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Electrocardiographic Criteria for the Diagnosis of Left Anterior Fascicular Block* Left Axis Deviation and Delayed lntraventricular Conduction Simdn Horrcita, hl.D.;OO Ettlo Lupi H., M.D.;? loseplz Hayes, A1.D.;; William Frishmun, h1.D.;: A.1anual Cardenas, M.D., F.C.C.P.,? and Thomas Killip, M.D.§ The two current criteria for diagnosis of left anterior fascicular block (LAFB) were evaluated; they are marked left axis deviation (LAD) and a delay in the time of inscription of the intrinsicoid deflection (ID) in lead aVL asynchronous to Vn. From 400 electrocardiograms with a L A D of -30" or greater, 6 2 percent showed asynchronous activation of the left ventricle. There was only a general relationship between the degree of L A D and delayed I D in aVL. The incidence of delayed I D in aVL was as fouows: 2 percent with mean frontal QRS axis at 0"; 9 percent at -15"; 41 percent at -30"; 6 9 percent at -45"; 8 2 percent at -60'; and 100 percent at -75" or greater. The lack of correlation between both criteria in many instances questions their validity. The L A D alone should not be considered synonymous with LAFB. Recognition of delayed inscription of the I D in aVL is a useful supplemental criterion for diagnosis. n recent years the left bundle branch has been Medrano and c o - ~ o r k e r s ~ . ~have ~ " ~ 'described ~ both clinically and experimentally a delay in the time of inscription of the intrinsicoid deflection ( I D ) in lead aVL due to a regional delay in the high lateral left ventricular activation as a consistent finding in block of the anterior superior division. More recently, Gallagher et all%ave reported a regional delay in high lateral left ventricular activation due to experimental interruption of the left anterior fascicle. This study was undertaken to determine whether there is a cvrrelation between L A D and possible regional delay in intraventricular conduction, represented by a delay of the ID in aVL as compared to Vs determined from the standard clinical ECG. We examined specifically the time of inscription of the ID in lead aVL and its relationship to the mean frontal QRS axis ( A Q R S )in paticmts with and without LAD. I viewed as having two major divisions, anterior and posterior.' The concept of selective block of the subdivisions of the left bundle, the so-called fascicular blocks or hemiblocks, has been advanced to explain deviations in the frontal plane QRS axis.'-' Rosenbaum and co-workersl~*have considered left anterior hemiblock or left anterior fascicular block ( LAFB ) to be present in those instances when left axis deviation (LAD) occurs on a standard electrocardiogram. However, there has not been agreement on the degree of axis deviation necessary to Although LAD is generally make the diagn~sis.'-~ considered to be due to block in the left anterior fascicle, other ventricular alterations can produce this shift of QRS axis.6-lo 'From the De artment of Medicine, Division of Cardiolo , the New ~ o r ~ospital-Cornell f 5ledical Center, Ke\v YO% and the Instituto Sacional de Cardiologia de hi6xico: hlexico Citv. Supported'in part by National Institutes of Health contract PH 43-67-1439. "'This \r,ork \\,as ~erformed\vhile Dr. Honvih \vas a fellow in cardiolon). at the Ke\v York Hospital-Cornell \ledical Center and a recipient of a scholarship of tlie National Council of Science and Technology of hlexico. l i e is prescently at the Instituto Nacional de Cardiologia de llbxico, Mexico City. tInstituto Nacional de Cardiologia de SICxico, IIexico Cit).. :Sew York Hospital-Cornell hledical Center, New York. §Currently Cliaimran, Deparhnent of Medicine, Evanston Hospital, Evanston, Ill. Manuscript received September 16; revision accepted January 21. Reprint requests: Dr. Homitz, Instituto Nacional de Cardiologia, Ao Cuauhtemoc 300, Mexico D.F.7, Mexico CHEST, 68: 3, SEPTEMBER, 1975 Tli? AQRS \\,as calculated to tlre nearest 15" in tlie 12lead standard ECG of 6,303 cnnsecutive patients in a general hospital adult popr~lation.In 500 tracings, an axis deviation of -30" or