Myocardial Infarction Chapter 18

1
Myocardial Infarction Chapter 18
2
Acute Myocardial Infarction (AMI)

• AKA ST segment elevation myocardial infarction
  (STEMI)
• Occlusion of coronary artery causes myocardium to
  be ischemic and tissue death occurs

3
AMI continued

• Until the 80s, AMI was treated symptomatically
• pain control, arrhythmias resolved, bed rest,
  nitrates, B-blockers to minimize oxygen
  requirement of heart

4
AMI continued

• Angiographic studies showed that 87 had occluded
  coronary arteries that led to development of
  thrombolytics and PTCA (percutaneous transluminal
  coronary angioplasty ) which are now first line
  therapies.

5
AMI continued

• 1/2 million have AMI every year
• 30 dead before hospital (v.fib)
• if make it to hospital, 1 year death rate is
  greater than or equal to 15
• usually located in specific region (anterior,
  lateral, inferior,posterior) see Fig. 18-3.
  (anterior worse than inferior or lateral)

6
AMI Continued

• Can develop permanent ECG changes after MI (Q
  waves)
• Q wave MI-STEMI
• Now Q wave MI - Non-ST segment elevation (NSTEMI)
  or acute coronary syndrome (ACS)

7
Clinical Presentation

• Substernal chest pain or pressure, short of
  breath, diaphoresis, nausea and vomiting.
• Can look like indigestion or other diseases may
  present like STEMI (table 18-1)
• 20 of AMI are silent - elderly and diabetics,
  may present with hypotension or cerebrovascular
  symptoms rather than chest pain.

8
Clinical Presentation continued

• Physical exam - may have increased or decreased
  BP, tachycardia (gt120 BPM) suggest large area of
  damage. Fourth heart sound (S 4 ) may be heard

9
Diagnosis

• In addition to HP, ECG and enzymes help to
  diagnose
• usually 2 of the 3 are needed to assign diagnosis
  of MI
• ECG- St segment elevation, 12-lead helps to
  determine location of infarct
• New Q wave, new bundle branch block, ST elevation
  are all consistent with/MI

10
Diagnosis Continued

• IF have chest pain without ST elevation or enzyme
  changes, then called Unstable Angina.
• IF have chest pain without ST elevation but have
  enzyme changes then called AMI, NSTEMI
• These pts have some limited blood flow with
  partial occlusion due to platelets and
  fibrinogen-Thrombolytics dont help these pts.

11
Cardiac Enzymes

• Released when cardiac cell is injured
• CK-MB - most specific of creatinine kinase (CK)
  enzymes for cardiac tissue
• appears 3-6 hrs. after damage, PK 12-24 hrs
• false elevations Table 18-2
• LDH - lactate dehydrogenase -24-48 hours after MI
  pk in 3-6 days
• false elevations-liver disease, hemolysis,
  leukemia, PE, etc.
• Troponin - most sensitive, has replaced LDH

12
Compilcations

• Pump failure, arrhythmias, recurrent ischemia and
  reinfarction
• H.F. common if MI affects 20-25 of left
  ventricle
• cardiogenic shock and death - gt40 of left
  ventricle

13
Complications continued

• Ventricular remodeling- results from decreased
  contractility and compensatory increase in left
  ventricle volume and pressure.
• Arrhythmias - post infarction, heart is irritable
  and subject to ventricular arrhythmias.

14
Drug Therapy (table 18-5)

• Thrombolytics- opens occluded artery, Timi grade
  3- (complete repurfusion), the earlier the
  better. Reduced mortality by 1/3,
• binds to plasminogen -gt plasmin -gt fibrinolytic
  (acts on fibrin clot)
• Table 18-3
• problems- doesnt open 100 of occlusions, may
  not remain open, bleeding (need to select
  properly)
• Table 18-4

15
Drug Therapy continued

• When fibrin clot disintegrates, paradoxical
  increase in local thrombin generation and
  increase platelet aggregability.
• So need heparin, LMWH and ASA / GPIIBIIIA
• B-blockers decrease morbidity and mortality
• decrease myocardial oxygen requirements
• limits damage and decreases complications
• should be used in AMI unless CI

16
Drug Therapy continued

• Vasodilators - decrease myocardial oxygen demand
  by decreasing afterload and decreasing preload
  and can limit remodeling.
• Also increase myocardium blood supply by coronary
  vasodilation

17
Acute Myocardial Infarction (AMI)

• AKA ST segment elevation myocardial infarction
  (STEMI)