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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)?
What is the shape of the QRS complex in lead V1 for a Left Bundle Branch Block (LBBB)?
Which ECG change is associated with a potassium level between 6.5 - 7.5 mEq/L?
Which ECG change is associated with a potassium level between 6.5 - 7.5 mEq/L?
What is the first and most common finding in hypocalcemia on an ECG?
What is the first and most common finding in hypocalcemia on an ECG?
What is a characteristic feature of hypothermia on an ECG?
What is a characteristic feature of hypothermia on an ECG?
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What is the most common cause of Left Ventricular Hypertrophy (LVH)?
What is the most common cause of Left Ventricular Hypertrophy (LVH)?
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Which of the following symptoms is typically associated with Sick Sinus Syndrome?
Which of the following symptoms is typically associated with Sick Sinus Syndrome?
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What ECG change is likely to occur with severe or symptomatic hypokalemia?
What ECG change is likely to occur with severe or symptomatic hypokalemia?
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What ECG finding is most indicative of hyperkalemia at potassium levels above 5.5 mEq/L?
What ECG finding is most indicative of hyperkalemia at potassium levels above 5.5 mEq/L?
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What characterizes First Degree AV Heart Block?
What characterizes First Degree AV Heart Block?
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Which feature is indicative of Second Degree AV Block: Mobitz Type I?
Which feature is indicative of Second Degree AV Block: Mobitz Type I?
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What is a potential treatment for Second Degree AV Block: Mobitz Type II?
What is a potential treatment for Second Degree AV Block: Mobitz Type II?
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What distinguishes Third Degree AV Block from other types?
What distinguishes Third Degree AV Block from other types?
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What is a common ECG characteristic of Left Bundle Branch Block (LBBB)?
What is a common ECG characteristic of Left Bundle Branch Block (LBBB)?
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What pattern is typically seen in Right Bundle Branch Block (RBBB)?
What pattern is typically seen in Right Bundle Branch Block (RBBB)?
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Which of the following describes the treatment for First Degree AV Block?
Which of the following describes the treatment for First Degree AV Block?
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What indicates a Symptomatic presentation in Second Degree AV Block: Mobitz Type II?
What indicates a Symptomatic presentation in Second Degree AV Block: Mobitz Type II?
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What is one of the primary causes of Third Degree AV Block?
What is one of the primary causes of Third Degree AV Block?
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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
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