Normal Ecg

Question 1

The electrocardiogram (ECG) is

Answer 1

graphical record of potential differences generated during cardiac electrical activity.

Question 2

The electrical potentials are produced in the heart as the sum of

Answer 2

of the potentials generated by the heart muscle cells during depolarization and repolarization.

Question 3

Depolarisation =

Answer 3

change of the transmembrane potential determinated by the movement of electrical charges (electrons or ions)

Question 4

Repolarisation=

Answer 4

restoration of the resting transmembrane potential, induced by the movement of the electric charges in the opposite direction, which compensates for depolarization

Question 5

Where are the V1, V2 electrodes placed?

Answer 5

4th intercostal space

Question 6

What is the most common error in performing an ECG?

Answer 6

L to R reversal

Question 7

V1 and V2 are often misplaced. Such misplacement usually involves placing these leads too high on the chest. The resulting ECG may generate erroneous ECG patterns:

Answer 7

incomplete right bundle branch block, anterior T wave inversion, septal Q waves, ST-segment elevation. These features may falsely suggest acute or old cardiac ischemia, pulmonary embolism, or a type-2 Brugada pattern. On rare occasion, conversely, high placement of V1 and V2 may reveal a true type-1 Brugada pattern. The emergency clinician needs to be aware of the possibility of lead misplacement, and should know how to suspect it based on unusual P wave morphology in V1 and V2.

Question 8

What physiological / pathological situation mimics the L to R reversal?

Answer 8

Dextrocardia

Question 9

The 6 chest electrodes

Answer 9

V1- 4th intercostal space ,right sternal border
V2 - 4th intercostal space , left sternal border
V3 - Midway b/w V2 + V4 , left anterior axillary line
V4 - 5th intercostal space , Left midclavicular line
V5 - level with V4 , left anterior axillary line
V6 - level with V4 , left mid axillary line

Question 10

ECG lead =

Answer 10

the spatial ratio between two points where the electrodes are placed in the electric field of the heart.

Question 11

Bipolar (standard) limb leads (I, II and III)

Answer 11

They form an equilateral triangle, with the heart located in the center
were introduced by Einthoven.

Question 12

Unipolar (augmented) limb leads (aVR, aVL, aVF)

Answer 12

were introduced by Wilson. „

Question 13

Precordial leads (V1-V6)

Answer 13

are unipolar leads, in which the (positive) exploratory electrode is placed on the chest, near the heart

Question 14

Limb leads – Eithoven’s triangle

The heart walls “seen” from the different ecg limb leads :

Answer 14

Lateral wall of the LV : DI, aVL
Inferior wall : DII,DIII, aVF
Endocavitary wall/layer of the heart: aVR

Question 15

Precordial leads

The heart walls “seen” from the precordial leads:

Answer 15

Anterior wall of the heart : V1,V2
Interventricular septum: V3
Apex : V4
Lateral wall of the LV : V5,V6

Question 16

Ecg graph paper: 
- Small boxes of 
- Large boxes of 
Paper speed :
Voltage calibration:

Answer 16

1) 1mm
2) 5mm
3) 25 mm/sec
4) 10 mm /mV

Question 17

ECG Recommended steps

Answer 17

Heart rate 
Axis 
Morphology of the waves
Segments and intervals analysis 
Chamber enlargements
Specific changes

Question 18

The cardiac cycle normally begins with initiation of the impulse at the

Answer 18

sinoatrial, or SA node.

Question 19

After the SA node fires, the resulting depolarization wave passes through

Answer 19

the right and left atria, stimulating atrial contraction and producing the P-wave on the surface ECG.

Question 20

Following activation of the atria, the impulse proceeds to the

Answer 20

trioventricular (AV) node, which is the only normal conduction pathway between the atria and the ventricles.

The AV node slows impulse conduction, allowing time for the atria to contract and blood to be pumped from the atria to the ventricles prior to ventricular contraction. Conduction time through the AV node accounts for most of the duration of the PR interval.

Just below the AV node, the impulse passes through the bundle of His.

Question 21

After the impulse passes through the bundle of His

Answer 21

it proceeds through the left and right bundle branches.

Question 22

After leaving the left and right bundle branches,

Answer 22

the impulse passes through the Purkinje fibers, which are interlacing fibers of modified cardiac muscle. On the ECG this is represented as the Q wave.

Question 23

The impulse passes quickly through the bundle of His, the left and right bundle branches, and the Purkinje fibers, leading to

Answer 23

depolarization and contraction of the ventricles.

