Myocardial Ischemia, Injury and Infarction

Question 1

Myocardial Ischemia

Answer 1

Definition
– Lack of blood flow (and therefore O2) to
myocardium due to narrowing and/or spasm of one or more coronary arteries
– Hypoxia may lead to injury or infarction

Question 2

Normal PaO2

Answer 2

normal PaO2 = 80-100mmhg

hypoxemia (like in lung disease patients) = less than 80mmHg

Question 3

cadiac vs somatic tissues use of O2

Answer 3

tissue at rest 100mlO2 are delivered but tissue will take 24mls (75 reserve)

but cardiac tissue is different - it takes 70% at rest - reserve is only 30%

**so the only way to get the heart more oxygen is to deliver more

Question 4

Left coronary arteries (3)

Answer 4

• Left anterior descending or left anterior interventricular
artery
• Circumflex artery
• Left marginal artery

Question 5

Right coronary arteries (2)

Answer 5

• Right marginal artery

* Posterior descending or interventricular artery

Question 6

Symptoms of myocardial ischemia

Answer 6

Sub sternal chest pressure or pain called angina pectoras 
– Pain radiates to Neck /Jaw or arm
– Shortness of breath
– Nausea/vomiting
– Tachycardia (or bradycardia)
– Diaphoretic
– Anxious/upset
– No symptoms?? --> or denial

Question 7

Treatment of myocardial ischemia

Answer 7

• Rest
• Coronary vasodilators (eg.nitroglycerin) (works by relaxing the smooth muscle in the coronary arteries.. often the problem is the plaque build up though)
• O2 Therapy (not used often anymore.. inhibits dialation and patients have worse outcomes)

Question 8

Myocardia Ischemia ECG changes

Answer 8

T wave inversion (abnormal repolarization)
• ST depression ( 1 to 2 mm or more for a
duration of 0.08 second)
• Normal ST segment?? (see handout)
- DIAGNOSTIC Positive Cardiac Stress Test indicator

Question 9

Myocardial Injury

STEMI – “ST Elevation Myocardial Infarction”

Answer 9

ECG changes
• ST elevation in leads measuring affected area –> ST depression in lead opposite affected area

ST Elevation: not more than 1 mm in Standard
leads; not more that 2 mm in Precordial (chest)
leads

Occurs in Early stages of STEMI (first few hours) “acute myocardial infarction” –> leads to full myocardial infarction

Question 10

Myocardial Infarction

Answer 10

AMI – Acute Myocardial Infarction
• Infarction = Cell death/necrosis
• Pathological Evolvement
• Starts at sub-endocardial level and moves like a “wave” across the myocardial thickness
• Transmural Infarction refers to full thickness tissue necrosis

Question 11

Myocardial infarction damage

Answer 11

Irreversible damage can occur at 20-40 post
arterial occlusion
• If coronary reperfusion occurs within 6 hours
tissue necrosis may be limited

Question 12

Myocardial infarction treatment

Answer 12

Drugs used early if possible – tPA and fibrinolytics (Streptokinase)
- Clotting is a positive feed back system drugs are used to breaks down fibrin and reduce blockage

Question 13

Myocardial infarction diagnosis

Answer 13

Symptoms as per ischemia (not relieved by nitro)
• ECG changes:
• Significant Q waves and ST elevation in leads of affected area with reciprocal ST depression
• Significant Q waves:
• usually 0.04 second (one small box) or more in width or one-fourth to one-third the height of the R wave
• May appear within few hours to over 24 hours

Question 14

Locating MI’s: Anterior

Answer 14

Leads V1-4

Question 15

Locating MI’s Septal

Answer 15

Leads V1, V2

Question 16

Locating MI’s lateral

Answer 16

Leads L1, AVL, V5, V6

Question 17

Locating MI’s inferior

Answer 17

Leads L2, L3, AVF

Question 18

Locating MI’s Posterior

Answer 18

large R’s and ST depression in V1,

V2, perhaps Q’s in V6 … can move over leads to 7,8,9 position