Basics of ECG (sbs w notes)

Question 1

WHAT IS AN ECG?

Answer 1

A recording of the electrical potentials generated by electrical currents from the heart into the adjacent tissues, which are detected by electrodes placed on the surface of the body.

Question 2

What is an ECG often used to diagnose?

Answer 2

○ Arrhythmias
○ Myocardial ischemia and infarction
○ Chamber hypertrophy
○ Pericarditis; Pericardial effusion/tamponade
○ Electrolyte disturbances
○ Drug toxicity

Question 3

Electrical stimulation and contraction:
○ Before the heart contracts, it must be

Answer 3

electrically stimulated leading to its depolarization

Question 4

THE CARDIAC CONDUCTION SYSTEM

Answer 4

• Sinus Node
• Atrioventricular Node
• Bundle of His
• Purkinje Network

Question 5

What is the heart’s natural pacemaker?

Answer 5

Sinus Node
○ Why? It paces the heart via the principle that it
depolarizes the fastest.
● 60-100 bpm at rest

Question 6

● Receives impulse from SA Node
● Delivers impulse to the His-Purkinje System
● 40-60 bpm if the SA node fails to deliver an impulse

Answer 6

Atrioventricular Node

Question 7

● Begins conduction to the ventricles
● AV junctional tissue: 40-60 bpm

Answer 7

Bundle of His

Question 8

● Bundle branches
● Purkinje fibers
● Moves the impulse through the ventricles for contraction
● Provides “escape rhythm” 20-40 bpm

Answer 8

The Purkinje Network

Question 9

Page 1 Diagrams

Question 10

What happens in Phase 0?

Answer 10

○ That is where depolarization happens brought about by sodium ions moving inwards, more positive inwards.

○ That is why you can see the potential from very
negative to very positive or a rapid upshoot of around a +25.

Question 11

What happens in Phase 1?

Answer 11

○ Initial repolarization (rep) brought about by potassium going out, that is why it tends to be negative again.

○ However, it is only for a very short period that is why it is called “transient outward/transient repolarization” which goes out into the plateau phase.

Question 12

What happens in Phase 2?

Answer 12

○ It is the plateau phase. which is characteristic of your cardiac muscle compared to your skeletal.

○ This is brought about by calcium moving inwards.

Question 13

What happens in Phase 3?

Answer 13

○ It is where the final repolarization happens.

○ It is brought about by potassium going outwards.

○ That’s why it becomes negative again to negative 80 to negative 90.

○ So, compare it to sinus nodal. So, grossly, there’s a big difference in the configuration of the graph, no? What’s the difference in potential? The resting.

○ In the sinus nodal, is it more negative or more
positive? It is more positive at around negative 50 to negative 60, and also, if you notice your phase 4, it does not stay in an isoelectric baseline. It tends to drift upward which is brought about by positive ions going in which include sodium and calcium. That’s why we call it currents.

Question 14

We have what we call in your sinus nodal funny channels because it’s naturally leaky to sodium. That’s why in the region of negative 55 to negative 60, it tends to be leaky to sodium (refer to the photo on page 2).

Answer 14

○ Sodium is slowly getting in. It doesn’t rest into a flat phase 4. It always tends to drift upwards until it reaches a threshold of negative 40. So, if it reaches
that, there’s no way to go but phase 0. So, this time phase 0 in the sinus node is more attributed to
calcium.

○ That’s why it’s slower. It’s kind of inclined compared to the very steep phase 0 in your ventricular myocytes. And then of course, repolarization is brought about by potassium.

○ So, if it’s repolarization, it’s always potassium going upwards. And then, if it reaches negative 55,
negative 60, your funny channels will be leaky again. And it slowly drifts upwards, reaching negative 40 and then it fires.

○ So, that’s why the sinus node is a natural battery
because of this. So, it overcomes everything because the ventricular muscle tends to rest

● The ventricular versus the sinus node (refer to the photo on page 2).

○ So, the flow of current from negative to positive is from base to apex. That’s why your apex is in relative positivity compared to your base. So, this is the time interval of your electrical stimulation from your sinus node.

○ Sinus node, look for the zero here. So, it depolarizes most of your atria at 0.03 seconds.

