Sinus Node Rhythms

Rhythms Originating in the Sinus Node

• The sinus node is the pacemaker and has the fastest inherent rate.
• If the sinus node fails, a lower pacemaker takes over at a slower inherent rate (escape).
• A lower pacemaker can take over at a faster rate (usurpation).
• Sinus rhythms serve as the standard for comparison against all other rhythms.
• Impulses in sinus rhythms originate in the sinus node, then travel through the atria and down to the ventricles.

Sinus Rhythm

• The rate is between 60-100 beats per minute.
• Regularity is regular.
• P waves are upright, matching, and married to the QRS complex.
• The PR interval is constant at 0.12–0.20 seconds.
• The QRS interval is less than 0.12 seconds.
• It is caused by normal function.
• There are no adverse effects.
• No treatment is needed.

Sinus Bradycardia

• The rate is less than 60 beats per minute.
• Regularity is regular.
• P waves are upright, matching, and married to the QRS complex.
• The PR interval is constant between 0.12-0.20 seconds.
• The QRS interval is less than 0.12 seconds.
• Causes include vagal stimulation, myocardial infarction (MI), hypoxia, digitalis toxicity, and being a well-trained athlete.
• Adverse effects include dizziness, pallor, weakness, syncope, diaphoresis, and hypotension.
• Treatment includes atropine if symptomatic, oxygen, pacemaker, and holding bradycardia-inducing medications.

Sinus Tachycardia

• The rate is between 101–160 beats per minute.
• Regularity is regular.
• P waves are upright, matching, and married to the QRS complex.
• The PR interval is constant between 0.12-0.20 seconds.
• The QRS interval is less than 0.12 seconds.
• Causes include atropine, emotions, pulmonary embolus, myocardial infarction (MI), congestive heart failure (CHF), fever, vagus nerve inhibition, and thyrotoxicosis.
• Adverse effects include decreased cardiac output.
• Treatment involves treating the underlying cause and considering beta-blockers.

Sinus Arrhythmia

• The rate varies with the respiratory pattern.
• Regularity is irregular.
• P waves are upright, matching, and married to the QRS complex.
• The PR interval is constant between 0.12-0.20 seconds.
• The QRS interval is less than 0.12 seconds.
• Causes include heart disease and breathing patterns.
• Adverse effects are usually none.
• Treatment is usually not required.

This lesson covers rhythms originating in the sinus node, including sinus rhythm and sinus bradycardia. It details the characteristics of each rhythm, such as rate, regularity, and P wave morphology. It also discusses causes, adverse effects, and treatment options.