Techniques are provided for assessing left atrial pressure (LAP) based on atrial electrocardiac signal parameters, particularly intra-atrial conduction delay (IACD) and P-wave duration. In one example, a pacemaker or other implantable device senses an intracardiac electrogram (IEGM) or a subcutaneous electrocardiogram (ECG), from which IACD and P-wave duration are derived. The device tracks changes, if any, in the parameters. A significant increase in either IACD or P-wave duration is associated with an increase in LAP. In some examples, conversion factors are calibrated for use with a particular patient to relate IACD and/or P-wave duration values to LAP values to provide an estimate of actual LAP. The conversion factors are pre-calibrated using LAP measurements obtained using a wedge pressure sensor. In other examples, IACD and P-wave duration are instead used to confirm the detection of an elevation in LAP initially made using impedance signals. Other confirmation parameters are described as well.