Electrocardiography in myocardial infarction

Electrocardiography in the context of myocardial infarction

Electrocardiography in myocardial infarction is a critical diagnostic tool used to assess and manage patients with suspected myocardial infarction (MI), commonly known as a heart attack. The electrocardiogram (ECG or EKG) records the electrical activity of the heart and can reveal patterns indicative of myocardial ischemia or infarction.

Overview

12-lead ECG showing ST elevation, color-coded for clarity

Myocardial infarction occurs when blood flow to a part of the heart is blocked, causing damage to the heart muscle. The ECG is a non-invasive test that helps in the early detection of MI by identifying characteristic changes in the heart's electrical activity.

ECG Changes in Myocardial Infarction

The ECG changes associated with myocardial infarction can be categorized into several phases:

Hyperacute Phase

In the initial minutes to hours of an MI, the ECG may show hyperacute T waves, which are tall and peaked. These changes are often transient and may not be captured unless the ECG is performed very early.

ST Elevation

ECG showing ST elevation in inferior leads

ST elevation is a hallmark of acute myocardial infarction, particularly in ST-elevation myocardial infarction (STEMI). It indicates transmural ischemia and is a critical finding that necessitates urgent reperfusion therapy.

Q Waves

Pathological Q waves may develop hours to days after the onset of an MI. They indicate necrosis and are often permanent, signifying a completed infarction.

T Wave Inversion

T wave inversion can occur in the later stages of an MI and may persist for weeks. It reflects changes in the repolarization of the heart muscle.

ST Depression and Non-ST Elevation MI

In non-ST elevation myocardial infarction (NSTEMI), the ECG may show ST depression or T wave inversion without the presence of ST elevation. These changes suggest subendocardial ischemia.

Localization of Myocardial Infarction

The location of the infarction can be inferred from the leads showing changes on the ECG:

• Inferior MI: Changes in leads II, III, and aVF.
• Anterior MI: Changes in leads V1-V4.
• Lateral MI: Changes in leads I, aVL, V5, and V6.
• Posterior MI: Reciprocal changes in V1-V3, often with ST depression and tall R waves.

Diagram showing localization of occlusion in STEMI

Management Based on ECG Findings

The management of myocardial infarction is heavily guided by ECG findings. In the case of STEMI, immediate reperfusion therapy, such as percutaneous coronary intervention (PCI) or thrombolysis, is indicated. For NSTEMI, management includes antiplatelet therapy, anticoagulation, and risk stratification for potential invasive procedures.

Related pages

• Myocardial infarction
• Electrocardiography
• Coronary artery disease
• Percutaneous coronary intervention