Cardiac Conduction System & ECG

Question 1

Which side of the heart has Purkinje fibers that divide into anterior and posterior branches?

Answer 1

The left

Question 2

The P wave is ____________.

Answer 2

atrial depolarization

Question 3

QRS is ___________.

Answer 3

ventricular depolarization

Question 4

T wave is _________.

Answer 4

ventricular repolarization

Question 5

The Q-T interval is usually ~ ________.

Answer 5

0.44 seconds

Question 6

The direction of the wave on an ECG varies with ___________.

Answer 6

position of the electrode in relation to the depolarization wave

Question 7

List the steps of depolarization of the ventricles.

Answer 7

(1) The upper portion of the septum is depolarized from left to right; (2) the septum is then depolarized in the direction of the apex; (3) first the endocardium depolarizes, then the epicardium; (4) depolarization then proceeds from apex to base along the walls; (5) finally, the base depolarizes.

Question 8

Describe the three degrees of AV blockage.

Answer 8

1°: delayed conduction, but all P waves conduct to the ventricles; 2°: some P waves conduct, but some do not; 3°: no P waves conduct to the ventricles–the ventricles are driven by a ventricular pacemaker.

Question 9

What happens to the QRS wave when a bundle is blocked?

Answer 9

The wave is widened; note, when just one fascicle of the left bundle is blocked, the wave is not widened, but it can change direction.

Question 10

Phase 0 of cardiac pacemaker cells (in the SA and AV nodes) does not rely on _______.

Answer 10

sodium channels–only calcium

Question 11

Describe afterpolarizations.

Answer 11

Myocytes can be depolarized when they have yet to fully repolarize, leading to tachyarrhythmia.