Cardio L3 ECG

Question 1

Electrical Conducting system:

consists of and function

Answer 1

1. Consists of modified myocytes with few contractile filaments.
    Function: Generates and conducts the electrical impulses that trigger contraction

Question 2

Valsalva manouevure 

Answer 2

Exhale against closed glottis therefore increase intrathoracic pressure and impeding return of blood to heart.

Question 3

Sinoatrial node: (5)

Answer 3

1. Physiological pacemaker
2. Excitability (generates AP
3. Automaticity (spontaneous – separate from CNS)
4. Rhythmicity (regular)
5. Dominance over other potential pacemakers by overdrive suppression.

Question 4

Electrophysiology of the SA Node:

Answer 4

1. Several currents are involved
2. No “fast” sodium channels (unlike neurone)
3. Unstable resting membrane potential or pacemaker potential – as membrane drifts towards threshold AP will occur.

Question 5

Process: of SA node

Answer 5

a. During pacemaker potential slow Na influx (funny current)
b. Upstroke  Calcium influx
c. Repolarisation  K current.

Question 6

Control of Heart rate:

Answer 6

1. Resting adult Human has a heart rate of 60-100 beats per minute
2. Autonomic control
3. Temperature

Question 7

a. Sympathetic 

Answer 7

Innervates large areas of heart and the artrioventricular and sinoatrial nodes.

Question 8

parasympathetic

Answer 8

 Carried in vagus nerve predominatly innervates sinoatrial node and atrioventricular node.

Question 9

Parasympathetic System and Acetylcholine: SLOW HR process

Blocked by

Answer 9

1. Fibres in the vagus (left and right) nerves
2. Release Ach
3. Ach binds to muscarinic receptors
4. Pacemaker cells become hyperpolarised
   a. Decreases rate at which pacemaker potential reaches threshold (Negative chronotropism) -> decreases heart rate.
   b. Block: atropine

Question 10

Sympathetic: SPEEDDS HR

Answer 10

1. Postganglionic fibres originate T1 to T5 and synapse in the paravertebral ganglia
2. Postganglionic fibres release noradrenaline]Noradrenaline agonises Beta-1 adrenoceptors
3. Increases slope of pacemaker potential
4. Increases heart rate (Positive chronotropism)

Question 11

Intrinsic Heart Rate:

Answer 11

1. At rest parasympathetic and sympathetic systems are tonically active.
2. Pharmacological blockade of both systems causes 50% increase in intrinsic heart rate, thus at rest the parasympathetic effects are dominant
   a. Tachycardia  >100/min
   b. Bradycardia  <60/min

Question 12

Atrial Conduction:

Answer 12

1. Atria acts as a syncytium  cells physically separate but electrically act together:
2. Myocytes are joined by intercalated dics containing gap junctions
3. Rapid propagation as myocytes have fast sodium channels.

Question 13

Atrioventricular Node: Calcium current
located at
lacks

Answer 13

1. Located in the right atrium
2. Lacks fast sodium channels
3. Dromotropism

Question 14

Atrioventricular Node: function

Answer 14

: A slow conduction velocity ensures that atria contract and fill the ventricles before the ventricles contract.

Question 15

Dromotropism

Answer 15

change in conduction velocity

a. Positive  during exercise
b. Negative  decrease in rate of conduction between two nodes.

Question 16

His Bundle, bundle Branches and purkinje Fibres:

Answer 16

1. All are formed from Purkinje cells
2. The bundle of His is the only electrical connection between the atria and ventricles.
3. Pathological connections such as the Bundle of Kent may predispose to arrhythmias (WPW syndrome)  extra pathological connection between atria and ventricles.

Question 17

Purkinje cells:

Answer 17

1. These are cells adapted for rapid conduction (200 cm//sec)
2. Wide diameter
3. Few myofibrils
4. Numerous gap junctions

Question 18

SA node and atrioventricular node channel typr

Answer 18

 shallow up stoke as they lack fast sodium channels and depend on calcium channels

Question 19

channel type

Atrial mycocytes, ventricular myocytes and purkinje

Answer 19

fast upstroke as they have fast Na channels.

Question 20

Chain of events:

Answer 20

1. SA Noda
2. Atrial
3. AV Node
4. Purkinje Fibres
5. Endocardial
6. Midmyocardial
7. Epicardial

Question 21

Ventricular myocyte AP: phase 0

Answer 21

Rapid depolarisation due to opening sodium channels (Na)

Question 22

Ventricular myocyte AP: phase 1

Answer 22

Inactivation of sodium channels

Question 23

Ventricular myocyte AP: phase 2

Answer 23

Slow inward calcium channels (L-type) (Ica). Also known as the Plateau phase – contraction of myocyte.

Question 24

Ventricular myocyte AP: phase 3

Answer 24

Rapid repolarisation including IK via delayed rectifier potassium channels

Question 25

Ventricular myocyte AP: phase 4

Answer 25

Resting membrane potential

Question 26

ECG Flat | description

Answer 26

Isoelectric line

Question 27

ECG pwave | description

Answer 27

Atrial depolarisation

Question 28

ECG PR segment | description

Answer 28

Delay due to atrial-ventricular node

Question 29

ECG P-R interval description Clinical

Answer 29

0.12-0.2s Atrioventricular conduction Clinically affected by diseases that affect conduction between atria and ventricle = heart block and increase in PR interval.

Question 30

ECG QRS complex | description

Answer 30

<0.10s | Generated by depolarisation of ventricles.

Question 31

ECG S-T segment description Clinical

Answer 31

Period that the ventricles are depolarised. Clinically: 1. ST elevation = can be an indicated of MI ST depression – indicator of myocardial ischemia in angina

Question 32

ECG T wave description Clinical

Answer 32

Repolarisation of ventricles – same as depolarisation as it occurs from the outer surface (epi) to endocardial. Can be altered with electrolyte disturbance – hyperkalaemia = tall peak T waves. (arryhtmias causing)

Question 33

ECG QT interval description Clinical

Answer 33

<0.44s duration of ventricular activation Varies with heart weight Inherited disorders Prolonged = major risk factor for arrhythmias. Combination of antihistamines and grapefruit juice to causes prolonged QT intervals

Question 34

ECG U wave description Clinical

Answer 34

Not in every ECG (more common in younger) or a sign hypokaelaemia (U prominent and T wave flatten)

Question 35

Sinus rhythm

Answer 35

 The heart rate is between 60-100 bpm.  Regular  Every P wave is followed by a QRS complex

Question 36

Sinus arrhythmia

Answer 36

Normal in young adults and children:  Can alter in expiration and inspiration  Inspiration – HR increased (QRS shorter) Expiration – HR reduced R waves further apart