1. An implantable or other ambulatory apparatus comprising: at least a first physiologic sensor circuit, configured to provide a first physiologic signal and a second physiologic sensor circuit configured to provide a second physiologic signal, wherein the first and second physiologic signals include physiological information of a subject; a processor circuit, communicatively coupled to the first and second physiologic sensor circuits, wherein the processor circuit includes a principal component analysis (PCA) circuit configured to: represent data determined from the at least first and second physiologic sensor circuits as at least first and second axes, respectively, in a multidimensional space; determine one or more principal components in the multidimensional space; determine a quantitative attribute of the first and the second physiologic signals using at least one of the determined principal components or a projection of the data along the at least one determined principal component; and provide an indication of heart failure (HF) status according to the quantitative attribute to at least one of a user or a process.