Question 24

P wave

Answer 24

atrial depolarisation

can be positive , equidiphasic or negative

Question 25

QRS complex

Answer 25

ventricular depolarisation Q wave : the first negative deflection before the R wave R wave: positive deflection S wave: the first negative wave after the R wave

Question 26

T wave

Answer 26

ventricular repolarization | can be positive , equidiphasic or negative

Question 27

Abnormalities of axis can hint at:

Answer 27

``` Ventricular enlargement Conduction blocks (i.e. hemiblocks) ```

Question 28

By near-consensus, the normal QRS axis is defined as ranging from : -30° to -90° is referred to as : +90° to +180° is referred to as :

Answer 28

1) -30° to +90 2) left axis deviation (LAD) 3) right axis deviation (RAD)

Question 29

Key Principles

Answer 29

If the QRS is POSITIVE in any given lead, the axis points in roughly the same direction as this lead. If the QRS is NEGATIVE in any given lead, the axis points in roughly the opposite direction to this lead. If the QRS is ISOELECTRIC (equiphasic) in any given lead (positive deflection = negative deflection), the axis is at 90° to this lead.

Question 30

Common causes of LAD

Answer 30

``` May be normal in the elderly and very obese Due to high diaphragm during pregnancy, ascites, or ABD tumors Inferior wall MI Left Anterior Hemiblock Left Bundle Branch Block WPW Syndrome Congenital Lesions RV Pacer or RV ectopic rhythms Emphysema ```

Question 31

Common causes of RAD

Answer 31

``` Normal variant Right Ventricular Hypertrophy Anterior MI Right Bundle Branch Block Left Posterior Hemiblock Left Ventricular ectopic rhythms or pacing WPW Syndrome ```

Question 32

Normal Sinus Rhythm

Answer 32

``` Originates in the sinus node Rate between 60 and 100 beats per min P wave axis of +45 to +65 degrees, ie. Tallest p waves in Lead II Monomorphic P waves Normal PR interval of 120 to 200 msec Normal relationship between P and QRS Some sinus arrhythmia is normal ```

Question 33

p wave upright in leads

Answer 33

I and II

Question 34

The P wave

Answer 34

< 3 small squares in duration | < 2.5 mm in amplitude

Question 35

Junctional escape

Answer 35

Depolarization initiated in AV junction when 1 or more impulses from the sinus node are ineffective or nonexistent. Rate : 40- 60 bpm Rhythm : Irregular in single junctional escape complex ; regular in junctional escape rhythm P waves : depends on the site of the ectopic focus.They will be inverted , and may appear before or after the QRS complex , or they might be absent , hidden by the QRS . QRS is usually normal

Question 36

Junctional escape

Answer 36

Depolarization initiated in AV junction when 1 or more impulses from the sinus node are ineffective or nonexistent. Rate : 40- 60 bpm Rhythm : Irregular in single junctional escape complex ; regular in junctional escape rhythm P waves : depends on the site of the ectopic focus.They will be inverted , and may appear before or after the QRS complex , or they might be absent , hidden by the QRS . QRS is usually normal ( No relation b/w P wave and QRS complex??)

Question 37

PR interval

Answer 37

AV node conduction From the beginning of P wave to the beginning of q wave 120-200 ms

Question 38

Short PR interval

Answer 38

``` WPW Syndrome delta wave short PR ( 0.08s) long QRS 0.12 sec ``` Accessory pathway ( Bundle of Kent ) allows early activation of the ventricle ( delta wave and short PR interval)

Question 39

Normal QRS complex

Answer 39

Completely negative in lead aVR , maximum positivity in lead II rS in right oriented leads and qR in left oriented leads (septal vector) Transition zone commonly in V3-V4 RV5 > RV6 normally Normal duration 50-110 msec, not more than 120 msec Physiological q wave not > 0.03 sec

Question 40

Amplitude of QRS

Answer 40

Depends on the following factors 1. electrical force generated by the ventricular myocardium 2. distance of the sensing electrode from the ventricles 3. Body build;a thin individual has larger complexes when compared to obese individuals

Question 41

Left ventricular hypertrophy Sokolow & Lyon criteria Cornel criteria others

Answer 41

S&L : S (V1) + R(V5 or V6)>35mm Cornel criteria : S(V3) + R(avL)> 28 mm ( men ) or > 20 mm ( women) others : R (avL) > 13mm

Question 42

Premature ventricular Complexes (PVCs)

Answer 42

is a relatively common event where the heartbeat is initiated by the heart ventricles ( arrow ) rather than by the SA node.Rate depends on underlying rhythm and number of PVCs. - Ocassionally ireegular rhythm . - no p wave associated with PVCs - May produce bizarre looking T wave

Question 43

Artificial pacemaker

Answer 43

Sharp , thin spike Rate depends on pacemaker , p wave may be absent or present Ventricular paced rhythm show wide ventricular pacemaker spikes

Question 44

localizing MI

Answer 44

Look at ST changes | Q wave in all leads

Question 45

Location of MI Anterior Septum Left lateral

Answer 45

Lead with ST change : Affected coronary artery : 1) V1,V2,V3,V4 , LAD 2) V1,V2 LAD 3) I ,avL ,V5,V6 Left circumflex artery

Question 46

