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Questions and Answers
What is the primary function of the coronary circulation in the heart?
Which artery carries the greatest blood volume in the heart's coronary circulation?
Where does the blood leave the tissues of the left ventricle and right ventricle?
What percentage of oxygen does the myocardium extract from blood in coronary vessels at rest?
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How does coronary blood flow increase to provide more oxygen supply to the myocardium during exercise?
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Why does the myocardium depend on adequate oxygen supply?
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What is the significance of a blood clot in a coronary vessel?
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What is the formula for Rate-Pressure Product (RPP)?
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What fuels are primarily used by the myocardium during rest?
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What is the purpose of using exercise to evaluate myocardial blood flow?
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How does intense exercise affect myocardial metabolism?
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What is the role of the Sinoatrial (SA) node in cardiac muscle?
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How does an Electrocardiogram (ECG) monitor heart rate during physical activity?
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What happens when an impulse originates from the sinoatrial (SA) node in the right atrium?
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Why does cardiac muscle maintain its own rhythm?
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How does an ECG lead create a composite electrical '3D picture' of myocardial activity?
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What is the primary function of repeating electrical impulses traveling through the heart in cardiac conduction?
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What is the function of the atrioventricular bundle in the heart's electrical conduction system?
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What does the QRS complex in an ECG represent?
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How would a large low space in the heart affect its function based on the text?
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Which phase of the normal ECG represents ventricular repolarization?
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What is a key indicator of allowing the cardiac system to relax and recover, based on HRV information provided in the text?
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How does the Sinoatrial node (SA) contribute to cardiac functioning?
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What is the main function of the Sinoatrial (SA) node in the heart?
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How does an Electrocardiogram (ECG) represent the heart's electrical activity?
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What causes a slight asynchrony in the contraction of the right and left sides of the heart?
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What is the role of the ECG leads in creating an electrical '3D picture' of myocardial activity?
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Where does the impulse originating from the Sinoatrial (SA) node travel first in the heart?
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What characterizes a valid ECG tracing according to the text?
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What is the purpose of the P wave in an ECG?
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Which structure allows the impulse to pass from the atria to the ventricles in the heart?
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What is the primary role of Purkinje's fibers in the heart's electrical conduction system?
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During which phase of a normal ECG does ventricular diastole occur?
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How does a heart block, as mentioned in the text, impact cardiac functioning?
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What does a greater Heart Rate Variability (HRV) indicate about the cardiac system's condition?
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What is the role of the Sinoatrial (SA) node in cardiac muscle?
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What happens when an impulse originates from the Sinoatrial (SA) node in the right atrium?
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How does the myocardium's electrical activity affect an Electrocardiogram (ECG)?
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What characteristic makes the Sinoatrial (SA) node stand out in terms of heart function?
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Why is proper electrode placement essential for obtaining a valid ECG tracing?
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How does myocardial impulse transmission differ from regular tissue impulse transmission?
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What is the main role of the Atrioventricular bundle (bundle of His) in the heart's electrical conduction system?
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During which phase of a Normal ECG does the QRS complex occur?
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What is the primary function of Purkinje's fibers in the heart?
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What happens during atrial repolarization in an ECG?
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How does Heart Rate Variability (HRV) typically indicate the condition of the cardiac system?
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What does a large low space in the heart suggest based on the text?
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Study Notes
Heart's Blood Supply
- The heart has its own circulatory network, the coronary circulation, which arises from the heart's top portion.
- The right and left coronary arteries supply blood to the heart muscle.
- The left coronary artery has the greatest blood volume flow, feeding the left atrium and left ventricle, and the right ventricle.
- Blood leaves the tissues of the left ventricle through the coronary sinus and the right ventricle through the anterior cardiac veins, both dumping into the right atrium.
- Normal blood flow to the myocardium at rest is 200-250 ml/min (5% of total output).
Myocardial Oxygen Supply and Use
- At rest, the myocardium extracts 70-80% of oxygen from the blood in coronary vessels.
- Proportionate increase in coronary blood flow during exercise provides the sole mechanism to increase myocardial oxygen supply.
- Two factors increase myocardial blood flow:
- Increase in metabolism dilates coronary vessels.
- Increase in aortic pressure during exercise forces a proportionately greater volume of blood into the coronary circulation.
Impaired Myocardial Blood Supply
- The myocardium depends on adequate oxygen supply because it has limited anaerobic capacity and can't make an extensive switch.
- Extensive vascular perfusion supplies at least one capillary to each of the heart's muscle fibers.
- Tissue hypoxia provides a potent stimulus to myocardial blood flow, which can produce chest pains (angina pectoris).
- A blood clot in a coronary vessel can impair normal heart function, leading to a myocardial infarction, where heart tissue will die due to lack of oxygen.
Rate-Pressure Product (RPP)
- RPP is an estimate of myocardial workload and VO2.
- RPP is computed from the product of peak SBP measured at the brachial artery and heart rate.
- RPP is an index of relative cardiac work and relates closely to directly measured myocardial VO2 and coronary blood flow in healthy subjects over a wide range of exercise intensities.
- RPP ranges from 6000 at rest to greater/equal to 40,000 during exercise, depending on intensity and mode.
Myocardial Metabolism
- At rest, the heart muscle uses fat/lipids as fuel.
- During moderate exercise, glucose and lactate are used more.
- During intense exercise, lactate is oxidized.
Intrinsic Regulation of Heart Rate
- Unlike other tissues, cardiac muscle maintains its own rhythm.
- Left to its inherent rhythmicity, the heart would beat around 100 bpm.
- The sinoatrial (SA) node provides the innate stimulus for heart action and is the "heart's pacemaker".
Normal Route of Myocardial Impulse Transmission
- The sinoatrial node (SA) in the right atrium is the origin of the impulse.
- The impulse spreads across the atria, causing them to contract.
- The impulse passes to the atrioventricular node (AV), travels along the atrioventricular bundle into its two branches (right and left crus), and spreads into the ventricles, causing them to contract.
- Dissipation of the impulse causes the atria and ventricles to relax or dilate.
Electrocardiogram (ECG)
- The myocardium's electrical activity creates an electrical field throughout the body.
- ECG represents a composite record of the heart's electrical events during a cardiac cycle.
- These electrical events can monitor HR during physical activity and exercise stress testing.
- A valid ECG tracing requires proper electrode placement.
- ECG leads transmit the electrical signal to a recorder, which creates a composite electrical "3D picture" of myocardial activity.
ECG Waves
- P wave: depolarization of atria before atria contract.
- QRS complex: signals electrical changes from ventricular depolarization before ventricles contract.
- Atrial repolarization after P wave, but it's obscured by the QRS complex.
- T-wave: represents ventricular repolarization that occurs during ventricular diastole.
Electrocardiogram (ECG) and Heart Rate
- Typically, R to R measurement is used to measure HR, which is typically irregular, indicating decent recovery.
- Greater HRV (heart rate variability) is a better indication of allowing the system to relax and recover.
Electrocardiogram (ECG) and Pathology Detection
- Large low spaces on the ECG can indicate that the heart is not told to contract, which can be an issue (e.g., heart block).
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Description
Explore the coronary circulation network providing blood supply to the heart, including the right and left coronary arteries. Learn about the distribution of blood to different parts of the heart and the role of coronary sinus and cardiac veins in returning blood to the right atrium.
