Clinical Signs and Management of Myocardial Infarction

Anatomical Correlation and ECG Findings

The location of an acute MI is often tied to the specific coronary artery involved, which in turn dictates the clinical complications a patient might face.

Anterior MI

An anterior MI is frequently associated with the development of heart failure.

Inferior MI

Typically associated with an occlusion of the Right Coronary Artery (RCA). Clinical findings often include:

• Heart blocks or bradyarrhythmias (such as sinus bradycardia or sinus rhythm abnormalities).
• ST elevations in the inferior leads: I, II, and aVF.
• Potential for mitral valve regurgitation due to papillary muscle rupture.

Acute inferior wall STEMI

Lateral MI

Involving the left circumflex artery, lateral MIs are categorized by their position on the ECG:

• High Lateral: ST elevation in leads I and aVL.
• Low Lateral: ST elevation in leads V5 and V6.

Right Ventricular (RV) and Posterior MI

• RV Infarct: Often occurs alongside an inferior MI; characterized by hypotension, clear lung sounds, and bradyarrhythmias. ECG may show ST elevation in V3R and V4R.
• Posterior MI: Also associated with the RCA.

Left Ventricular Systolic Dysfunction

A significant complication of an acute MI is the impairment of the heart's pumping ability. Left ventricular systolic dysfunction occurs when the heart muscle is damaged, reducing its ability to contract effectively.

A primary indicator of this dysfunction is a decreased Ejection Fraction (EF). In clinical assessments, an EF < 40% is a predominant sign of systolic dysfunction. Patients exhibiting this dysfunction may present with:

• Decreased $SaO_2$ (oxygen saturation).
• New cough or the presence of bibasilar crackles upon auscultation.
• Hypotension and signs of respiratory decline.

Emergency Management and Reperfusion

When a STEMI is suspected, an ECG must be performed and read within 10 minutes to allow for immediate risk stratification.

Reperfusion Strategies

If symptoms have been present for less than 12 hours, reperfusion is indicated:

1. Percutaneous Coronary Intervention (PCI): The gold standard treatment. The target "door-to-balloon" time is $\leq 90$ minutes.
2. Fibrinolytic Therapy: An alternative if PCI is unavailable. The target "door-to-drug" time is $\leq 30$ minutes.

Critical Contraindications for Fibrinolytics Do not administer fibrinolytic therapy if the patient has:

• Any prior intracranial hemorrhage.
• Known structural cerebral lesions (e.g., AVM).
• Malignant intracranial neoplasm.
• Ischemic stroke within the last 3 months (or 3 hours for acute stroke).
• Suspected aortic dissection.

Post-Procedure Monitoring

Following PCI, clinicians must monitor for several complications:

• Hemodynamics: Watch for vasovagal reactions and hypotension (systolic blood pressure $< 90$ mmHg).
• Bleeding: Assess the sheath site. If bleeding occurs, apply manual pressure for 20–30 minutes (longer if the patient is on GP IIb/IIIa inhibitors).
• Vascular/Neurological: Monitor for severe low back pain, which may indicate vascular complications.
• Reperfusion Arrhythmias: Be alert for Ventricular Tachycardia (VT) or Ventricular Fibrillation (VF) as the vessel opens and the myocardium undergoes "stunning".