greater \\,asol)sen,ed. Those having otlier kno\vn electroc:~rdiograpl~iccauses for LAD, sr~clias diapllragmatic ~nyocardial infarction (DXII) or left I)r~ndle-l)ranclil)lnck ( L B H R ) , \vercB rliminated. Tracings with, criteria for left ventric~~lar hypertrophy (LVII)'.' were eliminattrl, r~nless the onset of the ID in aVL was delayed at least 10 msec or more than in Vc;. The remaining ECGs were separated into to the AQRS: -00"; -45"; the follo\ring grorlps acc~~rtling -60"; and -75O. Two separate groups of 100 consecutive DIAGNOSIS OF LEFT ANTERIOR FASCICULAR BLOCK 317 Downloaded From: http://journal.publications.chestnet.org/pdfaccess.ashx?url=/data/journals/chest/20970/ on 05/06/2017 Table 1-Left Axis Deviation and Delayed Intrcmentricular Conduction .$QRs 30.of Cases 0" - 15" - 30" -4 5 O - 60" - 75" Total 100 100 160 158 11 38 Delayed I D in aVL 573 - - 600 2 9 66 109 2 9 36 38 260 100 -13 ECGs chtsen at rand0111 were reviewed with AQRS between 0' and -15'. In all tracings the time of inscription of the I D was measrlretl in lead a\'L and in V~I;measuren~entswere made from the onset of the QRS to the beginning of the downstroke of the R wave.'" regional delay in the inscription of the ID \vas considered present when it measured 50 msec or more in a\'L and was greater than 10 msec in aVL when compared to lead \'(I, thus suggesting a possible asynchrono~aactivation of the left ventricle. The reliability and reproductivity of measurements were ascertained by the analysis of 100 randornized ECGs in "l>lind" fashion on three different occasions; 93 percent of measurements were accurate within 10 rnsec. The AQRS and synchronous intraventricular time of conduction were then compared. Those ECGs with right I~undle-branchblock (RBBB) and LAD were analyzed as a s e ~ a r a t es u b e r o u ~ .~ l ECGs l were recorded with a threechannel automatic electrocardiograph (Marquette 3000) at 25 mm/sec and a freq~lencyresponse from flat at direct current to 100 hertz down -3 dB at 120 Hz. L. A Left axis deviation of -30" or greater was obsewed in 500 of 6,303 ECGs (7.9 percent). One hundred cases were eliminated, because they had other abnormalities that might result in LAD. This FIGURE1. Relationship between AQRS and signs of regional delay in left ventricular conduction. The greater the LAD, the more likely is I D in lead aVL delayed. AVL FIGURE 2 . Left axis deviation and delayed ID. Inscription of I D in lead aVL is prolonged to 70 msec but lneasures 50 msec in Va. This asynchrony suggests regional delay in high lateral left ventricular activation. The ECG meets both criteria for of LAFB. 20 patients with LBBB, 66 with group DMI, and 14 with LVH. There were five other instances in which LVH was suspected by voltage criteria; but, because of an asynchronous delay of the ID between aVL and Vs, they were included in the study. Of the remaining 400 ECGs, 249 (62 percent) showed a delay in the ID in aVL that was not detected in V6 ("regional delay"). The separation of groups according to the degree of LAD is shown in Table 1. The relationship between AQRS and the onset of the I D in aVL is shown in Figure 1. Examples of the different forms of the ECG are shown in Figures 2 to 5. Right bundle-branch block was associated with LAD in 35 cases. In every instance there was delayed onset of the ID in aVL. In contrast, not one of 20 ECGs with RBBB but without LAD had a 'delayed onset of I D in aVL. There are two suggested criteria for the diagnosis of LAFB. Rosenbaum and associates's2 proposed that a LAD of -45" or more may represent a hemiblock. This degree of LAD is usually accompanied by a Q I S ~pattern. However, Rosenbaum et a12 have also accepted a diagnosis of LAFB with a progressive leftward shift of the AQRS from a previously normal axis to minor degrees ( less than - 45" ) of LAD. They suggest that these changes represent an incomplete form of hemiblock and that differentiation from normal variants is possible because of the availability of serial ECGs. 318 HORWITZ ET A 1 Downloaded From: http://journal.publications.chestnet.org/pdfaccess.ashx?url=/data/journals/chest/20970/ on 05/06/2017 CHEST, 68: 3, SEPTEMBER, 1975 AVL FIGURE 3. Electrocardiogram similar to that in Figure 2 but with shorter inkrvals. Time of inscription of ID in aVL is prolonged to 50 msec, a value greater than measurement in Vs of 35 msec. Medrano and co-~orkers,~,~.ll.l* after experimental studies in dogs, suggested that more specific criteria should be used. They believe that a delay in the inscription of the ID in lead aVL not present in lead V6 is a consistent finding in LAFB. These authors observed that, after the interruption of the anterior superior division of the LBBB, the activation process was delayed 20 to 30 msec in the upper third of the left septa1 mass and in high anterolateral regions of the left free ventricular wall." The delay was recognized by a prolongation of the intrinsic deflection time in direct epicardial leads, reaching 50 to 55 msec in high lateral recordings. These delayed forces are represented in the dog by a vector pointing upward and leftward in the vertical heart and upward and to the right in the horizontal heart. This explains the deep S waves in leads 2, 3, and aVF with slight LAD in vertical hearts. In the experimental dog with a horizontal heart, the R wave increases in voltage with a delay of the ID in leads 1and aVL.4.5 Activation studies following experimental posterior fascicular block in the dog revealed a consistent area of delay of 5 to 25 msec in epicardial surface maps that is confined to the lateral basal surface of the left ventricle. Transmural activation the same area revealed a 10 to 20-msec delay in the Purkinje and endocardia1 activation.13 Most investigators agree that a LAFB will result in a 5- to 20-msec increase in the QRS duration in some leads of a standard ECG.1,4.5~11,12 Because the delay is regional, an asynchronous activation of the left ventricle occurs that may be recognized in the standard ECG. The inscription of the ID in lead CHEST, 68: 3, SEPTEMBER, 1975 aVL, the "exploring l e a d over the affected high lateral ventricular wall, is delayed 10 msec or more when compared to the ID in lead Vs, which explores the low free ventricular walL5 The present study was designed to evaluate the two suggested criteria, degree of LAD and regional prolongation of the QRS complex, for the diagnosis of LAFB. We found the two criteria satisfied in only 62 percent of cases with LAD of -30" or more. Thus, 38 percent considered LAFB by an axis criteria did not have a delayed ID. In contrast, 2 percent of cases with 0 axis and 9 percent with -15" axis had a significantly delayed ID in aVL compared to Vs but would not be recognized as possible instances of LAFB if the axis criterion alone was utilized. The association between a regional delay in intraventricular conduction and extent of LAD suggests that there is an incomplete but direct relationship between both. The greater the leftward shift, the greater the possibility of a delayed ID in aVL (Fig 1). With an axis of -75" or greater, a regional QRS-ID delay was invariable. A significant number of tracings with marked LAD did not have a "regional delay" in conduction. If both regional delay and LAD are necessary to establish LAFB, some other explanation for the LAD must be sought in these cases. There is no clear evidence to determine whether LAFB is or is not present in these tracings. Some could be explained by an electrical horizontal heart, obesity, or masked inferior myocardial infarction with an rS pattern in leads 2, 3, and aVF making diagnosis difficult by standard ECG. It is possible also that regional delay might not be manifest in aVL. Thus, in extreme horizontal hearts with LAFB, the delayed forces may be displaced rightward, so that the delay in the I IL FIGURE 4. Left axis deviation with normal inscription time (40 msec) of the ID in aVL. There is no evidence of regional delay of activation. OlAGNOSlS OF LEFT ANTERIOR FASCICULAR BLOCK 319 Downloaded From: http://journal.publications.chestnet.org/pdfaccess.ashx?url=/data/journals/chest/20970/ on 05/06/2017 REFERENCES V6 AVL / ! I , I / I I I I