AFib - Overview, Etiology, Pathophysiology, Diagnosis and Management

1. Atrial Fibrillation
17.06.2016

2. Background
• It is characterized by an irregular and often rapid heartbeat
• Published guidelines from an American College of Cardiology
(ACC)/American Heart Association (AHA)/European Society of Cardiology
(ESC) committee of experts on the treatment of patients with atrial
fibrillation recommend classification of AF into the following 3 patterns
:
1. Paroxysmal AF – Episodes of AF that terminate spontaneously within 7
days (most episodes last less than 24 hours)
2. Persistent AF - Episodes of AF that last more than 7 days and may require
either pharmacologic or electrical intervention to terminate
3. Permanent AF - AF that has persisted for more than 1 year, either
because cardioversion has failed or because cardioversion has not been
attempted
• This classification schema pertains to cases that are not related to a
reversible cause of AF (eg, thyrotoxicosis, electrolyte abnormalities, acute
ethanol intoxication).

3. Pathophysiology
Automatic focus
•The pulmonary veins appear to be the most frequent source of these
automatic foci, but other foci have been demonstrated in several areas
throughout the atria. Cardiac muscle in the pulmonary veins appears to
have active electrical properties that are similar, but not identical, to
those of atrial myocytes.
Multiple wavelet
•Fractionation of wave fronts propagating through the atria results in
self-perpetuating "daughter wavelets."
•Increased atrial mass, shortened atrial refractory period, and delayed
intra-atrial conduction increase the number of wavelets and promote
sustained AF

4. Etiology
Atrial fibrillation (AF) is strongly associated with the following risk factors:
•Hemodynamic stress e.g. mitral/tricuspid valve disease, HTN, intracardiac
tumors or thrombi.
•Atrial ischemia
•Inflammation – Myocarditis and Pericarditis (idiopathic or associated with
infections, collagen vascular disease or surgeries)
•Noncardiovascular respiratory causes – PE, pneumonia, lung cancers
•Alcohol and drug use e.g. cocaine, chronic alcohol use
•Endocrine disorders e.g. hyperthyroidism, DM, Pheochromocytoma
•Neurologic disorders e.g. SAH, stroke
•Genetic factors
•Advancing age - strongly age-dependent, affecting 4% of individuals older
than 60 years and 8% of persons older than 80 year

6. History
• Initial evaluation – hemodynamic stability (unstable pts refer to ACLS
protocols which includes cardioversion)
• While up to 90% of AF episodes may not cause symptoms,
many
patients experience a wide variety of symptoms, including
palpitations, dyspnea, fatigue, dizziness, angina, and
decompensated heart failure.
• Any precipitating factors, hx of heart disease, previous episode and
how was it terminated,

7. Physical Examination
• Heart rate, blood pressure, respiratory rate, and oxygen saturation
are particularly important in evaluating hemodynamic stability and
adequacy of rate control in AF.
• Patients will have an irregularly irregular pulse and will commonly be
tachycardic, with heart rates typically in the 110- to 140-range, but
rarely over 160-170. Patients who are hypothermic or who have
cardiac drug toxicity may present with bradycardic atrial fibrillation.
• The physical examination also provides information on underlying
causes and sequelae of atrial fibrillation.

8. Diagnosis
• The diagnosis of atrial fibrillation is based on the physical finding of an
irregular heart rhythm and is confirmed with an ECG or rhythm strip.
• It appears on ECG as irregularly irregular narrow complex
tachycardia
• Discrete P waves are absent, replaced by irregular, chaotic F waves,
in the setting of irregular QRS complexes
• The ventricular rate is usually between 80 and 180 bpm.
• It is important to pay attention to the electrocardiographic signs of
associated cardiac diseases, such as left ventricular hypertrophy and
preexcitation.

10. Investigations – Other..
• Include CBC count (anemia, infection), electrolytes, BUN/ creatinine,
cardiac enzymes, thyroid function tests
• ECHO - valvular heart disease, left and right atrial size, left ventricular
(LV) size and function, left ventricular hypertrophy (LVH), and
pericardial disease.
• CT angiography if PE is suspected
• CXR in cases suspected of CHF or Pneumonia

11. Treatment & Management
• The cornerstones of atrial fibrillation management are rate control and
anticoagulationand rhythm control for those symptomatically limited by
AF.
• One of the major management decisions in AF is determining the risk of
stroke and appropriate anticoagulation regimen for low-, intermediate-,
and high-risk patients. For each anticoagulant, the benefit in terms of
stroke reduction must be weighed against the risk of serious bleeding.
• Several risk factor assessment algorithms have been developed to aid the
clinician on decisions on anticoagulation for patients with AF. The
CHADS2 index (Cardiac failure, Diabetes, Stroke [or S2 = transient ischemic
attack]) is the most widely used of these algorithms.The CHADS2 index uses
a point system to determine yearly thromboembolic risk.

