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Questions and Answers
Which condition is most likely to cause decreased voltage of the QRS complex?
Which condition is most likely to cause decreased voltage of the QRS complex?
What can cause delayed conduction of the depolarization impulse in the ventricles?
What can cause delayed conduction of the depolarization impulse in the ventricles?
What is the significance of the J point in an electrocardiogram?
What is the significance of the J point in an electrocardiogram?
Which of the following conditions can contribute to low voltage in electrocardiographic leads?
Which of the following conditions can contribute to low voltage in electrocardiographic leads?
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How does digitalis affect the T wave in patients with coronary insufficiency?
How does digitalis affect the T wave in patients with coronary insufficiency?
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What characteristic is often seen in T waves when the depolarization impulse is delayed?
What characteristic is often seen in T waves when the depolarization impulse is delayed?
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Which of the following conditions is associated with T wave inversion?
Which of the following conditions is associated with T wave inversion?
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Which factor is least likely to cause current injury in the heart?
Which factor is least likely to cause current injury in the heart?
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What is the effect of a left bundle branch block on the cardiac depolarization of the left and right ventricles?
What is the effect of a left bundle branch block on the cardiac depolarization of the left and right ventricles?
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Which condition leads to a right axis deviation and a prolonged QRS complex?
Which condition leads to a right axis deviation and a prolonged QRS complex?
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What happens to the QRS complex duration in the presence of a left bundle branch block?
What happens to the QRS complex duration in the presence of a left bundle branch block?
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What is a characteristic feature of decreased voltage in an electrocardiogram?
What is a characteristic feature of decreased voltage in an electrocardiogram?
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In a left bundle branch block, how long can the left ventricle remain polarized after the right ventricle has depolarized?
In a left bundle branch block, how long can the left ventricle remain polarized after the right ventricle has depolarized?
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What is the primary cause of a right axis deviation during an ECG?
What is the primary cause of a right axis deviation during an ECG?
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Which component is primarily affected in cardiac myopathies leading to decreased voltage on an electrocardiogram?
Which component is primarily affected in cardiac myopathies leading to decreased voltage on an electrocardiogram?
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What is the typical consequence of a blocked bundle branch on the overall ECG pattern?
What is the typical consequence of a blocked bundle branch on the overall ECG pattern?
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Study Notes
ECG Abnormalities Part 1
- Bundle Branch Block (BBB): The Purkinje system usually transmits the cardiac impulse to both ventricles almost simultaneously. This normally results in the ventricles' electrical potentials canceling each other out. If one major bundle branch is blocked, the impulse travels through the healthy ventricle before the blocked one, causing delays.
- Left Bundle Branch Block (LBBB): Cardiac depolarization through the right ventricle occurs significantly faster than in the left ventricle. Consequently, the left ventricle remains polarized for about 0.1 seconds after the right ventricle has finished depolarizing. This leads to left axis deviation and a substantially prolonged QRS complex due to slow depolarization in the affected side of the heart.
- Right Bundle Branch Block (RBBB): When the right bundle branch is blocked, the left ventricle depolarizes considerably faster than the right ventricle. This causes the left side of the ventricles to become more electronegative for approximately 0.1 seconds before the right side. This results in right axis deviation and a prolonged QRS complex due to slow conduction.
Decreased Voltage of ECG
- Myopathies: A common cause of decreased voltage in a QRS complex is old myocardial infarctions resulting in reduced muscle mass. This slow movement of depolarization through the ventricles and decreased depolarization of significant portions of the heart contribute to QRS prolongation and decreased voltage.
- Conditions Surrounding the Heart: Fluid buildup in the pericardium (pericardial effusion) and pleural effusion or pulmonary emphysema can decrease voltage in the ECG.
Current Injury (Myocardial Ischemia)
- The J Point: The J point marks when depolarization wave finishes its passage through the heart, at the end of the QRS complex. This point is crucial for analyzing the electrical axis of injury potentials related to currents. A horizontal line is drawn at the J point to determine zero reference potential.
T Wave Abnormalities
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Slow Conduction and T-Wave Characteristics: If ventricular depolarization conduction is notably slow, the resulting T wave's polarity is frequently the opposite of the QRS complex.
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T-Wave Inversion: In myocardial ischemia, the T wave can invert reflecting the delay in depolarization.
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Digitalis Toxicity and the T Wave: Digitalis, a drug that increases cardiac muscle contractility, can cause T wave inversion or biphasic T waves at high dosages. This is due to varied depolarization durations across different parts of the ventricles.
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Description
Explore the complexities of ECG Abnormalities, focusing on Bundle Branch Blocks (BBB), Left Bundle Branch Block (LBBB), and Right Bundle Branch Block (RBBB). This quiz highlights how these conditions affect cardiac depolarization and the resultant ECG readings. Test your knowledge on essential cardiovascular concepts through this engaging quiz.
