Conquering the ECG

7/23/2019 Conquering the ECG

1/25

NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of

Health.

Ashley EA, Niebauer J. Cardioloy E!"lained. London# $e%edica& '(().

Chapter 3Conquering the ECG

Besides the stethosco"e, the electrocardiora% *EC+ is the oldest and %ost endurin tool of

the cardioloist. A basic kno-lede of the EC+ -ill enhance the understandin of cardioloy

*not to %ention this book.

Electrocardiography

At every beat, the heart is de"olaried to trier its contraction. /his electrical activity istrans%itted throuhout the body and can be "icked u" on the skin. /his is the "rinci"le

behind the EC+. An EC+ %achine records this activity via electrodes on the skin and

dis"lays it ra"hically. An EC+ involves attachin 0( electrical cables to the body# one to

each li%b and si! across the chest.

EC+ ter%inoloy has t-o %eanins for the -ord 1lead1#

the cable used to connect an electrode to the EC+ recorder

the electrical vie- of the heart obtained fro% any one co%bination of electrodes

Carrying out an ECG

0. Ask the "atient to undress do-n to the -aist and lie do-n

'. $e%ove e!cess hair -here necessary

2. Attach li%b leads *any-here on the li%b

). Attach the chest leads *see 3iure 0 as follo-s#

o 40 and 4'# either side of the sternu% on the fourth rib *count do-n fro% the

sternal anle, the second rib insertion

o 4)# on the a"e! of the heart *feel for it

o 42# half-ay bet-een 4' and 4)

o 45 and 46# horiontally laterally fro% 4) *not u" to-ards the a!illa

5. Ask the "atient to rela!

6. 7ress record

7/23/2019 Conquering the ECG

2/25

/he standard EC+ uses 0( cables to obtain 0' electrical vie-s of the heart. /he different

vie-s reflect the anles at -hich electrodes 1look1 at the heart and the direction of the heart8s

electrical de"olariation.

Limb leads

/hree bi"olar leads and three uni"olar leads are obtained fro% three electrodes attached to the

left ar%, the riht ar%, and the left le, res"ectively. *An electrode is also attached to the riht

le, but this is an earth electrode. /he bi"olar li%b leads reflect the "otential difference

bet-een t-o of the three li%b electrodes#

lead I# riht ar%9left ar%

lead II# riht ar%9left le

lead III# left le9left ar%

/he uni"olar leads reflect the "otential difference bet-een one of the three li%b electrodes

and an esti%ate of ero "otential 9 derived fro% the re%ainin t-o li%b electrodes. /hese

leads are kno-n as au%ented leads. /he au%ented leads and their res"ective li%b

electrodes are#

aVR lead# riht ar%

aVL lead# left ar%

aVF lead# left le

Chest leads

Another si! electrodes, "laced in standard "ositions on the chest -all, ive rise to a further

si! uni"olar leads 9 the chest leads *also kno-n as "recordial leads, 40946. /he "otential

difference of a chest lead is recorded bet-een the relevant chest electrode and an esti%ate of

ero "otential 9 derived fro% the averae "otential recorded fro% the three li%b leads.

Planes of ie!

/he li%b leads look at the heart in a vertical "lane *see 3iure ', -hereas the chest leads

look at the heart in a horiontal "lane. In this -ay, a three:di%ensional electrical "icture of

the heart is built u" *see /able 0.

Performing "ogs

British physiologist Augustus D Waller of St Mary's Medical School, London, published thefirst human electrocardiogram in theBritish Medical Journalin 1888 !t "as recorded from#homas $os"ell, a technician in the laboratory, using a capillary electrometer After that,Waller used a more a%ailable sub&ect for his demonstrations his dog (immy, "ho "ould

patiently stand "ith his pa"s in glass &ars of saline

7/23/2019 Conquering the ECG

3/25

"epolari#ation of the heart

/he route that the de"olariation -ave takes across the heart is outlined in 3iure 2./he

sinoatrial node *;AN is the heart8s "ace%aker. 3ro% the ;AN, the -ave of de"olariation

s"reads across the atria to the atrioventricular node *A4N. /he i%"ulse is delayed briefly at

the A4N and atrial contraction is co%"leted.

/he -ave of de"olariation then "roceeds ra"idly to the bundle of His -here it s"lits into t-o

"ath-ays and travels alon the riht and left bundle branches. /he i%"ulse travels the lenth

of the bundles alon the interventricular se"tu% to the base of the heart, -here the bundles

divide into the 7urkin

7/23/2019 Conquering the ECG

4/25

the $ -ave reflects de"olariation of the %ain %ass of the ventricles 9hence it is the

larest -ave

the ; -ave sinifies the final de"olariation of the ventricles, at the base of the heart

&$ segment

/he ;/ se%ent, -hich is also kno-n as the ;/ interval, is the ti%e bet-een the end of the

=$; co%"le! and the start of the / -ave. It reflects the "eriod of ero "otential bet-een

ventricular de"olariation and re"olariation.

