Podcast
Questions and Answers
What is a key characteristic of a Right Bundle Branch Block (RBBB)?
What is a key characteristic of a Right Bundle Branch Block (RBBB)?
Which ECG lead is typically examined to assess for changes indicative of a Left Bundle Branch Block?
Which ECG lead is typically examined to assess for changes indicative of a Left Bundle Branch Block?
What does ST segment elevation on an ECG primarily indicate?
What does ST segment elevation on an ECG primarily indicate?
What condition can lead to a Left Bundle Branch Block?
What condition can lead to a Left Bundle Branch Block?
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In the absence of reciprocal changes, which infarct location does not show any indicative ECG changes?
In the absence of reciprocal changes, which infarct location does not show any indicative ECG changes?
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Which of the following leads would display slurred S waves in a Right Bundle Branch Block?
Which of the following leads would display slurred S waves in a Right Bundle Branch Block?
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Which of the following describes a normal QRS complex duration?
Which of the following describes a normal QRS complex duration?
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Which of these leads would indicate inferior infarction on an ECG?
Which of these leads would indicate inferior infarction on an ECG?
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Which change in the ECG is associated with ischemia?
Which change in the ECG is associated with ischemia?
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What happens to the infarcted area in terms of electrical activity?
What happens to the infarcted area in terms of electrical activity?
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What event occurs during myocardial ischemia?
What event occurs during myocardial ischemia?
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Which physiological change is associated with prolonged ischemia?
Which physiological change is associated with prolonged ischemia?
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What is typically indicated by ST elevation on an ECG?
What is typically indicated by ST elevation on an ECG?
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Which artery supplies blood to the anterior wall of the heart?
Which artery supplies blood to the anterior wall of the heart?
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What can cause myocardial ischemia?
What can cause myocardial ischemia?
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Which leads are used to view the lateral wall of the heart?
Which leads are used to view the lateral wall of the heart?
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What distinguishes an infarct from ischemia?
What distinguishes an infarct from ischemia?
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What characterizes the T wave inversion in myocardial ischemia?
What characterizes the T wave inversion in myocardial ischemia?
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Which type of myocardial injury is primarily reversible?
Which type of myocardial injury is primarily reversible?
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Which statement is true regarding the physiological effects of hypoxia during ischemia?
Which statement is true regarding the physiological effects of hypoxia during ischemia?
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What leads are associated with viewing the inferior wall of the heart?
What leads are associated with viewing the inferior wall of the heart?
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What is the effect of decreased conduction velocity due to hypoxia?
What is the effect of decreased conduction velocity due to hypoxia?
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What is a major consequence of complete occlusion of a coronary artery?
What is a major consequence of complete occlusion of a coronary artery?
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Study Notes
Myocardial Oxygen Supply
- The heart requires a continuous blood supply to fulfill its high oxygen and nutrient demand.
Coronary Arteries
- There are two main coronary arteries: the right coronary artery (RCA) and the left coronary artery (LCA).
- The LCA further divides into the left anterior descending (LAD) branch and the left circumflex branch (LCX).
- These arteries provide smaller branches that supply blood to the heart muscle.
The Three Important Ischemia, Injury, Infarction (I's)
- Ischemia is limited blood flow within a coronary artery, leading to decreased oxygenation.
- Injury occurs with prolonged ischemia, causing chronic lack of oxygen and disabling ATP-driven cellular activity.
- Infarct is a complete occlusion of a coronary artery resulting in tissue death.
Physiological Findings in Ischemia
- Ischemia leads to hypoxia, a state where myocardial oxygen needs are not met.
- Cellular depolarization is prolonged due to a decrease in ATP production, hindering the Na/K ATPase pump's activity and causing potassium leakage.
- The decreased ATP also prevents the proper removal of sodium after depolarization, increasing intracellular sodium and calcium concentration, further depolarizing the cell.
- This prolonged depolarization inhibits sodium channels, reducing automaticity, conduction velocity, and refractory periods.
- The buildup of intracellular calcium leads to tachycardia.
ECG Views of the Heart
- Leads II, III, and aVF provide a view of the inferior heart wall, looking from the left leg upwards.
- Leads I and aVL provide a view of the lateral heart wall, looking from the left arm towards the heart; sometimes referred to as High Lateral.
- Leads V5 and V6 provide another view of the lateral heart wall, looking from the left lateral chest; this view also captures electrical activity from the heart's apex and sometimes referred to as Low Lateral or Apical view.
