Card 120- Sinus Rhythms

• Mechanism of Normal Sinus Rhythm:

  • Sinus node initiates regular impulses at a normal rate
  • Each impulse is conducted normally to the ventricles
• Rules for Normal Sinus Rhythm:

  • Regularity: Regular
  • Rate: 60–100 bpm
  • P Wave: Uniform shape; one P wave in front of every QRS complex
  • PRI: 0.12–0.20 second and constant
  • QRS: Less than 0.12 second
• Mechanism of Sinus Bradycardia:

  • The sinus node is the pacemaker, firing regularly at a rate of less than 60 times per minute
  • Each impulse is conducted normally through to the ventricles
• Rules for Sinus Bradycardia:

  • Regularity: Regular
  • Rate: Less than 60 bpm
  • P Wave: Uniform shape; one P wave in front of every QRS complex
  • PRI: 0.12–0.20 second and constant
  • QRS: Less than 0.12 second
• Mechanism of Sinus Tachycardia:

  • The sinus node is the pacemaker, firing regularly at a rate of greater than 100 bpm
  • Each impulse is conducted normally through to the ventricles
• Rules for Sinus Tachycardia:

  • Regularity: Regular
  • Rate: Greater than 100 bpm (usually does not exceed 160 bpm)
  • P Wave: Uniform shape; one P wave in front of every QRS complex
  • PRI: 0.12–0.20 second and constant
  • QRS: Less than 0.12 second
• Mechanism of Sinus Arrhythmia:

  • The sinus node is the pacemaker, but impulses are initiated in an irregular pattern
  • The rate increases as the patient breathes in and decreases as the patient breathes out
  • Each impulse is conducted normally through to the ventricles
• Rules for Sinus Arrhythmia:

  • Regularity: Irregular
  • Rate: 60–100 bpm (usually)
  • P Wave: Uniform shape; one P wave in front of every QRS complex
  • PRI: 0.12–0.20 second and constant
  • QRS: Less than 0.12 second
• The P wave is the atrial depolarization, while the QRS complex represents ventricular depolarization.
• Sinus rhythm refers to normal sinus node activity, where the SA node initiates electrical impulses that spread through the heart's conduction system.
• T waves are associated with repolarization of the ventricles.
• In sinus tachycardia, the sinus node fires more frequently than usual, resulting in a rapid heartbeat.
• In sinus tachycardia, there may be some variation in the PR interval due to variations in the time it takes for the impulse to travel from the SA node to the AV node.
• Sinus arrhythmia occurs when there is variation in the timing or frequency of sinus node discharges, leading to irregular intervals between successive beats.
• Sinus bradycardia occurs when the sinus node slows down its firing frequency, leading to a slower heartbeat.
• In sinus bradycardia, the sinus node fires less frequently than usual, leading to a slower heart rate.
• The P wave represents atrial depolarization.