$ !ae

/ -aves re"resent ventricular re"olariation *atrial re"olariation is obscured by the lare

=$; co%"le!.

(ae direction and si#e

;ince the direction of a deflection, u"-ard or do-n-ard, is de"endent on -hether the

electrical activity is oin to-ards or a-ay fro% a lead, it differs accordin to the orientation

of the lead -ith res"ect to the heart *see 3iure 5.

/he EC+ trace reflects the net electrical activity at a iven %o%ent. Conse>uently, activity in

one direction is %asked if there is %ore activity, e, by a larer %ass, in the other direction.

3or e!a%"le, the left ventricle %uscle %ass is %uch reater than the riht, and therefore its

de"olariation accounts for the direction of the biest -ave.

Interpreting the ECG

A nor%al EC+ tracin is "rovided in 3iure 6. /he only -ay to beco%e confident at readin

EC+s is to "ractice. It is i%"ortant to be %ethodical 9 every EC+ readin should start -ith

an assess%ent of the rate, rhyth%, and a!is. /his a""roach al-ays reveals so%ethin about an

EC+, reardless of ho- unusual it is.

Rate

Identify the =$; co%"le! *this is enerally the biest -ave& count the nu%ber of lares>uares bet-een one =$; -ave and the ne!t& divide 2(( by this nu%ber to deter%ine the rate

*see /able '.

Rhythm

7 -aves are the key to deter%inin -hether a "atient is in sinus rhyth% or not. If 7 -aves are

not clearly visible in the chest leads, look for the% in the other leads. /he "resence of 7

-aves i%%ediately before every =$; co%"le! indicates sinus rhyth%. If there are no 7

-aves, note -hether the =$; co%"le!es are -ide or narro-, reular or irreular.

)o P !aes and irregular narro! %R& comple'es

7/23/2019 Conquering the ECG

5/25

/his is the hall%ark of atrial fibrillation *see 3iure ?. ;o%eti%es the baseline a""ears

1noisy1 and so%eti%es it a""ears entirely flat. Ho-ever, if there are no 7 -aves and the =$;

co%"le!es a""ear at rando%ly irreular intervals, the dianosis is atrial fibrillation.

&a!tooth P !aes

A sa-tooth -avefor% sinifies atrial flutter *see 3iure @. /he nu%ber of atrial contractions

to one ventricular contraction should be s"ecified.

*'is

/he a!is is the net direction of electrical activity durin de"olariation. It is altered by left

ventricular or riht ventricular hy"ertro"hy or by bundle branch blocks. It is a very

straihtfor-ard %easure%ent that, once it has been ras"ed, can be calculated

instantaneously#

find the =$; co%"le! in the I and a43 leads *because these look at the heart at (

and (, res"ectively

deter%ine the net "ositivity of the =$; -ave fro% each of the t-o leads by

subtractin the ; -ave heiht *the nu%ber of s%all s>uares that it crosses as it di"s

belo- the baseline 9 if it does fro% the $ -ave heiht *the nu%ber of s%all s>uares

that it crosses as it rises *see 3iure a and b

"lot out the net sies of these =$; -aves aainst each other on a vector diara% *see

3iure c. 3or the I lead, "lot net "ositives to the riht and net neatives to the left&

for the a43 lead, "lot "ositive do-n-ards and neative u"-ards

the direction of the end"oint fro% the startin "oint re"resents the a!is or "redo%inant

direction of electrical de"olariation *deter%ined "ri%arily by the %uscle %ass of the

left ventricle. It is e!"ressed as an anle and can be esti%ated >uite easily *nor%al is

(90'(

+uman Resuscitation

#he first electrical resuscitation of a human too) place *almost certainly+ in 18- #he

resuscitation of a dro"ned girl "ith electricity is described by $uillaume Ben&amin AmandDuchenne de Boulogne, a pioneering neurophysiologist, in the third edition of his te.tboo)on the medical uses of electricity Although it is sometimes described as the first artificial

pacing, the stimulation "as of the phrenic ner%e and not the myocardium

ECG abnormalities

/his section discusses the %ost i%"ortant and %ost fre>uently encountered EC+

abnor%alities.

)ormal ariations

7/23/2019 Conquering the ECG

6/25

;%all = -aves and inverted / -aves in lead III often disa""ear on dee" ins"iration.

