This document provides an overview of interpreting electrocardiograms (ECGs). It begins with the cardiac anatomy and conduction system. It then outlines a 6-step approach to ECG interpretation: 1) rate, 2) rhythm, 3) P-wave, 4) PR interval, 5) QRS complex, and 6) ST segment and T wave. Key aspects of normal and abnormal findings are defined for each step. Common conditions are discussed like sinus bradycardia, sinus tachycardia, atrial fibrillation, bundle branch blocks, myocardial infarction, and Wolff-Parkinson-White syndrome. The document emphasizes interpreting ECGs systematically and identifying both normal and abnormal tracings.

1. MODULE2
Interpreting E C G rhythm STRIPS

2. Objectives
• Utilize asystematic process whenapproaching the
interpretation of theECG.
• Identify normal and abnormal components on the ECG.

3. ECG
interpretation

4. Cardiac Anatomy
▪ 2upper chambers
▪ Right and left atria
▪ 2lower chambers
▪ Right and left ventricle
▪ 2Atrioventricular valves
(Mitral &Tricuspid)
▪ Open with ventriculardiastole
▪ Closewith ventricularsystole
▪ 2Semilunar Valves(Aortic &Pulmonic)
▪ Open with ventricularsystole
▪ Open with ventriculardiastole

5. Anatomy
Coronary Arteries

6. ▪ 2major vessels of thecoronary circulation
▪ Left main coronaryartery
▪ Left anterior descending and circumflexbranches
▪ Right main coronaryartery
▪ Left and right coronary arteries originate at the base of the aorta
from openings called the coronary ostia behind the aortic valve
leaflets.
Anatomy Coronary Arteries

7. Normal Conduction System
Sinoatrial node
Internodalpathway
A
Vnode
Bundle of His
BundleBranches
Purkinjefibers

8. Pacemakers of the Heart
• SA Node -Dominant pacemakerwith an intrinsic rate of
60 -100beats/minute.
• AVNode -Back-up pacemaker with an intrinsic rate of
40 -60 beats/minute.
• Ventricular cells-Back-up pacemaker with an intrinsic rate
of 20 -45bpm.

9. ECGs?

10. Basic E C G Interpretation
STANDARD CALLIBRATION
Speed = 25mm/s
Amplitude = 0.1mV/mm
• 1large square: 0.2s(200ms)
1small square: 0.04s(40ms)
• 1mV:10mm high
• 0.1mV amplitude

11. OBTAINA NECG,ACT CONFIDENT,READ THE PT DETAILS

12. OBTAINA NECG,ACT CONFIDENT,READ THE PT DETAILS
• Some ECGmachines come with interpretation software.
• Thisone says the patient is fine. DONOTtotally trust this software.

13. ECGLIMB LEADREVERSAL
• LeadI or aVLis completely inverted (P wave, QRScomplex andTwave).
• Lead aVRoften becomespositive.
• The P-wave is unexpectedly larger in lead I than lead II (it is usually the other way around).

14. The best way to interpret an EC G is
to do it step-by-step
Step 1:Rate
Step 2:Rhythm +Regularity
Step 3:P-wave
Step 4: PR-interval
Step 5:QRSComplex
Step 6: STSegment andTwaves
Step 7:QTinterval (Include TandU wave)
Step 8 :CardiacAxis
Step 9: Other ECGsigns

15. THE NORMAL SIZE
<3small square
<3-5 small square
<2large square
<2small square

16. PQRSTConfiguration
One completecardiac cycle =P
,Q, R, S, (QRS
complex), and Twave
P wave First deflectionRounded
and upright in lead II
Amplitude: 0.5-2.5mn
Duration: 0.10s
Atrial depolarization
PR Interval Beginning of Pwaveto
beginning of QRS
complex
Duration: 0.12s-0.2s
Atrial depolarization +conductiondelay
through AVjunction (AVN+ Bundle ofHis)
QRS Complex Beginning of Qwaveto
the end of Swave
Duration: 0.06-0.12s
Ventricular depolarization
ST Segment Between Swave tothe
beginning of Twave
Normal STsegmentis
flat (isoelectric)
Isoelectric, ventricle stilldepolarized
QT Interval Beginning of QRS
complex to the end of T
wave
Duration: ½of the
distance of RRinterval
Ventricular depolarization +repolarization
Mechanical contraction of ventricle
T Wave End of STsegmentto
the end ofTwave
Rounded and
asymmetrical
Upright in lead II
Amplitude: <5mm
Ventricular repolarization