- Combining Leads I, aVL, V5, and V6 offers a complete view of the lateral wall from different angles.
- Leads V3 and V4 provide a view of the anterior heart wall, looking from the left anterior chest.
- Leads V1 and V2 provide a view of the septal heart wall, looking along the sternal borders.
- Leads V1 and V2 also provide a view of the posterior heart wall.
Well Perfused Myocardium
- The epicardial coronary artery provides oxygenated blood to the lateral wall of the left ventricle, the septum, and the interior wall of the left ventricle.
Normal ECG
- A normal ECG represents well-oxygenated myocardial tissue.
Ischemia ECG Changes
- Ischemia leads to a narrowed coronary artery lumen, usually due to a clot, and a poorly perfused subendothelium.
- ECG changes due to ischemia include ST depression or T inversion.
- Ischemia can be reversible and may not lead to infarction.
T Wave Inversion
- T wave inversion occurs as ischemic tissue does not repolarize normally.
- This can also be seen in myocardial infarction as the tissue surrounding the infarct becomes ischemic.
Causes of Myocardial Ischemia
- Atherosclerosis, Vasospasm, Thrombosis, Embolism, Decreased ventricular filling time, Tachycardia, and decreased filling pressure in coronary arteries due to severe hypotension or aortic valve disease are significant causes.
Injury ECG Changes
- Injury is a result of prolonged ischemia and is referred to as transmural ischemia.
- ECG changes include ST segment elevation because of complete or poor collateral circulation, leading to transmural ischemia.
- Injury often progresses to infarction.
Infarct ECG Changes
- Infarct is the death of tissue due to complete occlusion of a coronary artery.
- The infarcted area becomes electrically silent, potentially resulting in Q wave changes.
- ECG will show a Q wave and the absence of depolarization in the infarcted ventricular area.
ECG Indicators of Ischemia, Injury, and Infarction
- T wave changes, ST segment changes, Q wave changes are key indicators.
Bundle Branch Block
- Bundle branches are a crucial part of the heart's electrical conduction system.
- The bundle of His divides into the right and the left bundle branches.
- The left bundle branch further divides into the septal, anterior, and posterior fascicles.
Normal QRS Complex
- A normal QRS complex is characterized by a narrow duration of 0.06 to 0.10 seconds and an electrical axis between 0° and +90°.
Bundle Branch Block
- Bundle branch block occurs when one or both branches fail to conduct impulses, causing a delay in ventricular depolarization.
- The defining characteristic is a widened QRS complex (0.12 seconds or greater), with notched, slurred, or M-shaped QRS complexes in the chest leads.
Right Bundle Branch Block (RBBB)
- RBBB signifies a blockage in the right bundle branch, delaying right ventricular depolarization.
- ECG reveals wide, tall, notched QRS complexes in leads V1, V2, and slurred S waves in leads I, V5, and V6.
Causes of Right Bundle Branch Block
- Anterior wall MI, coronary artery disease, hypertension, scar tissue from heart surgery, viral or bacterial myocarditis, pulmonary embolism, drug toxicity, and congenital heart abnormalities can induce RBBB.
Left Bundle Branch Block (LBBB)
- LBBB involves a blockage in the left bundle branch, leading to delayed left ventricular depolarization.
- ECG shows wide, tall, notched, or slurred QRS complexes in leads V5, V6, and wide, largely negative rS complexes or entirely 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, and cardiomyopathy can contribute to LBBB.
Overview of Infarcts and ECG Changes
- Infarct location determines the arterial supply, the indicative changes, and the reciprocal changes in the ECG.
- Anterior Infarct: LAD supply, Indicative V1-V4, Reciprocal II, III, aVF.
- Inferior Infarct: RCA supply, Indicative II, III, aVF, Reciprocal I, aVL.
- Lateral Infarct: Circumflex supply, Indicative I, aVL, V5, V6, Reciprocal V1.
- Posterior Infarct: Posterior Descending (RCA) supply, Indicative None, Reciprocal V1, V2.
- Septal Infarct: Septal Perforating (LAD) supply, Indicative Loss of R wave in V1, V2, or V3, Reciprocal None.
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Description
This quiz focuses on the crucial aspects of myocardial oxygen supply, highlighting the role of coronary arteries and the implications of ischemia, injury, and infarction. It examines how restricted blood flow can impact heart function and cellular health. Test your understanding of these vital cardiovascular concepts.
