The document provides an overview of cardiac conduction systems and ECG interpretation. It describes the normal intrinsic conduction rates of the sinoatrial node, atrioventricular node, and bundle of His. It then details the components of the ECG like the P wave, PR interval, QRS complex, ST segment, and T wave. Various arrhythmias are explained like sinus bradycardia, premature atrial contractions, atrial flutter, atrial fibrillation, and different types of heart block. Methods for calculating heart rate from the ECG are also summarized.

1. CARDIAC ARRHYTHMIAS -
INTERPRETATION
P.M.Prathiba, M.Sc (N), (PhD)

2. Overview
● SHORT REVIEW OF
CONDUCTION SYSTEM OF
THE HEART
● ECG-INTERPRETATION
● DYSRHYTHMIAS -TYPES AND
INTERPRETATION

3. INTRODUCTION
● The ability to recognize normal and abnormal cardiac
rhythms, called dysrhythmias, is an essential skill for the
nurses.
● Prompt assessment of dysrhythmias and the patient's
response to rhythm is critical.

4. Intrinsic rate of impulse conduction
SA node : 60-100 times /min
AV node : 40-60 times/min
Bundle of His &
Purkinje fibers : 20-40 beats/min

5. ELECTROCARDIOGRAM - ECG

6. ELECTROCARDIOGRAPHIC MONITORING
● An electrocardiogram reflects the electrical activity of
the of cardiac cells and records electrical activity at a
speed of 25mm / Sec.
● The wave forms on the ECG are produced by the movement
of charged ions across the membranes of myocardial cells,
representing depolarization and repolarization.

7. ECG basics - Contd…

8. ECG basics - Contd…

9. The standard paper speed is 25mm/sec:
● 1 SMALL square (1mm) = 0.04 sec
(40ms)
● 5 SMALL squares (5mm) = 1 LARGE
square = 0.2 sec (200ms)
● 5 LARGE squares = 1 second

10. P - Wave
P Wave Represents Atrial Depolarization
● Normal:
○ Duration: 0.06 to 0.12 s OR 3 small boxes
○ Amplitude: < 2.5mm OR 2.5 small boxes)

11. PR Interval
Measured from beginning of P wave
to beginning of QRS complex
Normal:
● Duration: 0.12- 0.2s OR 3-5 small boxes
● Will shorten during exercise as heart
rate increases

12. PR Segment
The PR segment is the flat, usually
isoelectric segment between the end of
the P wave and the start of the QRS
complex.

13. QRS - Complex
The Q wave is the first negative deflection after
the P wave and the first element in the QRS
complex.
The R wave is the first upward deflection after
the P wave..
The S wave is the first downward deflection of
the QRS complex that occurs after the R wave.

14. QRS - Complex Cntd…
Indicates Ventricular Depolarization
❖ Duration: 0.04- 0.12s OR 1-2.5 small
boxes
❖ Amplitude:
➢ 5 to 30mm height or 0.5 to 2.5 or
3.0mV

15. ST segment:
● Represents: The interval between
ventricular depolarization and
repolarization.
● Normal: Measured from the S wave
of the QRS complex to the beginning
of the T wave.
● Isoelectric line
● 0.12 Sec

16. T - Wave:
● Represents: Time for ventricular repolarization
● Duration: 0.16 Sec
● Amplitude: 3 to 6 mm

17. QT interval
It represents the time taken for
ventricular depolarisation and
repolarisation.
● QT interval is the time from the start of the Q
wave to the end of the T wave.
● Normal
○ Duration: 0.34- 0.44s OR
10-11 small boxes
.

18. J Point
Junction between the
termination of the QRS complex and
the beginning of the ST segment.
● Represents: The initiation of
ventricular repolarization
Q S
P
R

19. RR Interval
In an electrocardiogram, the
interval from the onset of one R wave to
the onset of the next one, one complete
cardiac cycle
● Normal: 0.6-1.2 seconds
.

20. Intervals and Segments
● PR Interval:From the start of
the P wave to the start of the
QRS complex
● PR Segment:From the end of
the P wave to the start of the
QRS complex
● J Point:The junction between
the QRS complex and the ST
segment
● QT Interval:From the start of
the QRS complex to the end of
the T wave

21. Normal values
● Heart rate 60 - 100 bpm
● P wave < 0.12 s OR 3 small boxes
● PR interval 0.12 - 0.20 s
● QRS interval ≤ 0.12 s
● QT interval < half RR interval (males < 0.40 s; females < 0.44 s)
● Q wave < 0.04 s (1 mm) and < 1/3 of R wave amplitude in the
same lead

22. Methods of Heart rate calculation:
1. Triplet HR technique.
2. Large square method
3. Small square method
4. R - R method and
5. 6 second method

23. ● With the Triplets HR technique we obtain a quick 'estimate' of heart rate to get
1.

