Dysrhythmia of the SA Node Quiz

Dysrhythmia of the SA Node

• Sinus Tachycardia

  • Rate: >100 bpm

  • Regularity: regular

  • P waves: normal

  • PR interval: normal/less

  • QRS duration: normal

  • ST segment: isoelectric

  • P:QRS ratio: 1:1

  • Causes: stimulation of the sympathetic nervous system, response to fear, pain, or anxiety, hyperthyroidism, heart failure, anemia, exercise, stimulants (caffeine, decongestants, stress, and pain), high temperature (fever), and alterations in fluid status (hypovolemia)

  • Patient response: Decreased ventricular filling time -> Low cardiac output, Decrease coronary filling during diastole

  • Treatment: Treat the underlying cause, for example, pain medications are administered to treat pain or antipyretics are given to treat fever, no medication is given to slow down the heart rate.

• Sinus Bradycardia

  • Rate: <60 bpm
  • Regularity: regular
  • P waves: normal
  • PR interval: normal
  • QRS duration: normal
  • ST segment: isoelectric
  • P:QRS ratio: 1:1
  • Causes: athletes, increased vagal stimulation (parasympathetic nervous system), drug effects e.g., digoxin, or AV nodal blocking agents, including calcium channel blockers and beta-blockers; or (sometimes, a desired result), myocardial infarction (MI), SA node diseases, hypoxemia and hypothermia, and increased intracranial pressure
  • Patient response: Decreased cardiac output -> hypotension -> decrease organ perfusion
  • Treatment: Treat the underlying cause, assess for hemodynamic instability related to the bradycardia. If the patient is symptomatic, administer atropine and/ or TCP (transcutaneous pacing) when symptomatic bradycardia.

• Sinus Arrhythmia

  • Rate: May be normal
  • Regularity: irregular
  • P waves: normal
  • PR interval: normal/abnormal
  • QRS duration: normal
  • ST segment: isoelectric
  • P:QRS ratio: 1:1
  • Patient response: This rhythm is tolerated well.
  • Treatment: No treatment is required.

• Sinus Pauses

  • Rate: May be normal
  • Regularity: Irregular for the period of the pause, but regular when sinus rhythm resumes.

Dysrhythmia of the Atria

• Atrial Tachycardia

  • Rate: 150 - 250 bpm
  • Regularity: regular
  • P waves: merged with the T wave if present
  • PR interval: not measurable
  • QRS duration: normal/less
  • Causes: Patients with cardiac diseases, could occur in healthy patients, electrolyte imbalance, digitalis toxicity, ischemic heart disease, valvular abnormalities, lung disease.
  • Patient response: Low cardiac output, life-threatening.
  • Treatment: Assessing patient tolerance to tachycardia, cardioversion, medications include adenosine, beta-blockers, calcium channel blockers, and amiodarone.

• Atrial Flutter

  • Rate: Atrial rate (250 to 350 bpm), Ventricular rate (varies)

  • Regularity: Regular

  • P waves: Classic saw-tooth in leads II, III, and a VF

  • PR interval: Unmeasurable

  • QRS duration: Normal to wide

  • P:QRS ratio: No. of P waves: 1

  • Arises from a single irritable focus in the atria.

  • Causes: hyperthyroidism, hypoxemia, ischemic heart disease, heart failure, lung disease, alcoholism.

  • Patient response: Asymptomatic, fast ventricular rate could result in low cardiac output.

  • Treatment: Anticoagulation therapy, cardioversion done after receiving anticoagulation for 6 weeks, electrophysiological treatment (ablation of the irritable focus).

• Atrial fibrillation

  • Rate: Atrial (indiscernible from 350 to 500 bpm), Ventricular (varies)

  • Regularity: Irregular

  • P waves: Absent (fine waves)

  • PR interval: Unmeasurable

  • QRS duration: Normal/wide

  • Arises from multiple ectopic foci in the atria, causing chaotic quivering of the atria and ineffectual atrial contraction.

  • Most common rhythm with clinical importance

  • Erratic impulses formation throughout the atria.

  • Causes: Hyperthyroidism, valvular disease, ischemic heart disease, heart failure, lung disease.

  • Patient response: Patient may or may not be aware of atrial fibrillation, fast ventricular rate could result in low cardiac output.

  • Treatment: Anticoagulation therapy, cardioversion done after receiving anticoagulation for 4 to 6 weeks, emergent cardioversion is done if hemodynamically unstable, electrophysiological treatment (ablation of the irritable focus).

Dysrhythmia of the AV node

• Junctional Escape Rhythm

  • Rate: 40 to 60 bpm.

  • Regularity: Regular.

  • P wave: Absent/inverted/following QRS.

  • PR interval: Normal to short.

  • QRS: Normal.

  • ST segment: Isoelectric.

  • Occurs when the dominant pacemaker (SA node) fails to fire.

  • Causes: Loss of SA node activity.

  • Patient response: Assessed for tolerating bradycardia

  • Treatment: Administer atropine and/ or TCP (transcutaneous pacing), dopamine infusion, or epinephrine when symptomatic bradycardia.

Dysrhythmia of the Ventricles

• PVCs (Premature Ventricular Contractions)

  • Early beats that interrupt the underlying rhythm.

  • They can arise from a single ectopic focus or from multiple foci within the ventricles.

  • Unifocal PVCs: Arise from a single irritable focus.

  • Multifocal PVCs: Arise from multiple irritable foci.

  • PVC Patterns:

    • Bigeminy: Every other beat is a PVC
    • Trigeminy: Every third beat is a PVC
    • Quadrigeminy: Every fourth beat is a PVC
    • Couplet: Two consecutive PVCs
    • Pairs: Two or more consecutive PVCs
    • Triplet: Three consecutive PVCs

  • Causes: Hypokalemia, hypomagnesemia, hypoxemia, acid-base imbalance, ischemic heart disease.

  • Patient response: May be experienced as palpitations. Patients may become symptomatic if the PVCs occur frequently.

  • Treatment: Treat the underlying cause.

  • When are PVCs Dangerous?

    • Frequent
    • Multifocal
    • Two or more in a row
    • R on T: PVC falls into the vulnerable period of the T wave, ventricular tachycardia, or fibrillation can result.

• Ventricular Tachycardia (VT)

  • Rapid, life-threatening dysrhythmia originating from a single ectopic focus in the ventricles.
  • Rate: Usually > 100 bpm.
  • Patient response: Reduced cardiac output, decreased BP, palpitations, syncope or sudden death
  • Treatment:
    • For stable VT: Medications (amiodarone, lidocaine, procainamide), electrical cardioversion
    • For unstable VT: Immediate defibrillation

This quiz covers the key aspects of dysrhythmia related to the SA node, focusing on sinus tachycardia and sinus bradycardia. Understand the characteristics, causes, patient responses, and treatments for these conditions. Test your knowledge and enhance your understanding of cardiac rhythm disorders.