○ What’s the natural time delay of your AV node? It is 0.09. And then you have an additional 0.04 in your penetrating bundle or bundle of His.

○ Such that the total would be 0.16 from sinus node to penetrating bundle. So, this is important because this is reflected in the PR interval of your BCG.

○ Any abnormalities or prolongation of the time? So, you would suspect abnormalities probably in your AV node or you have a block or something like that.

Question 15

Precordial (Chest) Leads

Answer 15

0 degrees: I
60 degrees: II
90 degrees: aVF
120 degrees: III

-150 degrees: aVR
-30 degrees: aVL

Question 16

These are the placements of the precordial (chest) leads

Answer 16

Septal: V1, V2
Anterior: V3, V4
Lateral: V5, V6

Question 17

TABLES on page 3:

These illustrations show the arrangement of leads on an ECG. So, leads, you have a positive and a negative input.

● If the depolarization wave is going to the positive input of that ECG lead, it would record a positive deflection in your ECG. The reverse is true depolarization.

Answer 17

● Leads are grouped according to the general area of the heart (left ventricle) that they represent.
● Limb Leads
○ Generally view the heart in a supero-inferior and
medial to lateral dimension.
● Precordial Leads (chest leads)
○ Generally view the heart (LV) in an Antero-Posterior dimension.

Question 18

THE ECG WAVEFORMS
table page 3

Answer 18

● So, atrial depolarization would record the P wave.

● So, that baseline there is sort of more rest. So, that is what I said about the natural delay of the AV node. So, it is recorded as the PR interval.

● The junction between the P and the R, or the Q. That’s the PR interval. So, if you prolong PR, what would you expect? The AV node is slower than usual.

● And then the QRS complex represents ventricular depolarization.

● And then your ST segment is the start of your rest, or the plateau, and then ventricular depolarization is your P wave. That’s why you don’t see any activity there because the heart is resting.

● So, when I say, what’s the interval representing your ventricular depolarization and repolarization? QRST, or you call it the QT interval.

● So, what represents the ECG in the entire sequence of atrial depolarization and AV nodal conduction? PR segment.

Question 19

THE ECG PAPER

Answer 19

● There are light lines and there are dark lines. The dark lines represent big squares, and the light lines represent small squares.

● So, a big square has 5 small squares horizontally and 5 small squares vertically. So, horizontally, it is a function of time. Vertically, it is voltage or amplitude.

● So, the smallest square horizontally is how much time interval? 0.04.

● Such that one big box is 0.2 seconds. And then one smallest square vertically is 0.1 millivolts. And then one big square vertically is 0.5 millivolts.

Question 20

Horizontal

Answer 20

Time:
- One small box is 0.04s
- One large box is 0.20s

Question 21

Vertical

Answer 21

Amplitude
- One small box is 0.1 mV
- One large box is 0.5 mV

Question 22

THE NORMAL ECG

Answer 22

● PR interval is normally not more than 0.16. In ECG reading, it should be less than 0.2 seconds or 5 small squares. The QT interval is 0.35. These are the normal intervals.

● This is what a normal ECG looks like (refer to photo on page 4).

● The ECG leads measure the potential between two points, positive and negative.

● As a review, there are two types of leads. You have a bipolar lead, where you place two different points in the body. A positive input and a negative input.

● And then you have a unipolar lead, you only place the positive input. The negative is determined by your machine. So, the bipolar leads, you have three: Leads 1,
2, and 3. And then the unipolar leads, you have two types: you have the augmented, which are UVBR, UVL, and UVF, and then you have the precordials, V1, V2, and V6.

● So, that’s the bipolar leads, augmented, and the
procordials. So, if you arrange your ECG strips, that’s how you should arrange it.

○ Lead 1 - left arm (+), right arm (-)
○ Lead 2 - left leg (+), right arm (-)
○ Lead 3 - left leg (+), left arm (-)
○ avR - right arm
○ avL - left arm
○ avF - left foot

● If you can see your avR, it is negative. Why? Because
there’s no depolarization waveform going to the right arm and upwards. So, that’s why when you read an ECG, look at avR first. It should be negative. Otherwise, the leads are misplaced or probably you have an extracardia, which is rare.