Dccasional se"tal = -aves can be seen in other leads.

;/ elevation follo-in an ; -ave *1hih take off1 is co%%on in leads 4'94) and is

>uite nor%al. ifferentiatin this fro% "atholoical ;/ elevation can be difficult and

relies on the "atient8s history and the availability of a "revious EC+. /hese1re"olariation abnor%alities1 are %ore co%%on in the youn and in athletes.

/:-ave inversion is co%%on in Afro:Caribbean blacks.

F -aves 9 s%all e!tra -aves follo-in / -aves 9 are seen in hy"okale%ic "atients,

but can also re"resent a nor%al variant.

4entricular e!trasystoles 9 no 7 -aves, broad and abnor%al =$; co%"le!es, and /

-aves inters"ersed bet-een nor%al sinus rhyth% 9 so%eti%es occur and do not

re>uire further investiation unless they are associated -ith sy%"to%s *such asdiiness, "al"itations, e!ercise intolerance, chest "ain, shortness of breath or occur

several ti%es every %inute.

Pathological ariations

Long PR interal

A distance of %ore than five s%all s>uares fro% the start of the 7 -ave to the start of the $

-ave *or = -ave if there is one constitutes first:deree heart block *see3iure 0(. It rarely

re>uires action, but in the "resence of other abnor%alities %iht be a sin of hy"erkale%ia,

dio!in to!icity, or cardio%yo"athy.

E,G or ECG-

#here is some debate o%er e.actly "ho in%ented the electrocardiogram #he Dutch /0/*ele)tro)ardiogram+ is often used as a tribute to the !ndonesianborn physician Wilhelm

2intho%en "ho, "hile "or)ing in #he 3etherlands in 14-5, recei%ed the 3obel pri6e for /thedisco%ery of the mechanism of the electrocardiogram/ !n fact, it "as Augustus D7sir7 Waller,a physician trained in 2dinburgh, "ho presented to the students of St Mary's ospitalmedical school, London, at the introductory lecture of the 1888 academic year his

/cardiograph/, the first e%er 29$ recording in man !t "as some years later, in 14:1, thatWilhelm 2intho%en reported his string gal%anometer "ith the limb leads labeled !, !!, and!!! and the "a%es labeled ;,

7/23/2019 Conquering the ECG

7/25

Large %R& comple'es

Left ventricular hy"ertro"hy *L4H is one of the easiest and %ost useful dianoses to %ake

*see 3iure 0'. /he ;okolo-9Lyon inde! is the %ost co%%only calculated inde! of

esti%ation. oes the su% of the ; -ave in lead 40 *;40 and the $ -ave in 46 *$46 add u"

to %ore than 2.5 %4, ie, 25 s%all or seven bi s>uaresG If so, the "atient has L4H by voltaecriterion. $iht ventricular hy"ertro"hy is indicated by a do%inant $ -ave in 40 *ie, $ -ave

bier than follo-in ; -ave& ;okolo-9Lyon inde!# $ in 40 ; in 45 or 46 0.(5 %4

and riht a!is deviation.

.road %R& comple'es and strange/loo0ing ECGs

A -ide =$; co%"le! des"ite sinus rhyth% is the hall%ark of bundle branch block. Left

bundle branch block *LBBB can cause the EC+ to look e!tre%ely abnor%al *see3iure 02.

hen faced -ith such an EC+ 9 after calculatin rate, rhyth%, and a!is 9 check the -idth of

the =$; co%"le!. If it is %ore than three s%all s>uares -ide, it is abnor%al. Bundle branch

block can then be dianosed by "attern reconition of the =$; co%"le!es in the 40 and 46leads *see 3iure 0). Ne- LBBB can be dianostic of %yocardial infarction *MI.

&$ segment changes

/he ;/ se%ent e!tends fro% the end of the ; -ave to the start of the / -ave. It should be

flat or slihtly u"slo"in and level -ith the baseline. Elevation of %ore than t-o s%all

s>uares in the chest leads or one s%all s>uare in the li%b leads, co%bined -ith a

characteristic history, indicates the "ossibility of MI *see 3iure 05, "revious "ae. ;/

de"ression is dianostic of ische%ia *see3iure 06. It is -orth notin that althouh ;/

elevation can localie the lesion *e, anterior MI, inferior MI, ;/ de"ression cannot.

Concave u"-ards ;/ elevation in all 0' leads is dianostic of "ericarditis.

