ECG Changes in Myocardial Infarction

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ECG Changes in Myocardial Infarction

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Q1.

A 55-year-old man presents with crushing chest pain for 2 hours. His ECG shows ST elevation in leads II, III, and aVF with reciprocal changes in leads I and aVL. Which coronary artery is most likely occluded?

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A. Left Anterior Descending (LAD)
B. Left Circumflex
C. Right Coronary Artery (RCA)
D. Posterior Descending Artery

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Answer: C. Right Coronary Artery (RCA)

Explanation

ST elevation in the **inferior leads (II, III, aVF)** indicates an inferior MI. If **lead III > lead II** in elevation, it suggests **RCA occlusion** over left circumflex. Reciprocal ST depression in I and aVL supports RCA involvement.

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✅ Answer: C. Right Coronary Artery (RCA)
Explanation:
ST elevation in inferior leads (II, III, aVF) indicates an inferior MI. If lead III shows more ST elevation than lead II, the RCA is usually the culprit. Reciprocal ST depression in I and aVL supports this.

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Q2.

Which of the following ECG changes is most specific for a posterior myocardial infarction?

A. ST elevation in V1–V2
B. Tall R waves in V1–V2 with ST depression
C. T wave flattening in aVL
D. Q waves in I and aVL

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✅ Answer: B. Tall R waves in V1–V2 with ST depression
Explanation:
The posterior wall is not directly visualized on a standard 12-lead ECG. However, reciprocal changes appear in anterior leads (V1–V3): ST depression with tall R waves, the mirror image of posterior Q waves.

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Q3.

Which of the following best describes “tombstone” ST elevations?

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A. ST depression with biphasic T waves
B. ST elevations merging with T waves, wide and convex
C. J-point elevation with notched QRS
D. Flattened ST segment followed by inverted T waves

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✅ Answer: B. ST elevations merging with T waves, wide and convex
Explanation:
“Tombstone” ST elevation refers to massive, convex-shaped ST elevation that merges into broad T waves. It’s usually seen in large anterior STEMIs and indicates a severe, transmural infarction.

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Q4.

A new onset of a left bundle branch block (LBBB) on ECG in a patient with chest pain is considered equivalent to STEMI when:

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A. The PR interval is shortened
B. The QRS axis is normal
C. ST elevation >1 mm in leads with positive QRS (concordant)
D. ST depression in V2 and V3

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✅ Answer: C. ST elevation >1 mm in leads with positive QRS (concordant)
Explanation:
This is part of the Sgarbossa criteria for identifying MI in the presence of LBBB. Concordant ST elevation (in the same direction as the QRS complex) is highly specific for acute MI.

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Q5.

In the context of acute anterior MI, which of the following findings on ECG indicates a larger infarct size and worse prognosis?

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A. ST elevation in V1–V4
B. New RBBB with ST elevation in anterior leads
C. Q waves in leads III and aVF
D. Biphasic T waves in V2–V3

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✅ Answer: B. New RBBB with ST elevation in anterior leads
Explanation:
A new RBBB (right bundle branch block) in the context of anterior MI usually suggests a proximal LAD occlusion with extensive infarction involving the septum. It’s associated with worse outcomes and higher mortality.

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Q6.

Which lead combination best helps differentiate a high lateral MI?

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A. II, III, aVF
B. V1–V4
C. I, aVL
D. V7–V9

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✅ Answer: C. I, aVL
Explanation:
High lateral MIs affect the upper portion of the lateral wall of the left ventricle, best seen in leads I and aVL. Leads II, III, aVF are for inferior MI; V1–V4 for anterior MI; V7–V9 for posterior MI.

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ECG Changes in Myocardial Infarction

ECG in Myocardial Infarction

An electrocardiogram (ECG or EKG) showing myocardial infarction (MI) typically exhibits specific characteristic changes. These vary depending on the type and timing of the infarction (acute, evolving, or old) and the area of the heart involved (anterior, inferior, lateral, posterior, etc.).

Common ECG Findings in Myocardial Infarction

1. ST-Elevation Myocardial Infarction (STEMI)

• Hyperacute T waves: Tall, peaked T waves in early minutes.
• ST-segment elevation: ≥1 mm in two contiguous leads.
  • Anterior MI: ST elevation in V1–V4.
  • Inferior MI: ST elevation in II, III, aVF.
  • Lateral MI: ST elevation in I, aVL, V5–V6.
  • Posterior MI: ST depression in V1–V3 (with tall R waves).
• Q waves: Develop after several hours; signify necrosis.
• T wave inversion: Usually follows ST elevation.

2. Non-ST Elevation Myocardial Infarction (NSTEMI)

• ST-segment depression or T wave inversion without ST elevation.
• Indicates subendocardial ischemia.
• Q waves typically do not develop.

