ECG and Cardiac Conduction System
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These flashcards cover key terms and concepts related to ECG and the cardiac conduction system to aid in exam preparation.
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29 Terms
What is an ECG?
Electrocardiogram; a recording of the heart’s electrical activity.
What is a node?
A specialized area of cardiac muscle that generates electrical impulses (action potentials).
Where does a normal heartbeat start?
Sinoatrial (SA) node in the right atrium.
What is the SA node also called?
Pacemaker node.
What is the SA node’s firing rate?
60–100 beats per minute.
Why is the SA node unique?
It automatically cycles between depolarization and repolarization.
Where does the impulse go after the SA node?
Atrioventricular (AV) node.
What is the function of the AV node delay?
Allows atria to fully contract before ventricles contract.
How long is the AV node delay?
About 100 milliseconds.
What is the AV node’s intrinsic rate?
40–60 beats per minute.
What happens if the SA node fails?
The AV node takes over pacing at 40–60 bpm.
What is the max conduction rate of the AV node?
About 230 bpm.
When does heart efficiency decrease?
Around 180 bpm.
Where does the impulse go after the AV node?
AV bundle (Bundle of His).
What is the AV bundle’s intrinsic rate?
20–40 bpm.
What does the AV bundle connect?
Atria to ventricles.
What structures carry impulses through the ventricles?
Right & left bundle branches and Purkinje fibers.
What do Purkinje fibers do?
Rapidly conduct impulses for coordinated ventricular contraction.
Why do papillary muscles contract before ventricles?
To tighten chordae tendineae and prevent backflow.
What does the P wave represent?
Atrial depolarization.
When do atria contract relative to the P wave?
About 25 ms after it begins.
What does the QRS complex represent?
Ventricular depolarization.
Why isn’t atrial repolarization visible on ECG?
It is hidden by the stronger ventricular signal.
What does the T wave represent?
Ventricular repolarization.
What is the P-R interval?
Time from start of P wave to start of QRS complex.
What can a prolonged P-R interval indicate?
A conduction delay/problem.
What is the Q-T interval?
Time from start of QRS complex to end of T wave.
What does the Q-T interval represent?
Ventricular systole.
What can a prolonged Q-T interval indicate?
Heart damage or electrolyte imbalance.