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Respiratory Sinus Arrhythmia

Sinus arrhythmia, Respiratory sinus arrhythmia

Nervus Vagus and Sinus Rhythm

• Autonomic nervous system has two parts
• that generally have opposite effects:
• Sympathetic nervous system
• Ensures immediate energy mobilization
• Operates under the "fight or flight" principle
• Stimulates organs (e.g., sinus tachycardia)
• Parasympathetic nervous system
• Ensures energy storage and body regeneration
• Operates under the "rest and digest" principle
• Inhibits organs (e.g., sinus bradycardia)

• Nervus vagus (10th cranial nerve)
• It is the main nerve of the parasympathetic nervous system
• Also innervates the sinoatrial node (SA node) and acts inhibitory
• Causes sinus bradycardia

• During breathing, the tone of the vagus nerve changes physiologically
• Inhalation increases frequency
• Inhalation decreases the tone of the vagus nerve
• The SA node is "released" and the automaticity of the SA node increases
• Exhalation decreases frequency
• Exhalation increases the tone of the vagus nerve
• The SA node is "braked" and the automaticity of the SA node decreases

ECG and Respiratory Sinus Arrhythmia

• Physiological P waves (they are a fundamental sign of sinus rhythm)
• positive in leads I, II
• negative in lead aVR
• Heart rate is irregular
• (PP and RR intervals regularly change with breathing)
• P-P interval changes by more than 120ms (3 small squares)
  
  
• Impulses then pass to the ventricles via the AV junction
• Results in narrow QRS complexes (< 0.12s) if there is no aberrant conduction
  
  

Respiratory Sinus Arrhythmia

• Sinus Rhythm
• P waves are present
• Respiratory Sinus Arrhythmia
• PP (and RR) interval changes with breathing
• Inhalation - PP interval shortens (frequency increases)
• Exhalation - PP interval lengthens (frequency decreases)

Respiratory Sinus Arrhythmia

• Frequency 80/min. (six-second rule)
• Sinus Rhythm
• P waves are present
• P mitrale (left atrial hypertrophy)
• PQ interval remains unchanged
• Heart rate is irregular
• PP interval changes by 0.44s with breathing
• Longest PP interval is 1.04s (frequency 57/min.)
• Shortest PP interval is 0.6s (frequency 100/min.)

Atrial Fibrillation

• No P waves on the ECG, so it is not
• Respiratory sinus arrhythmia
• Sinus bradycardia
• Heart rhythm is irregularly irregular (RR intervals are of varying lengths)
• Heart rate <60/min. (6-second rule)
• ECG shows atrial fibrillation
• The patient is likely on medication to slow AV node conduction
• Digoxin
• Beta-blockers
• Calcium channel blockers
• Hypothermia can also slow AV conduction
• It is fine atrial fibrillation
• Amplitude of fibrillatory waves in V1 <0.5mm
• ST depressions and negative T waves in lateral leads (I, aVL, V5, V6) are seen with
• Ischemia
• Digoxin