LU6 Enhancement Lectures PGH IM Residents 2011

This slide shows the conduction system of the heart This slide shows the conduction system of the heart. First the SA node located at the postero-superior part of the right atrium. It is the heart’s predominant pacemaker. Each depolarization wave proceeds outwards from the SA node and stimulates both atria to contract. Then the AV node, where the depolarization slows down, then it reaches the ventricular conduction system, beginning at the His bundle. Thereafter, conduction proceeds very rapidly to the right and left bundle branches. The terminal filaments of the Purkinje fibers spread out just beneath the endocardium lining both ventricles, and proceeding towards the outside surface.

Generation of action potential This shows the correlation of the ECG tracing with the action potential, most specifically the ventricular contraction with the action potential. The QRS complex corresponds to the upward stroke at phase 0 to 1. Then at the end of phase 1 to phase 2 (the plateau) until the beginning of phase 3 corresponds with the ST segment; and the T wave with the rapid phase of repolarization. Generation of action potential

The ECG is recorded in a long strip of ruled paper The ECG is recorded in a long strip of ruled paper. The smallest subdivisions are 1 mm long and 1mm high. Between the heavy black lines are 5 small squares. Each small square is equivalent to 0.04 seconds horizontally and 1 millivolt vertically. ECG Graph paper

Unipolar precordial leads This shows the position of the unipolar precordial leads. V1 at the 4th ICS RPSB, V2 at the same level LPSB, V4 at 5th ICS LMCL, V# in between V2 and V4, V% at 5th ICS LAAL and at Lmid axillary line V6.

Normal ECG

These are the waves and important intervals that you will see in an ECG tracing: 1.) P wave – corresponding to the atrial contraction 2.) PR segment – corresponds to the pause of the conduction of depolarization from the SA node to the AV node 3.) PR interval – corresponds to the length of time the depolarization from AV node proceeds to the AV node (normally ,0.20 s) 4.) QRS complex – ventricular contraction, normally <0.12 s 5.) ST segment – is the plateau phase of the ventricular repolarization 6.) ST interval – length of ventricular repolarization 7.) T wave – rapid phase of repolarization 8.) QT interval – length of ventricular contraction 9.) u wave – usually reflects hypokalemia

Guide in Reading ECG Standardization & technique Rhythm Rate: atrial & ventricular P wave morphology & duration P-R interval QRS complex morphology & duration ST segment T-wave U wave Q-T interval Hypertrophy and enlargement arrhythmias

Standardization Heart rate 60 - 100 beats/min bradycardia < 60 tachycardia > 100 PR interval 0.12 – 0.20 sec QRS < 0.12 sec QRS axis - 30º to + 110º QTc < 0.47 sec males < 0.48 sec females

Guide in Reading ECG Standardization & technique Rhythm Rate: atrial & ventricular Axis P wave morphology & duration P-R interval QRS complex morphology & duration ST segment T-wave U wave Q-T interval Hypertrophy and enlargement arrhythmias

Rhythm SA node – sinus AV node – junctional Ventricular rhythm

Rhythm Are there p waves?  sinus, atrial fibrillation Do they look similar?  MFAT, wandering pacemaker Are they regular?  AF Does a QRS complex follow each p wave?  SVT, junctional rhythm, ventricular rhythm

Guide in Reading ECG Standardization & technique Rhythm Rate: atrial & ventricular Axis P wave morphology & duration P-R interval QRS complex morphology & duration ST segment T-wave U wave Q-T interval Hypertrophy and enlargement arrhythmias

Determination of Heart Rate Heart rate assessment by “rule of 300”

Measurement of Rate Formula 1: 300 # big squares between R-R # small squares between R-R

Determination of Heart Rate Is the atrial rate same as ventricular rate? PVC’s, PAC’s, 3rd degree AV block Is there normal-looking QRS complex after each p wave? What if there are no p waves? Six second strip heart rate

RATE Sinus Bradycardia Sinus Tachycardia AV junctional rhythm Inherent rate of 40-60/min No p waves Normal looking QRS complex Ventricular rhythm Inherent rate of 20-40/min Bizaare-looking QRS complex

