Q: Which formula is used to estimate the ventricular rate from an EKG when using the large box method?

$$\text{Rate} = \frac{300}{\text{Number of large boxes between R-R intervals}}$$

Question 1

Which phase of the myocardial action potential is primarily responsible for rapid depolarization, and which ion is most involved in this process?

Accepted Answer

Phase 0; sodium ($$Na^+) $$influx

Question 2

A patient presents with a heart rate of 45 bpm and an EKG showing absent P waves and a narrow QRS complex. Which arrhythmia is most likely present?

Accepted Answer

Junctional rhythm

Question 3

Which of the following best describes the mechanism of AV nodal conduction during a normal heartbeat?

Accepted Answer

Action potential propagation via $$Ca^{2+}$$ influx, resulting in slower conduction

Question 4

Which EKG finding is most characteristic of atrial fibrillation?

Accepted Answer

Irregularly irregular rhythm with no discernable P waves

Question 5

A patient with atrial fibrillation is at increased risk for ischemic stroke primarily due to which pathophysiological mechanism?

Accepted Answer

Stasis of blood in the atria leading to thrombus formation and embolization

Question 6

Which formula is used to estimate the ventricular rate from an EKG when using the large box method?

Accepted Answer

$$	ext{Rate} = \frac{300}{	ext{Number of large boxes between R-R intervals}}$$

Question 7

Which of the following arrhythmias is most commonly associated with a prolonged QT interval and can be triggered by hypokalemia or certain medications?

Accepted Answer

Torsades de Pointes

Question 8

What is the primary difference between AVRT (Atrioventricular Reentrant Tachycardia) and AVNRT (Atrioventricular Nodal Reentrant Tachycardia)?

Accepted Answer

AVRT involves an accessory pathway outside the AV node, while AVNRT involves dual pathways within the AV node

Question 9

Which medication class is most likely to cause AV block by prolonging AV nodal conduction?

Accepted Answer

Non-dihydropyridine calcium channel blockers (e.g., verapamil, diltiazem)

Question 10

During which phase of the myocardial action potential does $$K^+$$ efflux predominate, leading to repolarization?

Accepted Answer

Phase 3

Question 11

A patient with a history of heart failure presents with dizziness and syncope. EKG shows a prolonged PR interval (\u003e0.20 sec) but all QRS complexes are present. What is the most likely diagnosis?

Accepted Answer

First-degree AV block

Question 12

Which property allows certain cardiac cells to spontaneously generate action potentials without external stimulation?

Accepted Answer

Automaticity

Question 13

Which of the following is a life-threatening arrhythmia characterized by multiple reentry circuits in the ventricles and complete loss of cardiac output?

Accepted Answer

Ventricular fibrillation

Question 14

Which phase of the action potential corresponds to the ST segment on the EKG?

Accepted Answer

Phase 2

Question 15

A patient with atrial flutter has an atrial rate of 300 bpm and a ventricular rate of 100 bpm. What is the AV node's filtering ratio?

Accepted Answer

$$3:1$$

Question 16

Which of the following is the most common symptom associated with both bradycardia and tachycardia arrhythmias?

Accepted Answer

Syncope or presyncope

Question 17

Which antiarrhythmic drug class is most likely to prolong the refractory period by blocking potassium channels?

Accepted Answer

Class III antiarrhythmics (e.g., amiodarone, sotalol)

Question 18

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

Accepted Answer

SA node → AV node → Bundle of His → Right and Left bundle branches → Purkinje fibers

Question 19

A patient with a history of taking digoxin presents with arrhythmia. Which type of arrhythmia is most commonly associated with digoxin toxicity?

Accepted Answer

Triggered arrhythmias due to delayed afterdepolarizations (DADs)

Question 20

Which of the following best describes the absolute refractory period (ARP) in cardiac cells?

Accepted Answer

The time during which $$Na^+$$ channels are inactive and no new action potential can be generated

Cardiac Conduction and Rhythm Disorders: Study Notes

Guida di studio - Domande di pratica

Study guide - Flashcard