Exercise 28: Electrical conductivity of the Heart

The sinoatrial node has a common name. What is it?

“pacemaker”

Which two chambers of the heart (atria or ventricles) contract last in a normal cardiac cycle?

ventricles

Which two chambers are stimulated immediately after the SA node depolarizes?

left and right atrium 

After the AV node depolarizes, which structures conduct the impulse to the myocardium of the ventricles? 

atrioventricular bundle, bundle branches, purjinke fibers 

What electrical event in the heart does the QRS complex represent?

ventricular depolarization (contraction)

Ventricular repolarization is represented by which part of an ECG?

T-wave

Which ECG wave represents atrial depolarization? 

P-wave

Why is the ECG event indicating atrial repolarization not seen in an ECG? 

Occurs at the same time as ventricular depolarization and is masked by this larger event

What consequences does fibrillation have for cardiac muscle contraction and for the pumping efficiency of the heart? Which is more serious atrial or ventricular fibrillation?

random contractions in cardiac muscle results in numerous loci of contractions, atria and ventricles could at different rates could reduce efficiency.

• Ventricular fibrillation is much worse

If a myocardial infarct (heart attack) destroyed a portion of the right or left bundle branches, what potential change might you see in an ECG?

You would see an increase of time of QRS complex