Areas of Focus

Atrial Fibrillation  

Atrial fibrillation is the most common arrhythmia, presenting with an irregular and often rapid heart rate that may increase the risk of stroke, heart failure, and other heart-related complications. 

During atrial fibrillation, the heart’s two upper chambers, or atria, beat chaotically, irregularly, and out of coordination with the two lower chambers, or ventricles. Atrial fibrillation symptoms often include heart palpitations, shortness of breath, and weakness.

Episodes of atrial fibrillation may come and go, or patients may have permanent atrial fibrillation. Although atrial fibrillation itself is not usually life-threatening, it is a serious medical condition. It may require emergency medical treatment and is associated with a significant increase in the risk of stroke and sudden cardiac death.


Prevalence estimates range from three to six million patients suffering from atrial fibrillation in the United States. Approximately 25% of these patients have paroxysmal atrial fibrillation, another 25% have persistent atrial fibrillation, and 50% have chronic or permanent atrial fibrillation.

Our Approach

There are two pharmacological approaches to managing atrial fibrillation: rate control to lower a rapid heartbeat, and rhythm control to restore and maintain a regular rhythm. Unfortunately, “breakthrough” episodes—where atrial fibrillation recurs, or the heartbeat becomes elevated—are common regardless of which approach is used. When this happens, rate or rhythm control drugs do not provide immediate ventricular rate control due to the delayed 30 to 90-minute onset of action. Patients living with breakthrough

episodes often require visits to the emergency department for urgent administration of IV calcium channel blockers or beta blockers to acutely slow their heartbeat. We plan to study how etripamil can be used by patients to rapidly reduce their heartbeat in the outpatient setting alone or in combination with previously prescribed medications, thereby reducing the need to go to the emergency department for treatment.

Clinical Trials

Milestone is planning a Phase 2 proof-of-concept study with etripamil in patients with atrial fibrillation.