Acute Coronary Syndrome (ACS): This is the most likely diagnosis due to the classic presentation of sharp midsternal chest pain radiating down the right arm, which is highly suggestive of myocardial ischemia or infarction.

Gastroesophageal Reflux Disease (GERD): GERD can cause sharp chest pain that may radiate to the arm, especially after eating or at night, due to acid reflux irritating the esophagus.
Musculoskeletal Pain: Costochondritis or musculoskeletal strain in the chest wall can cause sharp pain that may radiate down the arm, especially with movement or deep breathing.
Pulmonary Embolism: While less common, pulmonary embolism can cause sharp chest pain that may radiate to the arm, especially if the embolism is large or involves the upper lobes.

Aortic Dissection: A life-threatening condition that requires immediate attention, aortic dissection can cause severe, tearing chest pain that may radiate to the back or arm.
Pneumothorax: A collapsed lung can cause sharp chest pain that may radiate to the arm, especially if the pneumothorax is large or under tension.
Esophageal Rupture: A rare but deadly condition, esophageal rupture can cause severe chest pain that may radiate to the back or arm, especially after vomiting or eating.

Pericarditis: Inflammation of the pericardium can cause sharp chest pain that may radiate to the arm, especially with deep breathing or movement.
Panic Disorder: Severe anxiety or panic attacks can cause sharp chest pain that may radiate to the arm, especially if accompanied by other symptoms like shortness of breath or palpitations.
Thoracic Outlet Syndrome: Compression of the nerves or blood vessels in the thoracic outlet can cause sharp pain that may radiate down the arm, especially with movement or activity.