Intro to EKG Interpretation - Myocardial Infarctions (Part 1 of 2)

Summary

In this detailed video, Eric explains the key characteristics and diagnosis of myocardial infarction (MI) through EKG analysis. The video covers various types of MI, including STEMI, NSTEMI, and Q-wave vs. non-Q-wave infarctions, and discusses how to localize the infarct region using EKG leads. It also addresses the evolution of EKG changes over time, from acute to old infarcts. The video highlights how to determine the age of an MI and emphasizes the significance of reciprocal changes. In the second part, advanced topics like posterior infarcts and conduction system complications will be explored.

Takeaways

• 😀 ST Elevation MI (STEMI) and Non-ST Elevation MI (NSTEMI) are two major classifications of myocardial infarctions, distinguished by the presence or absence of ST elevations on an EKG.
• 😀 Acute Coronary Syndrome (ACS) encompasses STEMI, NSTEMI, and unstable angina, with EKG changes varying depending on the severity and type of infarction.
• 😀 STEMIs are characterized by ST elevations in two or more anatomically contiguous leads and may also show ST depressions and/or Q wave inversions in other leads.
• 😀 NSTEMI and unstable angina differ from STEMI primarily by the elevation of biomarkers like troponin, with NSTEMI showing signs of ischemia on the EKG without ST elevation.
• 😀 The evolution of an MI's EKG changes follows a timeline, starting with hyperacute T waves, progressing to ST elevations, T-wave inversions, and eventually Q waves.
• 😀 Q waves can become permanent, signaling the completion of infarction, whereas ST elevations typically last for days and may resolve with time.
• 😀 It can be challenging to determine the exact age of an MI beyond several days since ST elevations resolve, and biomarkers return to baseline.
• 😀 STEMIs can often be localized to specific regions of the heart based on the affected leads, corresponding to particular coronary vessels like the LAD, circumflex, and RCA.
• 😀 Reciprocal changes on an EKG occur on the opposite side of the infarction, with ST depressions seen in regions opposite the injury, aiding in localization.
• 😀 Identifying the age of the infarction and localizing it to a coronary vessel involves analyzing the timing of EKG changes and the regional leads affected.

Q & A

What is the difference between STEMI and NSTEMI in terms of EKG findings?

STEMI is characterized by ST elevation in two or more contiguous leads, often with reciprocal changes in other leads, such as ST depression and T-wave inversions. NSTEMI, on the other hand, shows no ST elevation but may have ST depression and T-wave inversions, with a key differentiator being elevated biomarkers like troponin.

What are hyperacute T waves, and when do they appear during a myocardial infarction?

Hyperacute T waves are early EKG changes that appear within the first minutes of a myocardial infarction. They are often transient and may disappear before the patient reaches medical attention.

How does the development of ST elevation differ between STEMI and NSTEMI?

ST elevation is a hallmark of STEMI, typically appearing within an hour after an acute occlusion and lasting for several days. In NSTEMI, ST elevation is absent, and the EKG may only show ST depression or T-wave inversion.

What is the significance of Q waves in diagnosing myocardial infarction?

Q waves are typically indicative of a previous infarction and are usually permanent. Their development occurs hours to days after the initial injury, and their presence can help determine the age of an infarct. However, they are not always present in all MIs, particularly in NSTEMI or non-Q wave MIs.

How can an EKG help estimate the age of a myocardial infarction?

The age of a myocardial infarction can be estimated by observing EKG changes such as the duration of ST elevation, the development of Q waves, and T-wave inversions. Early signs like hyperacute T waves and ST elevation suggest an acute infarct, while Q waves and T-wave inversions indicate a more established infarction.

Why can't the age of an infarction be determined once ST elevations have resolved and biomarkers return to baseline?

Once ST elevations have resolved and biomarkers return to baseline, the EKG changes are no longer sufficient to differentiate between a recent and an old infarct. The resolution of ST elevations means the acute phase has passed, and any ongoing abnormalities are typically non-specific.

How does the EKG help in localizing the myocardial infarction to a specific region of the heart?

By analyzing the EKG lead groupings and the regions they represent, it is possible to localize the infarction. For example, leads 2, 3, and AVF represent the inferior wall, while leads V1 and V2 represent the septal wall. Specific patterns of ST elevation, depression, and reciprocal changes provide clues to the infarct's location.

What is the significance of reciprocal changes in an EKG during a myocardial infarction?

Reciprocal changes are seen in leads opposite the site of infarction, typically as ST depressions. They are an important diagnostic feature, helping to confirm the location of the infarct. For example, an inferior STEMI can cause reciprocal changes in the anterior leads.

How does the vascular territory of the heart impact EKG interpretation?

Different regions of the heart are supplied by specific coronary arteries, and each region has its corresponding EKG leads. For example, the left anterior descending (LAD) artery supplies the anterior wall, while the circumflex artery supplies the lateral wall. Understanding these territories helps in localizing the infarction to the affected artery.

How can you localize a STEMI or Q wave MI based on the affected myocardial region and culprit coronary vessel?

STEMIs and Q wave MIs can often be localized by analyzing the pattern of ST elevation or Q waves in specific leads. For example, ST elevations in leads V2-V4 suggest an anterior wall infarct, often due to an LAD occlusion, while ST elevations in leads 2, 3, and AVF suggest an inferior wall infarct, potentially due to RCA or circumflex occlusion.