● What will you place first? V1.
● So, the fourth interspace close to the sternum is V1. And then exactly the opposite is V2, and then you place V4 next, the fifth left intercostal space, midclavicular.
○ V1 - 4th RICS (right intercostal space) parasternal
○ V2 - 4th LICS (left intercostal space) parasternal
○ V4 - 5th LICS midclavicular line
○ V3 - between V4 and V2
○ V5 - 5th LICS anterior axillary line
○ V6 - 5th LICS midaxillary line

● And then you place V3 next between 2 and 4. And then V5 is still in the fifth left intercostal space, a clear axillary line. And then V6 is still in the same interspace of the fifth left mid-axillary line. So, no leads should be placed in the sixth intercostal space.

● So, the positive or the negative input, you call it the Wilson’s terminal, determined by your machine.

Question 23

The Einthoven’s Triangle

Answer 23

● It is drawn around the area of the heart which illustrates that the two (2) arms and the left leg form apices of a triangle surrounding the heart.

● The two (2) apices at the upper part of the triangle represent the points at which the two (2) arms connect electrically with the fluids around the heart, and the lower apex is the point at which the left leg connects with the fluids.

Question 24

ANATOMIC GROUPS BASED ON CONTIGUOUS ECG
LEADS

Answer 24

The Septum
V1, V2

The Anterior Wall
V3, V4

The Lateral Wall
I, aVL, V5, V6

The Inferior Wall
II, III, aVF

NONE
aVR

Question 25

BASIC ECG RULES
○ The heart rate is the reciprocal time interval between two successive beats.

● The formulas include the 1500 and the 300.
○ So, you use 300 and then divide it by the number of big squares between two successive R waves or you can use 1500 divided by the number of small squares in between two R waves.

● So, if the rate is faster, closer to the R waves, maybe use the 1.5. But if the rate is slower, meaning the R to the next R is a bit far, then you may use the big squares. 1500 is more accurate because you’re counting the last grid of the ECG paper.

Answer 25

Refer on the tracings on page 5-6

Rule 1
● PR interval should be 120 to 200 milliseconds or 3 to 5 little squares.

Rule 2
● The width of the QRS complex should not exceed 110 milliseconds, less than 3 little squares.

Rule 3
● The QRS complex should be dominantly upright in leads I and II.

Rule 4
● QRS and T waves tend to have the same general
direction in the limb leads.

Rule 5
● All waves are negative in lead aVR.

Rule 6
● The R wave must grow from V1 to at least V4.
● The S wave must grow from V1 to at least V3 and disappear in V6.

Rule 7
● The ST segment should start isoelectric except in V1 and V2 where it may be elevated.

Rule 8
● The P waves should be upright in I, II, and V2 to V6.

Rule 9
● There should be no Q wave or only a small q less than 0.04 seconds in width in I, II, V2 to V6.

Rule 10
● The T wave must be upright in I, II, V2 to V6

Question 26

CALCULATING THE HEART RATE
Determining the Heart rate

Answer 26

● Heart Rate – is the reciprocal of the time interval between 2 successive heartbeats.

● If the interval between two beats as determined from the time calibration lines is 1 second, the heart rate is 60 beats per minute.

● The normal interval between two successive QRS
complexes in the adult person is about 0.83 second.

● HR of 60/0.83 times per minute, or 72 beats per minute

● We have two (2) different strips to determine the heart rate of a person.

Question 27

3-second Strip

Answer 27

HR calculated by counting the number of QRS complexes within 3 seconds and multiplied by 20. The first complex is the reference point and is not counted.

Question 28

6 or 12-second Strip

Answer 28

Refer on page 7:

● If the HR is irregular or very slow, a longer time interval such as 6-second time marker or even 12-second time marker is chosen.

● Calculated by counting the number of QRS complexes within 6 seconds and multiplied by 10.

● If 12 seconds are used, the number of complexes is multiplied by 5, to obtain the HR per minute.

● It may be easiest to memorize the table:

● If the R to R to R to R occurs at the exact same time, which is the normal. So what if your rhythm is abnormally irregular? You cannot apply that formula. So you use a long strip. So you can use a three-second strip. So count three-second strips, which is how many big squares? One small square is 0.24 seconds. (2:06) So if you want a three-second strip, that would be 15 big squares.

● So you count the number of R’s within the chosen three-second and you multiply it by 20.