12. CHADS2 Score for Stroke Risk Assessment
in Atrial Fibrillation
Score CHADS2 Risk Criteria
1 point Congestive heart failure
1 point Hypertension
1 point Age >75 years
1 point Diabetes mellitus
2 points Stroke/transient ischemic attack
Table 1. CHADS2
Score: Stroke Risk Assessment in Atrial Fibrillation

13. Treatment Recommendations Based on
CHADS2
Score
CHADS2Score Risk Recommendation
0 Low Aspirin (81-325 mg) daily
1 Intermediate
Aspirin (81-325 mg) daily or warfarin
(INR 2.0–3.0), based on patient
preference
2 or more
High (CHADS2 revised) or
intermediate (CHADS2 classic)
Warfarin (INR 2.0-3.0), unless there
are reasons to avoid it
()

14. • The American Heart Association (AHA), American College of Cardiology (ACC), and Heart
Rhythm Society (HRS), in collaboration with the Society of Thoracic Surgery, released
new AF guidelines in 2014, including the recommendation that for estimation of the
stroke risk in patients with nonvalvular AF, the CHADS2 score be replaced with the more
comprehensive CHA2 DS2 -VASc score.
• In this scoring system, 1 point is assigned for each of the following: congestive heart
failure (CHF), hypertension, diabetes, vascular disease (myocardial infarction [MI],
peripheral arterial disease, aortic plaque), age 65-74 years, and female sex. Two points
each are assigned for age 75 years or older and prior stroke/transient ischemic attack
(TIA)/thromboembolism.
The updated guidelines also state the following:
• Evidence indicates that aspirin’s use as a means of lowering stroke risk in patients with
AF should be reduced or eliminated
• In addition to warfarin, 3 new anticoagulants are recommended for patients with
nonvalvular AF who have previously suffered a stroke or TIA or whose CHA 2 DS 2 -VASc
score is 2 or above: dabigatran etexilate, rivaroxaban, and apixaban
• Radiofrequency catheter ablation can be used as initial treatment in recurrent
symptomatic paroxysmal AF

15. Rate control
• Control of ventricular rate is a critical component of management of new-
onset AF
• Beta-blockers and calcium channel blockers are first-line agents for rate
control in AF. These drugs can be administered either intravenously or
orally. Commonly used are IV metoprolol or diltiazem in AF with RVR.
• Amiodarone can be used as a rate-controlling agent for patients who are
intolerant of or unresponsive to other agents, such as patients with CHF
who may otherwise not tolerate diltiazem or metoprolol.
• In patients with inadequate ventricular rate control despite drug therapy,
atrioventricular (AV) nodal ablation and pacemaker implantation may be
considered

16. Anticoagulation
• Acute cardioversion for AF carries a risk of thromboembolism unless
anticoagulation therapy is initiated prior to the procedure and
continued post procedure. Risk of thromboembolism is similar in
patients undergoing either pharmacologic or electrical cardioversion.
The risk of thromboembolic events is greatest when AF has been
present for longer than 48 hours.
• Patients with newly diagnosed AF and patients awaiting electrical
cardioversion can be started on intravenous heparin (activated partial
thromboplastin time [aPTT] of 45-60 seconds) or low-molecular-
weight heparin (1 mg/kg bid).
• Patients can be started concomitantly on warfarin in an inpatient
setting while awaiting a therapeutic INR value (2-3).
• New anticoagulants: dabigatran, rivaroxaban, apixaban

