It is now an accepted fact that, in the absence of tachycardia, pulsus alternans in cardiac or cardiorenal disease indicates a grave prognosis. Lewis 1 says:
Alternation of the pulse belongs to a small group of phenomena witnessed by those who attend the sick, which, treated as isolated signals, are in themselves emphatic and portentous. It ranks with subsultus tendinum, with optic neuritis, with the risus sardonicus, and other ill omened messengers. It is the faint cry of an anguished and fast failing muscle, which, when it comes, all should strain to hear, for it is not long repeated. A few months, a few years at most, and the end comes.
A perusal of the litearture is apt to convey the impression that pulsus alternans is uncommon and that a tracing of the radial pulse is necessary for its detection. Vaquez 2 refers to it as "at once the rarest
MORRIS RS. THE CLINICAL RECOGNITION OF PULSUS ALTERNANS. JAMA. 1926;87(7):463-464. doi:10.1001/jama.1926.02680070009003