Guide in Reading ECG Standardization & technique Rhythm Rate: atrial & ventricular Axis P wave morphology & duration P-R interval QRS complex morphology & duration ST segment T-wave U wave Q-T interval Hypertrophy and enlargement arrhythmias

Determination of Axis Hexaxial System Axis refers to the direction of the movement of depolarization. The QRS complex represents depolarization of the ventricles. The mean QRS vector is the sum of all the smaller vectors of ventricular depolarization. Normally, it points downward and to the patient’s left, as this is the general direction of ventricular depolarization. The limb leads are used to determine the axis. If the heart is displaced, the axis is also displaced - with hypertrophy, axis is displaced ipsilaterally - in infraction, a necrotic area of the heart does not depolarize and the unopposed vectors from the other side draw the axis away from the infarct. To obtain the limb leads, electrode are placed on the right arm, the left arm, and the left leg, forming a triangle. A bipolar limb is formed by two electrodes, and it represents one side of the triangle. Each of these limb leads consists of a pair of electrodes, one is positive and the other negative. Hexaxial System

A positive QRS deflection denotes depolarization towards the mean QRS, which is downwards and to the left. For example, if the QRS complex in lead I is negative, it denotes that the vector points to the right side. QRS axis

By eyeballing the limb leads, the tallest deflection or the degree perpendicular to the smallest deflection represents approximately the axis Vectorial Analysis

Determination of Axis Axis = 90 x QRS in AVF QRS in [ I] + QRS in [AVF] Special cases: negative QRS deflection in I Add 90 to result

Guide in Reading ECG Standardization & technique Rhythm Rate: atrial & ventricular Axis P wave morphology & duration P-R interval QRS complex morphology & duration ST segment T-wave U wave Q-T interval Hypertrophy and enlargement arrhythmias

These are the waves and important intervals that you will see in an ECG tracing: 1.) P wave – corresponding to the atrial contraction 2.) PR segment – corresponds to the pause of the conduction of depolarization from the SA node to the AV node 3.) PR interval – corresponds to the length of time the depolarization from AV node proceeds to the AV node (normally ,0.20 s) 4.) QRS complex – ventricular contraction, normally <0.12 s 5.) ST segment – is the plateau phase of the ventricular repolarization 6.) ST interval – length of ventricular repolarization 7.) T wave – rapid phase of repolarization 8.) QT interval – length of ventricular contraction 9.) u wave – usually reflects hypokalemia

P wave morphology and duration No p waves Atrial fibrillation Multiple p waves Multifocal atrial tachycardia Wandering pacemaker Notched p wave Left atrial enlargement Peaked p wave Right atrial enlargement

Guide in Reading ECG Standardization & technique Rhythm Rate: atrial & ventricular Axis P wave morphology & duration P-R interval QRS complex morphology & duration ST segment T-wave U wave Q-T interval Hypertrophy and enlargement arrhythmias

P-R Interval These are the waves and important intervals that you will see in an ECG tracing: 1.) P wave – corresponding to the atrial contraction 2.) PR segment – corresponds to the pause of the conduction of depolarization from the SA node to the AV node 3.) PR interval – corresponds to the length of time the depolarization from AV node proceeds to the AV node (normally ,0.20 s) 4.) QRS complex – ventricular contraction, normally <0.12 s 5.) ST segment – is the plateau phase of the ventricular repolarization 6.) ST interval – length of ventricular repolarization 7.) T wave – rapid phase of repolarization 8.) QT interval – length of ventricular contraction 9.) u wave – usually reflects hypokalemia

P-R interval Prolongation Shortening Hypokalemia 1st degree AV block Wolff-Parkinson White

Guide in Reading ECG Standardization & technique Rhythm Rate: atrial & ventricular Axis P wave morphology & duration P-R interval QRS complex morphology & duration ST segment T-wave U wave Q-T interval Hypertrophy and enlargement arrhythmias

QRS morphology and duration Normal looking Supraventricular origin Bizarre looking Ventricular in origin Paced rhythm

Guide in Reading ECG Standardization & technique Rhythm Rate: atrial & ventricular Axis P wave morphology & duration P-R interval QRS complex morphology & duration ST segment T-wave U wave Q-T interval Hypertrophy and enlargement arrhythmias

ST segment Elevation depression Infarction >1mm in limb leads >2 mm in chest leads depression Ischemia >1 mm in all leads from the J point

