Atrial fibrillation is the most common arrhythmia in America — and the most common cause of preventable stroke.

In a normal heart, the sinoatrial node — the heart's natural pacemaker — sends an organized electrical signal that spreads across both atria, causing them to contract together and push blood into the ventricles. In atrial fibrillation, that organization breaks down. Multiple chaotic electrical wavelets circulate through the atria simultaneously, so instead of contracting, the atria quiver at 300 to 600 impulses per minute. The ventricles continue to beat — but irregularly, and often rapidly, because only some of those atrial impulses get through the AV node.

The consequence is twofold. First, cardiac output becomes less efficient — the atria no longer contribute their "atrial kick" to ventricular filling, which is why some patients feel fatigued or short of breath even before the rate becomes alarming. Second, and more importantly, blood pools in the left atrial appendage — a small pouch attached to the left atrium that is difficult for the heart to empty during AFib. Stagnant blood is prone to forming clots, and if a clot is ejected into circulation, it can travel to the brain and cause a stroke.

The most common underlying conditions that create the substrate for AFib are hypertension, coronary artery disease, heart failure, valvular disease, hyperthyroidism, sleep apnea, and advancing age. Excess alcohol consumption ("holiday heart"), stimulant use, and acute illness can trigger episodes in otherwise healthy people. In about 10 to 15 percent of cases, no clear cause is identified — this is called "lone AFib," and it is more common in younger patients.

What AFib does over time is progressive. The atria that fibrillate undergo electrical and structural remodeling — they dilate, fibrose, and become more prone to sustaining AFib. This is why the pattern often evolves from paroxysmal (episodes that stop on their own within 7 days) to persistent (lasting more than 7 days or requiring intervention to stop) to permanent (where rate control is accepted as the long-term strategy). Early intervention is increasingly favored because of this remodeling.

Anticoagulation decisions are separate from rate vs rhythm. Even patients who achieve and maintain normal sinus rhythm usually remain on anticoagulation based on their CHA2DS2-VASc score — because asymptomatic episodes of AFib can still occur and still carry stroke risk. The exception is patients who have undergone successful ablation with documented absence of AFib over time, where the decision can be reconsidered with a cardiologist.

Warfarin is inexpensive — a few dollars per month, plus the cost of INR monitoring. DOACs are expensive — typically $500 to $600 per month at list price, though most commercial insurance plans cover them with a copay. Manufacturer copay assistance programs and foundation grants are available, and Medicare Part D patients may qualify for the Extra Help program. The 2025 Medicare Part D redesign caps annual out-of-pocket costs at $2,000, which has substantially improved affordability for patients on DOACs.

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Before filling from any seller — online or local — verify them. A working VIPPS seal that resolves to a live NABP record, a real U.S. street address, and a prescription requirement that cannot be waived. Anything less is not a pharmacy worth trusting with anticoagulation, which carries real bleeding risk if mismanaged.