Clinical Quiz on Prolonged P-R Interval

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Questions and Answers

What does a prolonged P-R interval indicate in a clinical context?

Atrial fibrillation

Normal heart function

Increased heart rate

A potential conduction block (correct)

In an electrocardiogram, which interval would specifically be considered prolonged in this context?

Q-T interval

P-R interval (correct)

S-T segment

Q-R interval

Which of the following is NOT a consequence of a prolonged P-R interval?

Increased risk of arrhythmias

Decreased cardiac output

Symptoms of heart block

Improved electrical conduction (correct)

Which heart condition could potentially be indicated by a prolonged P-R interval?

First-degree heart block (A) Signup and view all the answers

If a patient exhibits a prolonged P-R interval, which of the following tests is likely most relevant for further investigation?

Electrophysiology study (B) Signup and view all the answers

How many beats of the atria typically occur for each beat of the ventricles?

Two to three beats (B) Signup and view all the answers

What is the relationship between atrial and ventricular beats?

Atrial beats exceed ventricular beats (D) Signup and view all the answers

In a normal heart rhythm, what is the maximum expected ratio of atrial beats to ventricular beats?

3:1 (C) Signup and view all the answers

Which of the following statements about heartbeats is true?

Atria beat more frequently than ventricles (A) Signup and view all the answers

What does an increased number of atrial beats relative to ventricular beats indicate?

Potential arrhythmia (B) Signup and view all the answers

What is the calculated heart rate when 1500 is divided by 20?

75 beats per minute (C) Signup and view all the answers

What physiological response is triggered in athletes by the sympathetic nervous system?

Increase in heart rate (A) Signup and view all the answers

What physiological change was observed in the ECG during deep inspiration?

Increase in heart rate (C) Signup and view all the answers

How many small squares are mentioned in relation to calculating heart rate?

20 small squares (A) Signup and view all the answers

Which of the following is not a function of the sympathetic nervous system in athletes?

Stimulate digestion (C) Signup and view all the answers

Why is the calculated heart rate of 75 beats per minute significant?

It indicates a resting heart rate. (C) Signup and view all the answers

During intense physical activity, what is one key effect of the sympathetic nervous system?

Increased heart rate (C) Signup and view all the answers

In the context of athletics, how does the sympathetic nervous system primarily affect heart function?

Increases the force of heart contractions (B) Signup and view all the answers

Which of the following calculations reflects the relationship between the number of small squares and the heart rate?

1500 / 20 (C) Signup and view all the answers

What role does the sympathetic nervous system play in athletes' performance?

Prepares the body for vigorous activity (B) Signup and view all the answers

What is the voltage of the current used in electroshock defibrillation?

1000 volts (D) Signup and view all the answers

How long is the current applied during electroshock defibrillation?

For a few thousands of seconds (D) Signup and view all the answers

What type of current is used in electroshock defibrillation?

Direct current (D) Signup and view all the answers

What is the primary purpose of applying a high voltage current during electroshock defibrillation?

To reset the heart's rhythm (D) Signup and view all the answers

Which of the following describes the nature of the current used in electroshock defibrillation?

It is strong and high voltage (B) Signup and view all the answers

What happens to the ventricles when there is no pacemaker present?

The ventricles enter a state of stand still. (C) Signup and view all the answers

What is the consequence of decreased blood supply to the brain during this period?

Loss of consciousness. (A) Signup and view all the answers

What initiates a new pacemaker to take over from the SA node?

The Purkinje fibers. (D) Signup and view all the answers

What is the rate of impulses generated by the new pacemaker in the absence of the SA node?

15-40 beats/min (C) Signup and view all the answers

Which condition can occur due to the lack of pacemaker activity?

Stokes-Adams syndrome. (B) Signup and view all the answers

Study Notes

Electrophysiology (Abnormal Rhythms & Conduction Defects)

This study covers abnormal heart rhythms and conduction defects
Topics include tachycardia, bradycardia, sinus arrhythmia, AV nodal block, and more.
A 20-year-old patient with a fever of 104°F, nausea, and vomiting, was diagnosed with malaria. The patient also experienced palpitations requiring an ECG.
Palpitations are a feeling of heart sounds.
Sinus tachycardia is when the heart rate is above 100 beats per minute(bpm).
A normal heart rate is around 70-80 bpm.
ECG is normal except for the intervals between QRS complexes. These intervals are around 150 bpm, instead of 72 bpm.
Causes of tachycardia include increased body temperature (10 bpm increase per °F) and stimulation of the sympathetic nerves.

