Myocardial Infarction Flashcards Preview

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Flashcards in Myocardial Infarction Deck (33):
1

Ischemic Heart Disease

  • Ischemia
  • Infarction
  • Ischemic heart disease

  • Ischemia
    • Compromised blood supply or increased oxygen demand (supply-demand mismatch)
  • Infarction
    • Cell death due to ischemia
  • Ischemic heart disease
    • Chronic ischemia +/- infarction

2

Ischemic Heart Disease

  • Causes
  • What happens

  • 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

Blood Supply

  • Right coronary artery
  • Left anterior descending
  • Left circumflex

  • 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

Quality of Myocardial Ischemia Depends On...

  • Degree of arterial occlusion
  • Collateral circulation
  • Overall "health" of the heart
  • Arrhythmia

5

A patient has an acute right coronary artery thrombus.  Where is the infarct most likely to occur?

Posterior septum

6

What Happens in Acute MI

  • Acute change in coronary artery plaque
    • Rupture
    • Hemorrhage
    • Thrombosis
  • Thrombosis
  • Ischemic damage to myocardium
  • Myocyte necrosis
  • Other complications

7

MI: Timing & Cellular Changes after Arterial Occlusion

  • 2 mins
  • 30 mins
  • 1 hour
  • 2-4 hours

  • 2 mins = loss of contractility
  • 30 mins = irreversible cell injury
  • 1 hour = microvascular injury
  • 2-4 hours = permanent damage

8

Myocardial Infarction

  • Progression of ischemia
  • Predominance of occluded arteries
  • Rare infarcts

  • 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

Infarct Histology

  • General
  • Cells involved
  • Early changes
  • Middle changes
  • Later changes
  • Healing

  • 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

Post-Infarct Complications

  • Arrhythmia
  • Myocardial rupture
  • Pericarditis
  • Mural thrombus
  • Ventricular aneurysm
  • Ventricular remodeling

11

What complication is most likely to occur 3-7 days after acute infarction?

Papillayr muscle rupture

12

Arrhythmia

  • Myocardial irritability
  • Heart block (depending on location)
  • Bradycardia, ventricular tachycardia, premature ventricular contractions

13

Myocardial Rupture

  • Free wall
    • Hemopericardium
  • Septum
    • Causes acute VSD w/ left-to-right shunt
  • Pappillary muscle
    • leads to acute mitral valve insufficiency

14

Dressler's Syndrome

  • aka
  • After acute MI
  • After bypass graft surgery

  • 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

Mural Thrombus

  • Akinesis / hypokinesis of infarcted myocardium
    • Blood pools on endocardial surface
    • Thrombus forms
  • Complication: embolization of thrombus
    • Leads to stroke or gangrene

16

Ventricular Aneurysm

  • Infarcted myocardium thinned
  • "Balloons outward" w/ forceful contractions of adjacent myocardium
  • Thrombus can form in aneurysm

17

Ventricular Remodeling

  • Infarcted mycoardium dies (scar tissue)
  • Surrounding myocardium hypertrophies
  • Result: zones of fibrosis w/ surrounding hypertrophy
    • Myocardium can become thick & stiffened

18

Sudden Cardiac Death

  • Patient has severe coronary artery atherosclerosis
  • No occlusive thrombus &/or no myocardial infarction
  • Death due to arrhythmia, not infarction
    • Typically ventricular fibrillation

19

Treatment of Acute Myocardial Infarction

  • 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

Angina Pectoris

  • Stable angina
  • Unstable angina
  • Prinzmetal angina

  • 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

Reperfusion Injury

  • General
  • Damaged myocardium is susceptible to...

  • 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

Myocardial Stunning & Hibernation

  • Stunned
  • Hibernating

  • 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

Serum Biomarkers

  • Troponins T & I
  • CK-MB
  • Best for diagnosis
  • Biochemical markers
    • Myoglobin
    • CK-MB
    • Troponins

  • 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

24

Scenario 1

  • 60yo man w/ acute posterior wall MI
  • Which vessel is involved?

Right coronary artery (75%)

Could be left circumflex in left dominant system

25

Scenario 2

  • 60yo man w/ acute anterior wall MI
  • Which vessel is involved?

Left anterio descending (most common)

26

Scenario 3

  • 60yo man w/ acute anteroir wall MI
  • What is the vessel pathology that's involved?

Vulnerable plaque: hemorrhage, thrombosis, rupture

27

Scenario 4

  • 75yo woman w/ acute anterior wall
  • MI happened 12 hours ago
  • What do you expect to see in the myocardium?

Nothing or coagulative necrosis (contraction bands)

28

Scenario 5

  • 75yo woman
  • Acute anterior wall MI happened 2 days ago
  • What do you expect to see in the myocardium?

Neutrophils, cellular debris

29

Scenario 6

  • 68yo woman
  • Acute anterior wall MI happened 5 days ago
  • What is the most concerning risk at this point?

Ventriuclar rupture w/ hemopericardium

30

Scenario 7

  • 52yo man
  • Acute posterior wall & septal MI happened 4 days ago
  • Now has acute mitral valve insufficiency
  • What is the problem?

Papillary muscle rupture

31

Scenario 8

  • 58yo man
  • CABG surgery 5 days ago
  • Now has chest pain & friction rub
  • What is the problem?

Dressler's syndrome, pericarditis

32

Scenario 9

  • 79yo woman
  • large lateral wall MI 6 months ago
  • Has ischemic stroke
  • What is the complication?

Mural thrombus

33

Scenario 10

  • 53yo man dies suddenly at home
  • Autopsy only shows LAD w/ 95% proximal stenosis
  • What happened?

Sudden cardiac death, fatal arrhythmia