MP323 - ACUTE MI

Question 1

myocardial infarction

Answer 1

HEART ATTACK
the interruption of blood supply to part of the heart, causing some heart cells to die

Question 2

NSTEMI

Answer 2

non-ST-segment elevation MI

Question 3

how does NSTEMI occur

Answer 3

occurs by developing a complete occlusion of a minor coronary artery or a partial occlusion of a major coronary artery previously by atherosclerosis.

this causes a partial thickness damage of heart muscle

Question 4

STEMI

Answer 4

ST-segment elevation MI

Question 5

how does STEMI occur

Answer 5

occurs by developing a complete occlusion of a major coronary artery previously affected by atherosclerosis

this causes full thickness damage of heart muscle

Question 6

how many hours are required for substantial amount of myocardial tissue to be saved

Answer 6

6 hours

Question 7

cellular changes associated with MI

Answer 7

1. development of infarct extension (new necrosis)
2. thinning and dilation of the infarct zone
3. ventricular remodelling (enlarged heart)

begin within hours of MI and reach peak at 7 to 14 days

Question 8

MI symptoms

Answer 8

• chest pain, nausea, vomiting, sweating, breathing difficulty
• substernal pain can radiate to neck, left arm, back or jaw
• not relieved by rest or GTN
• GI upsets from pain resulting in vagal stimulation

Question 9

biochemical markers in MI

Answer 9

a rise and gradual fall (troponin) or more rapid rise and fall (creatine kinase MB) are indicators of myocardial necrosis with…
1. ischaemic symptoms
2. development of pathologic Q waves on the ECG
3. ECG changes indicative of ischaemia

Question 10

creatine kinase MB

Answer 10

• enzyme found primarily in heart muscle cells
• used as biochemical marker
• catalyses the conversion of creatine and utilizes ATP to create phosphocreatine (PCr) and ADP
• enzyme reaction is reversible and so ATP can be generated

Question 11

creatine kinase isoforms as biochemical markers

Answer 11

• CK-MB1 is the isoform found in plasma, CK-MB2 is found in tissues
• in MI patients, CK-MB2 levels rise, resulting in a CK-MB2 to CK-MB1 ratio greater than one

Question 12

diagnostic tests - troponin

Answer 12

sensitive marker of myocardial necrosis

necessary for establishing the diagnosis of MI consistent with ischaemia

Question 13

diagnostic tests - myoglobin

Answer 13

• myoglobin is an oxygen-binding protein found in skeletal and cardiac muscle
• myoglobin’s release from ischaemic muscle occurs earlier than the release of CK
• levels peak at 3 to 15 hours
• present in skeletal muscle so diagnostic value is limited

Question 14

diagnostic tests - lactate dehydrogenase (LDH)

Answer 14

• LDH is an enzyme of the anaerobic metabolic pathway
• function of LDH is to catalyse the reversible conversion of lactate to pyruvate with reduction of NAD+ to NADH
• blood levels of LDH are usually low
• when tissues are damaged they release more LDH into the bloodstream
• made up of two sub-units; H = heart, M = skeletal muscle

Question 15

electrical conduction

Answer 15

• sinoatrial node (SA)
• atrioventricular node (AV)
• bundle of His (common bundle)
• bundle branches
• Purkinje fibres

Question 16

the sinoatrial node (SA node)

Answer 16

• in the right atrium
• natural pacer of the heart
• self-initiates electrical activity in the heart at the rate of 60 - 100bpm

Question 17

the atrioventricular node (AV node)

Answer 17

• on the floor of the right atrium above the tricuspid valve
• electrical activity is delayed about 0.05sec which allows for atrial contraction and more complete filling of ventricles with blood

Question 18

bundle of His

Answer 18

conducts electrical activity from AV node to bundle branches

Question 19

Purkinje fibres

Answer 19

fine network that conduct the electrical impulses to the ventricular muscle

Question 20

ECG components

Answer 20

P-wave
QRS complex
T-wave

Question 21

P-wave (ECG)

Answer 21

represents firing of the SA node and depolarisation of the atria

Question 22

PR-interval (ECG)

Answer 22

the delay of the electrical impulse at the AV node and the depolarisation of the atrium

Question 23

PR segment (ECG)

Answer 23

the electrical conduction through the atria and the delay of the electrical impulse in the atrioventricular node

Question 24

Q-wave (ECG)

Answer 24

first negative deflection

Question 25

R-wave (ECG)

Answer 25

first positive deflection

Question 26

S-wave (ECG)

Answer 26

second negative deflection

Question 27

ST-segment (ECG)

Answer 27

the beginning of ventricular repolarisation, should be isoelectric (flat)

Question 28

T-wave (ECG)

Answer 28

the ventricles repolarise and recover to their normal electrical state

Question 29

what does an MI look like on an ECG

Answer 29

During the earliest stages, T-waves become tall and narrow - hyperacute stage

within a few hours, myocardial ischaemia results in the hyperacute T-waves inverting

inverted T-waves of ischaemia are symmetrical and relatively narrow

Question 30

Q-waves (ECG)

Answer 30

• last stage of an MI, initial downward deflection of the QRS complex
• represent the flow of electrical forces toward the septum
• with MI usually 0.04 seconds or more in width
• Q-waves indicate tissue necrosis and are permanent
• provide ECG evidence of a previous MI