● So what if the three-second strip has no R? So 0 heart rate, your patient is dead?
○ For slower irregular rhythms, you use a longer strip.
So you can use a six-second strip, which is how
many big squares? 30. So if it’s slow, and you can’t
count one? So it’s not representative.

● So it’s up to you to use a longer strip. So if you use a 6-second strip, that would be 30 big squares. And then you multiply it by 10.

● If you have a very slow rhythm, you can actually use a much longer strip. Use a 12-second strip. So that would be around 60 big squares and then you multiply it by 5.

Example (ID heart rate): page 7

Question 29

● Always positive in leads I and II
● Always negative in lead avR
● < 3 small squares in duration
● < 2.5 small squares in amplitude
● Commonly biphasic in lead V1
● Best seen in lead II

● Example (refer to photo above): Tall (> 2.5 mm), pointed P waves → P pulmonale

● Example (refer to photo above): Notched/bifid (“M” shaped) P wave in limb leads → P mitrale

● Example (refer to photo above): The P waves in lead II are notched → Left atrial enlargement

● The table below shows the common diagnostic criteria for left and right atrial abnormalities.

Answer 29

P wave
- page 7 tables & diagrams

Question 30

● It is the isoelectric segment beginning with the end of the P wave and ending with the onset of the QRS complex.

● There are instances where you have a shortened PR. This is not so common. As I said before, the normal communication between your atria and ventricles electrically should be only through the AV node.

● If you have other pathways other than the AV node, so, it will be manifested in your ECG as a shortened PR interval.

Why is that?
○ Because an accessory pathway, meaning a pathway beyond the AV node, does not have the normal AV delay. So, it conducts faster.
○ That’s why the PR interval shortens. This is the
accessory pathway somewhere in the posterior right atrial. So, this conducts faster.

● So, you have a shortened PR. And then once it collides, the electrical depolarization collides with the potential coming from the normal AV node, it’s somewhat like a crash. And then you have to go back to the initial QRS.

● That’s the delta wave. And then you combine the
potentials from here to this, from here and this, so that would be a prolongation of your QRS. That’s why you have the triad of shortened PR, a delta wave and a wide QRS.
○ So, you call it the WPW pattern or the Wolff-Parkinson-Weinberg pattern. This is not so common.
○ So, if you see patients with an ECG that represents WPW, you do not know the patient, so you just call it pattern. But if it’s your patient, and then you know that the patient has symptoms of tachycardia already, or loss of consciousness already, so you call it the syndrome– WPW syndrome.

Answer 30

PR interval
page 8 figures

Question 31

What represents ventricular depolarization
and the longest part?

Answer 31

The QRS Complex

Question 32

Left Ventricular Hypertrophy (LVH)

Answer 32

● Different criteria exists for the diagnosis of LVH
○ Example: R wave in V5 or V6 + S wave in V1 or V2 >35 mm

● Common cause: systemic hypertension (HPN)

● LVH or hypertrophy of your left or right ventricles are manifested by increased voltages of your QRS. The criteria for your LVH, the easiest to memorize, there are a lot actually. One of them is the Socolione criteria.

● The Socolione is R-wave in V5 or V6 plus the S-wave in V1 or V2 should be more than 35 millimeters. So that is the voltage criteria for that LVH.

Question 33

Right Ventricular Hypertrophy (RVH)

Answer 33

● Criteria: Right axis deviation + R wave in V1 > 7mm

● Common cause: COPD

● So, you have evidence of right axis deviation from some very tall R in V1 more than 7 small squares. Because the R wave progresses from V1 to V6.

● So if V1 is already tall, and then plus you have evidence of. You have evidence of right axis deviation, so R-VH.

● Give me some causes of R-VH.Hypertrophy of what? If you have, let’s say, obstruction to R-V outflow.
○ Obstruction in your pulmonic valve. So, you need to produce R-VH. So any condition that will produce increased muscle in the right ventricle.

Question 34

ST segment

Answer 34

● ST segment is flat (isoelectric)

● ST segment deviation: elevation of depression of ST segment by greater than or equal to 1 mm

● “J” junction point is the point between QRS and ST segment

● J point elevation in systemic hypothermia: Osborn Wave

● The photo on page 9 shows the variable shapes of the ST segment elevations in acute myocardial infarctions (AMI).