$ !aes

In a nor%al EC+, / -aves are u"riht in every lead e!ce"t a4$. /:-ave inversion can

re"resent current ische%ia or "revious infarction *see 3iure 0?. In co%bination -ith L4H

and ;/ de"ression, it can re"resent 1strain1. /his for% of L4H carries a "oor "ronosis.

Long %$ interal

/he =/ interval should be less than half of the $9$ interval. Calculation of the corrected =/*=/c is enerally not necessary and usually -ill have been done by the EC+ %achine *but

be-are of blindly believin any auto%ated dianostic syste%. Conditions associated -ith a

lon =/ interval are outlined in /able 2*see 3iure 0@.

Lon =/ syndro%e %ay also be dru:induced *see /able ), ". 2'. Dnce this occurs, the

res"onsible dru needs to be discontinued.

Pattern combinations

"igo'in

7/23/2019 Conquering the ECG

8/25

A reverse tick ;/ de"ression is characteristic and does not indicate to!icity. io!in to!icity

can result in dysrhyth%ia.

Pulmonary embolism

;inus tachycardia is seen in %any "atients -ith "ul%onary e%bolis%. Ne- riht bundlebranch block *$BBB or riht a!is deviation -ith 1strain1 can also indicate 7E. /he classic

;I=III/IIIis less co%%on.

+yper0alemia

/he absolute "otassiu% level is less i%"ortant than its rate of rise. EC+ chanes reflectin a

ra"id rise de%and i%%ediate action *see 3iures 09'0. /he level of daner increases as the

EC+ chanes "roress. /he se>uence enerally follo-s the order#

tall, tented / -aves *see 3iure 0

lenthenin of the 7$ interval

reduction in the 7:-ave heiht

-idenin of the =$; co%"le! *see 3iure '(

1sinus1 -ave =$; "attern *see 3iure '0

A sinus:-ave =$; should be treated i%%ediately -ith calciu% chloride, -hilst hy"erkale%ia

associated -ith lesser EC+ chanes can be treated -ith insulinlucose infusion.

P%R&$-

3obody )no"s for sure "hy these letters became standard 9ertainly, mathematicians used tostart lettering systems from the middle of the alphabet to a%oid confusion "ith the freuentlyused letters at the beginning 2intho%en used the letters C to to mar) the timeline on his

29$ diagrams and, of course, ; is the letter that follo"s C !f the image of the ;

7/23/2019 Conquering the ECG

9/25

Figures

Figure 1

;tandard attach%ent sites for chest leads.

7/23/2019 Conquering the ECG

10/25

Figure 2

/he li%b leads lookin at the heart in a vertical "lane.

Figure 3

7/23/2019 Conquering the ECG

11/25

/he cardiac de"olariation route. A4N# atrioventricular node& ;AN# sinoatrial node.

$e"roduced -ith "er%ission fro% B ;aunders *+uyton A, Hall J. #e.tboo) of Medical;hysiology. 7hiladel"hia# B ;aunders, 06.

Figure

/he basic "attern of electrical activity across the heart.

7/23/2019 Conquering the ECG

12/25

Figure 4

*a A horiontal section throuh the chest sho-in the orientation of the chest leads -ith

res"ect to the cha%bers of the heart. *b In lead 40, de"olariation of the interventricular

se"tu% occurs to-ards the lead, thus creatin an u"-ard deflection *$ -ave on the EC+. It

is follo-ed by de"olariation of the %ain %ass of the L4, -hich occurs a-ay fro% the lead,

thus creatin a do-n-ard deflection *; -ave. /his "attern is reversed for lead 46,

e!"lainin the different sha"es of the =$; co%"le!. /his "attern should be checked in every

EC+. LA# left atriu%& L4# left ventricle& $A# riht atriu%& $4# riht ventricle.

7/23/2019 Conquering the ECG

13/25

Figure 5

E!a%"le of a nor%al EC+.

Figure 6

EC+ de%onstratin atrial fibrillation.

7/23/2019 Conquering the ECG

14/25

Figure 7

EC+ de%onstratin atrial flutter 9 note the characteristic sa-tooth -avefor%.

Figure 8

4ector diara% to deter%ine the =$; a!is.

Figure 19

EC+ de%onstratin first:deree heart block.

7/23/2019 Conquering the ECG

15/25

Figure 11

EC+ de%onstratin abnor%al = -aves in 4094). /his is indicative of a "revious infarction.

Figure 12

EC+ de%onstratin left ventricular hy"ertro"hy. Note also the /:-ave inversion in leads 4)9

46. /his is often labeled 1strain1.

7/23/2019 Conquering the ECG

16/25

Figure 13

EC+ de%onstratin left bundle branch block.

