Arrhythmias

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Arrhythmias
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Definitions

• Arrhythmias abnormalities of the heart rate or
  the heart rhythm
• Tachycardia is a HR gt100
• Increased pacemaker activity faster
  depolarization, lower thresholds, or oscillations
  during repolarization trigger early action
  potentials
• Re-entry circuits depolarization travels in a
  circleif tissue is not refractory when the
  impulse returns, it will depolarize again
  producing a recurring circuit
• Bradycardia
• HR lt60
• Due to abnormal and/or delayed conduction

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General Management

• Prevention
• Early correction of
• Hypoxemia
• Electrolyte imbalances
• Acid-base imbalances
• Cardiac ischemia
• Arrhythmogenic factors
• Pain
• Vagal stimulation
• Drugs
• Cardiac irritants

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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 treatmentif the person is
  stable and asymptomatic you can treat the cause
  without converting the rhythm

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General Management, cont

• Vagal stimulation
• Carotid sinus massage
• Slows HR and may cardiovert some SVTs
• 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

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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

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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)i
  f no response, then try adenosine

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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

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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 condutionconsidere
  d controlled as long as ventricular rate lt100
• 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

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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

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Tachyarrhythmias, cont

• Ventricular fibrillation
• Chaotic ventricular rhythm that frequently
  follows an acute MI
• Immediate loss of CO with unconsciousness
• Treat with defibrillationthe sooner the better
• May use drugs to prevent recurrence or
  implantable defibrillator

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Bradyarrhythmias

• Well tolerated by normal hearts, but CO and BP
  will fall if SV cant increase
• Types
• Sinus bradycardia
• Normal EKG with rate lt60
• Causes
• vagal reflexes (pain, hypoxemia)
• Drug toxicity (beta blockers, digoxin)
• AV node ischemia
• Treatment
• Atropine
• Beta agonists
• Drug antidotes

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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 conductionPR interval exceeds 0.2
  seconds
• Usually benign
• Second degree
• Some atrial beats are not conducted to the
  ventricles

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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 contractionthe others are blocked
• May require pacemaker insertion

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Bradyarrhythmias, cont

• Third degree heart block (complete heart block)
• Conduction between the atria and ventricles
  ceases
• The atria contract at one ratethe ventricles
  contract at another rate (usually 20-40)
• Requires pacemaker insertion

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