Physiological monitoring is provided through a lightweight wearable monitor (12) that includes a flexible extended wear electrode patch (15) and a reusable monitor recorder (14) that removably snaps into a receptacle (25) on the electrode patch (15). The wearable monitor (12) sits centrally on a patient's chest along the sternum (13) oriented top-to-bottom. Placement of the wearable monitor (12) at the sternal midline (16), with its unique narrow "hourglass"-like shape, significantly improves the ability of the wearable monitor (12) to cutaneously sense cardiac electrical potential signals, particularly P-wave and QRS interval signals indicating ventricular activity in the ECG waveforms. ECG electrodes (38, 39) on the electrode patch (15) are tailored to be positioned axially along the midline (16) of the sternum (13) for capturing action potential propagation in an orientation that corresponds to the aVF lead used in a conventional 12-lead ECG used to sense positive or upright P-waves (121).