Figure 1

/he sha"es of 40 and 46 =$; co%"le!es in left and riht bundle branch block.

7/23/2019 Conquering the ECG

17/25

Figure 14

EC+ de%onstratin anterose"tal %yocardial infarction. Note the ;/:se%ent elevation.

Figure 15

EC+ de%onstratin ;/:se%ent de"ression *I, 42946.

7/23/2019 Conquering the ECG

18/25

Figure 16

EC+ de%onstratin /:-ave inversion.

7/23/2019 Conquering the ECG

19/25

Figure 17

EC+ de%onstratin a lon =/ interval.

7/23/2019 Conquering the ECG

20/25

Figure 18

Hy"erkale%ia. Note the tall, tented / -aves.

7/23/2019 Conquering the ECG

21/25

Figure 29

EC+ de%onstratin a -idenin of the =$; co%"le!.

Figure 21

EC+ de%onstratin a sinus:-ave =$; "attern.

$ables

$able 1ECG leads and their respectie ie!s of the heart

7/23/2019 Conquering the ECG

22/25

Vie! Lead

Inferior II, III, a43

Anterior I, a4L, 40942

;e"tal 42, 4)

Lateral 4)946

$able 2&ome common heart rates as determined by analysis of the %R&

comple'

)umber of large squares bet!een %R& comple'es +eart rate :bpm;

5 6(

) ?5

2 0((

' 05(

$able 3Causes of a long %$ interal

Congenital *cquired

Jervell and Lane9Nielsen syndro%e A%iodarone, sotalol

$o%ano9ard syndro%e 3lecainide

Hy"ocalce%ia

Hy"okale%ia

Hy"o%anese%ia

7henothiaines

/ricyclic antide"ressants

$able "rug/induced increase in the %$ interal and torsade de pointes

Generic name

%$

interal

$orsade de

pointes Generic name

%$

interal

$orsade de

pointes

*ntiarrhythmics &electie serotonin re/upta0e inhibitors

A

7/23/2019 Conquering the ECG

23/25

Generic name

%$

interal

$orsade de

pointes Generic name

%$

interal

$orsade de

pointes

Lithiu%

Clinda%ycin

Naratri"tan

Erythro%ycin

;u%atri"tan

$o!ithro%ycin

;"ira%ycin 4enlafa!ine

*ntibiotics :quinolones; ol%itri"tan

+atiflo!acin *nti/Par0inson=s

+re"aflo!acina

A%antadine

Levoflo!acin

Budi"inec

Mo!iflo!acin

;"arflo!acin *ntimalarials

uine

Halofantrine

/ri%etho"ri%:

sulfa%etho!aole

Meflo>uine

*ntihistamines

Aste%iolea "iuretics

Cle%astine Inda"a%ide

i"henhydra%ine

Hydro!yine Lipid/lo!ering agents

/erfenadine 7robucol

*ntidepressants

>otility enhancers

A%itri"tyline

Cisa"ridea

Clo%i"ra%ine

esi"ra%ine )ootropic geriatrics

o!e"ine 4inca%ine

I%i"ra%ine

Chemotherapeutics

Ma"rotiline

/a%o!ifen

)euroleptics

7enta%idine

7/23/2019 Conquering the ECG

24/25

Generic name

%$

interal

$orsade de

pointes Generic name

%$

interal

$orsade de

pointes

A%isul"ride

Cloa"ine Immunosuppressants

Chlor"ro%aine

/acroli%us

ro"eridola

3lu"henaine Peptides

Halo"eridol

Dctreotide

Mel"erone

Dlana"ine Virostatics

7i%oide 3oscarnet

=uetia"ine

>uscle rela'ants;ul"iride

/hioridaine /ianidine

$is"eridone

?/ray contrast agents

;ertindoleb

/ia"ride Io!alate

%elu%ine

/raodone

A "roloned =/ interval can occur or torsade de "ointes -as observed

a

/aken off the %arket.

b

;us"ended fro% the %arket, final decision by the reulatory authorities still a-aited.

c

Indication li%itations have been e!"ressed.

I%"ortant ti"s on the use of the table# infor%ation is based on the latest scientific

kno-lede as far as it is enerally available fro% "ublished studies *Medline

research, case re"orts, internet "ublications, s"ecialist infor%ation, the $ed List, and

infor%ation fro% the reulatory authorities. In the case re"orts available about torsade

de "ointes, the causal relationshi" to the inestion of the "articular %edication is no

loner a""arent& "ure coincidence cannot be e!cluded in individual cases.

Co"yrihtO '((), $e%edica.

Bookshelf I# NBK''0)

7/23/2019 Conquering the ECG

25/25