Final answer:
The ratio used in mIBG scanning for predicting worse outcomes in heart failure is called the heart-to-mediastinum (H/M) ratio. A low H/M ratio indicates increased risk of mortality and progression of heart failure, whereas a higher H/M ratio suggests better heart function.
Step-by-step explanation:
The ratio that predicts worse outcomes in heart failure using mIBG scanning is commonly known as the heart-to-mediastinum (H/M) ratio. This involves a nuclear imaging test called mIBG scintigraphy, where a substance called metaiodobenzylguanidine labeled with radioactive iodine is used to image the heart. A low H/M ratio is associated with worse cardiac outcomes, including increased risk of mortality and heart failure progression.
In these scans, a higher uptake of mIBG by the heart tissue typically indicates better cardiac sympathetic innervation, which relates to better heart function. On the contrary, a reduction in mIBG uptake, implying a lower H/M ratio, points to a deterioration in cardiac sympathetic innervation, predictive of worse heart failure outcomes. Thus, measurement of this ratio can provide valuable prognostic information for patients with heart failure.