24. Triplets HR technique Cntd…
The rhythm above is a REGULAR rhythm. With a REGULAR rhythm you can do the T

25. Find the heart rate ( with in 2 sec.)

26. 2. Large squares method:

27. Calculate the heart rate using large square method

28. 3. Small square method:

29. Calculate the heart rate: Use first two R waves in this
case for uniformity.

30. 4.

31. R to R method contd….
Step: 1
19.5 X 0.04 =0.78
Step 2:
60/0.78=77.6=78

32. Calculate the heart rate using R to R method:

33. 5.

34. Systemic approach to ECG assessment
1. Determine the rate
2. Determine rhythm ( compare P-P intervals, R-R
intervals)
3. Evaluate P waves
4. Measure the duration of PR interval
5. Evaluate the ventricular rhythm
6. Measure the duration of QRS complex
7. Assess the ST segment
8. Evaluate the T wave
9. Measure the duration of QT interval
10.Look for other abnormality

35. Arrhythmias:
The term "arrhythmia" refers to any change from the
normal sequence of electrical impulses. The electrical
impulses may happen too fast, too slowly, or erratically –
causing the heart to beat irregularly.
- American Heart Association

36. Types of arrhythmias:
In general, heart arrhythmias are grouped by the speed of the
heart rate. For example:
● Tachycardia or tachyarrhythmias: Is a fast heart beat.
The resting heart rate is greater than 100 beats a minute.
● Bradycardia or bradyarrhythmia : Is a slow heartbeat.
The resting heart rate is less than 60 beats a minute.

37. Common dysrhythmias :
1. Sinus bradycardia
2. Sinus tachycardia
3. Premature Atrial Contraction
4. Paroxysmal Supraventricular Tachycardia
5. Atrial flutter
6. Atrial fibrillation
7. Junctional dysrhythmias
8. Premature ventricular contractions
9. Ventricular tachycardia
10.Ventricular fibrillations
11.Asystole

38. Sinus rhythm:
First always determine whether the rhythm is Sinus rhythm or Non - Sinus rhythm
● Look at P wave
● Every QRS is preceded by a P wave
● P waves appear normal, that is they
are of sinus node origin
Normal morphology:
1. P - wave duration <0.12 Sec (<3boxes)
2. P - Wave height < 2.5 mm

39. Sinus bradycardia:
In sinus bradycardia the conduction pathway is the same as that in sinus rhythm, but SA node fires at a rate less
than 60 beats/minute

40. ECG characteristics:

41. Sinus tachycardia:
The conduction pathway is the same in sinus tachycardia as that in normal sinus
rhythm. The discharge rate from the sinus node is increased. The sinus rate is
greater than 100 beats/ min

42. Sinus tachycardia:
Rate : 100 or greater. In adults, rates higher
than 160 are rarely
sinus in origin
P wave : Normal
P-R interval : Normal
QRS : Usually narrow
Ratio : 1:1
Rhythm : Regular

43. Premature atrial contraction:
Premature atrial contractions (PACs) are contractions of the atria that are
triggered by the atrial myocardium but have not originated from the sinoatrial
node (SA node). PACs are also commonly referred to as atrial premature
complexes (APCs), premature supraventricular complexes, premature
supraventricular beat, and premature atrial beat.
This phenomenon can be caused by an assortment of medical diseases,
structural abnormalities, pharmaceuticals, and non-regulated compounds.

44. Premature atrial contraction:
Rate : The underlying heart rate may vary
P wave : In order for the premature beat to be called a PAC, it
must have an
upright P wave
P-R Interval : Normal or prolonged
QRS : Usually narrow
Ratio : 1:1
Rhythm : Underlying rhythm is regular except where it is distributed

45. Paroxysmal supraventricular tachycardia (PSVT)
Paroxysmal supraventricular tachycardia (PSVT) is a type of
abnormal heart rhythm, or arrhythmia. It occurs when a short circuit
rhythm develops in the upper chamber of the heart. This results in a
regular but rapid heartbeat that starts and stops abruptly.
PSVT occurs because of a short circuit — an abnormal electrical
pathway made of heart cells — that allows electricity to speed around in a
circle and repeat the signal over and over. As a result, the chambers

46. Paroxysmal supraventricular tachycardia (PSVT)
Rate : 150 to 300, usually ranges from
120-200
P wave : Often hidden
QRS : Usually narrow
Ratio : 1:1 if visible P wave
Rhythm : Regular

47. Atrial flutter
Atrial flutter is a tachydysrhythmia
identified by recurring regular, saw tooth-
shaped flutter waves that originate from a
single ectopic focus in the right atrium.

48. Atrial flutter:
Atrial Rate : Usually ranges from 250 to 350
Ventricular rate : Depends on the impulse conducted through,
approximately 150
P wave : Multiple F waves or flutter waves ( saw
tooth shape)
Ratio : 2:1 or 3:1
Rhythm : Regular, can be irregular

49. Atrial flutter 2:1 block

50. Atrial flutter 4:1 block

51. Atrial fibrillation:
In atrial fibrillation, electrical signals fire
from multiple locations in the atria
(typically pulmonary veins), causing
them to beat chaotically. Since the
atrioventricular (AV) node doesn't
prevent all of these chaotic signals from
entering the ventricles, the heart beats
faster and irregularly.

