Techniques are provided for corroborating a preliminary detection of pulmonary fluid overload within a patient made initially based on transthoracic impedance. In one example, corroborative parameters pertaining to hematocrit, device pocket fluid accumulations, heart rate variability (HRV) and mean atrial tachycardia/atrial fibrillation (AT/AF) times are evaluated to confirm the fluid overload. Techniques are also provided for generating proxies for evaluating hematocrit and device pocket fluid accumulation based on certain impedance measurements. Still further, techniques are provided for predicting a possible pulmonary fluid overload based on trends in HRV or mean AT/AF times. System and method examples are set forth herein.
