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103: Theme 3 - 304 - Cardiovascular > Heart Contraction and ECG! > Flashcards

Heart Contraction and ECG! Flashcards

1
Q

What causes the delay in the AV node during a contraction?

A
  • decreased number of gap junctions in successive cells in the conduction pathway
  • smaller fibres
  • more cell junctions per cell junctions per length distance travelled
  • results in a greater resistance to conduction of excitatory ions between conducting fibres
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2
Q

What is a functional syncytium?

A
  • many cells with their own cell membrane that function as one
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3
Q

What are the three types of cardiomyocytes

A
  • Pacemaker cells
  • Conducting cells
  • Contractile cells
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4
Q

What is the speed of a Purkinje fibres?

A
  • up to 5 m/s (running)
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5
Q

What is the speed of an AV node?

A
  • 0.05m/s (walking)
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6
Q

What are gap junctions?

A
  • they are tiny holes found within intercalated discs
  • this is where two cell membranes of cardiomyocytes fuse to form permeable ‘communicating’ junctions
  • the more gap junctions that are open the less resistance present therefore faster conduction times
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7
Q

What is the journey of electrical conduction in the heart?

A

SA node -(via internodal bundles)-> AV node: conducted very slowly 0.05m/s. –> Bundle of His: –> bundle branches of ventricles –> ventricular contractile myocardium: to Purkinje cells

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8
Q

What is the function of Internodal Bundles?

A
  • conduct impulses from the SA node to the AV node
  • ensures the atria contracts in synch
  • provides faster contraction than atrial muscle 1.0m/s
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9
Q

Why is the atrial conduction slower?

A
  • delay in AV node conduction
  • less gap junctions, and smaller cells therefore greater resistance
  • allows ventriculare refill before ventricular systole
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10
Q

What is the order of ventricular depolarisation?

A

Septum –> Apex –> atrioventricular groove

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11
Q

What is a Holter Monitor?

A
  • 24/7 determination of the heart rate via the ECG
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12
Q

What is a Lead?

A
  • a configuration of electrodes that is on the skin

- looks at the change of electrical potential in the direction of the Lead configuration (diagonal for Lead II)

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13
Q

Describe the configuration of Lead II

A
  • the +ve on the left leg
  • the -ve on the right arm
  • a ground on the right leg
  • a bipolar lead
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14
Q

What bipolar leads are there?

A
  • Lead I, II, II

- all on the frontal plan

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15
Q

What is an augmented lead?

A
  • when a positive electrode is compared to a composite reference electrode made of the two other limb electrodes connected
  • there are three of these Lead II
  • aVR, aVL, aVF: all on the frontal plane
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16
Q

What is a precordial lead?

A
  • a positive electrode is compared to an estimate of what is happening at the centre of the heart
  • V1-V6, starting in the 4th intercostal space
  • a ‘chest’ lead: a configuration one electrode is placed on the chest and the ‘negative’ terminal being Wilson’s central terminal
  • makes measurements of electrical activity in the transverse plane
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17
Q

What action potential gives the P-wave?

A
  • depolarization of atria in response to the SA node being stimulated
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18
Q

What action potential gives the PR segment?

A
  • this is the delay occuring in the AV node that allows the ventricles to fill
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19
Q

What does the QRS complex show?

A
  • the depolarization of ventricles, triggers main pumping contractions
  • the direction of travel of the electrical potential around the ventricles
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20
Q

What action potential gives the the ST segment

A
  • the beginning of ventricle repolarization

should be flat

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21
Q

What action potential gives the T-wave

A

ventricular repolarization

22
Q

What does a wide QRS complex show?

A
  • the ventricular conduction is abnormal

- ectopic pacemaker or bundle branch block

23
Q

What does a large (deep) Q wave show?

A
  • a sign of dead tissue, usually from an old MI
24
Q

What is Sinus Rhythm?

A
  • when every P wave has a QRS complex and every QRS complex has a P wave
  • when the PR interval is always 3-5 little boxes- 120-200 millisec.
25
Q

What are the timings for the ECG graph paper intervals?