``` Location of MI Inferior Right atrium Posterior Right ventricle ```

Answer 46

``` Lead with ST change : Affected coronary artery : 1)II,III,avF RCA 2) aVR ,V1 RCA 3) Posterior chest leads RCA 4) Right sided leads RCA ```

Question 47

T wave

Answer 47

Reflects ventricular repolarization ( epicard -> endocard) Aspect : rounded , assymetric, with steeper downward slope Consostent with QRS complex positive in most derivatives negative :avR +/- in LIII,avF,V1 Amplitude < 1/3 QRS ( <6 mm) Duration : 0.13 - 0.30 s Modified by factors: Physiological : SNVP -> T high asymmetric ( precordial) Humoral factors : Decreased PO2 ,Ca++,K+

Question 48

U wave

Answer 48

corresponds to papillary muscle repolarization or post-depolarization in Purkinje fibers Aspect : small , rounded Same direction with T waves from the same derivation Amplitude < 1/4 from the same derivation : more obvious decreased FC , [K+] Better expressed in chest precrodial leads ( V1 ,V2)

Question 49

QT interval

Answer 49

Normally corrected for HR Bazett's formula Normal 350 to 430 msec With a normal HR (60-100), the QT interval should not exceed half of the RR interval roughly

Question 50

Measurement of QT interval

Answer 50

The beginning of the QRS complex is best determined in a lead with an initial q wave -> LI,II,avL,V5 or V6 QT interval shortens with tachycardia and lenghthenswith bradycardia

Question 51

QTc

Answer 51

``` Normal QTc Men < 0.43 - borderline 0.43 - 0.45 - prolonged >0.45 Women <0.43 - borderline 0.43 - 0.47 - prolonged >0.47 ```

Question 52

Causes of Long QTc

Answer 52

``` Congenital - Romano Ward - Jervell and Lange Nielson Drugs - Antiarrhythmics - Class Ia and III - Antibacterials - Erythromycin Other drugs - Terfanidine, cisapride, TCA ``` ``` Electrolyte disturbances - Low K and Mg Other causes - IHD - SAH - Bradycardia due to SSS or AV block - Hypothyroidism ```

Question 53

Shortened QT

Answer 53

Digitalis effect Hypercalcemia Hyperthermia Vagal stimulation

Question 54

Normal variants in ECG

Answer 54

Sinus arrhythmia Persistent juvenile pattern Early repolarisation syndrome Non specific T wave changes

Question 55

Features of ERPS

Answer 55

``` Vagotonia / athletes’ heart Prominent J point Concave upwards, minimally elevated ST segments Tall symmetrical T waves Prominent q waves in left leads Tall R waves in left oriented leads Prominent u waves Rapid precordial transition Sinus bradycardia ``` Early Recognition Prevents Streptokinase infusion !

Question 56

ECG Motion Artifacts Overview

Answer 56

Motion artefact due to tremor or shivering can obscure the waveforms of the ECG or stimulate pathology , making ECG interpretation difficult In certain circumstances ( e.g hypothermia ) the presence of shivering artefact may actually aid diagnosis

Question 57

Causes of Tremor

Answer 57

``` Benign Essential Tremor (physiological tremor ) Parkinsons Disease (resting tremor ) Cerebellar disease (intention tremor) Alcohol /Benzodiazepine withdrawal Anxiety Thyrotoxicosis Multiple sclerosis Drugs : Amphetamines , cocaine , β- agonists (adrenaline , salbutamol) theophylline,caffeine , lithium ```

Question 58

Other types of motion artefacts

Answer 58

Fever ( rigors) Hypothermia (shivering) Cardiopulmonary resuscitation ( chest compressions) A non-compliant , mobile ,talkative patient ( = the most common cause)

Question 59

The role of ECG

Answer 59

HR determination; Assessment of cardiac conduction function; Determination of the electrical axis of the heart; Determination of: cardiac arrhythmias and conduction disorders; Determination of ischemic changes It does NOT provide information about the pump function of the heart.