3. Old (previous) MI

• Persistent pathologic Q waves (≥1 mm wide and ≥1/3 of R wave height) in relevant leads without acute ST or T wave changes.

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ECG Changes in Myocardial Infarction

Example ECG Interpretation

Anterior STEMI:

• ST elevation in V1–V4
• Possible Q waves in V2–V4
• Reciprocal ST depression in inferior leads (II, III, aVF)

Inferior STEMI:

• ST elevation in II, III, aVF
• Reciprocal ST depression in I, aVL

Posterior MI:

• ST depression and tall R waves in V1–V3
• Often confirmed with posterior leads (V7–V9)

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ECG Changes in Myocardial Infarction

An Electrocardiogram (ECG or EKG) is a crucial tool for diagnosing myocardial infarction (MI), commonly known as a heart attack. A heart attack occurs when blood flow to a part of the heart muscle is blocked, leading to damage or death of heart tissue. This damage disrupts the heart’s electrical activity, which is then reflected in specific changes on the ECG.

Here’s a breakdown of the typical ECG changes seen in myocardial infarction:

Key ECG Features of Myocardial Infarction:

1. ST Segment Changes:
   • ST Segment Elevation (STEMI): This is the most well-known and often the earliest recognized sign of an acute MI, particularly in ST-elevation myocardial infarction (STEMI), which indicates a complete blockage of a coronary artery. The ST segment, which is normally flat, becomes elevated above the baseline. The elevation can vary in degree and often appears convex or “tombstone” shaped.
   • ST Segment Depression (NSTEMI/Ischemia): In non-ST elevation myocardial infarction (NSTEMI) or myocardial ischemia (reduced blood flow without complete blockage), the ST segment may be depressed below the baseline. This can be horizontal or downsloping. Widespread ST depression, especially with ST elevation in lead aVR, can suggest a serious issue like left main coronary artery occlusion.
2. T Wave Changes:
   • Hyperacute T Waves: These are often the very first signs, appearing within minutes to half an hour of the infarct. They are tall, broad, and symmetrical T waves. These are transient and usually followed by ST elevation.
   • T Wave Inversion: As the infarct evolves, the T waves in the affected leads often become inverted (point downwards). This can persist for months or even permanently.
3. Pathological Q Waves:
   • Pathological Q waves develop as a result of irreversible myocardial necrosis (tissue death). They are typically wider (duration > 0.04 seconds) and/or deeper (depth > 25% of the R wave height) than normal Q waves. These can appear within hours but sometimes take up to 24 hours to fully develop. Once present, they often serve as a permanent marker of a past myocardial infarction.

Evolution of ECG Changes over Time:

The ECG changes in MI often follow a characteristic progression:

• Initial Phase (minutes to hours): Hyperacute T waves, followed by significant ST segment elevation.
• Evolving Phase (hours to days): ST segment elevation may begin to resolve, T waves become inverted, and pathological Q waves may start to appear.
• Chronic Phase (days to weeks/months/years): ST segment elevation usually resolves, T wave inversion may persist or normalize, and pathological Q waves often remain as a permanent sign of the infarct.

Localization of Myocardial Infarction based on ECG Leads:

The 12-lead ECG provides different views of the heart, allowing clinicians to pinpoint the location of the MI:

• Inferior MI: Leads II, III, aVF (often associated with occlusion of the Right Coronary Artery – RCA)
• Anterior/Septal MI: Leads V1, V2, V3, V4 (often associated with occlusion of the Left Anterior Descending artery – LAD)
• Lateral MI: Leads I, aVL, V5, V6 (often associated with occlusion of the Left Circumflex artery – LCx, or diagonal branches of the LAD)
• Posterior MI: (Requires additional leads V7-V9, but may show reciprocal changes like ST depression and prominent R waves in V1-V3 on a standard ECG)
• Right Ventricular MI: (Requires right-sided leads V3R-V6R, but may show ST elevation in V1 and V4R)

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ECG Changes in Myocardial Infarction

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Important Considerations:

• Reciprocal Changes: ST elevation in one set of leads is often accompanied by reciprocal ST depression in leads that view the opposite side of the heart. These reciprocal changes can help confirm the diagnosis.
• Clinical Context: ECG findings must always be interpreted in conjunction with the patient’s symptoms (e.g., chest pain), medical history, and cardiac biomarker levels (like troponin).
• ECG Mimics: Other conditions can cause ECG changes that resemble MI, such as pericarditis, early repolarization, left ventricular hypertrophy, or left bundle branch block.
• Normal ECG does not rule out MI: In some cases, especially in the very early stages or with smaller infarcts, the initial ECG may be normal. Serial ECGs are often performed.

It’s important to remember that interpreting an ECG requires specialized training and should always be done by a qualified healthcare professional.

Where is the ischemic lesion?

ECG Changes in Myocardial Infarction

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