Myocardial Infarction Flashcards
1
Q
Ischemic Heart Disease
- Ischemia
- Infarction
- Ischemic heart disease
A
- Ischemia
- Compromised blood supply or increased oxygen demand (supply-demand mismatch)
- Infarction
- Cell death due to ischemia
- Ischemic heart disease
- Chronic ischemia +/- infarction
2
Q
Ischemic Heart Disease
- Causes
- What happens
A
- Causes
- Coronary atherosclerosis
- Hypertension
- Heart failure
- Obesity
- Chronic pulmonary disease
- Anything that decreases O2 delivery or increases O2 demand
- What happens
- Supply-demand mismatch
- Myocardial ischemia in affected region
- Myocaridla infarction
- Other complications
3
Q
Blood Supply
- Right coronary artery
- Left anterior descending
- Left circumflex
A
- Right coronary artery
- RV
- Posterior LV / septum (75% of cases)
- Posteromedial papillary muscle
- SA & AV nodes
- Left anterior descending
- Anterior LV / septum
- Apex
- Left circumflex
- Lateral LV
- Posterior LV / septum (25% of cases)
4
Q
Quality of Myocardial Ischemia Depends On…
A
- Degree of arterial occlusion
- Collateral circulation
- Overall “health” of the heart
- Arrhythmia
5
Q
A patient has an acute right coronary artery thrombus. Where is the infarct most likely to occur?
A
Posterior septum
6
Q
What Happens in Acute MI
A
- Acute change in coronary artery plaque
- Rupture
- Hemorrhage
- Thrombosis
- Thrombosis
- Ischemic damage to myocardium
- Myocyte necrosis
- Other complications
7
Q
MI: Timing & Cellular Changes after Arterial Occlusion
- 2 mins
- 30 mins
- 1 hour
- 2-4 hours
A
- 2 mins = loss of contractility
- 30 mins = irreversible cell injury
- 1 hour = microvascular injury
- 2-4 hours = permanent damage
8
Q
Myocardial Infarction
- Progression of ischemia
- Predominance of occluded arteries
- Rare infarcts
A
- Progression of ischemia
- Typically begins in subendocardial region
- Can progress outward to transmural injury
- Predominance of occluded arteries
- LAD 40-50%
- RCA 30-40%
- LCx 15-20%
- Rare infarcts
- Isolated RV infarcts are rare
- Atrial infarcts rae even more rare
9
Q
Infarct Histology
- General
- Cells involved
- Early changes
- Middle changes
- Later changes
- Healing
A
- General
- Series of progressive changes
-
Cells involved
- Neutrophils
- Macrophages
- Fibroblasts (granultaion tissue)
-
Early changes (<24 hours)
- Initially no visible histology
- Then coagulative necrosis: “contraction band necrosis”
- Then neutrophil response
-
Middle changes (1-3 days)
- Initially neutrophils
- Then cellular debris
- Then macrophages
-
Later changes (3-7 days)
- Initially macrophages
- Then phagocytosis
- Then fibroblasts (granulation tissue)
- Greatest risk of myocardial rupture
-
Healing (7 days - weeks)
- Initially fibroblasts
- Then neovascularization
- Then collagen / fibrin
- Result: myocardial scar
10
Q
Post-Infarct Complications
A
- Arrhythmia
- Myocardial rupture
- Pericarditis
- Mural thrombus
- Ventricular aneurysm
- Ventricular remodeling
11
Q
What complication is most likely to occur 3-7 days after acute infarction?
