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The heart is encased in a protective fluid-filled sac called?
Three layers of the heart
- epicardium (the outermost layer),
- myocardium (the middle and thickest layer that contracts with each heartbeat)
- endocardium (innermost layer)
- venticular diastole (relaxation)
- ventricular systole (contraction)
- 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)
ventricles contract and blood is ejected into the pulmonic and systemic circulation system.
- HR x SV (amount of blood ejected with each ventricular contraction)
- determined by three factors: preload, afterload and myocardial contractility
the degree of stretch on muscle fibers when they begin to contract (end diastolic pressure)
is the amount of pressure which the left ventricle must work against to eject blood during systole
- the ability of the ventricles to contract
- can be affected by sympathetic inneveration and parasympathetic stimulation
causes the release of norepinephrine, increasing the heart rate and accelarating AV node conduction
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