• Sinoatrial Node
• Frequency and Sinus Rhythm
• Inappropriate Sinus Tachycardia
• ECG and Inappropriate Sinus Tachycardia

Sinoatrial Node

• Automaticity
• Each part of the conduction system and the working myocardium
• Has the ability to spontaneously generate impulses
  
  
• Overdrive suppression
• Impulses spread through the conduction system from the focus
• that generates impulses at the highest frequency
• The focus with the highest frequency deactivates other foci
• with a lower frequency (overdrive suppression)
  
  
• Sinoatrial Node (SA node)
• Spontaneously generates impulses at a frequency of 60 - 100/min.
• Other foci generate impulses at a lower frequency

Inappropriate Sinus Tachycardia

• It is a sinus tachycardia that has no cause, not a secondary compensatory mechanism
• SA node has increased automaticity without an explainable cause
• It mainly occurs in young healthy women under 30 years old
• The cause is unknown, it is assumed to be:
• Autoimmune mechanism. Autoantibodies stimulate the SA node
• Hypersensitivity of the SA node to molecules: histamine, serotonin, adrenaline, noradrenaline
• Interestingly, the SA node is damaged in such a way that it goes into the range of tachycardia, and not bradycardia
• The frequency of the SA node inadequately increases with minimal exertion
  
  
• Diagnosis is difficult, all causes of sinus tachycardia must be ruled out
• Inappropriate sinus tachycardia is:
• Resting sinus tachycardia (f: >100/min.) mainly during the day, without cause
• Average heart rate over 24 hours is > 95/min.

Sinus Tachycardia

• Frequency: 150/min. (>100/min.)
• P waves are less visible, overlapping with T waves
• QRS alternans: the amplitude of QRS complexes changes
• The patient has inappropriate sinus tachycardia if:
• There is no cause for sinus tachycardia
• They have resting tachycardia (f > 100/min.)
• Average heart rate over 24 hours is > 95/min.
• Inappropriate sinus tachycardia is a very rare diagnosis

Sinus Tachycardia

• Frequency: 120/min.
• Physiological P wave
• Positive (I, II)
• Negative (aVR)
• P waves are better discernible, not overlapping with T waves
• The patient has inappropriate sinus tachycardia if:
• There is no cause for sinus tachycardia
• They have resting tachycardia (f > 100/min.)
• Average heart rate over 24 hours is > 95/min.
• Inappropriate sinus tachycardia is a very rare diagnosis