Chapter 11 - The Normal Electrocardiogramh Flashcards
What is the P wave caused by?
Electrical potentials generated when the atria depolarise before atrial contraction begins.
What is the QRS complex caused by?
Potentials generated when the ventricles depolarise before contraction: that is as the depolarisation wave spread through the ventricles.
What causes the T wave?
Potentials generated as the ventricles recover from the state of depolarisation. It’s known as a repolarisation wave.
What happens to the charge during depolarisation?
The normal negative potential inside the fibre reverses and becomes slightly positive inside and negative outside.
Is there a potential recorded in the ECG when the ventricular muscle is either completely polarised or completely depolarised?
No
What is the P-Q interval?
The time between the beginning of the P wave and the beginning of the QRS complex is the interval between the beginning of electrical excitation of the atria and the beginning of excitation of the ventricles.
What is the Q-T interval?
Contraction of the ventricle lasts almost from the beginning of the Q wave to the end of the T wave. This interval is called the Q-T interval.
How does the average current flow in the heart?
With negativity toward the base of the heart and with positivity toward the apex.
Which part of the ventricular muscle mass repolarises first?
The greatest portion of ventricular muscle mass to repolarise first is the entire outer surface of the ventricles, especially near the apex of the heart.
Why is the spreading of depolarisation through the atrial muscle much slower than in the ventricles?
Because the atria have no Purkinje system for fast conduction of the depolarisation signal.
Therefore the musculature around the sinus node becomes depolarised a long time before the musculature in distal parts of the atria. Because of this, the area in the atria that also becomes repolarised first is the sinus nodal region, the area that had originally become depolarised first.
What is one of the most important causes of decreased voltage in electrocardiographic leads?
Fluid in the pericardium