17. 6-STEPSAPPROACHFORECGRECOGNITION
STEP1–
HEARTRA
TE
Bpmcalculation=ventricularrate
 6smethod:countRwaveswithin6sstripmultiplyby10
 300method:300/nolargesquaresbetweenQRS
 Normal:60-100bpm
 Bradycardia:<60bpm
 Tachycardia:>100
STEP2–
HEARTRHYTHM
IntervalsbetweenRwaves(measurefromRtoR)
 Regularorirregular?
 AretherhythmSINUS?
 Regular: Intervalconsistent
 Irregular: Irregularpattern
 Sinus rhythm: P-QRS-T
STEP3–
PWAVE
LookatthePwaves
 ArePwavespresent?
 ArePwavesoccurringregularly?
 IsthereonePwavepresentforeveryQRScomplex
present?
 ArethePwavessmooth,rounded,anduprightin
appearance,oraretheyinverted?
 5.DoallPwaveslooksimilar?
 Every1PforeachQRScomplex
 More than 1Pwave indicates AVblock
 None: rhythm isjunctional/ventricular
STEP4 –
PRINTERVAL
Onset of Pwave to onset of QRScomplex
Normal=0.12–0.20seconds(3-5smallsquares)
 ArethePRintervalsgreaterthan0.20seconds?
 ArethePRintervalslessthan0.12seconds?
 3.ArethePRintervalsconsistentacrosstheECGstrip?
 PRIshorter:presenceof accessorypathwaysthat
bypassedtheAVN
 PRIlonger: AVblock
STEP5–
QRSCOMPLEX
Measuredfromthestartof Qwaveto theendof theSwave
Normal=0.06-0.12seconds(1½to 3smallboxes)
 AretheQRScomplexesgreaterthan0.12seconds(in
width)?
 AretheQRScomplexeslessthan0.06seconds(in
width)?
 3.AretheQRScomplexessimilarinappearanceacross
theECGstrip?
 WidenedQRS:
BBB
Pre-excitation syndrome
Electrolytes imbalance:Hyperkalemia
Pacedrhythm
 Impulse originated from the ventricle
STEP6–
EXTRASorIDENTFYING
FEA
TURES
 Anyectopicbeats?
 ConsiderACSandMI(STsegmentandTwave)
 Identifyingfeatures?
 ProlongedQTIsyndrome

18. STEP 1: RATE

19. CALCULATING RATE
• Asa general interpretation, look at lead II at the bottom part of the ECGstrip
Thislead is the rhythm strip which shows the rhythm for the whole time the
ECGis recorded. Lookat the number of squarebetween one R-Rinterval
• Tocalculate rate, use any of the following formulas:
OR
Rate =
300
the number of BIG SQUARE between R-Rinterval
1500
the number of SMALL SQUARE between R-R interval
Rate =

20. CALCULATING RATE
For example:
Rate =
300
3
Rate =
1500
15
or
Rate = 100 beats per minute

21. CALCULATING RATE
• If you think that the rhythm isnot regular, count the number of electrical beats
in a6-secondstrip andmultiply that number by10.(Note that some ECGstrips
have 3seconds and 6 seconds marks) Example below:
1 2 3 4 5 6 7 8
= (Number of R waves in 6-second strips) x 10
= 8 x 10
= 80 bpm
Rate
There are 8 R waves in this 6-seconds strip.

22. INTERPRETATION
Interpretation Bpm Causes
Normal 60-99
Bradycardia <60 Hypothermia, increased vagal tone (due to vagal
stimulation or e.g. drugs), athletes (fit people)
hypothyroidism, beta blockade, markedintracranial
hypertension, obstructive jaundice, and even in uremia,
structural SAnode disease, or ischaemia.
Tachycardia >100 Any cause ofadrenergic stimulation (including
pain); thyrotoxicosis; hypovolaemia; vagolyticdrugs
(e.g. atropine) anaemia, pregnancy; vasodilatordrugs,
including many hypotensive agents;FEVER,
myocarditis

23. SinusBradycardia
• Rate < 60bpm, otherwise normal

24. SinusTachycardia
Rate >100bpm
• Rate > 100bpm, otherwise normal

25. STEP 2: RHYTHM

26. RHYTHM
• If in doubt, use apaper strip to map out consecutive beats and see whether the
rate is the same further along the ECG.
• Measure ventricular rhythm bymeasuring the R-Rinterval
• Isthe rhythm regular orirregular?

