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Cytochrome 450-2D6 Genotype Definition May Improve Therapy for Paroxysmal Atrial Fibrillation. A Case of Syncope Following

An 81-year-old marathon runner-internist developed syncope followed by myocardial stunning two hours after conversion to normal sinus rhythm and 4 hours after adding a single 150mg dose of propafenone to 650mg of quinidine gluconate which he had ingested 3 hours earlier.  Cardiac isoenzyme, electrolyte, CBC, TSH and EKG were normal.  Echocardiogram one week later revealed left ventricular hypertrophy with an enlarged left atrium typical of men with habitual endurance-associated atrial fibrillation.  Over the previous 24 years he had successfully converted more than 100 episodes of PAF with PIP oral quinidine sulfate (200mg-600mg) or quinidine gluconate (650-975mg) without utilizing other cardiac, anti-arrhythmic, or anti-coagulation therapy. Several months after we published his adverse event (37) CYP2D6 analysis demonstrated alleles 4 and 41, identifying him as an IM/PM 2D6-deficient subject.

Within the next year, he successfully converted episodes of PAF on 2 occasions with 100mg of oral flecainide,  but both were accompanied by mildly symptomatic EKG-documented atrial flutter with 2/1 AV block and a ventricular rate of 120-140 beats per minute, resulting in a return to PIP quinidine and successful conversion of over 60 additional mildly symptomatic but increasingly frequent episodes of PAF over the next 3 years by utilizing 200-600mg of oral quinidine sulfate each resolving within 4-8 hours, during which he was able to continue his daily exercise and other daily activities without interruption.

Credits: Harry W. Daniell, MD

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Introduction to AFib
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