Final answer:
Increased myocardial contractility is not a direct benefit of converting from atrial fibrillation with a high heart rate to a sinus rhythm with a lower heart rate; the heart's contractility is influenced by other factors beyond heart rhythm.
Step-by-step explanation:
The question tackles the beneficial effects of converting fibrillation from a high heart rate to a normal sinus rhythm and the implications on cardiac performance. Although most options listed are indeed benefits, increased myocardial contractility is not a direct result of converting atrial fibrillation with a heart rate of 120 beats per minute to a sinus rhythm with a heart rate of 80 beats per minute. The heart's contractility is influenced by other factors and not solely by the heart rhythm. Therefore, the correct answer, the option that is not a benefit of conversion to sinus rhythm, is increased myocardial contractility.
Atrial fibrillation impairs coordinated atrial contractions, which can affect ventricular filling (restoration of atrial contributors to ventricular filling) and can increase myocardial oxygen consumption due to inefficiency. Upon conversion back to sinus rhythm, the heart typically operates more efficiently, increasing the time for ventricular filling and potentially reducing myocardial oxygen consumption. Over time, this can help in reducing ventricular hypertrophy that may have resulted from the persistent strain of atrial fibrillation.