27. Regular rhythm
• Sinus rhythm
• Sinus bradycardia
• Sinustachycardia
• Atrial tachycardia
• Junctional rhythm
• SVT(AVNRT,AVRT)
• Atrial flutter with fixed block
Irregular rhythm
• Atrial fibrillation
• Atrial flutter with variable
block
• SRwith ectopicbeats
• Multifocal Atrialtachycardia
(MAT)

28. STEP 3: P- WAVE

29. P -WAVE
Normal P-wave
• 3small square wide, and 2.5small square high
• Always positive in lead I and II in NSR
• Always negative in lead aVRin NSR
• Commonly biphasic in leadV1

30. P wave
1. Are Pwaves present?
2. Is there 1Pfor each QRScomplex?
3. Are the Pwaves smooth, rounded and upright in appearance except
inverted Pwaves in leadaVR?
4. Do all Pwaves look similar?

31. INTERPRETATION
• Sinus rhythm: Every 1Pfor each QRScomplex
• More than 1Pwave indicates AVblock
• None: Rhythm is junctional or ventricular in origin

32. RHYTHM
Normal SinusRhythm
• ECGrhythm characterized by a usual rate of anywhere between 60-99 bpm, every
Pwave must be followed byaQRS.Normal duration of PRinterval is3-5small
squares.ThePwave isupright in leadsI andII.

33. P -WAVE
Ppulmonale
• Tall peaked Pwave
• Generally due to enlarged rightatrium- commonly
associated with congenital
• heart disease, tricuspid valve disease,pulmonary
hypertension and diffuse lungdisease
BiphasicPwave
• It’s terminal negative deflection more than 40
ms wide and more than 1mm deep is an ECGsign
of leftatrial enlargement
Pmitrale
• Wide Pwave, often bifid, may be due to mitral
stenosisor left atrialenlargement

34. STEP 4: PR- INTERVAL

35. PR INTERVAL
NORMALPRINTERVAL
PR-Interval 3-5 small square (120-200ms)
Long PRinterval
may indicate heart
block
Short PRinterval
may disease like
Wolf-Parkinson-
White

36. PR-INTERVAL
Wolff–Parkinson–White Syndrome
Wolf ParkinsonWhiteSyndrome
• One beat from arhythm strip in V2
demonstrating characteristic findingsin
WPWsyndrome
• Note the characteristic:
• Delta wave (above the blue bar),
the short PRinterval (red bar) of 0.08
seconds, and the longQRScomplex
(green) at 0.12seconds
• Accessory pathway (Bundle of
Kent) allows early activation of the
ventricle (delta wave and short PRI)

37. STEP 5: QRS-COMPLEX

38. QRScomplex< 3small square (0.10sec)
QRS COMPLEX
Prolonged indicates hyperkalemia or BBB
Qwave amplitude lessthan
1/3QRSamplitude(R+S)or
<1small square

39. INTERPRETATON
• Narrow complexes (QRS<100ms) are supraventricular inorigin.
• Broad complexes (QRS>100ms) may beeither:
– Ventricular in origin
– Due to aberrant conduction e.g. due to bundle branch block
– Electrolytes imbalance e.g.Hyperkalaemia
– Ventricular pacedrhythm

40. QRS COMPLEX
Left Bundle BranchBlock(LBBB)
indirect activation causes left ventricle contracts
later than the right ventricle.
QSor rScomplex in V1-W-shaped RsR'wave in
V6-M-shaped
Right bundle branchblock (RBBB)
Indirect activation causesrightventricle
contracts later than the left ventricle
Terminal Rwave (rSR’) in V1-M-shaped
Slurred Swave in V6 -W-shaped
Mnemonic: WILLIAM Mnemonic: MARROW

41. STEP 6: ST-SEGMENT
and T WAVE

42. ST SEGMENT
NORMALSTSEGMENT
STsegment <2-3small square (80 to 120ms)
STsegment is isoelectric and
at thesame level as
subsequent TPsegment

43. ST SEGMENT
WE DECIDE THIS BY LOOKING AT THE ST SEGMENT IN ALL LEADS
Flat (isoelectric) ± Same level with subsequent TP segment
Elevation or depression of STsegment by 1mm or
more, measured at Jpoint is abnormal.
Jpoint is the point between QRSandSTsegment
NORMAL
STSEGMENT
OK,WEGONNATALKABOUTMYOCARDIAL INFARCTION
(MI)
THEREARE2TYPESOFMI
ST-ELEVATION MI (STEMI) NON ST-ELEVATION MI (NSTEMI)
AND

