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BundleBundle-branch blocks Understanding the 12-lead ECG, part II Right bundlebundle-branch block (RBBB) Appears as a wider than normal QRS complex Occurs when one of the two bundle branches can’t conduct the impulse Most common cause: ischemic heart disease 2 Left bundle branch block (LBBB) Impulse conduction to right ventricle is blocked Examine lead V1 to identify RBBB ECG show delayed or positive R wave Key identifier is QRS complex wider than 0.12 second, with positive R wave in V1 Most common electrocardiogram (ECG) abnormality Electrical impulses don’t reach left side of the heart QRS wider than 0.12 second Key to recognizing LBBB is a wide downward S wave or rS wave in leads V1 and V2 3 4 5 6 1 7 8 9 10 11 12 2 What do you think? What do you think? •Sinoatrial block, type II •Sinoatrial block, type II •Second-degree atrioventricular (AV) block, type I •Second-degree atrioventricular (AV) block, type I •Second-degree AV block, type II •Second-degree AV block, type II •Nonconducted atrial premature impulse 13 •Nonconducted atrial premature impulse 14 What do you think? •Second-degree AV block, type II P 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 15 block, type II. 17 16 18 3 Recognizing myocardial infarction (MI) Series of predictable ECG changes occur in MI - 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; STST-segmentsegment-elevation MI (STEMI)-serious type (STEMI)--serious of MI, associated with more complications, higher risk of death This is SA block. Because the pause is twice the shorter cycle, it is type II. 19 20 Characteristic changes in AMI • • • • • ST elevation ST segment elevation over area of damage ST depression in leads opposite infarction Pathological Q waves Reduced R waves Inverted T waves • Occurs in the early stages R ST • Occurs in the leads facing the infarction P Q • Slight ST elevation may be normal in V1 or V2 21 22 Deep Q wave • Only diagnostic change of myocardial infarction R • At least 0.04 seconds in duration ST P T Q T wave changes • Depth of more than 25% of ensuing R wave 23 • Late change R ST P • Occurs as ST elevation is returning to normal T • Apparent in many leads Q 24 4 Sequence of changes in evolving AMI Bundle branch block Anterior wall MI Left bundle branch block R I II III aVR aVL aVF V1 V2 V3 V4 V5 V6 I II III aVR aVL aVF V1 V2 V3 R R ST T V4 V5 V6 ST P P Q S P T Q Q 1 minute after onset 1 hour or so after onset A few hours after onset R ST P ST P T T P T Q Q Q A day or so after onset Later changes A few months after AMI 25 26 Inferior wall STEMI Inferior infarction Inferior infarction Elevated ST segments in leads II, III, and aVF, aVF, which monitor the heart’s inferior or bottom wall I II III Right coronary artery Septal MI V1 V2 V3 V4 V5 V6 Area of the heart perfused by the right coronary artery 27 aVR aVL aVF 28 AnteriorAnterior-wall STEMI Perfused by the left anterior descending (LAD) coronary artery STST-segment elevation seen in leads V1 and V2, the precordial or chest leads located on the anterior chest wall over the septum Directly to the left of the septal area Also perfused by the LAD 29 Most muscular, powerful pumping wall of the heart, responsible for large proportion of cardiac output ST elevation seen in V3 and V4 30 5 Anterior infarction LateralLateral-wall STEMI Anterior infarction I II III aVR aVL aVF V1 V2 V3 V4 V5 V6 Left coronary artery Perfused by the circumflex artery Muscular, contributes significantly to the heart’s pumping ability Monitored by precordial (chest) and frontal (limb) leads STST-segment elevation will appear in leads I, aVL, V5, V6 31 32 Lateral infarction Lateral infarction I II III aVR aVL aVF V1 V2 V3 V4 V5 V6 Common dysrhythmias Left circumflex coronary artery 33 34 Sinus bradycardia Sinus bradycardia Sinus rhythm slower than 60 beats per minute Commonly caused by ischemic heart disease causing sinoatrial (SA) node to malfunction Signs and symptoms: hypotension, lethargy, fatigue, chest pain, difficulty breathing Also seen in MI, some medications (such as betabeta-blockers), and wellwell-conditioned athletes 35 36 6 Sinus tachycardia Sinus rhythm faster than 100 beats per minute Related to physiologic cause: fever, infection, pain, physical exertion, anxiety, shock, hypoxia May need betabeta-blocker if cause unknown 37 38 Atrial fibrillation (AF) Common dysrhythmia Irregular heart rhythm with no meaningful P waves Atrial kick lost, atrias quiver due to depolarization of atrial cells Causes irregular ventricular rate, 40 to 180 beats per minute 39 40 Premature ventricular contractions (PVCs) 41 Wide abnormal premature QRS complex Due to conduction through the ventricle instead of HisHis-Purkinje system QRS greater than 0.12 second 42 7 Ventricular tachycardia (VT) Rapid rate, 100 to 250 beats per minute Wide, bizarre, QRS complex followed by large T wave Patient may be unconscious, pulseless, pulseless, apneic-initiate CPR apneic--initiate If patient awake, treat as medical emergency 43 44 45 46 47 48 8 49 50 51 52 53 54 9 55 56 57 58 Hypercalcemia Shortened QT interval (short/absent ST segment) Digitalis Scooping of ST segment Shortening of QT interval Low amplitude of T wave Elongation of PR interval High amplitude of U wave 59 60 10 Digitalis poisoning Digitalis poisoning Atrial tachycardia with AV block 1st degree AV Block Mobitz I AF with accelerated junctional rhythm 61 62 63 64 Digitalis poisoning Bidirectional VT Ventricular bigeminy Tricyclic antidepressants (TAD) HYPOTHERMIA Sinus tachycardia with a prolonged QRS interval Sinus bradycardia with first-degree AV block is evident. Rightward axis Tall R wave in lead aVR Markedly abnormal repolarization changes suggests TAD poisoning 65 The downstroke of each QRS complex is slurred and is typical of a J (Osborne) wave (↓). 66 11