Guide in Reading ECG Standardization & technique Rhythm Rate: atrial & ventricular Axis P wave morphology & duration P-R interval QRS complex morphology & duration ST segment T-wave U wave Q-T interval Hypertrophy and enlargement arrhythmias

T and U waves T wave Shortening Hypokalemia 1st degree AV block Wolff-Parkinson White

Guide in Reading ECG Standardization & technique Rhythm Rate: atrial & ventricular Axis P wave morphology & duration P-R interval QRS complex morphology & duration ST segment T-wave U wave Q-T interval Hypertrophy and enlargement arrhythmias

Determination of QT interval Corrected QT interval = QT (actual) R-R

QT interval prolongation hypocalcemia shortening hypercalcemia

Chamber Enlargement

Atrial Enlargement (due to chronic lung disease or pulmonay embolus Since the P wave represents the depolarization and contraction of both atria, we examine the P wave for evidence of atrial enlargement.

Atrial Enlargement (commonly seen in mitral valve disease) B V1 II V1

Ventricular Enlargement

Ventricular Enlargement Right Ventricular Hypertrophy R in V1 + S in V5-V6 >11 mm R in V1 >7mm R:S in V1 >1 RAD > +90 degrees

Ischemic Heart Disease

Anatomy of Myocardial Infarction *LAD = left anterior descending aretery; LCX = left circumflex artery LM = left main artery; PDA = posterior descending artery; PL = posterolateral branches

Evolution of Infarct ST segment elevation Progressive decrease in ST segment elevation Q wave formation T wave flattening/inversion Q wave with upright T wave

Significant Q wave

RULES on Q waves Not significant in aVR Ignored in V1 unless with abnormalities in other precordial leads Ignored in III unless with abnormalities in II, AVF more reliable if with St-T segment changes Not significant if located in V1-V3 in LBBB Significant in V1-V2 in the presence of RBBB Pathologic if >= 0.04 sec and >25% of R wave amplitude

RHYTHM DISORDERS

ATRIAL Arrhythmias Atrial fibrillation Atrial flutter Wandering Pacemaker Multifocal Atrial tachycardia

ATRIAL FIBRILLATION Most common sustained arrhythmia associated with increased CV mortality and morbidity Prevalence increasing with age, doubling with each successive decade, 70% in ages 65-85 Multiplier effect on risk 3-5x stroke 3x CHF 1.5-3x death Associated with heart disease but ~30% are without underlying heart disease

ATRIAL FIBRILLATION Rapid and irregular atrial fibrillatory waves at a rate of 350 to 600/minute CRITERIA Absent P waves F waves vary in amplitude, morphology and intervals R-R intervals are irregularly irregular Ventricular rate usually ranges from 90-170 QRS complexes are narrow unless AV conduction is abnormal Hypothesized to be due to multiple wavelets in the atrium competing for the conduction to the AV node

ATRIAL FIBRILLATION

ATRIAL FLUTTER Atrial rate of 220 to 350/minute CRITERIA Absent p waves Biphasic saw-toothed flutter waves, fairly regular F waves vary in amplitude, morphology and intervals R-R intervals are irregularly irregular Ventricular rate usually ranges from 90-170 QRS complexes are narrow unless AV conduction is abnormal Hypothesized to be due to multiple wavelets in the atrium competing for the conduction to the AV node

ATRIAL FLUTTER

Escape Rhythm/Beat Atrial Junctional Ventricular Sinus arrest causing escape rhythm With p’ waves Junctional No P waves 40-60/min inherent rate Produces a series of lone QRS complexes Ventricular - may occur in complete AV block

Escape Rhythm/Beat

Sinoatrial block Complete failure of a P wave to appear A cycle appears which is twice the anticipated P-P interval Transient doubling of P-P interval SA exit block No visible P-QRST complex for more than 1 cycle Normal P wave morphology, before and after the pause Pause is preceded and followed by a normal P-P cycle P-P interval is a mutliple of the normal P-P interval

SA block

SINUS ARREST vs SINUS PAUSE

Wandering Pacemaker Impulses originate from different foci in the atrium and even AV node Sinus node may still be dominant >= 3 P wave morphologies, with varying P-R intervals, resulting in varying R-R intervals Heart rate <100 May be seen in Increased vagal tone Digitalis effect Organic heart disease