45. ST-SEGMENT
Localizing MI
Look at ST changes, Q wave in all leads.
Grouping the leads into anatomical location,we
Ischemic change can be attributed to
differentcoronary arteries supplying the
area.
Location of
MI
Lead with
ST changes
Affected
coronary
artery
Anterior V1, V2, V3,
V4
LAD
Septum V1, V2 LAD
left lateral I, aVL, V5,
V6
Left
circumflex
inferior II, III, aVF RCA
Right atrium aVR, V1 RCA
*Posterior Posterior
chest leads
RCA
*Right
ventricle
Right sided
leads
RCA
* T
ohelp identify MI,
right sided andposterior
leads can beapplied
haveI.this:
II.
III.
aVR V1
aVL V2
aVF V3
V4
V5
V6
(LAD)

46. ST SEGMENT
ST-ELEVA
TIONMI(STEMI)
0 HOUR
• Pronounced TWave
• STelevation (convextype)
1-24H
• Depressed RWave, and Pronounced TWave
• Pathological Qwaves may appear within hours or may take greater
than 24hr indicating full- thickness MI.
• Qwave is pathological if it is wider than 40 ms or deeper than athird
of the height of the entire QRScomplex
Day 1-2 • Exaggeration of TWave continues for24h
Days later • TWave inverts asthe STelevation begins toresolve
• Persistent STelevation is rare except in the presenceof a
ventricular aneurysm
Weeks later • ECG returns to normal T wave, but retains pronounced Q wave
• An old infarct may look likethis

47. I
II
III
aVR
aVL
aVF
V1
V2
V3
V4
V5
V6
Inferior MI
ST SEGMENT
How about thisone?

48. ST SEGMENT
NONST-ELEVA
TIONMI (NSTEMI)
• NSTEMIis also known assubendocardial or non Q-wave MI
• In apt with Acute Coronary Syndrome (ACS)in which the ECGdoes not show ST
elevation, NSTEMI(subendocardial MI)is suspected if
• ST Depression (A)
• T wave inversion with or without ST depression (B)
• Q wave and ST elevation will never happen
To confirm a NSTEMI, do Troponin test:
• If positive: NSTEMI
• If negative: Unstable angina

49. ST SEGMENT
NONST-ELEVA
TIONMI (NSTEMI)
• N-STEMI:acute coronary syndrome (with troponin increase)
• Arrows indicate ischemic STsegmentchanges.
• Without appropriate treatment in many cases STEMIinfarction will occur

50. MYOCARDIALISCHEMIA
• 1mmST-segmentdepression
• Symmetrical
• Tall Twave
• Long QT-interval
• STdepression ismore suggestive of myocardialischemia
than infarction
ST SEGMENT

51. T wave
• Twave is the positivedeflection
after each QRScomplex
• It representsventricular
repolarisation
• Upright in all leads except aVR
and V1
• Amplitude
– <5mm in limb leads
– <15mmin precordial leads

52. Step 7: QT- INTERVAL

53. QT- INTERVAL
• QTinterval decreases when heart rate increases
• Asageneral guide theQTinterval shouldbe 0.35- 0.45 s,(<2 large square) and
shouldnot be more than half of the interval between adjacent Rwaves(R-R
interval)
< 2 large square

54. T-WAVE
Normal T wave
• Asymmetrical, the first half having more gradual slope
than the secondhalf
• >1/8and <2/3 of the amplitude of corresponding Rwave
Amplitude rarely exceeds10mm
• Abnormal Twaves are symmetrical, tall, peaked, biphasic,
or inverted
LONGQT SYNDROME
• LQTis a rare inborn heart condition in
which repolarization of the heart is
delayed following aheartbeat
• Example: Jervell and Lange-Nielsen
Syndrome or Romano-WardSyndrome

55. STEP 8: CARDIAC AXIS

56. CARDIAC AXIS
• Todetermine cardiac axis look at QRScomplexes of lead I , II, III.
Axis Lead I Lead II Lead III
Normal Positive Positive Positive/Negative
Right axis.
deviation
Negative Positive Positive
Left axis
deviation
Positive Negative Negative
• Remember, positive(upgoing) QRScomplex means theimpulse
travels towards thelead.
• Negative means movingaway

