Download Electrocardiographic Criteria for the Diagnosis of Left Anterior

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