are at increased risk for thrombus

19 Premature ventricular contractions (PVCs) Wide abnormal premature QRS complex Wide abnormal premature QRS complex Due to conduction through the ventricle instead of His-Purkinje system Due to conduction through the ventricle instead of His-Purkinje system QRS greater than 0.12 second QRS greater than 0.12 second

20 Causes of PVCs Heart failure Heart failure Electrolyte imbalances Electrolyte imbalances Caffeine Caffeine Hypoxia Hypoxia Mitral valve prolapse Mitral valve prolapse Thyroid disease Thyroid disease Acute MI Acute MI

21 Ventricular tachycardia (VT) Rapid rate, 100 to 250 beats per minute Rapid rate, 100 to 250 beats per minute Wide, bizarre, QRS complex followed by large T wave Wide, bizarre, QRS complex followed by large T wave Patient may be unconscious, pulseless, apneic--initiate CPR Patient may be unconscious, pulseless, apneic--initiate CPR If patient awake, treat as medical emergency If patient awake, treat as medical emergency