150 Practice ECGs Interpretation and Review 3ed

150 Practice ECGs: Interpretation and Review Third Edition 'EORGE*4AYLOR -$ 0ROFESSOROF-EDICINE 4HE-EDICAL5NIVERSITYOF3OUTH#AROLINA 4HE2ALPH(*OHNSON6!-EDICAL#ENTER #HARLESTON 3OUTH#AROLINA 53! 150 Practice ECGs: Interpretation and Review Third Edition 0ART)(OWTO)NTERPRET%#'S #HAPTER"ASELINE$ATA #HAPTER-ORPHOLOGIC#HANGESIN0 123 34 AND4 0ART))0RACTICE%#'S 0ART))))NTERPRETATIONAND#OMMENTS For Marilyn PEAKED0WAVESININFERIORLEADSATLEASTMMINONE OFTHELEADS  left ventricular activation—are thus unchanged What is different is an extra deflection at the end of the QRS caused by late, right ventricular depolarization I will restate this with reference to specific changes on the ECG But first, recall a basic principle of electrocardiography regarding the polarity of leads Each lead has spatial orientation and polarity (see Fig 1.2) A wave of depolarization that moves toward the positive pole of a lead produces a positive (upright) deflection, an R wave If the wave of depolarization moves away from the positive and toward the negative pole of a lead, it still is detected, but it produces a negative (downward) deflection, an S wave Back to RBBB (see Fig 2.3): Lead V1, on the right side of the chest, sits just over the right ventricle (RV) and is a sensitive detector of right ventricular events In RBBB, lead V1 first records normal septal activation, a positive deflection, or R wave, because the septum depolarizes from left to right The left ventricle (LV) is activated normally, and in lead V1 this produces a negative deflection, or S wave, as the wave of depolarization moves posteriorly and to the left Finally, current works its way from the LV to the RV—remember, it could not get there directly because of the blocked right bundle The vector of RV depolarization is aimed at V1; thus, the terminal deflection in V1 is positive (upright), another R wave RBBB thus produces an RSRb pattern in V1 In other leads, terminal forces (the RV vector) also are oriented toward the right Thus, terminal QRS forces in the left-side leads, such as I, aVL, and V6, would be negative (an S wave) RBBB diagnosis: RSR’ pattern in V1, and QRS s 0.12 second  0RACTICE%#'S)NTERPRETATIONAND2EVIEW &)'52% 2IGHTBUNDLEBRANCHBLOCK2""" &OLLOWTHESEQUENCEOFVENTRICULARACTIVATION ANDITS EFFECTONLEADS)AND6 WHICH INTHEFIGURE AREAPPROPRIATELYPOSITIONED 4HEREISNORMALSEPTAL ACTIVATIONFROMLEFTTORIGHT ,EFTVENTRICULARACTIVATIONISNORMAL "ECAUSETHERIGHTBUNDLE BRANCHISBLOCKED CURRENTMUSTMOVEFROMTHELEFTVENTRICLETOTHERIGHT ANDTHISOCCURSLATE4HETAILEND OFTHE123ISSLURREDBECAUSEOFLATEDEPOLARIZATIONOFTHERIGHTSIDE0ATTERNRECOGNITION232IN6 WIDE 123 #(!04%2-ORPHOLOGIC#HANGESIN0 123 34 AND4  Incomplete Right Bundle Branch Block Incomplete right bundle branch block (IRBBB) is usually a normal variant, but in some cases it reflects RV hypertrophy or dilatation Our ECG computer program interprets it as “RV volume overload.” IRBBB is a common, almost invariable, finding with atrial septal defect (ASD), in which the RV may pump two or three times as much blood as the LV ASD may cause no symptoms until a person reaches age 50 Thus, the diagnosis of ASD may be suggested by a routine ECG in an otherwise healthy young adult IRBBB diagnosis: RSR’ pattern in V1, and QRS duration  0.12 second #,).)#!,).3)'(4 When I ask students how to exclude atrial septal defect (ASD) in a young person with incomplete right bundle branch block (IRBBB), the usual answer is an echocardiogram However, ASD is a rare finding in people with IRBBB, so you would order many normal echocardiograms before finding an ASD A more reasonable approach would be a physical exam looking for fixed splitting of the second heart sound It is not a subtle finding, and its absence excludes ASD If there is uncertainty a relatively inexpensive chest x-ray can also exclude the diagnosis; the radiologist easily recognizes pulmonary plethora Finally, the more expensive echocardiogram is indicated if these screening studies are abnormal ASD is a common congenital heart abnormality, and for this reason it is commonly encountered on board exams If you suspect ASD expect to see IRBBB on the ECG Without it the diagnosis is unlikely Left Bundle Branch Block (LBBB) In LBBB, the sequence of ventricular activation is almost the opposite of that described with RBBB The left bundle innervates the interventricular septum, so initial septal depolarization, normally from left to right, is lost (Fig 2.4) The initial small negative deflection in left-side leads (I, aVL, V6) is lost—the so-called septal Q wave The septum is instead activated from right to left, causing an initial positive deflection in left-side leads Because the right ventricle is thin walled, little current is produced by RV excitation Septal and early left ventricular activation predominate, and current generated by RV discharge (which would be oriented anterior and to the right) is buried within the LV complex LV activation is slow because of the blocked left bundle, and the QRS complex is wide The terminal forces are aimed at the blocked side, to the left; therefore, the terminal portion of the QRS is positive in left-side leads such as I, aVL, and V6 (see Fig 2.4)  0RACTICE%#'S)NTERPRETATIONAND2EVIEW &)'52% ,EFTBUNDLEBRANCHBLOCK,""" &OLLOWTHESEQUENCEOFVENTRICULARACTIVATION 4HENOR MALLEFT TO RIGHTDEPOLARIZATIONOFTHESEPTUMISINTERRUPTEDBYTHEBLOCKEDLEFTBUNDLEBRANCH4HESEPTUM ISACTIVATEDFROMRIGHTTOLEFT !CTIVATIONOFTHETHIN WALLEDRIGHTVENTRICLEPRODUCESLITTLECURRENT 4HELEFTVENTRICLEISDEPOLARIZEDLATEBYCURRENTWORKINGITSWAYOVERFROMTHERIGHTSIDE ANDTERMINAL123 FORCESAREORIENTEDTOWARDTHELEFT 0ATTERNRECOGNITIONBROADPOSITIVECOMPLEX°OFTENNOTCHED°INLEFT SIDELEADS) ... #HARLESTON3OUTH#AROLINA53! 150 Practice ECGs: Interpretation and Review Third Edition 0ART)(OWTO)NTERPRET%#'S #HAPTER"ASELINE$ATA #HAPTER-ORPHOLOGIC#HANGESIN012334 AND 4 0ART))0RACTICE%#'S... #HAPTER-ORPHOLOGIC#HANGESIN012334 AND 4 0ART))0RACTICE%#'S 0ART))))NTERPRETATION AND #OMMENTS For Marilyn 150 Practice ECGs: Interpretation and Review Third Edition 'EORGE*4AYLOR-$ 0ROFESSOROF-EDICINE... 2006 Library of Congress Cataloging-in-Publication Data Taylor, George Jesse 150 practice ECGs : interpretation and review / George J Taylor.—3rd ed p ; cm Includes index ISBN-13: 978-1-4051-0483-8