Causes of Tachycardia

Increased body temperature (10 beats per minute for each degree Fahrenheit increase.)
Stimulation by sympathetic nerves.
Toxic heart conditions.

Hypertension and Bradycardia

A 40-year-old woman with hypertension was prescribed beta-blockers.
She started experiencing lethargy, dyspnea (difficulty breathing), and excessive sweating.
An ECG assessment revealed bradycardia.
Bradycardia is a slow heart rate, typically below 60 bpm.
Bradycardia can occur in athletes
Beta-blockers can cause bradycardia
Vagal stimulation can decrease the heart rate.

Sinus Arrhythmia

Heart rate increases and decreases by 5% during quiet respiration.
Inspiration causes increased heart rate.
Results from signals spilling over from the respiratory center to the vasomotor center.

AV Nodal Block

Impulses from the sinoatrial (SA) node to the atrioventricular (AV) node might be blocked.
Reasons include inflammation, ischemia, scarring/compression, and extreme vagal nerve stimulation.
First-degree AV block: PR interval greater than 0.20 seconds.
This type of block is typically associated with rheumatic fever and is common, especially during periods of swelling in the joints, and may be present when there is a high temperature from infections like strep throat (streptococcal throat infections)

Second-Degree AV Block

Some impulses from the SA node reach the AV node but are delayed
PR interval continues to extend until a QRS beat is missed
two types of 2nd Degree block include Mobitz type 1 and type 2
Mobitz type 1 block leads to progressive increases in the PR Interval and a drop in ventricular beats.
Mobitz type 2 block is when an impulse from the AV node is dropped without increasing the PR interval.

Third-Degree AV Block (Complete Heart Block)

Complete blockage of impulses from the SA to AV node
Ventricles create their own pacemaker (usually 40 beats per minute)
Atrial (atria) rate (100 bpm) is not synchronized with ventricular rate due to the disrupted conduction.
Treatment often involves a pacemaker.

Stokes-Adams Syndrome

In some cases with complete AV block, ventricles may pause momentarily before restarting.
This temporary pause in conduction leads to a loss of blood supply to the brain, causing a brief period of unconsciousness.
Ventricles escape: ventricles start to beat on their own.

Re-entry Phenomena (Circus Movements)

Impulse repeatedly circulates through the heart, causing continuous stimulation and potentially irregular heart beats
3 causes of re-entry include: longer than normal pathways, decreases in velocity of conduction, and a shortened refractory period

Ventricular Fibrillation

Irregular, rapid, and often chaotic contraction of the ventricles.
No coordinated pumping action.
Requires emergency intervention (defibrillation).

Atrial Fibrillation

Irregular, rapid contraction of the atria, usually 350-600 bpm
Atrial muscle is separated by fibrous tissue from ventricular muscle.
Doesn't affect ventricle rhythm unless it is very rapid
Reduction in the efficiency of overall heart pumping by ~20-30%.

Atrial Flutter

Rapid, regular atrial contractions, often 200-300 bpm.
Impulses that reach the ventricles are reduced because of the A-V node and A-V bundle refractory periods
Typically results in a 2:1 (or 3:1) atrial-ventricular conduction ratio.

Angina Pectoris

Chest pain due to reduced blood supply to the heart (myocardium).
ST-segment elevations are common on an ECG during an angina attack.

Myocardial Infarction

Heart attack, resulting in reduced blood flow to the heart muscle (myocardium), often from a blood clot.
Common findings include prominent Q waves and elevated ST segments on an ECG.

Premature Contractions

Contractions of the heart occur before the expected time.
Ectopic foci may cause premature contractions, which are abnormal areas that start impulses spontaneously.

Different Types of Premature Contractions

Atrial Premature Contractions (PACs).
Ventricular Premature Contractions (PVCs).

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Description

This quiz focuses on the clinical significance of a prolonged P-R interval observed in electrocardiograms (ECGs). Test your knowledge on the implications, diagnostic tests, and heart conditions associated with this key interval. It's essential for medical students and healthcare professionals alike.