Our max sampling rate for BioZ is 64SPS. We have had some customers successfully use this BioZ circuit for an impedance cardiography application; so apparently, 32Hz of Nyquist was adequate.
One can think of it like this: impedance cardiography is a use-case where one is trying to evaluate the mechanical properties of the heart; the signal range of interest (after mixing to baseband) is very similar to that of the ECG signal itself.
A 1993 paper suggested that one needed a 50Hz Nyquist; but if one looked more closely they were comparing a system with 15Hz BW to that one with 50Hz; and the 15Hz bandwidth usage was reported to have caused some attenuation and distortion. The 1993 paper is entitled “Signal fidelity requirements for deriving impedance cardiographic measures of cardiac function over a broad heart rate range” by Hurewitzh, Shyu, Lu, Reddy Schneiderman and Nagel.
A 2016 paper suggesting that using a HPF of 0.1Hz and a LPF of 20Hz gives excellent cardiographic impedance monitoring results. The 2016 paper is entitled “Design and Implementation of a Portable Impedance Cardiography System for Noninvasive Stroke Volume Monitoring” by Yazdanian, Mahnam, Edrisi and Esfahani.