A 38-year-old female with a diagnosis of moderate mitral stenosis (MS) due to rheumatic heart disease (RHD) presents with sudden-onset palpitations for 2 days, accompanied by dyspnea and inability to lie flat. Examination reveals: BP 95/75 mmHg, cyanosis of the lips, bilateral lung crackles, heart rate 150 bpm, irregularly irregular rhythm with variable intensity of the first heart sound, diastolic rumbling murmur at the apex, no hepatomegaly, and no lower limb edema. On palpation of the radial pulse, which finding is most likely?