Acute Myocardial Infarction (AMI) Causes PATHOPHYSIOLOGY and Etiology

Acute Myocardial Infarction AMI Causes PATHOPHYSIOLOGY  Atherosclerosis and Etiology

  • Acute coronary syndrome (ACS) may present as unstable angina (no ST segment elevation), or acute myocardial infarction. Acute myocardial infarction (AMI) implies irreversible damage to the myocardium.
  • MI Causes usually occurs when an atheromatous plaque in a coronary artery ruptures, and the resulting clot obstructs the injured blood vessel

Ischemic Heart Disease (IHD) 1

Acute Myocardial Infarction AMI Causes PATHOPHYSIOLOGY Atherosclerosis and Etiology

Causes Acute Myocardial Infarction Etiology:

  • Proven risk factors for MI are tobacco use,
  • high blood pressure, male sex, advanced age, obesity, physical inactivity
  • diabetes mellitus, abnormal cholesterol levels,
  • high blood pressure, male sex, advanced age, obesity, physical inactivity
  • AMI may be associated with ST elevation or ST de­pression in the ECG.
  • AMI With ST elevation is called STEMI (ST segment elevation MI) and AMI without ST segment elevation is called NSTEMI (Non ST seg­i]1ent elevation MI).
  • In NSTEMI cardiac markers like troponins are normal (not elevated).
  • In TEMI~ardc markers like  troponins are elevated.
  • Q waves do not evolve in NSTEMI but Q waves are
  • seen to evolve in STEMI. ~
  • Mortalit is 30%. 25% die in 1st year after AMI

Atherosclerosis 1

Acute Myocardial Infarction AMI Causes PATHOPHYSIOLOGY Atherosclerosis and Etiology

PATHOPHYSIOLOGY Causes of Acute Myocardial Infarction

I. Atherosclerosis

  • Coronary arteries are narrowed by athero­sclerosis.
  • Abrupt closure can occur by throm­botic occlusion.
  • Very gradual narrowing leads to development of collaterals and therefore lesser incidence of MI.

 

Factors which precipitate thrombotic occlusion of coronary vessels are:

   

  • Vascular injury (damage to endothelium of coro­naries)
  • Vascular injury is precipitated by cigarette smoking, hypertension and hyperlipidemia.
  • Fissuring of atherosclerotic plaque
  • Rupture of atherosclerotic plaque
  • Ulceration

Acute Myocardial Infarction Causes Thrombogenesis

  • Atherosclerotic plaque with rich lipid core and thin @:>rous cap are very p..!:one to rupture.
  • Iatelets are activated by: ADP
  • Collagen Epinephrine  Serotonin.
  • There is release of thromboxane A2

 

Thtrhromboxane A2 is a potent

  • vasoconstrictor which causes coronary spasm and precipitates total coro­nary oc~sion and infarctio’!.
  • activated platelets are resistant to thrombolysis.
  • Platelets also bring about a change in GP IIb / IIIa
  • receptors which can now bind to 2 platelets at a time involving von Willebrand factor and fibrinogen.
  • Prothrombin is converted to thrombin and fibrinogen to fibrin resulting in formation of clots.

II. Total Coronary occlusion resulting in Acute MI occurs due to :

  • Presence of multiple risk factors
  • Hypercoagulability
  • Collagen vascular disease
  • Cocaine abuse
  • Intracardiac thrombi or masses leading to coronary embolization.

III. Other causes of Coronary occlusion are less important e.g. :

  • Coronary embolism
  • Congenital abnormalities
  • Coronary spasm
  • Systemic and inflammatory disease .
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