Question 35

T wave

Answer 35

● Abnormalities in the T wave:
○ The T wave becomes abnormal when the normal
sequence of repolarization does not occur.

● Several factors can change the sequence of
repolarization:
○ Slow conduction of the depolarization wave
○ Shortened depolarization in portions of the
ventricular muscle

● As a general rule, T wave amplitude corresponds with the amplitude of the preceding R wave, though the tallest T waves are seen in leads V3 and V4

● Tall T waves may be seen in acute myocardial ischemia and are a feature of hyperkalemia.

Question 36

QT Interval

Answer 36

● The QT interval represents ventricular depolarization and repolarization.

● It extends from the onset of the QRS complex to the end of the T wave.

● Total duration of depolarization and repolarization.

● It is rate-dependent: decreases when the HR increases

● Bazett formula:
○ Corrects the measured QT interval to the effects of the HR

TABLE on page 9

Question 37

U wave

Answer 37

● U wave is related to after depolarizations which follow repolarization.

● They are small, round, symmetrical and positive in lead II, with an amplitude of < 2 mm.

● Its direction is the same as the T wave.

● More prominent when the HR is slow

● Seen in hypokalemia

Question 38

What Principles of Vectorial Analysis?

Answer 38

● Heart current flows in a particular direction in the heart at a given instant during the cardiac cycle.

● Vector → an arrow that points in the direction of the electrical potential generated by the current flow, with the arrowhead in the positive direction.

● Each lead is a pair of electrodes connected to the body on opposite sides of the heart. And the direction from negative to positive is called the axis of that lead.

Question 39

Represents overall direction of the heart’s electrical activity.

Answer 39

QRS Axis

Question 40

● Abnormalities hint at:

Answer 40

○ Ventricular enlargement
○ Conduction blocks
○ Anatomic malposition of the heart

Question 41

● Instantaneous mean vector
○ It is the summated vector of the generated potential.

● Normal QRS axis from -30°to +90°.

● -30° to -90° is referred to as a Left Axis Deviation (LAD)

● +90° to +180° is referred to as a Right Axis Deviation (RAD).

Answer 41

Diagram on page 10

Question 42

The Mean QRS Vector

Answer 42

● Average direction of the vector during spread of the depolarization wave through the ventricles.

● It is about +59 degrees.

● During most of the depolarization wave, the apex of the heart remains positive with respect to the base of the heart.

Question 43

The Vectorcardiogram:

page 10

Answer 43

● Vector of current flow through the heart changes rapidly as the impulse spreads through the myocardium.

● The vector increases and decreases in length because of the increasing and decreasing voltage of the vector.

● The vector changes direction because of changes in the average direction of the electrical potential from the heart.

Question 44

The Mean Electrical Axis of the Ventricular QRS

Answer 44

● The preponderant direction of the vectors of the ventricles during depolarization is mainly toward the apex of the heart. = 59 degrees

● During most of the cycle of ventricular depolarization, the direction of the electrical potential (negative to positive) is from the base of the ventricles toward the apex.

● The photo below shows how to determine the average QRS volume.

Question 45

Determining the Electrical Axis

page 11

Answer 45

● These are the steps in determining the electrical axis:
○ QRS complex in leads I and aVF.
○ Determine if they are predominantly positive or
negative.
○ The combination should place the axis into one of the 4 quadrants below.
● Example (what is the electrical axis?):

page 11

Question 46

Plotting the Electrical Axis

Answer 46

● The mean force during activation is represented by the area under the QRS waveforms, after plotting the vectors of 2 limb leads.

page 11

Question 47

Axis Deviation caused by Change in the Position of
the Heart in the Chest

Answer 47

● Shift to the left:
○ At the end of deep expiration
○ Supine position
○ Obesity

● Shift to the right:
○ At the end of deep inspiration
○ Standing position
○ Tall, lanky people whose hearts hang downward

Question 48

Abnormal Ventricular Conditions that cause Axis
Deviation

Answer 48

● Change in the Position of the heart in the chest

● Hypertrophy of 1 Ventricle
○ LVH
○ RVH

● Bundle Branch Blocks
○ LBBB (left)
○ RBBB (right)

Question 49

● Shift toward the hypertrophied ventricle

● Far greater quantity of muscle exists on the hypertrophied side allows greater electrical potential on that side.

