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Arrhythmias. Definitions. Arrhythmias = abnormalities of the heart rate or the heart rhythm Tachycardia is a HR >100 Increased pacemaker activity: faster depolarization, lower thresholds, or oscillations during repolarization trigger early action potentials

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definitions
Definitions
  • Arrhythmias = abnormalities of the heart rate or the heart rhythm
  • Tachycardia is a HR >100
    • Increased pacemaker activity: faster depolarization, lower thresholds, or oscillations during repolarization trigger early action potentials
    • Re-entry circuits: depolarization travels in a circle…if tissue is not refractory when the impulse returns, it will depolarize again producing a recurring circuit
  • Bradycardia
    • HR <60
    • Due to abnormal and/or delayed conduction
general management
General Management
  • Prevention
    • Early correction of
      • Hypoxemia
      • Electrolyte imbalances
      • Acid-base imbalances
      • Cardiac ischemia
    • Arrhythmogenic factors
      • Pain
      • Vagal stimulation
      • Drugs
      • Cardiac irritants
general management cont
General Management, cont…
  • Tachyarrhythmias
    • Detrimental when they cause symptoms or reduce tissue perfusion
    • Must be terminated immediately if they cause hypotension, pulmonary edema, or angina
  • Bradyarrhythmias
    • Treated with atropine, beta agonists, or pacemaker if symptomatic
    • Not all will require treatment…if the person is stable and asymptomatic you can treat the cause without converting the rhythm
general management cont1
General Management, cont…
  • Vagal stimulation
    • Carotid sinus massage
    • Slows HR and may cardiovert some SVT’s
  • Antiarrhythmic drugs
    • Selected according to the rhythm and the underlying pathophysiology
    • Therapeutic windows are often narrow
    • Side effects are common
    • Therapy is frequently ineffective
    • They may cause other arrhythmias
    • Arrhythmia suppression does not always improve outcomes
general management cont2
General Management, cont…
  • Non-pharmacologic therapies
    • DC cardioversion
      • Uses 50-360 joule shocks
      • Timed to deliver on the QRS
    • Defibrillation
      • Uses 50-360 joule shocks
      • Not timed
      • May be external or implanted
    • Radiofrequency catheter ablation (RFCA)
      • Heat is delivered through a catheter to a specific site in the heart
diagnosis
Diagnosis
  • Not always easy because artifact can interfere with the EKG tracings
  • Narrow QRS complex tachycardias
    • Usually due to SVT
    • Can be terminated with IV adenosine
  • Wide QRS complex tachycardias
    • Usually due to V tach, but could also be SVT with abnormal conduction
    • Treat as if it were VT (cardioversion/lidocaine)…if no response, then try adenosine
tachyarrhythmias
Tachyarrhythmias
  • Supraventricular tachycardias
    • Orginate above the AV node
    • Present with dizziness, palpitations, dyspnea
    • Are not usually life-threatening
    • Types
      • Sinus tachycardia
        • a normal response to stress, exercise, hypoxemia, fever, increased sympathetic tone
        • Treat by removing the cause
      • Atrial tachycardia:
        • due to ectopic atrial automaticity in chronic heart/lung dx
        • associated with metabolic, acid-base, or drug toxicity
        • Treat by correcting the underlying metabolic defect or with RFCA
tachyarrhythmias cont
Tachyarrhythmias, cont…
  • Atrial flutter
    • A re-entry tachycardia involving the whole atrium
    • Atrial rate is ~300/min
    • Ventricular rate depends on AV conduction
    • Treated with digoxin
  • Atrial fibrillation
    • Multiple re-entry circuits with chaotic atrial rhythm
    • Atrial rate is ~500/min
    • Ventricular rate depends on AV condution…considered controlled as long as ventricular rate <100
    • Stasis of blood from ineffective contraction predisposes to thrombus formation
    • Treat with digoxin, anticoagulants, cardioversion
  • Re-entry tachycardia
    • Re-entry circuits via many AV node conduction pathways
    • Responds to vagal stimulation and drugs that slow AV conduction, such as adenosine
tachyarrhythmias cont1
Tachyarrhythmias, cont…
  • Ventricular tachycardias
    • Arise in the ventricles of patients with heart dx, cardiomyopathy, or congential heart dx
    • Generally more serious than atrial tachs
    • Types
      • Ventricular tachycardia
        • Usually caused by re-entry circuits that form with scarring but can be ectopic automaticity
        • Usually causes hemodynamic decompensation
        • Ventricular rate ~150-250
        • Treat with cardioversion or drugs to suppress the rhythm
tachyarrhythmias cont2
Tachyarrhythmias, cont…
  • Ventricular fibrillation
    • Chaotic ventricular rhythm that frequently follows an acute MI
    • Immediate loss of CO with unconsciousness
    • Treat with defibrillation…the sooner the better
    • May use drugs to prevent recurrence or implantable defibrillator
bradyarrhythmias
Bradyarrhythmias
  • Well tolerated by normal hearts, but CO and BP will fall if SV can’t increase
    • Types
      • Sinus bradycardia
        • Normal EKG with rate <60
        • Causes:
          • vagal reflexes (pain, hypoxemia)
          • Drug toxicity (beta blockers, digoxin)
          • AV node ischemia
        • Treatment:
          • Atropine
          • Beta agonists
          • Drug antidotes
bradyarrhythmias cont
Bradyarrhythmias, cont…
  • Heart block
    • Usually due to ischemic damage to nodal or conducting tissue
    • Common after an inferior MI b/c right coronary artery supplies the AV node in most people
    • Presence after an anterior MI suggests a large infarction
    • First degree
      • slow AV conduction…PR interval exceeds 0.2 seconds
      • Usually benign
    • Second degree
      • Some atrial beats are not conducted to the ventricles
bradyarrhythmias cont1
Bradyarrhythmias, cont…
  • Types of second degree heart block
    • Mobitz I (Wenckebach)
      • Causes PR interval to lengthen with each beat, culminating in the failure of an atrial impulse to be transmitted to the ventricle (dropped beat)
      • Sequence is repetitive
      • Treatment is usually not needed
    • Mobitz II
      • Originates below the AV node in the bundle of HIS or Purkinje fibers
      • Every 2nd or 3rd atrial impulse initiates a ventricular contraction…the others are blocked
      • May require pacemaker insertion
bradyarrhythmias cont2
Bradyarrhythmias, cont…
  • Third degree heart block (complete heart block)
    • Conduction between the atria and ventricles ceases
    • The atria contract at one rate…the ventricles contract at another rate (usually 20-40)
    • Requires pacemaker insertion