18. Long-Term Management
• Long-term management of atrial fibrillation is focused on reducing the
likelihood of AF recurrence, reducing AF-related symptoms, control of
ventricular rate, and reducing stroke risk.
• Anticoagulation with either aspirin or warfarin should be initiated for all
individuals with AF, except those with contraindications. Selection of the
appropriate antithrombotic regimen for a given patient should be balanced
between the risk of stroke and the risk of bleeding.
• Antiarrhythmic therapy can aid in maintenance of sinus rhythm in certain
patients but requires close monitoring
• As a rule, younger patients with more severe symptoms and fewer
comorbidities tend to derive greater benefit from a long-term focus on
rhythm control. Older patients with structural heart disease (e.g., left
ventricular hypertrophy, prior MI, depressed ejection fraction, atrial dilation)
are less likely to remain in sinus rhythm and are more likely to have serious
side effects from antiarrhythmic drugs, most clinicians focus on long-term
rate control

19. Anticoagulation
• The goal of long-term anticoagulation in atrial fibrillation is to reduce
the risk of thromboembolism.
• Anticoagulation therapy with warfarin is significantly more effective
than antiplatelet therapy if the INR is adjusted. The INR goal in AF is
usually between 2 and 3.
• The major adverse effect of anticoagulation therapy with warfarin is
bleeding
• Factors that increase the risk of bleeding include: hx of bleeding, age
more than 75 years, liver or renal dse, HTN, DM, anemia, prior stroke,
subtherapeutic INR, genetic predisposition, thrombocytopenia or
aspirin use, malignanacy.
• If risk outweighs benefit then avoid and contraindicated in pregnant
women too.

20. New anticoagulant regimens
• Compared with warfarin, low-dose new anticoagulant regimens showed
similar overall reductions in stroke or systemic embolic events and a more
favorable bleeding profile, but significantly more ischemic strokes
• Guidelines from the American College of Cardiology Foundation
(ACCF)/American Heart Association (AHA)/Heart Rhythm Society (HRS) on
atrial fibrillation have been updated to include the use of oral direct
thrombin inhibitors (ie, dabigatran)
• The guidelines recommend dabigatran may be used as an alternative to
warfarin for the prevention of stroke and systemic thromboembolism in
patients with paroxysmal-to-permanent atrial fibrillation and risk factors
for stroke or systemic embolization. Patients with atrial fibrillation who are
not candidates include those with prosthetic heart valves or
hemodynamically significant valve disease, severe renal failure (creatinine
clearance ≤15 mL/min), or advanced liver disease.

21. Rate control
• Strict rate control in patients with stable ventricular function is no longer
recommended.
• AV nodal blocking medications are the cornerstone of rate control in long-
standing AF, oral beta-blockers, nondihydropyridine calcium channel
blockers, and digoxin are effective. Generally, coadministration of beta-
blockers and calcium channel blockers is reserved for patients in whom
adequate rate control cannot be achieved with a single agent.
• Digoxin can be effective in sedentary patients (especially in those with
heart failure) but requires close monitoring of drug levels and renal
function.
• Heart rate control (defined as <80 bpm at rest) may be considered for less
symptomatic patients with AF; a more lenient rate-control strategy (<110
bpm at rest) is reasonable when patients remain asymptomatic and left
ventricular (LV) systolic function is preserved

22. Rhythm control
• Maintenance of sinus rhythm requires treatment of cardiovascular risk
factors and any underlying disorder (ie, hyperthyroidism) that may have
triggered AF.
• Antiarrhythmic drugs include amiodarone, dofetilide, dronedarone,
flecainide, propafenone, and sotalol; drug selection should be based on
underlying heart disease and comorbidities
• In patients with cardiac disease such as coronary artery disease or systolic
or diastolic heart failure, amiodarone becomes the drug of choice because
of its decreased proarrhythmic effects compared with other
antiarrhythmic drugs.
• Discontinue antiarrhythmic drugs, including dronedarone, when AF
becomes permanent
• Dronedarone is contraindicated for treatment of AF in patients with New
York Heart Association (NYHA) class III and IV HF or patients who have had
an episode of decompensated heart failure in the past 4 weeks

23. Catheter Ablation
• The goal of catheter ablation and surgical treatment of atrial
fibrillation is to disconnect triggers and/or to modify the substrate
for AF. Mapping and radiofrequency (RF) ablation of AF is one of the
most complex ablation procedures.
• First-line therapy in recurrent symptomatic paroxysmal or persistent
AF
• AF catheter ablation is contraindicated for patients who cannot be
treated with anticoagulant therapy during and after the procedure
and should not be performed with the sole intent of eliminating the
need for anticoagulation.