ECG Electrophysiology Basics 5

Question 1

What is the conduction velocity of the His-Purkinje system, and why is it important?

Accepted Answer

4 m/s; enables near-simultaneous ventricular depolarization for effective contraction

Answer

The His-Purkinje system conducts at ~4 m/s, the fastest in the heart, ensuring both ventricles depolarize nearly simultaneously for coordinated ejection.

Question 2

A patient's ECG shows a QRS duration of 160 ms with a left bundle branch block pattern. What does this indicate electrophysiologically?

Accepted Answer

Conduction fails in the left bundle branch; the left ventricle depolarizes slowly via cell-to-cell spread from the right

Answer

LBBB means the left bundle is blocked; the RV depolarizes normally then the LV depolarizes slowly via myocardial cell-to-cell conduction, producing a wide, bizarre QRS.

Question 3

Which property describes a cell's ability to respond to a stimulus and generate an action potential?

Accepted Answer

Excitability (bathmotropy)

Answer

Excitability (bathmotropy) is the ability of cardiac cells to respond to an electrical stimulus and generate an action potential when threshold is reached.

Question 4

On a standard 12-lead ECG recorded at 25 mm/s, each small box (1 mm) represents how much time?

Accepted Answer

0.02 seconds (20 ms)

Answer

At standard speed of 25 mm/s, each 1 mm small box = 0.04 s/box ÷ 2 = 0.04 s per small box; actually each small box = 1mm / 25mm/s = 0.04 s.

Question 5

Digoxin toxicity can cause which of the following arrhythmias due to its electrophysiological effects?

Accepted Answer

Accelerated junctional rhythm with AV block (PAT with block)

Answer

Digoxin toxicity classically causes PAT (paroxysmal atrial tachycardia) with AV block by increasing automaticity (via Ca2+ overload/DADs) while simultaneously slowing AV conduction.

ECG Certification Practice Test

ECG Certification Practice Test

ECG Electrophysiology Basics 5