57. Positive
Positive
Positive
Normal Axis Deviation
CARDIACAXIS

58. Negative
Positive
Positive
RightAxis Deviation
CARDIACAXIS

59. Positive
Negative
Negative
Left AxisDeviation
CARDIACAXIS

60. I (0º)
I
I
aVF
aVF (+90º)
(180º)
NORMAL AXIS
LEFT AXIS
DEVIATION
RIGHT AXIS
DEVIATION
EXTREME
RIGHT AXIS
DEVIATION
I
aVF
I
aVF

61. Cardiac Axis Causes
Left axis deviation Normal variation in pregnancy, obesity; Ascites,
abdominal distention, tumour; left anterior
hemiblock, leftventricular hypertrophy, QWolff-
Parkinson-White syndrome, Inferior MI
Right axis deviation Normal finding in children and tall thin adults,
chronic lung disease(COPD), left posterior
hemiblock, Wolff-Parkinson-White syndrome,
anterolateral MI
North West Emphysema, hyperkalaemia. leadtransposition,
artificial cardiac pacing, ventriculartachycardia
CARDIACAXIS

62. STEP 9: OTHER ECG
SIGNS

63. LEFT VENTRICULAR
HYPERTROPHY
RIGHT VENTRICULAR
HYPERTROPHY
AND
So, we have to start looking at the S waves and R waves

64. Left ventricular hypertrophy (LVH)
Criteria:
Example:
• Todetermine LVH,use one of the following:
Sokolow & Lyon Criteria: S (V1) + R(V5 or V6) > 35mm
Cornell Criteria: S (V3) + R (aVL) > 28 mm (men) or > 20 mm (women)
Others: R (aVL) > 13mm
S (V1) + R(V5) = 15 + 25 = 40mm
S(V3) + R (aVL)= 15 + 14 =29mm
R(aVL) =14 mm
LVH!

65. • Tall Rwaves in V4and V5with down sloping STsegment depression and Twave
inversion are suggestive of left ventricular hypertrophy (LVH) with strain pattern
• LVHwith strain pattern usually occurs in pressure overload of the left ventricle as
in systemic hypertension or aortic stenosis
Let’s see another example of LVH
LVH strain pattern

66. Right ventricular hypertrophy (RVH)
Example:
Right axis deviation (QRS axis >100o) V1(R>S), V6 (S>R)
Right ventricular strain T waveinversion
So, it’s RVH!

67. CommonCausesof LVHand RVH
LVH RVH
• Hypertension (most common
cause) Aortic stenosis
• Aortic regurgitation Mitral
regurgitation
• Coarctation of theaorta
• Hypertrophic cardiomyopathy
• Pulmonary hypertension
• Tetralogy of Fallot
• Pulmonary valve stenosis
• Ventricular septal defect(VSD)
• High altitude
• Cardiac fibrosis COPD
• Athletic heart syndrome

68. • Narrow and tall peaked Twave (A) is an early sign PRinterval becomes longer
• Pwave loses its amplitude and may disappear QRScomplex widens(B)
• When hyperkalemia is very severe, the widened QRScomplexes merge with their
• corresponding Twaves and the resultant ECGlooks like a series of sine waves (C)
• If untreated, the heart arrests in asystole
HYPOKALAEMIA
• Twave becomes flattened together with appearance of a prominent U wave
• The STsegment may become depressed and the Twaveinverted
• These additional changes are not related to the degree of hypokalemia
HYPERKALAEMIA

69. E C G RULES
• ProfessorChamberlains10 rules of a normal ECG,afoundation to ECG
interpretation usedall over the world to this date

70. 10RULESOFA NORMALECG
Rule1
PRIshould be 120to 200ms
(3 to 5smallsquares)
Rule2
QRScomplex width should not
exceed 120ms(<3 smallsquares)
Rule3
QRScomplex should be
Rule4
QRSand Twaves tend to have
dominantly uprightin lead 1and the samedirection in the limb
II leads
Rule5
All waves are negative in lead
Rule6
Rwave must grow from V1tov4
AVR and
Swave must grow from V1toV3
and disappear inV6
Rule7
STsegment shouldstart
Rule8
Pwaves should be upright inI,II
isoelectric except V1andV2 and V2to V6
(maybe elevated)
Rule9
No Qwave or only asmall q wave
(<0.04 in width) in I,II,V2 to V6
Rule10
Twave must be upright in 1,II,V2-
V6

71. THANK YOU