Lecture Notes on Sinus Node Dysfunction

Jul 1, 2024

Lecture Notes: Dr. Joshua Cooper on Sinus Node Dysfunction

Importance of Sinus Node

  • Key Function: Acts as the heart's natural pacemaker, located in the top part of the right atrium near the superior vena cava.
  • Response to Body Needs: Fires more slowly at rest or sleep, and speeds up with adrenaline or activity.
  • Result: Each firing causes atria to contract, creating a P wave on EKG/telemetry.

Sinus Node Dysfunction Indicators

  • Sinus Bradycardia: <60 beats per minute; normal in younger, athletic people but may indicate malfunction if symptomatic and no reversible cause.
  • Sinus Pause/Arrest: Sudden stop in sinus node firing; if long enough to cause lightheadedness/fainting and no reversible cause, indicates pacemaker need.
  • Telemetry Observations: Various patterns can mimic or indicate dysfunction, requiring careful diagnosis.

Presentation Examples

  • Case 1: Sinus rhythm followed by sinus arrest with junctional escape beat.
  • Case 2: Brief sinus arrest with prolonged AV node-induced rhythm.
  • Case 3: Premature atrial beat suppressing sinus node.
  • Case 4: Sinus node recovery time post atrial arrhythmia.

Atrial Arrhythmias

  • Atrial Fibrillation/Tachycardia: After stopping, can delay sinus node recovery, indicating pacemaker if symptomatic with no reversible cause.

Specific Dysfunction Types

  • Sinoatrial Exit Block: Failure of impulses to exit perinodal tissue, causing specific EKG patterns and potentially bradycardia.
  • Diagnosis: Mathematically compare normal and bradycardic rates. Patterns like 4:3 exit Wenckebach observed.

Mimics of Sinus Node Dysfunction

  • Sinus Arrhythmia: Normal fluctuation with breathing, called respirophasic sinus arrhythmia, does not require treatment.
  • Cardio Inhibitory Reflex: Involves vagus nerve influencing both sinus and AV nodes, can cause simultaneous slow down; self-limited.
  • Obstructive Sleep Apnea: High vagal tone during apnea may cause episodic bradycardia; treat apnea, not with pacemaker.
  • Accelerated Junctional Rhythm: Faster AV node rhythm competing with sinus node activity.
  • Premature Atrial Beats (PACs): Can be blocked or conducted, influencing sinus node firing.
  • 2:1 AV Block: Typically not mistaken for sinus dysfunction but must be carefully distinguished.

Diagnostic Strategy

  • Identify P Waves: Compare EKG segments with and without bradycardia to identify extra P waves or unique patterns.
  • EKG Review: Look for distinctive waveform changes to diagnose accurately.

Summary

  • Recognize Patterns: Differentiate between true sinus node dysfunction and other causes like atrial/junctional rhythms or external influences.
  • Treatment Indications: Pacemakers for symptomatic dysfunction without reversible causes; treat underlying conditions like sleep apnea for self-limiting events.

Hope this presentation was helpful!