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Theme 3 > ECG > Flashcards

ECG Flashcards

1
Q

Syncytium

A

One large “cell” having many nuclei that are not separated by cell membrane

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2
Q

Functional syncytium

A

Many cells functioning as one

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3
Q

Propagation speed

A

Contractile - atrial and ventricular myocytes 0.3-0.5 m/s
Conducting system (modified cardiomyocytes)
Purkinje fibres up to 5 m/s
cf fastest neurons ~100 m/s
AV node 0.05 m/s

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4
Q

Impulse spread in atria

A

Internodal Bundles conduct impulse from SA node to AV node
Bundles ensure synchronous contraction of the atria

Conducting via atrial muscle would be slow
0.3-0.5 m/s
Conducting via bundles is much faster
1.0 m/s

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5
Q

Delay at AVN

A

30 ms from SA to AV node
90 ms delay before enters penetrating portion of AV bundle
40 ms delay in penetrating bundle

Increased RESISTANCE
smaller fibres which lead to:
More resistance along length of fibre (smaller diameter)
More intercellular junctions (shorter length)
With diminished numbers of gap junctions per surface area

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6
Q

ventricular propagation

A

AV node connects to the bundle of His followed by Purkinje fibre system

Purkinje fibres are very large myocytes - transmit the impulse faster
Bigger diameter cells conduct faster - 5m/s

After slower conduction between contractile myocytes can occur
0.3 - 0.5 m/s

First part of ventricular wall to be depolarised is septum, then apex
Last part is atrioventricular groove

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7
Q

Ventricular propagation order

A

First part of ventricular wall to be depolarised is septum, then apex
Last part is atrioventricular groove

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8
Q

ECG definition

A

The ECG is a gross electrical measurement of the heart

The electrical activity of the heart is measured on the skin

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9
Q

ECG use in diagnosis

A

Excellent for rate
Holter monitor (ECG) allows 24/7 rate determination
Esp. useful when Atrial rate ≠ Ventricular rate

Many Subtleties
Not a one-stop-diagnosis
Patient Hx essential for interpretation

Diagnosis requires other techniques
ECG is very fast and affordable

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10
Q

Lead

A

A configuration of electrodes (usually consisting of a positive electrode, a negative electrode, and sometimes a ground).

A standard “12-lead ECG” looks at the heart from 12 different angles, creating measurements for 12 leads, using 10 separate electrodes.
Lead II has the positive electrode on left leg, negative electrode on right arm, and the ground electrode on the right leg (although the ground could be almost anywhere).

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11
Q

12 standard leads

A

3 bipolar leads
I, II, III
Frontal plane

3 “augmented” leads,
aVR, aVL, and aVF
Frontal plane

6 “precordial”
on the thorax near the heart
called V1, V2, V3, V4, V5, V6
transverse plane (spine to sternum)

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12
Q

Augmented Lead

Precordial chest

Bipolar Leads

A

Augmented Lead – a positive electrode is compared to a composite reference electrode made of the two other limb electrodes connected

Precordial chest (Unipolar) Leads – a positive electrode is compared to an estimate of what is happening at the centre of the heart

Bipolar Leads: a positive electrode is compared to a negative electrode (e.g. lead II)
Coronal plane

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13
Q

QRS complex

A

QRS = Transmission of depolarisation through the ventricular myocardium

If QRS is wide or misshapen, then ventricular conduction is abnormal, e.g. ectopic pacemaker or bundle branch block

More cells -> bigger contribution
Almost no contribution from His and conduction system

Large (deep) Q waves are a sign of dead tissue (old MI)

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14
Q

Sinus Rhythm

A

When the heart rhythm is generated from the Sino-Atrial Node

Each P wave is followed by a QRS complex

Each QRS complex is preceded by a P wave

When PR interval is always normal (3-5 little boxes)

Sinus Tachycardia is a tachycardia driven by the SA node beating too quickly
It has normal PR intervals, and each P matched with a QRS

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15
Q

ECG timing

A

PR interval - from start of P wave to start of QRS complex (name is misleading)

QT interval - from start of QRS complex to end of T wave

ST segment - from end of QRS complex to start of T wave

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16
Q

Normal intervals

A

PR interval Duration = 3-5 boxes
120 – 200 ms

QRS complex Duration = 2-3 boxes
80 – 120 ms

QT interval Duration = 9-11.5 boxes
360 – 460 ms

17
Q

Calculating rate

A

Horizontal scale is 2.5 cm/sec.
One little box = 1 mm = 40 ms (milliseconds)
A big box = 5 little boxes = 200 ms

To calculate rate, count how many big boxes occur between two P waves
For ventricular rate, count between R waves

18
Q

Autonomic Control of CVS

Rate & Contractility

A

The Heart: parasympathetic input
Vagus nerve: Muscaranic stim -> Decrease HR + contractility + conduction velocity
Parasympathetic withdrawal -> Increase HR +  contractility +  conduction velocity

The Heart: sympathetic input
Sympathetic stimulation -> Increase HR +  contractility +  conduction velocity

Stellate nerves
Beta agonists increased rate
Beta blockers  decreased rate

19
Q

Activation of

Beta(1)-adrenoceptors
Beta(2)-adrenoceptors
Alpha-adrenoceptors

A

Activating Beta(1)-adrenoceptors cause inotropism and chronotropism

Activating Alpha-adrenoceptors cause vasoconstriction

Activating Beta(2)-adrenoceptors cause vasodilatation in skeletal muscle (decreases peripheral resistance during exercise)

20
Q

Atropine

A

Anticholinergic drug that reduces parasympathetic activity. Until recently it was medically used to treat asystole and extreme bradycardia

21
Q

Heart Blocks

A

A type of dysrhythmia
any kind of impulse conduction block of the heart
Includes AV block, Bundle Branch Block, etc

22
Q

Atrio-ventricular Heart Blocks

A

Delay or failure of atrial signal stimulating ventricle

CAUSES
Ischaemia of AV node or AV bundle
Compression of AV bundle by scar or calcified tissue
Inflammation of the AV node or bundle
SYMPTOMS (esp. for serious 3rd degree heart block)
Can be asymptomatic
Palpitations
Hypotension-like: Dizziness, Malaise, Syncope
Risk of Sudden Death

23
Q

First degree heart block

A

When PR interval > 5 little boxes (200 ms)
Normal PR < 5 little boxes
But all P’s followed by QRS

Almost always asymptomatic
Often young people (adolescents)
Delayed AV node transmission
Rarely treated

24
Q

Mobitz Type I

Second degree heart block

A

Second degree Heart Block = Some P waves are blocked and are not followed by QRS – Some QRS complexes are “”missing”

Mobitz Type I (Wenckebach)
PR interval gets longer until QRS wave fails to follow P wave
Likely cause is AV node damage
Usually no treatment given *E

25
Q

Mobitz Type II

Second degree heart block

A 
Mobitz Type II (Hay)
Some P waves are blocked and are not followed by QRS 
PR interval remains the same
Likely Problem in Bundle of His
High risk 
Can progress to 3rd degree heart block
Treatment: Implant Pacemaker

Theme 3 (16 decks)

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