Cardiac Cycle Flashcards
Which electrical event occurs first in the cardiac cycle?
The SAN activates automatically, causing electrical charge to spread throughout the atria.
What occurs at the AVN?
The electrical current is held up for 100 msec, allowing the ventricles to fill. Current then passes from the AVN to the septum of the heart.
How does electrical current travel from the AVN?
It travels down the left of the septum, then crosses over to the right side before moving up the ventricular walls.
What is sinus arrhythmia?
The normal increase in heart rate during inspiration.
What is heart block?
1st degree - delayed signals between atria and ventricles.
2nd degree - some signals get through to ventricle, but not all.
3rd degree - atria and ventricles become dissociated.
What are ectopic foci?
Areas of the heart firing off signals which should not do this.
What is re entry phenomena?
When current is flowing in the opposite direction to which it is supposed to.
What occurs in late diastole?
AV valves open. Blood flows to the atria and ventricles passively.
What occurs in atrial systole?
Atrial contraction primes the main pump - contraction of muscle prevents back flow of blood to great veins. A wave of atrial pressure is shown in JVP.
What occurs in ventricular systole?
Ventricles contract against closed valves. Aortic and pulmonary valves then burst open, causing ventricular ejection.
What occurs in early diastole?
Ventricles stop contracting, blood continues to flow out until aortic and pulmonary valves close. Pressure falls below atrial pressure, and AV valves open.
