Question 1

Which ion is primarily responsible for the rapid depolarization phase of the cardiac action potential in ventricular myocytes?

Accepted Answer

Sodium ($$Na^+)$$

Question 2

A patient presents with a widened QRS complex ($$\u003e0.12$$ seconds) on their EKG. Which of the following is the most likely cause?

Accepted Answer

Right or left bundle branch block

Question 3

The PR interval on an EKG is measured from the beginning of the P wave to the beginning of which wave?

Accepted Answer

QRS complex

Question 4

A positive deflection on an EKG tracing occurs when electrical activity moves:

Accepted Answer

Toward the positive electrode

Question 5

Which property allows pacemaker cells in the heart to generate impulses without external stimulation?

Accepted Answer

Automaticity

Question 6

A patient with hyperkalemia is most likely to show which EKG change?

Accepted Answer

Peaked T waves

Question 7

Which of the following best describes the function of myocardial cells?

Accepted Answer

Contract to produce the mechanical force of the heartbeat

Question 8

A patient’s EKG shows a regular rhythm with a constant PR interval of $$0.24$$ seconds and a QRS complex following every P wave. What is the most likely diagnosis?

Accepted Answer

First-degree AV block

Question 9

Which equation is used to correct the QT interval for heart rate (Bazett’s formula)?

Accepted Answer

$$QT_c = \frac{QT}{\sqrt{RR}}$$

Question 10

A 25-year-old athlete has a resting heart rate of 50 bpm and high QRS voltages on EKG. What is the most likely explanation for these findings?

Accepted Answer

Normal physiologic adaptation to exercise

Question 11

Which of the following EKG findings is most characteristic of acute ST-elevation myocardial infarction (STEMI)?

Accepted Answer

ST segment elevation in contiguous leads

Question 12

A patient’s EKG shows no P waves, irregularly irregular rhythm, and narrow QRS complexes. What is the most likely diagnosis?

Accepted Answer

Atrial fibrillation

Question 13

Which of the following is the main vector direction of ventricular depolarization as seen on the EKG?

Accepted Answer

From right to left and superior to inferior

Question 14

A patient with a Mobitz type II second-degree AV block will have which EKG finding?

Accepted Answer

Constant PR intervals with intermittent dropped QRS complexes

Question 15

Which of the following is the correct sequence of electrical conduction in the heart?

Accepted Answer

SA node → AV node → Bundle of His → Purkinje fibers

Question 16

A patient’s EKG shows ST segment depression in leads V1-V3. Which coronary artery is most likely involved?

Accepted Answer

Left anterior descending (LAD)

Question 17

Which of the following best describes the clinical significance of a prolonged QT interval?

Accepted Answer

Increased risk of ventricular arrhythmias such as Torsades de Pointes

Question 18

A patient with a left bundle branch block (LBBB) will most likely have which EKG finding in lead V1?

Accepted Answer

Predominantly negative QRS complex

Question 19

Which of the following formulas is used to calculate heart rate from an EKG with a regular rhythm?

Accepted Answer

$$	ext{Heart Rate} = \frac{300}{	ext{Number of large boxes between R waves}}$$

Question 20

A patient with a history of chest pain has an EKG showing pathologic Q waves in leads II, III, and aVF. What does this most likely indicate?

Accepted Answer

Inferior wall myocardial infarction

Anatomy & Physiology Study Guide: Cardiac Electrophysiology and EKG Interpretation

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