electrocardiography

Question 1

what are the components of the intrinsic conduction system (nodal system)

Answer 1

1.Sinoatrial (SA) node, located in the right atrium just inferior to the
entrance to the superior vena cava.
2. Atrioventricular (AV) node in the lower atrial septum at the junction of
the atria and ventricles.
3. AV bundle (bundle of His) and right and left bundle branches, located in
the interventricular septum.
4. Purkinje fibers, essentially long strands of barrel-shaped cells called
Purkinje myocytes, which ramify within the muscle bundles of the
ventricular walls (denser and more elaborate in the left ventricle because
of its larger size).

Question 2

what is an electrocardiogram (ECG/ EKG) ?

Answer 2

The recording of the electrical changes (depolarization followed by repolarization) occurring during the cardiac cycle. It records the electrical events occurring in the bulk of the heart muscle (not the activity of nodal tissue).

Question 3

what does the P wave represent?

Answer 3

depolarization of the right and left atria

Question 4

what does the QRS component represent?

Answer 4

depolarization of the right and left ventricles. Atrial repolarization is also a part of the segment but the electrical signal for atrial repolarization is masked by the larger QRS complex

Question 5

what does the T wave represent?

Answer 5

repolarization of the right and left ventricles

Question 6

what does the P-R interval represent?

Answer 6

time from the onset of atrial depolarization to the onset of ventricular depolarization

Question 7

what does the Q-T interval represent?

Answer 7

time from onset of ventricular depolarization to the end of ventricular repolarization. It represents the refractory period of the ventricles

Question 8

what does the R-R interval represent?

Answer 8

time between two successive ventricular depolarizations

Question 9

what does the P-R segment represent?

Answer 9

time of impulse condition from the AV node to the ventricular myocardium

Question 10

what does the S-T segment represent?

Answer 10

period of time representing the early part of ventricular repolarization during which ventricles are more or less uniformly excited

Question 11

what does the T-P segment represent?

Answer 11

time from the end of ventricular repolarization to the onset of atrial depolarization

Question 12

summarize the ECG

Answer 12

1. SA node initiates depolarization in the right and left atria causing contraction
   (corresponds to the P wave).
2. SA node also sends the depolarization wave to the AV node (with a 0.1 sec delay
   to let the atria finish contracting), which in turn, causing contraction in both
   ventricles (corresponds to the QRS wave). At the same time, the atria repolarize and
   relax (hidden by the QRS complex).
3. Ventricles repolarize and relax (corresponding to the T wave).