Atrial fibrillation

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  1. The most frequent cardiac arrhythmia (2.2 million adult Americans; 85% are older than 60 years of age)
  2. Etiology: ischemic cardiac disease, valvular disease, rheumatic heart disease, cardiomyopathy, post-operative ( CABG, valve surgery)
  3. adverse consequences
    1. impaired cardiac filling (contraction of atria is responsible for 25% of preload) – this is well tolerated in a normal heart but in a heart with impaired performance it may be a problem
    2. creation of mural thrombus
      1. 15% of patients with atrial fibrillation more than three days develop a thrombus
  4. most important control parameter in atrial fibrillation is controlling ventricular rate
    1. if immediate intervention is necessary to adequately perfuse the patients organs then cardioversion is the treatment of choice
      1. monophasic shocks- start with 200 J, if additional shocks are needed, increase the strength od successive shocks by 100J to a maximum of 400J
      2. biphasic shocks, use half the energy of monophasic shocks
    2. if not immediate danger and patient is hypotensive then resuscitate with fluids
    3. a number of pharmacologic agents can be used to control ventricular rate such as:
      1. Ibutilide 1mg IV over 2 min, repeat one if needed
      2. Ca channel blockers such as verapamil and diltiazem (diltiazem dose .25 mg/kg IV over 2 minutes then repeat in 10 minutes if no response)
      3. B-blockers- esmolol 500 mcg IV over 1 min, then infusion 50 mcg/kg/min, increase the rate by 25 mcg/kg/min if needed to a maximum of 200 mcg/kg/min; metoprolol 2.5 to 5 mg IV over 2 min, repeat every 10-15 min as needed for 3 doses total
      4. amiodarone- 300 mg IV over 15 min, then 45 mg/h infusion for 24 h.
      5. Digoxin (only long term – not in the acute setting)
      6. Antcoagulation according with the risk stratification
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