A wearable cardioverter defibrillator (WCD) system includes a support structure that the patient may wear, and one or more sensors that may acquire patient physiological signals, such as ECG and others. A processor of the WCD system may determine diagnostics from the patient physiological signals. These diagnostics include a six-second ECG portion, heart rates as histograms, heart rates against QRS width, heart rate trends, clinical event counters, diagnostics relating to heart rate variability and about the atrial arrhythmia burden of the patient. In some embodiments, the WCD system includes a user interface with a screen that displays these diagnostics. In some embodiments, the WCD system exports these diagnostics for viewing by a different screen. When viewed, these diagnostics permit more detailed analysis of the state of the patient.