Wandering Pacemaker

Multifocal Atrial Tachycardia Irregular atrial rate > 100 P wave shows >= 3 different morphologic patterns and varying PR intervals Varying P-P and P-R intervals result in avrying R-R intervals

Multifocal Atrial Tachycardia

HEART BLOCKS 1st degree 2nd degree Complete AV block Type 1 Wenkeboch Type 2 Mobitz II Complete AV block Bundle Branch Block Right bundle branch block Left bundle branch block Hemiblocks Left anterior hemiblock Left posterior hemiblock

1st degree 2nd degree (type1 and 2) 3rd degree PR interval > 0.20s Type 1 – PR interval becomes longer until depolarization is not conducted anymore Type 2 – AV conduction is blocked 3rd degree AV dissociation Variable PR and RP intervals QRS rate is usually constant and lies within the range of 15-70 beats /min

Trifascicular Conduction System

Right Bundle Branch Block Lead V1 late intrinsicoid, M-shaped QRS (RSR pattern) Lead V6 early intrinsicoid, wide S wave Lead I wide S wave

Right Bundle Branch Block Associated with RHD Cor pulmonale/RVH Myocarditis IHD Degenerative disease of the conduction system Pulmonary embolus ASD

Right Bundle Branch Block

Left Bundle Branch Block Lead V1 QS or rS Lead V6 late intrinsicoid, no Q waves, monophasic R Lead I monophasis R, no Q wave

Left Bundle Branch Block Associated with CAD HHD Dilated cardiomyopathy -- unusual for LBBB to exist in the absence of organic disease

Left Bundle Branch Block

Left Anterior Hemiblock LAD (usually -30 to -60 degrees) Small Q in leads I and aVL, small R in II, III and aVF Usually normal QRS duration Late intrinsicoid deflection in aVL Increased QRS voltage in limb leads

Left Anterior Hemiblock Usually benign in the absence of apparent organic heart disease and not associated with block in the other fascicles Can also occur in CAD Chagas disease Infiltrative and inflammatory diseases CHDs Sclerodegenerative disorder

Left Anterior Hemiblock

Left Posterior Hemiblock RAD (usually + 120 degrees) Small R in leads I and aVL, small Q in II, III and aVF Usually normal QRS duration Late intrinsicoid deflection in aVF Increased QRS voltage in limb leads No evidence of RVH

Left Posterior Hemiblock Can occur in Cardiomyopathies Myocarditis Hyperkalemia Acute cor pulmonale chronic degeneerative and fibrotic processes of the conducting system Aretriosclerotic cardiovascular disease

Left Posterior Hemiblock

Bifascicular Block Complete LBBB RBBB with either LAHB or LPHB Duration of QRS complex is prolonged to 0.12s

Bifascicular Block

Trifascicular Block Bifascicular block associated with 1st degree AV block

Trifascicular Block

Premature Complexes Premature Atrial Complex Junctional Premature Beats Ventricular Premature Beats

Premature Complexes - PACs Premature atrial activation arising from a site other than the sinus node P wave occuring relatively early in the cardiac cyle - with a different morphology from the sinus P wave PR interval different from that during the sinus rhythm

Premature Complexes - PACs Not life-threatening by themselves But may also start a VT May be asymptomatic or cause a sensationof “skipping” or palpitations May be associated with normal conduction or aberrant conduction

Premature Complexes - PACs

Premature Complexes – Junctional Premature Beats Arise from the AV node or in the His bundle A premature normal QRS complex is closely accompanied by an “upside down” P wave

Premature Complexes – Ventricular Premature Beats Duration of more than 0.12s Bizarre morphology T wave in the opposite direction from the QRS vector A fully compensatory pause Ventricular bigeminy, trigeminy, quadrigeminy, couplet

Premature Complexes – Ventricular Premature Beats May be present in Normal individuals MVP Hypertension and LVH Chronic HD Acute MI cardiomyopathy

Poor R wave progression Low QRS Miscellaneous Poor R wave progression < 3mm R wave in V3 Low QRS < 5mm QRS amplitude in limb leads <10mm QRS amplitude in chest leads

Questions???