A 58-year-old woman with a 10-year history of atrial fibrillation presents to the emergency department with acute dyspnea and orthopnea that began 2 days ago. She reports no recent fevers or chest pain. Vital signs: BP 148/92 mmHg, HR 112 bpm and irregularly irregular, RR 22/min, SpO2 88% on room air. Lung auscultation reveals bilateral basilar crackles. Cardiac examination is notable for an opening snap heard 0.08 seconds after the second heart sound, followed by a low-pitched diastolic rumble best appreciated at the left fifth intercostal space with the patient in the left lateral decubitus position. Transthoracic echocardiography demonstrates restricted mitral valve leaflet motion with commissural fusion and a mitral valve area of 0.9 cm². Which of the following best explains the pathophysiologic basis for the opening snap heard on auscultation?

1. A)Sudden cessation of leftward atrial wall motion during the transition from atrial systole to ventricular systole
2. B)Abrupt tensioning of the chordae tendinae as the posterior mitral leaflet reaches its maximal opening excursion during early ventricular diastole
3. C)Abrupt halting of posterior mitral leaflet motion when it reaches the limit imposed by commissural fusion and leaflet rigidity during early ventricular diastoleGABARITO
4. D)Forceful opening of the aortic valve as left ventricular pressure exceeds aortic pressure during ventricular systole
5. E)Pericardial friction rub resulting from inflammation of the visceral pericardium due to chronic mitral stenosis