Atrial Fibrillation (AFib) (Last Updated - 3/2/2005)
-most common sustained arrythmia
-increased mortality rate -> 2x that of people w/ NSR (normal sinus rhythm)
-affex 6% > 80 y.o. -> prevalence increases w/ age
-risk factors:
-valvular HD
-heart failure
-HTN
-diabetes
-previous MI (in men)
-alcohol ingestion
-thyrotoxicosis
-increased vagal tone (causes postprandial Afib)
-increased sympathetic tone (causes exercise-related Afib)
-"lone Afib" -> 17% of cases -> no clinical, EKG or echo evidence of risk factors
-familial cases -> rare, assoc. w/ chromosome 10 abnormalities
-fibrosis and inflammation -> decreased conduction
-thyrotoxicosis -> decreased refractoriness
-ischemia and changed autonomic tone -> both decreased conduction and refractoriness
-atrial enlargement helps to sustain Afib by accomodating more Afib wavelets
-some episodes initiated by firing of atrial myocytes in muscle sleeves located in pulm. veins
-produces:
-myocyte degeneration
-focal accumulation of ER and mitochondria
-widening of some intercalated disks
-replacement of myofibrils
-above contribute to patchy fibrosis and dilation
-shortened refractory period
-loss of normal adaptation of refractoriness to changes in HR
-above 2 contribute to recurrence
-most assoc. symptoms caused by poorly controlled ventricular rates
-assoc. w/:
-palpitations
-decreased exercise tolerance
-dyspnea
-serious complications:
-thromboembolus
-stroke (Afib accounts for ~15% of strokes)
-may induce a hypercoagulable state:
-increased plasma fibrin D-dimer concentration
-increased plasma beta-thromboglobulin concentration
-2 approaches to therapy:
1) Ventricular Rate Control Approach:
-allowing Afib to persist while controlling HR
-avoidance of anti-arrhythmic drugs is desirable
-risk of stroke reduced w/ anti-coags
-drugs commonly used:
-beta-blockers
-Ca channel blockers (verapamil and diltiazem)
-digoxin
-done via AV nodal blocking agents or ablation of the AV junction w/ pacemaker implantation
-advantage:
-decreased drug toxicity w/ absence of anti-arrythmics
2) Rhythm Control Approach:
-goal is to maintain sinus rhythm
-cardioversion
-escalating doses of increasingly potent anti-arrhythmic drugs administered until Afib is abolished or drug toxicities develop
-anti-arryhthmics commonly used:
-amiodarone
-disopyramide
-flecainide
-moricizine
-procainamide
-propafenone
-quinidine
-sotalol
-dofetilide
-advantages:
-possibly fewer symptoms
-better exercise tolerance
-decreased risk of stroke
-eventual discontinuation of anti-coag's
-better quality of life
-better survival (if NSR is reinstated)
-disadvantage:
-Afib often unresponsive to anti-arrhythmics
-Anti-coags (warfarin) are recommended for both approaches
-"A Comparison of Rate Control and Rhythm Control in Patients with Atrial Fibrillation" - NEJM, Vol. 347, Number 23, 12/5/2002 shows that rhythm
control provides no advantage over rate control with respect to survival and that rate control can now be considered as primary approach to Afib
treatment
-increased rates of mortality (23.8% vs. 21.3%, though not statistically significant 95% confidence interval 0.99 to 1.34), hospitalizations (80.1%
vs. 73.0%, p < 0.001) and adverse drug effex in rhythm-controlled subjects vs. rate-controlled subjects
-uncontrolled symptoms due to Afib and CHF -> switch to rhythm control if using rate control
Chronic Afib:
-pts. must be on chronic anti-coagulation to prevent left-sided emboli inducing strokes or acute MI --> Warfarin (Coumadin)
-target INR's in pts. taking oral anti-coagulation with Warfarin (Coumadin) --> 2.0 - 3.0 (3)
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References:
1) Cain, Michael E., M.D. "Perspective: Atrial Fibrillation - Rhythm or Rate Control". NEJM, Vol. 347, Number 23, pgs. 1822-1823. 12/5/2002.
2) Massachusetts Medical Society. "A Comparison of Rate Control and Rhythm Control in Patients with Atrial Fibrillation" - NEJM, Vol. 347, Number 23,
pgs. 1825-1833. 12/5/2002.
3) Journal of the American College of Cardiology - May 7, 2003 - Vol. 41 (#9) - Pages 1646-1647.