-
The heart is encased in a protective fluid-filled sac called?
Pericardium
-
Three layers of the heart
- epicardium (the outermost layer),
- myocardium (the middle and thickest layer that contracts with each heartbeat)
- endocardium (innermost layer)
-
Cardiac cycle
- venticular diastole (relaxation)
- ventricular systole (contraction)
-
Ventricular diastole
- blood flows from the atria into relaxed ventricles
- About 70-75% of blood flows passively from the atria into the ventricles
- The remaining 25-30% of blood is delivered to the ventricles via atrial contraction (atrial kick)
-
Ventricular systole
ventricles contract and blood is ejected into the pulmonic and systemic circulation system.
-
Cardiac output
- HR x SV (amount of blood ejected with each ventricular contraction)
- determined by three factors: preload, afterload and myocardial contractility
-
Preload
the degree of stretch on muscle fibers when they begin to contract (end diastolic pressure)
-
Afterload
is the amount of pressure which the left ventricle must work against to eject blood during systole
-
Myocardial contractility
- the ability of the ventricles to contract
- can be affected by sympathetic inneveration and parasympathetic stimulation
-
Sympathetic Inneveration
causes the release of norepinephrine, increasing the heart rate and accelarating AV node conduction
-
Parasympathetic Stimulation
causes the release of acetycholine which slows heart rate and conduction through the AV node
-
Three basic methods to measure HR
- six second method
- grid or rate calculation method
- ruler method
-
Steps required to properly assess an ECG rhythm
- 1. Atrial and ventricular HR. Rhythm regular or irregular? fast or slow?
- 2. P waves, QRS complex and T waves present? what is the PR interval, QRS complex, QT interval?
- 3. ST segment is isoelectric, elevated or depressed?
- 4. T wave is upright or inverted?
- 5. interpretation (Also, consider the hemodynamic significance and possible causes; and nrsg axns)
-
Conduction systems of the heart
- SA node
- AV node
- Bundle of His
- bundle branches
- Purkinje fibres
|
|