A
Papillayr muscle rupture
12
Q
Arrhythmia
A
- Myocardial irritability
- Heart block (depending on location)
- Bradycardia, ventricular tachycardia, premature ventricular contractions
13
Q
Myocardial Rupture
A
- Free wall
- Hemopericardium
- Septum
- Causes acute VSD w/ left-to-right shunt
- Pappillary muscle
- leads to acute mitral valve insufficiency
14
Q
Dressler’s Syndrome
- aka
- After acute MI
- After bypass graft surgery
A
- aka
- Fibrinous pericarditis
- After acute MI
- 1-7 days later: acute inflammatory exudate
- 6-8 weeks later: autoimmune
- After bypass graft surgery
- Post-pericardotomy syndrome
15
Q
Mural Thrombus
A
-
Akinesis / hypokinesis of infarcted myocardium
- Blood pools on endocardial surface
- Thrombus forms
- Complication: embolization of thrombus
- Leads to stroke or gangrene
16
Q
Ventricular Aneurysm
A
- Infarcted myocardium thinned
- “Balloons outward” w/ forceful contractions of adjacent myocardium
- Thrombus can form in aneurysm
17
Q
Ventricular Remodeling
A
- Infarcted mycoardium dies (scar tissue)
- Surrounding myocardium hypertrophies
-
Result: zones of fibrosis w/ surrounding hypertrophy
- Myocardium can become thick & stiffened
18
Q
Sudden Cardiac Death
A
- Patient has severe coronary artery atherosclerosis
- No occlusive thrombus &/or no myocardial infarction
- Death due to arrhythmia, not infarction
- Typically ventricular fibrillation
19
Q
Treatment of Acute Myocardial Infarction
A
- Coronary artery bypass graft (CABG)
- Saphenous vein or synthetic vein
- Internal mammary artery (LAD): best result
- Percutaneous coronary intervention (PCI)
- aka Percutaneous transluminal coronary angioplasty (PTCA) or “angioplasty”
20
Q
Angina Pectoris
- Stable angina
- Unstable angina
- Prinzmetal angina
A
-
Stable angina
- Imbalance in coronary perfusion & oxygen demand
- Exercise induced
- Chronic atherosclerosis
-
Unstable angina
- Myocardial ischemia
- Thrombosis of coronary artery from plaque pathology
- “Preinfarction agina”
- At rest or minimal exertion
-
Prinzmetal angina
- Episodic ischemia from coronary vasospasm
- Occurs at rest
21
Q
Reperfusion Injury
- General
- Damaged myocardium is susceptible to…
A
- General
- Blood flow restored by PTCA, thrombolysis
- Usually ~30 mins to 3-4 hours after ischemic event
- Damaged myocardium is susceptible to…
- Hemorrhage
- Arrythmia
- Further ischemia
22
Q
Myocardial Stunning & Hibernation
- Stunned
- Hibernating
A
- Stunned
- Myocytes not acutely lethally damaged can recover function in a few days w/ reperfusion
- Hibernating
- Myocytes that have chronic, sublethal ischemia may “hibernate” for days to weeks then recover function later
23
Q
Serum Biomarkers
- Troponins T & I
- CK-MB
- Best for diagnosis
- Biochemical markers
- Myoglobin
- CK-MB
- Troponins
A
- Troponins T & I
- Both sensitive & specific
- Troponins not normally found in circulation
- CK-MB
- Sensitive but not as specific
- MB can also be found in skeletal muscle
- Best for diagnosis
- Combination of the two
- Biochemical markers
- Myoglobin
- Out 1st, gone 1st
- (-) sensitive, (-) specific
- CK-MB
- Out 2nd, gone 2nd
- (+) sensitive, (-) specific
- Troponins
- Out last, gone last
- (+) sensitive, (+) specific
- Myoglobin
24
Q
Scenario 1
- 60yo man w/ acute posterior wall MI
- Which vessel is involved?
A
Right coronary artery (75%)
Could be left circumflex in left dominant system
25
Q
Scenario 2
- 60yo man w/ acute anterior wall MI
- Which vessel is involved?
A
Left anterio descending (most common)
26
Q
Scenario 3
- 60yo man w/ acute anteroir wall MI
- What is the vessel pathology that’s involved?
A
Vulnerable plaque: hemorrhage, thrombosis, rupture
27
Q
Scenario 4
- 75yo woman w/ acute anterior wall
- MI happened 12 hours ago
- What do you expect to see in the myocardium?
A
Nothing or coagulative necrosis (contraction bands)
28
Q
Scenario 5
- 75yo woman
- Acute anterior wall MI happened 2 days ago
- What do you expect to see in the myocardium?
A
Neutrophils, cellular debris
29
Q
Scenario 6
- 68yo woman
- Acute anterior wall MI happened 5 days ago
- What is the most concerning risk at this point?
A
Ventriuclar rupture w/ hemopericardium
30
Q
Scenario 7
- 52yo man
- Acute posterior wall & septal MI happened 4 days ago
- Now has acute mitral valve insufficiency
- What is the problem?
A
Papillary muscle rupture
31
Q
Scenario 8
- 58yo man
- CABG surgery 5 days ago
- Now has chest pain & friction rub
- What is the problem?
A
Dressler’s syndrome, pericarditis
32
Q
Scenario 9
- 79yo woman
- large lateral wall MI 6 months ago
- Has ischemic stroke
- What is the complication?
A
Mural thrombus
33
Q
Scenario 10
- 53yo man dies suddenly at home
- Autopsy only shows LAD w/ 95% proximal stenosis
- What happened?
A
Sudden cardiac death, fatal arrhythmia