● More time is required for the depolarization wave to travel through the hypertrophied ventricle.

● (Illustrations were presented earlier).

Answer 49

Axis Deviation caused by Hypertrophy of 1 Ventricle

Question 50

● If only one of the major bundle branches is blocked, the cardiac impulse spreads through the normal ventricle long before it spreads through the other.

● Therefore, depolarization of the 2 ventricles does not occur even nearly simultaneously, and the depolarization potentials do not neutralize each other. As a result, axis deviation occurs.

Answer 50

Axis Deviation caused by Bundle Branch Blocks

Question 51

Page 12: Illustration

Answer 51

● If you have a block in the right bundle branch, it would be manifested as a right bundle branch block or if you have a block there in the left, left bundle branch block. If you have to be very strict about it in the left bundle branch block, actually you can determine if it’s left anterior fascicular block or left posterior fascicular block.

● Current focus is on the left complete and right incomplete block. Okay, so if you have blocks in either of the major branches, it would be manifested as in the ECG as the widening of your QRS.

Question 52

Conditions that cause Abnormal Voltages of the QRS Complex
:

Increased VS Decreased Voltage

Answer 52

● Increased Voltage:
○ LVH
○ RVH

● Decreased Voltage
○ Caused by Cardiac Myopathies
○ Caused by conditions surrounding the heart:
■ Pericardial effusion
■ Pleural effusion
■ Pulmonary emphysema

Question 53

Conditions that cause Bizarre QRS Complexes

Answer 53

● Destruction of cardiac muscle in various areas throughout the ventricular system, with replacement of this muscle by scar tissue.

● Multiple small local blocks in the conduction of impulses at many points in the Purkinje system.

● As a result, cardiac impulse conduction becomes irregular, causing rapid shifts in voltages and axis deviations.

● Prolonged QRS Complex
○ Cardiac Hypertrophy or Dilatation
■ Longer pathways of conduction
■ QRS complex > 0.09 to 0.12 second
○ Purkinje system blocks

● Current of Injury
○ Damage of the heart muscle itself often causes part of the heart to remain partially or totally depolarized all the time.
○ Current flows between the pathologically depolarized and the normally polarized areas even between heartbeats.
○ The injured part of the heart is negative, because this is the part that is depolarized and emits negative charges into the surrounding fluids, whereas the remainder of the heart is neutral or positive polarity.
○ Abnormalities that can cause current of injury:
■ Coronary ischemia
■ Mechanical trauma
■ Infectious processes

Question 54

ECG DIAGNOSIS OF MYOCARDIAL INFARCTION (MI)

Answer 54

Diagnosing MI
● To diagnose a myocardial infarction you need to go beyond looking at a rhythm strip and obtain a 12-Lead ECG.

● ST Segment Elevation
○ One way to diagnose an acute MI is to look for
elevation of the ST segment.
○ Elevation of the ST segment (greater than 1 small
box) in 2 contiguous leads is consistent with an
acute myocardial infarction.

Question 55

Views of the Heart (Left Ventricle) in MI

Answer 55

● ECG localization of Areas of Infarction
○ Remember that the 12-leads of the ECG look at
different portions of the heart.

○ The limb and augmented leads “see” electrical
activity moving:
■ inferiorly (II, III and aVF),
■ to the left (I, aVL) and
■ to the right (aVR).

○ Whereas, the precordial leads “see” electrical activity in the posterior to anterior direction.

Question 56

Anterior MI
○ Best viewed using leads V1-V4

Page 13

Answer 56

Lateral MI
○ Best viewed using Leads I, avL and V5-V6

Page 13

Question 57

Inferior MI
○ Best viewed using leads II, III and avF

Page 14

Answer 57

Anterolateral Wall MI

Page 14

Question 58

Normal Impulse Conduction

Answer 58

● The illustration below shows the normal impulse
conduction.

● SA node → AV node → Bundle of His → Bundle Branches → Purkinje fibers

Page 14 Illustration

Question 59

Bundle Branch Blocks

Answer 59

● To Conduction in the Bundle Branches and Purkinje fibers are seen as the QRS complex on the ECG

● Therefore, a conduction block of the Bundle Branches would be reflected as a change in the QRS complex.