A
  • little box = 40 milliseconds

- big red box = 200 milliseconds

26
Q

What are the normal PR interval duration?

A
  • 3-5 little boxes

- 20 - 200 milliseconds

27
Q

What are normal QRS complex duration?

A
  • 80-120 ms

- 2-3 boxes

28
Q

What is normal QT interval Duration?

A
  • 360-460 milliseconds

- 9-11.5 little boxes

29
Q

Describe is the autonomic control of the heart

A
  • parasympathetic input: via the vagus nerve- muscarinic stimulation, decrease contractility and heart rate
  • sympathetic input- increase in contractility and HR
30
Q

What are Heart blocks?

A
  • a type of dysrhythmia
  • any kind of impulse conduction black of the heart
  • AV block, Bundle Branch block
31
Q

What effects parasympathetic supply of the heart?

A
  • Muscarinic antagonist: Atropine
32
Q

What is sympathetic input to the heart?

A
  • Beta agonists and Beta blocker
33
Q

What causes heart blocks?

A
  • Ischaemia of AV node or AV bundle

- Compression of AV bundle by scar or calcified tissue

34
Q

What are the symptoms of heart block?

A
  • asymptomatic
  • palpitations
  • dizziness, syncope, malaise
  • risk of sudden death
35
Q

Describe and explain first degree heart block

A
  • When the PE interval is > 5 little boxes
  • all P waves have a QRS complex
  • asymptomatic
  • young people
  • due to delayed AV node transmission
36
Q

Describe and explain Mobitz type 1, second degree heart block

A
  • Wenckebach:
  • some P-waves are blocked and are not followed by QRS ( some atrial signals fail to get to the ventricles)
  • the PR interval gets longer until the QRS is missing
  • usually followed and watched
37
Q

Describe and explain Mobitz type II second degree heart block

A
  • Hay: higher risk than Wenckebach
  • some P waves are blocked and are not followed by QRS complex
  • PR interval remains the same
  • likely a problem with the Bundle of HIs
  • can progress to 3rd degree heart block
38
Q

Third degree heart block

A
  • P-waves are out of sync
  • PR intervals are not all the same: shows that AV node is being conducted
  • symptomatic of insufficient output of the ventricles
39
Q

What are escape beats?

A
  • when the atrial beats are delayed or prevented

- ectopic beats or the AV node trigger theses escape or premature beats

40
Q

What are premature beats?

A
  • triggered by irritable heart tissue
  • wide and weird looking ventricular activity
  • no S wave
  • wide QRS complex
41
Q

What does the ECG of Atrial Fibrillation show?

A
  • no P wave

- you see Flat line or wiggly line instead of P waves

42
Q

What is the effect of Atrial fibrillation?

A
  • often occur in the elderly
  • due to slow flow of blood
  • stroke risk
  • require anticoagulants
43
Q

What is 2nd degree heart block show?

A
  • something wrong with the transmission from the atria to the ventricles
44
Q

What is respiratory Sinus Arrhythmia?

A
  • heart beat is slightly faster during inspiration, slightly sower during expiration
  • shorter RR interval in inspiration than in expiration
45
Q

What does ST Segment Elevation indicate

A
  • Acute MI
  • STEMI
  • looks like a bed with a spiky headboard
46
Q

What is a P-Q/P-R interval?

A
  • beginning of the P wave and beginning of the QRS complex
47
Q

What is Wilson’s central terminal?

A

a combination of electrodes that act together as if they were a reference electrode positioned in the centre of the heart

48
Q

What are the speed of ventricular myocytes?

A

0.3-0.5 m/s

49
Q

What is the speed of the fastest neurons?

A

~100m/s

50
Q

What is the scale used to calculate rate from an ECG?

A
  • the horizontal scale is 2.5cm/sec:
  • 1mm per 40ms
  • 5 big boxes = 1 sec
  • 300/ no. big boxes
    or use 1 big box = 300 bpm

103: Theme 3 - 304 - Cardiovascular (12 decks)

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