USMLE/COMLEX 3 - AV Node Block, Sick Sinus Syndrome, & Bundle Branch Block

Here are key facts for USMLE Step 3 & COMLEX-USA Level 3 from the AV Node Block, Sick Sinus Syndrome, & Bundle Branch Block tutorial, as well as points of interest at the end of this document that are not directly addressed in this tutorial but should help you prepare for the boards. See the tutorial notes for further details and relevant links.

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1. Clinical management: Usually no treatment required for asymptomatic patients. 2. Medication review: Consider channel blockers or digoxin as potential causative agents and adjust accordingly. 3. Risk stratification: Monitor for potential progression to atrial fibrillation. 4. Electrolyte management: Address underlying hypokalemia or hypomagnesium if present. 1. Clinical decision-making:

• Type 1: Conservative management if asymptomatic; identify and adjust medications that may be responsible.
• Type 2: Prompt pacemaker implantation indicated due to risk of progression.

2. Disease monitoring:

• Type 1 patients require monitoring but may not need intervention.
• Type 2 requires close surveillance for progression to complete heart block.

3. Differential considerations:

• Evaluate for underlying cardiac injury, Lyme disease, valvulopathy.
• Review medications including beta blockers, calcium channel blockers, digoxin, amiodarone.

1. Urgent management: Pacemaker implantation is indicated. 2. Immediate concerns: Address low cardiac output to prevent end-organ damage. 3. Medication management: Identify and discontinue potential causative agents (digoxin, calcium-channel blockers, beta blockers, tricyclic antidepressants, clonidine). 4. Etiology workup: Investigate for infection (diphtheria, rheumatic fever), hypertension, cancer. 1. Diagnostic criteria: Presence of bradycardia, sinus pauses or arrest, and junctional escape beats. 2. Definitive therapy: Pacemaker implantation is often required. 3. Risk assessment: Evaluate for underlying causes of SA node damage.

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1. Special populations: Recognition that this finding is common in highly-trained athletes due to physiologic adaptation. 2. Secondary prevention: Monitor for development of myocarditis in appropriate clinical context. 1. Symptom correlation:

• Type 1: May present with dizziness, fainting.
• Type 2: Often presents with chest pain, difficulty breathing, tiring easily, hypotension.

2. Clinical trajectory: Type 2 can progress to complete heart block, requiring proactive management. 3. Population considerations:

• Type 1 may be physiologic in healthy athletes.
• Type 2 is always pathologic and requires intervention.

1. Patient presentation: Fatigue/lethargy, dizziness, fainting, slow heart beat. 2. Diagnostic hallmark: AV dissociation with no relationship between P waves and QRS complexes. 3. Etiologic considerations:

• Congenital: In infants from mothers with autoimmune conditions.
• Iatrogenic: Complications of heart surgery, radiotherapy, radiofrequency ablation.
• Medical: Evaluate for hypertension, infection, cancer.

1. Diagnostic parameters: QRS complex greater than 120 ms defines complete bundle branch block. 2. Right Bundle Branch Block interpretation:

• May be incidental in otherwise healthy individuals.
• ECG findings: rsR' "bunny ear" pattern in leads V1-V3; slurred S waves in I, aVL, V5 and V6.
• Requires evaluation for possible right heart damage in appropriate clinical context.

3. Left Bundle Branch Block management:

• Always indicative of left heart disease requiring further workup.
• ECG patterns: Broad monophasic R wave and absent Q waves in I, V5, V6; ST and T wave displacement opposite to QRS.

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Below is information not explicitly contained within the tutorial but important for USMLE & COMLEX 3. 1. Shared decision-making: Discussing risks and benefits of pacemaker implantation with patients. 2. Perioperative considerations: Management of patients with conduction disorders during non-cardiac surgery. 3. Driving restrictions: Evidence-based counseling for patients with symptomatic conduction disorders. 1. Device selection: Choosing between single vs. dual-chamber pacemakers based on patient characteristics. 2. Medication interactions: Managing rate-controlling medications in patients with dual pathology. 3. Remote monitoring: Implementation and interpretation of pacemaker telemetry data. 1. Cardiac resynchronization therapy: Patient selection and outcome expectations. 2. Screening protocols: Evidence-based approach to monitoring for progression of conduction disease. 3. Risk stratification tools: Using imaging and electrophysiologic data to predict adverse outcomes.