FI(:URE5. Left axis deviation due to DSII. The ID in aVL is of nonnal duration (40 rnsec), suggesting that activation of high lateral \\.all of left ventricle is norn~al. ID may not be recognized in aVL but is present in aVRS5 The value of the criteria suggested by Medrano et a l V s revealed by analysis of the data in patients with LAD and RBBB. All 35 cases with RBBB and L.4D had delayed regional left ventricular activation. Hegional delay was not seen in RBBB without L.4D. If, in some cases an LAD less than -45' may represent LAFB, whereas in other instances an LAD of more than -45" may not, we are faced with the problem of applying simple and conventional recognition criteria (left axis) that are neither sensitive nor specific. If the criteria suggested by Medrano et a1 arc accepted as valid, it must be shown that they arc. spwific. LAFB can be diagnosed utilizing these criteria in the presence of LVH, a condition that can produce LAD and a delay of the ID by itself but not in an asynchronous manner.I4 Certainly LAD cannot bc considered alone as an absolute criterion for the diagnosis, since many causes are known. It is not appropriate at the present time to consider LAD and LAFB synonymous. In our present state of knowledge, it seems reasonable to suggest a diagnosis of LAFB only when both an abnormal degree of left axis and a delay of conduction in the region of the affected fascicle can be detected. It should be recognized that the validity of'the proposed criteria has not yet been demonstrated in the human heart. 1 Rosenl)ar~m SIB, Elizari kI\', Lazzari JO: The Hemi1)locks: Sen. Concepts of Intraventricular Contlr~ction Based on Hunlan .4natomical, Physiological and Clinical Studies. Oldsmar, Fla, Tampa Tracings, 1970 2 Rosenl)alim IlB, Elizari >I\', Lazzari JO, et al: The differential electrocardiograpllic manifestations of hemiI)locks, I~ilateral I~rlndleI~ranch /)lock, and trifascicrllar blocks. In Advances in Electrocardiograpl~y(Schlant HC, Hurst WJ, eds). New York, Grune & Stratton, 1972, pp 145-182 3 Pryor R, Blunt G: The clinical significance of t n ~ eleft axis deviation: Left intraventricular blocks. Am Heart J 72: 391-113, 1966 4 Sledrano G.4, Brenes PC, de Slicheli .4, et al: El bloqueo de la sul~division anterior de la rama izquierda s61o o asociaclo al I~loqr~eo de la rama derecha: Estudio clinico, electro y vectorcardiogrBfico. Arch Inst Cardiol \1ex 393672-677, 1969 5 kfedrano GA, Brenes PC, de \licheli A, et al: Clinical and electxocardiographic diagnosis of the left anterior subdivision block isolated or associated \\.it11 RBBB. An1 Heart J 83:447458, 1972 6 Corne RA, Parkin TW, Brandenllurg RO, et d : Significance of marked left avis deviation: Electrocardiographic pathologic correlative study. .Am J Cardiol 15:60.5-610, 1% 7 Curd GW, Hichs VlI, Gyokey I?: Slarked left axis deviation: Indication of cardiac al,nc>nnality. Am Heart J &2:462-469, 1961 8 Banta D, Greenfield JC, Estes EH: Left axis de\riation. An1 J Cardiol 14:330-338, 1964 9 Grant RP: Left axis deviation. Circulation 14:233-240, 1956 10 Ostrander LD: Left axis deviation: Prevalence, associated conditions, and prognosis. Ann Intern bled 75:23-28, 1971 11 Xfedrano GA, de klicheli .4, Cisneros F, et al: The anterior subdivision block of the left I)r~ndle1)ranch of His: I. The ventricular activation process. J Electrocardiol 3:i-11, 1970 12 Xledrano GA, Cisneros F, de \licheli A, et al: The anterior subdi\rision block of the left 1)rlndle I)ranch of His: 11. Experinlentd vectocardiographic ol,servations. J Electrcoardiol 3: 13-19, 1970 13 Gallagher JJ, Tixzon AR, Kasell J : Activation studies following experimental 1iemil)lock in the dog. Circulation 48 ( sr1ppl4):62, 1973 14 Sodi-Pallares D, Xledrano G: Deductive and Polyparan~etric Electrocardiography. blexico City, Institr~toXacional de Cardiologia de hlCxico, 1970, pp 68-73 15 Sodi-Pallares D: Ne\v Bases of Electrocardiography. St. Louis, CV Slosby Co, 1956, p 231 CHEST, 68: 3, SEPTEMBER, 1975 Downloaded From: http://journal.publications.chestnet.org/pdfaccess.ashx?url=/data/journals/chest/20970/ on 05/06/2017