Cardiovascular System MCAT Practice Question

A 72-year-old man with a history of hypertension and left ventricular hypertrophy presents with palpitations and dyspnea on exertion. On examination, an irregularly irregular pulse is noted at 88 bpm. An electrocardiogram confirms new-onset atrial fibrillation with a rapid ventricular response. His blood pressure is 168/98 mmHg. Echocardiography demonstrates reduced left ventricular compliance and impaired early diastolic filling (E/A ratio 0.8). The patient reports feeling more symptomatic now compared to his baseline, with exertional dyspnea that was not present before the arrhythmia onset. Which of the following best explains why this patient is experiencing greater hemodynamic compromise from the loss of atrial contraction compared to a younger patient with normal ventricular function?