● With Bundle Branch Blocks you will see

● two changes on the ECG.
○ QRS complex widens (> 0.12 sec if block
complete).
○ QRS morphology changes (varies depending on ECG lead, and if it is a right vs. left bundle branch block).

Question 60

For ________, the wide QRS complex assumes a unique, virtually diagnostic shape in those leads overlying the right ventricle (V1 and V2).

Answer 60

Complete Right Bundle Branch Blocks (CRBBB)

Question 61

Complete Left Bundle Branch Blocks (CLBBB)

Pade 15

Answer 61

● For LBBB the wide QRS complex assumes a characteristic change in right ventricular leads - V1 and V2

● Well, this left bundle branch block is more malignant than your right, especially if it is acute.
○ Because it may represent acute MI. So, if it is not your old patient, the first time you see it in the ECG, you always investigate if it’s an acute MI or not.

● But if it’s your old patient, you already know that this patient is a complete left bundle branch block, then you don’t have to worry. The right bundle branch block is common in younger female patients, probably your age group. You don’t have to do anything about it.

● It does not cause any major abnormalities. So, I usually refer to patients coming to me for clearance from work because they read the complete bundle branch block. The company that is blocking it, so immediately clear this patient.

Question 62

The difference between RBBB and LBBB Illustration: page 15

Question 63

Sample ECGs page 15-17 tracings

Answer 63

• Sinus Tachycardia
• Sinus Bradycardia
• Sinoatrial Block
  ● The impulse from the sinus node is blocked before it enters the atrial muscle.
  ● Sudden cessation of P waves, with resultant standstill of the atria. However, the ventricles pick up a new rhythm, with the impulse usually originating spontaneously in the AV node, so the rate of the ventricular QRS-T complex is slowed but not otherwise altered.
• 1st Degree AV Block
• 2nd Degree AV Block
  ● Atrial P wave but no QRS-T wave, “dropped beats” of the ventricles.
• Mobitz Type 1 (Wenckebach) - 2nd Degree AV Block
• Mobitz Type 2 - 2nd Degree AV Block
• 3rd Degree/Complete AV Block
• Premature Ventricular Contractions (PVC)
  ● Characteristics of PVCs:
  ○ The QRS complex is usually considerably prolonged.
  ○ The QRS complex has a high voltage.
  ○ After almost all PVCs, the T wave has an electrical
  potential polarity exactly opposite to that of the QRS complex because the slow conduction of the impulse through the cardiac muscle causes the muscle fibers that depolarize first also to repolarize first.
• Premature Atrial Contractions
  ● Numerous small depolarization waves spread in all directions through the atria during atrial fibrillation because the waves are weak and many of them are of opposite polarity at any given time, they usually almost completely electrically neutralize one another.
  ○ In ECG, either no P waves from the atria or only a
  fine, high-frequency, very low voltage wavy record.
  ○ The QRS-T complex is normal unless there is some pathology of the ventricles, but their timing is irregular.
• Atrial Fibrillation
• Ventricular Tachycardia (VT)
  ● Paroxysmal VT
  ○ Three or more ventricular beats with a maximal
  duration of 30 seconds
  ● Sustained VT
  ○ A VT of more than 30 seconds duration (or less if
  treated by electrocardioversion within 30 seconds)
• Ventricular Fibrillation
• Asystole
• Acute Pericarditis
  ● Characterized by diffuse ST elevation and PR depression
• Cardiac Tamponade
  ● Characterized by low-amplitude complexes or presence of electrical alternans
  ○ Alternating beat to beat variation in the direction, amplitude, and duration of ECG waveforms
• Hypothermia - Osborne Wave (J point elevation)

Question 64

KEY POINTS FOR PRACTICING ECG READING

Answer 64

Obtain a 12-Lead ECG or a 10-second Lead II or Lead III Rhythm Strip

● Output should include:
○ Determine the rhythm
○ Determine the HR (show computation)
○ Plot and determine the mean QRS axis using Leads I and III/avF
○ Describe the P waves
○ Describe the PR interval
○ Describe the QRS complex
○ Describe the T waves
○ Complete ECG diagnosis

● Samples:
pages 17 & 18