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Questions and Answers
Which lead would typically show changes during an anterior wall myocardial infarction?
What is a key characteristic of a right bundle branch block on an ECG?
In which leads would you likely find the characteristic QRS patterns of left bundle branch block?
Which of these conditions can cause right bundle branch block?
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What ECG changes might be observed in an inferior wall myocardial infarction?
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Which layer of heart tissue undergoes necrosis during an infarct?
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What does ST segment elevation on an ECG typically indicate?
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What defines the QRS complex duration in a normal ECG?
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How may QRS complexes appear in cases of right bundle branch block?
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What represents the complete occlusion of a coronary artery?
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Which physiological change occurs first in myocardial ischemia?
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Which coronary artery is responsible for branching into the Left Anterior Descending (LAD) and the Left Circumflex (LCX) branches?
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What is the physiological effect of hypoxia within myocardial cells?
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Which leads are used to view the inferior wall of the heart on an ECG?
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Which condition is characterized by prolonged ischemia and results in ST elevation?
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What occurs due to decreased intracellular ATP during ischemia?
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Which of the following is a cause of myocardial ischemia?
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Which view does leads V5 and V6 provide on an ECG?
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What happens to K+ during myocardial ischemia?
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What is typically seen on an ECG during myocardial ischemia?
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What can tachycardia lead to in terms of myocardial perfusion?
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What physiological effect does prolonged depolarization have during ischemia?
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What does an ST elevation in an ECG primarily indicate?
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Study Notes
Myocardial Oxygen Supply
- The heart has a high demand for oxygen and nutrients.
- The heart requires a continuous blood supply.
Coronary Arteries
- The right coronary artery (RCA) and the left coronary artery (LCA) are the two main arteries supplying the heart.
- The LCA divides into the left anterior descending (LAD) branch and the left circumflex branch (LCX).
- These arteries provide smaller branches that penetrate the heart muscle and supply it with blood.
The Three Important I’s
- Ischemia: Limited blood flow within a coronary artery resulting in decreased oxygenation.
- Injury: Prolonged ischemia leading to chronic oxygen deprivation and disruption of cellular activity.
- Infarct: Complete blockage of a coronary artery leading to tissue death.
Physiological Findings in Ischemia
- Hypoxia: Reduced blood flow leads to inadequate oxygen supply to the heart muscle.
- Depolarization: Hypoxia decreases intracellular ATP production, impacting the Na/K ATPase pump activity.
- Prolonged Depolarization: Reduced pump activity results in an accumulation of potassium (K+) outside the cells and sodium (Na+) inside the cells, increasing depolarization duration.
- Inactivation of Na+ Channels: The prolonged depolarization inactivates sodium channels and affects the automaticity of conducting cells, slowing conduction velocity and increasing refractory periods.
- Increased Intracellular Ca2+: Hypoxia triggers a buildup of intracellular calcium, potentially leading to tachycardia.
ECG Leads and Heart Views
- Inferior Heart Wall: Leads II, III, and aVF view the inferior heart wall from the perspective of the left leg.
- Lateral Heart Wall: Leads I and aVL view the lateral heart wall from the perspective of the left arm.
- Low Lateral/Apical: Leads V5 and V6 view the lateral heart wall from the left lateral chest perspective, including some activity from the apex.
- Entire Lateral Heart Wall: Leads I, aVL, V5, and V6 provide a comprehensive view of the lateral wall.
- Anterior Heart Wall: Leads V3 and V4 view the anterior heart wall from the left anterior chest.
- Septal Heart Wall: Leads V1 and V2 view the septal heart wall from the sternal borders.
- Posterior Heart Wall: Leads V1 and V2 are used to assess the posterior heart wall.
ECG Views Summary Table
| Lead | View |
|---|---|
| I | Lateral |
| II | Inferior |
| III | Inferior |
| aVR | |
| aVL | Lateral |
| aVF | Inferior |
| V1 | Septal |
| V2 | Septal |
| V3 | Anterior |
| V4 | Anterior |
| V5 | Lateral |
| V6 | Lateral |
ECG Indicators
- T-wave changes: Indicate ischemia.
- ST-segment changes: Indicate injury.
- Q-wave changes: Indicate infarction.
Bundle Branch Block
- Bundle Branches: The bundle of His branches into the right and left bundle branches, with the left branch further splitting into septal, anterior, and posterior fascicles.
Normal QRS Complex
- Narrow: Lasts 0.06 to 0.10 seconds.
- Electrical axis: Between 0° and +90°.
Bundle Branch Block
- Key characteristic: Wide QRS complexes lasting 0.12 seconds or longer.
- QRS appearance: Often notched, slurred, or M-shaped in the chest leads.
Right Bundle Branch Block (RBBB)
- Cause: Blocked conduction through the right bundle branch, delaying right ventricular depolarization.
- ECG findings: Wide, tall, notched QRS complexes in leads V1 and V2, and slurred S waves in leads I, V5, and V6.
Causes of Right Bundle Branch Block
- Anterior wall myocardial infarction (MI)
- Coronary artery disease
- Hypertension
- Scar tissue from heart surgery
- Viral or bacterial myocarditis
- Pulmonary embolism
- Drug toxicity
- Congenital heart abnormalities (e.g., atrial septal defect)
Left Bundle Branch Block (LBBB)
- Cause: Blocked conduction through the left bundle branch, delaying left ventricular depolarization.
- ECG findings: Wide, tall, notched, or slurred QRS complexes in leads V5 and V6; wide, largely negative rS complexes or completely negative QS complexes in V1 and V2.
Causes of Left Bundle Branch Block
- Anterior wall MI
- Hypertensive heart disease
- Aortic stenosis
- Degenerative changes in the conduction system
- Cardiomyopathy
Overview of Infarcts: Location, Arterial Supply, Indicative Changes, and Reciprocal Changes
| Infarct Location | Arterial Supply | Indicative Changes | Reciprocal Changes |
|---|---|---|---|
| Anterior | LAD | V1-V4 | II, III, aVF |
| Inferior | RCA | II, III, aVF | I, aVL |
| Lateral | Circumflex | I, aVL, V5, V6 | V1 |
| Posterior | Posterior Descending (RCA) | None | V1, V2 |
| Septal | Septal Perforating (LAD) | Loss of R wave in V1, V2, or V3 | None |
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Description
Explore the vital role of oxygen supply in the heart's function, focusing on the coronary arteries' structure and significance. Learn about the critical concepts of ischemia, injury, and infarct, as well as physiological changes during these conditions. This quiz will deepen your understanding of cardiovascular health.