52. Atrial fibrillation:
Atrial Rate : 350 to 600 beats/min
Ventricular rate : Rapid ventricular response (RVR): >100,
controlled
ventricular response(<100)
P wave : Non discernable, may be flutter waves
sometimes
QRS : Usually narrow

53. Junctional dysrhythmias:
Junctional rhythm refers to a rhythm originating at the
atrioventricular node, with P waves buried in the QRS
complex, which is traveling towards the base of the heart as
well as to the bundle branches in the ventricular septum. It
results primarily as the SA node has failed or the signals are
been blocked.

54. Junctional dysrhythmias cntd…

56. HEART BLOCK OR AV BLOCK
1. FIRST DEGREE AV BLOCK
2. SECOND DEGREE AV BLOCK
TYPE I ( MOBITZ I OR WENCKEBACH HEART BLOCK)
TYPE II ( MOBITZ II HEART BLOCK)
1. THIRD DEGREE AV BLOCK ( COMPLETE HEART BLOCK)
TYPES:

57. HEART BLOCK OR AV BLOCK
A first - degree atrioventricular node block occurs when
conduction through the AV node is slowed, thereby delaying the time it
takes for the action potential to travel from the sinoatrial node through
the AV node, and to the ventricles.
First degree AV block

58. First degree heart block:

59. SECOND DEGREE AV BLOCK
It includes a gradual lengthening of PR interval and absence of QRS
complex. It occurs because of a prolonged AV conduction time until an
atrial impulse is non conducted and a QRS complex is blocked.
TYPE I / Mobitz I / Wenckebach Heart Block

60. Second degree AV block

62. SECOND DEGREE AV BLOCK
In Mobitz II heart block a P wave is non conducted without
progressive antecedent PR interval lengthening. It almost occurs when
there is a block in one of the bundle branches.
TYPE II / Mobitz II

64. Second degree AV block

66. Third degree AV block cntd….

68. A premature ventricular contraction is a contraction originating in an ectopic
focus in the ventricles. It is the premature occurence of a QRS complex, which is
wide and distorted in shape compared with a QRS complex initiated from normal
conduction pathway
It can be Unifocal or multifocal:
● PVCs that appear to have the same shape are called unifocal PVCs, that arise from
single ectopic foci
● PVCs that are initiated from different foci appear different in shape from each other
and are called multifocal PVCs
PVC: Premature Ventricular contractions

69. ECG characharacteritics:
● Can occur at any time and with any rate
● Different QRS morphology
● T waves in opposite direction
● Usually followed by a compensatory pause
Types
● When every other beat is a PVC, it is called ventricular
Bigeminy
● When third beat is a PVC, it is called ventricular Trigeminy
● Two consecutive PVCs are called Couplet.
PVC: Premature Ventricular contractions cntd…

70. PVC: Premature Ventricular contractions- Unifocal

74. Ventricular tachycardia:

75. Ventricular tachycardia:
Ventricular tachycardia is made when a run of three or more PVCs
occur. It occurs when an ectopic foci fire frequently and the ventricles
takes control as the pacemaker.
Types:
Monomorphic VT: Waves that appear same in shape
Polymorphic VT : waves that appear abnormal shapes of varied types.

76. Ventricular tachycardia:
ECG changes:
● Ventricular rate: 150-250 beats/min
● Atria are depolarized by ventricles in retrograde manner
● P wave: no P waves preceding QRS, Av dissociation ( P
waves marching through)

77. Monomorphic VT:
Monomorphic Vt has QRS complexes that are the same in size, shape
and direction

78. Polymorphic VT
Polymorphic VT occurs when the QRS complexes gradually change back and
forth one shape, size, and direction to another over a series of beats

79. Ventricular fibrillation:

80. Ventricular fibrillations:
● Ventricular fibrillation is a severe derangement of the heart
rhythm characterized on ECG by irregular undulations of
varying shapes and amplitude. This represents the firing of
multiple ectopic foci in the ventricle.
● Mechanically the ventricles are simply quivering and no effect
of contraction, and consequently no CO, occurs.
● Heart rate is not measurable, needs immediate cardiac
resuscitation

82. Asystole
● Represents the total absence of ventricular electrical activity
● Occasionally p waves are seen, no QRS complexes as there is no
depolarization of the ventricles
● Life threatening condition

84. Conclusion:
● Continuous electrocardiographic (ECG) monitoring is one of the
most common technologies used in acute care today. ECG
monitoring guides patient care, particularly for patients with or
at risk for arrhythmias and myocardial ischemia.
● Prompt and right time identification of arrhythmias aids in proper
cardiac resuscitation and life saving.
● Though the presentation consists of basic arrhythmias we strongly
believe that this session would have ignited an interest to look into
the details which might just be a beginning.