no antiarrhythmic effect

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Phenprocoumon, Marcoumar, Marcumar, Coumarin

an oral anticoagulant drug

Reported activity includes anti-HIV, anti-tumor, anti-hypertension, anti-arrhythmia,...

as opposed to rate control in AF.
Heart rate control and rhythm control are two different major concepts in the treatment of AF. Regaining sinus rhythm by DC cardioversion/synchronized defibrillation or anti-arrhythmic drugs (RF ablation is another option) or just maintenance of comparably normal heart rate irrespective of ongoing AF.

Rate versus rhythm control and outcomes in patients with atrial fibrillation...
http://www.ncbi.nlm.nih.gov/pubmed/23913464

Atrial fibrillation in heart failure: drug therapies for rate and rhythm control.
http://www.ncbi.nlm.nih.gov/pubmed/23690262

Electrophysiology providers employed rate control in 55% of patients (with the remainder of their patients on rhythm control), whereas cardiology and internal medicine/ primary care providers employed a rate control strategy in 70% of patients.
http://jaha.ahajournals.org/content/2/4/e000110.full.pdf htm...

These therapies may already alleviate symptoms, but symptom relief may require additional rhythm control therapy by cardioversion, antiarrhythmic drug therapy, or ablation therapy.
http://www.escardio.org/guidelines-surveys/esc-guidelines/gu...

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Note added at 4 hrs (2013-08-13 16:46:01 GMT)
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fn three patients with atrial flutter, no conversion to sinus rhythm was obtained...
https://auth.cardiosource.org/EasyConnect/Integration/Post.a...

Because rhythm control was not achieved, digoxin was added to the treatment and the sotalol dosage was increased to 80 mg 4 times per day.
http://causes.cardiovasculardiseasestips.com/verapamil-muscl...

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Note added at 4 hrs (2013-08-13 16:47:07 GMT)
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Thus, 'conversion to SR' is another option...