An ultra-high common-mode rejection ratio (CMRR) AC instrumentation amplifier for laplacian electrocardiographic measurement.

Laplacian electrocardiograms (LECGs) localize the moment of activation (MOA) of the heart noninvasively at a nearby point on the chest surface. Tripolar concentric ring (TCR) electrodes provide small, but well-defined, site-specific second spatial derivative signals of the potential on the chest surface for studying the activation sequence of the myocardium. A battery-powered, modified AC instrumentation amplifier (IA) was used as preamplifier to obtain signals with a high common-mode rejection ratio (CMRR). The authors' direct-coupled quasi-high-pass IA has high input impedance and high CMRR, without the need to match capacitors and resistors. The amplifier circuit and two lithium cells were integrated with the substrate for the TCR sensor to minimize inductive pickup by the leads. Combining the natural ability of the TCR electrodes to reject common-mode signals with the high CMRR of the IA made it possible to obtain LECG signals in real time with good signal-to-noise ratio (SNR). The authors observed and recorded the MOAs from 16 sites in a 4-by-4 matrix from the left side of the thorax of each subject. Beat-by-beat changes were observed from one subject showing episodes of bigeminal rhythm. The authors were able to obtain localized signals representing the right and left ventricles from surface TCR electrodes in real time.