Untitled Quiz

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Questions and Answers

What is the shape of the QRS complex in lead V1 for a Left Bundle Branch Block (LBBB)?

H-shaped

V-shaped

M-shaped

W-shaped (correct)

Which ECG change is associated with a potassium level between 6.5 - 7.5 mEq/L?

Tall, peaked T waves

QT interval shortening

First-degree AV block (correct)

ST segment depression

What is the first and most common finding in hypocalcemia on an ECG?

Prolonged QT interval (correct)

Widening of the QRS complex

Shortened QT interval

Tall, peaked T waves

What is a characteristic feature of hypothermia on an ECG?

Osborne 'J' waves Signup and view all the answers

What is the most common cause of Left Ventricular Hypertrophy (LVH)?

Hypertension Signup and view all the answers

Which of the following symptoms is typically associated with Sick Sinus Syndrome?

Dizziness Signup and view all the answers

What ECG change is likely to occur with severe or symptomatic hypokalemia?

Depression of ST segment Signup and view all the answers

What ECG finding is most indicative of hyperkalemia at potassium levels above 5.5 mEq/L?

Tall, peaked T waves Signup and view all the answers

What characterizes First Degree AV Heart Block?

Prolonged PR interval greater than 200 msec with equal PR intervals Signup and view all the answers

Which feature is indicative of Second Degree AV Block: Mobitz Type I?

Regularly irregular PR intervals with active block of QRS complexes Signup and view all the answers

What is a potential treatment for Second Degree AV Block: Mobitz Type II?

Insertion of a pacemaker Signup and view all the answers

What distinguishes Third Degree AV Block from other types?

Independent atrial and ventricular pacing with no association Signup and view all the answers

What is a common ECG characteristic of Left Bundle Branch Block (LBBB)?

Tall R waves in lateral leads with deep S waves in right precordial leads Signup and view all the answers

What pattern is typically seen in Right Bundle Branch Block (RBBB)?

rSR' pattern with 'bunny ears' in V1-V2 Signup and view all the answers

Which of the following describes the treatment for First Degree AV Block?

No treatment is required Signup and view all the answers

What indicates a Symptomatic presentation in Second Degree AV Block: Mobitz Type II?

Presyncope and fatigue Signup and view all the answers

What is one of the primary causes of Third Degree AV Block?

Myocardial infarction (MI) Signup and view all the answers

Study Notes

AV Conduction Blocks

Delay or interruption in the transmission of the impulse from the atria to the ventricles
Can be caused by medications
Usually asymptomatic
No treatment required

First Degree AV Heart Block

Delayed conduction from atrium to ventricle (but no interruption)
Prolonged PR interval (> 200 msec)
All PR intervals are equal
Usually asymptomatic
Can be caused by medications
No treatment required

Second Degree AV Block: Mobitz Type I (Wenckebach)

The PR interval progressively increases until one p-wave is blocked and isn’t transmitted to the ventricles
Notable PR interval lengthening with a P-wave not followed by a QRS complex
The cycle starts all over again after that drop (regularly irregular)
Treatment is usually not indicated as this rhythm usually is asymptomatic

Second Degree AV Block: Mobitz Type II

Dropped QRS complex that is NOT preceded by a lengthening of the PR interval
The PR interval is consistent (either normal or prolonged), until one p-wave is blocked and isn’t transmitted to the ventricles
Symptoms may be present and are more common than Mobitz Type I and include presyncope, syncope, fatigue, or SOB
More serious than type I second-degree AV block
May progress to third degree (complete) AV block
Often treated with a pacemaker

Third Degree (Complete) Heart Block

The atria and ventricles beat independently of each other
P-waves are not associated with QRS complexes
Atrial pacing is greater than ventricular pacing
ECG will show equal RR intervals and equal PP intervals but no association
May be caused by MI, degeneration of the conductive tissue, and Lyme Disease
Treated with a Pacemaker

Left Bundle Branch Block (LBBB)

Normally, the septum is activated from left to right
In LBBB, septal depolarization is reversed
Leads to QRS duration > 120ms
- Produces tall R waves in the lateral leads (I, V5-6) and deep S waves in the right precordial leads (V1-3)
Produces a broad or notched (‘M’-shaped) R wave in the lateral leads (V5, V6) and (‘W’-shaped) dominant deep S waves in V1

Right Bundle Branch Block (RBBB)

QRS duration is greater than 120 msec
QRS in V1-V2 displays rSR’ pattern “bunny ears” or the letter “M”
Lateral leads (I, V6) broad deep S-wave that is greater than R-wave duration.

Bundle Branch Block “Turn Signal Theory”

Criteria: QRS complex > 120 msec, reference lead V1
LBBB: ‘W’-shaped in V1
RBBB: ‘M’-shaped in V1

Hyperkalemia

Potassium (K+): 3.5-5.0 mEq/L
ECG changes depend on serum level and how rapid of a change
K+ = 5.5 - 6.5 mEq/L
- Tall, peaked, narrow based T waves
- QT interval shortening
K+ = 6.5 - 7.5 mEq/L
- First-degree AV block
- QRS widening
K+ > 7.5 mEq/L
- Disappearance of P waves

Hypokalemia (HypUkalemia)

Severe or symptomatic hypokalemia
- Depression of the ST segment, decrease in the amplitude of the T-wave, and an increase in the amplitude of U waves
- U-waves are often seen in the lateral precordial leads V4 to V6
- Prolongs the QT interval
- Increased amplitude and width of the P-wave

Hypercalcemia

Calcium, serum (total): 8.5-10.2 mg/dL
QT interval shortening (usually due to shortening of the ST segment)
Note: Little if any effect on P, QRS, or T wave

Hypocalcemia

Prolonged QT interval (earliest and most common finding) due to ST segment prolongation
No change in the duration of the T wave (seen only with hypocalcemia or hypothermia)

Hypothermia: Osborne “J” Waves

Hypothermia results in sinus bradycardia with widening of the QRS
Prolongation of PR and QT intervals
Osborne (“J”) waves, which are late upright terminal deflections of the QRS complex (“camel hump” sign)

Summary

Hyperkalemia: tall peaked T-waves, QT interval shortening
Hypokalemia: ST segment depression, shallow T-waves, U-waves
Hypercalcemia: QT interval shortening
Hypocalcemia: Prolonged QT interval
Hypothermia: Osborne “J” waves

Left Ventricular Hypertrophy (LVH)

Response to pressure overload states
Increase in size of the myocardial fibers
- Parallel addition of sarcomeres
Causes
- Hypertension (most common cause)
- Aortic stenosis
- Aortic regurgitation
- Mitral regurgitation
- Coarctation of the aorta
- Hypertrophic cardiomyopathy

Sick Sinus Syndrome

When the SA node is damaged and no longer generates normal heartbeats at a normal rate
- Another cause of Pathologic Bradycardia
Most common caused is gradual loss of SA node function that comes with age
Sx: Dizziness, Pre-syncope, Syncope, SOB, Fatigue
Tx: Pacemaker