Myocardial Infarction

General Information

Classification: Cardiovascular

What is it?

Figure 1 EKG myocardial infarction with classic ST segment elevation (Source: Adobe)

Colloquially “heart attack”, characterized by complete or partial ischemia to a portion of the heart muscle/myocardium

Risk Factors: *underlying ischemia heart disease or coronary artery disease/CAD (most commonly, secondary to atherosclerosis), smoking, hypertension (HT), diabetes mellitus, lack of physical activity, alcohol abuse, hyperlipidemia, LV hypertrophy

Evaluation:

  • Symptoms:
    • Chest discomfort, angina (that may radiate into left arm, left jaw, or left neck), epigastric pain (if inferior STEMIs)
    • Autonomic reflexes: nausea, vomiting, diaphoresis, syncope
  • *EKG evaluation:
    • ST segment elevation in two contiguous leads
    • ST segment depression
  • Biomarkers: *Elevated troponins
  • Imaging (to examine myocardial thickness and perfusion): echocardiography (ECG), cardiac MRI

Classification: see below

Pathophysiology:

  • Ischemic heart disease/coronary artery disease: occlusion in coronary vessels diminishes O2 supply and increases its consumption, leading to hypoxia (disrupting sarcolemma structure) → liquefactive necrosis

Classification

Figure 2 Cardiogenic pulmonary edema secondary to LV MI (Source: MedPix)

Categorization by region

Right ventricular MI (RV MI):

Leads to backflow into superior/inferior vena cava

Presentation: jugular venous distension, hepatomegaly, edema, hypotension (due to diminished SV, CO), sinus bradyarrhythmia/AV block (due to diminished conduction capacity at SA/AV node due to RCA occlusion)

Left ventricular MI (LV MI):

Blood backs into pulmonary vessels, causing edema

Presentation: dyspnea, decreased ejection fraction/EF (causes reflex tachycardia due to stimulation of ANS) s4 sound prominence, cold extremities, cyanosis

Categorization by EKG*

Non-ST-elevation MI (NSTEMI):

Myocardial necrosis without persistent ST elevation (troponin elevation): instead, may present with ST depression, T-wave inversion

The infarction is typically subendocardial (where necrosis due to ischemia begins)

Causative agent: typically thrombus formation which leads to ≥90% occlusion

Pain at rest

ST-elevation MI (STEMI):

Myocardial necrosis with persistent ST elevation, and potentially LBBB

The infarction is typically transmural (encompasses full thickness of myocardium, not just subendocardial)

Causative agent: thrombi/emboli that leads to total occlusion

    *NSTEMI and STEMI also fall more broadly under categories of ischemic heart disease, as acute coronary syndrome.

    Complications

    Categorized based on 24h mark: when major complications tied to necrosis begin to appear, and coagulative necrosis is well underway

    Within 24h

    • Increased tissue permeability → increase frequency of APs → ventricular tachycardias (potentially VF)
      • Other arrhythmias: reflexive tachycardia, SVTs,
    • If LV MI: hypotension, cold extremities
    • Cardiogenic shock
    • Pulmonary edema (Figure 2)
    • Reperfusion injury: free radical and calcium overload secondary to intervention

    After 24h

    • Interventricular septal rupturing → holosytolic murmur
    • Free wall rupture → LV blood enters pericardial cavity → cardiac tamponade → triad (hypotension, jugular venous distension, muffled heart sounds)
    • Papillary muscle rupture → severe mitral regurgitation/MR
    • Pericarditis
    • Arrhythmias

    Treatment

    Acute management

    Reperfusion therapy

    • Particularly essential for STEMI: Primary PCI (<120 min), fibrinolysis
    • NSTEMI: fibrinolysis is contraindicated

    Pain relief: intravenous opioids

    Adjunctive medication: beta blockers, anti-coagulents, antiplatelets (especially aspirin), nitrates

    Long term management & lifestyle modifications

    Treat causative agent of CAD (likely atherosclerosis): statins to reduce LDLs, stabilize plaques

    Medication: ACE inhibitors, beta blockers, glucose-lowering therapy if diabetic

    Smoking cessation, weight control, minimize alcohol consumption

    Comments!

    Leave a comment

    More posts