Sinus Rhythms: Chapter 7

• Chapter 7 explores rhythms originating in the sinus node, which is the natural pacemaker of the heart.

Sinus Rhythms

• Sinus rhythms serve as the standard for comparing all other heart rhythms.
• The sinus node is the primary pacemaker due to its fastest inherent rate.
• When the sinus node fails, a lower pacemaker will take control at a slower rate, known as an "escape" rhythm.
• If a lower pacemaker takes over at a faster rate, this is called "usurpation".

Conduction in Sinus Rhythms

• Impulses starts in the sinus node and travels through the atria and down to the ventricles.
• This process involves interatrial tracts, internodal tracts, the AV node, the Bundle of His, bundle branches, and Purkinje fibers.

Sinus Rhythm

• Heart Rate falls between 60-100 beats per minute.
• Rhythm demonstrates regularity.
• Visible and upright P waves are present, each married to a QRS complex.
• The PR interval measures 0.12–0.20 seconds and remains constant.
• QRS duration is less than 0.12 seconds.
• Cause of a sinus rhythm is normal heart function.
• There are typically no adverse effects or need for specific treatment.

Sinus Bradycardia

• Heart rate is slower that 60 beats per minute
• Rhythm is regular
• P waves are upright and precede each QRS complex.
• PR interval ranges from 0.12 to 0.20 seconds and remains constant.
• QRS duration is less than 0.12 seconds.
• Causes include vagal stimulation, myocardial infarction (MI), hypoxia, digitalis toxicity, or being a well-trained athlete.
• Adverse effects can include dizziness, pallor, weakness, syncope, diaphoresis, and hypotension.
• Treatment may involve atropine for symptomatic individuals, oxygen therapy, a pacemaker, or adjusting bradycardia-inducing medications.

Sinus Tachycardia

• Heart rate is between 101 and 160 bpm.
• Rhythm is regular
• P waves appear upright, matching, and married to the QRS complexes.
• PR interval falls between 0.12 to 0.20 seconds and remains constant.
• QRS duration is less than 0.12 seconds
• Causes may include atropine, emotions, pulmonary embolus, MI, CHF, fever, vagus nerve inhibition, or thyrotoxicosis.
• Adverse effects can include decreased cardiac output.
• Treatment focuses on addressing the underlying cause and may involve beta-blockers.

Sinus Arrhythmia

• Heart rate varies with the respiratory pattern.
• Rhythm is irregular.
• P waves are upright, matching, and married to the QRS complexes.
• PR interval ranges from 0.12 to 0.20 seconds and is constant.
• QRS duration is less than 0.12 seconds.
• Causes include heart disease or breathing patterns.
• Generally doesn't have adverse effects
• Usually requires no treatment.