Myocardial Oxygen Supply and Coronary Arteries

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

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

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.