Electrophysiology of the Heart

Heart Function and Electrophysiology

• The SA node initiates heartbeat and starts cardiac contraction.
• Electrical impulses spread from the SA node, causing ventricular contraction and expelling blood from the heart.
• The sequence of contraction and relaxation is crucial for effective circulation of oxygen and nutrients.

Cardiac Conduction System

• Key components include the SA node, AV node, Bundle of His, and Purkinje fibers.
• The conduction system ensures coordinated heartbeats and muscle contractions.

Ion Channels and Membrane Potentials

• Ligand-gated and voltage-gated ion channels play essential roles in action potential generation.
• Potassium ions leak out of cells to maintain resting membrane potential (RMP).
• Sodium concentration is typically high outside the cell; influx leads to depolarization when threshold is reached.

Action Potential Sequence

• Influx of sodium ions leads to depolarization, while potassium ions leak out, causing a drop in membrane potential.
• Following depolarization, calcium enters, while potassium exits during repolarization, preparing the cell for the next contraction.

Pacemaker Cells

• Pacemaker cells can generate impulses independently of leakage from surrounding cells.
• They maintain more negative potentials than typical resting cells to initiate heartbeats effectively.

Stroke Volume and Cardiac Mechanics

• Ventricular filling influences stroke volume; increased filling correlates to more stroke volume.
• Distinctions made between preload (the initial stretching of heart muscles) and stroke volume to understand cardiac efficiency.

Vascular Considerations

• Resistance is determined by pressure exerted on muscle and vessel stiffness.
• Conditions such as hypertension increase pressure and strain, impacting endothelial cells and risking blood clots.

Blood Vessel Characteristics

• Thick walls and lumen size contribute to the capacity to hold blood;
• Adequate blood pressure is essential for effective circulation and vessel function.