Based on prior knowledge, beta-blockers are commonly used for the treatment of chronic heart failure. Therefore, it is expected that patients with chronic heart failure would have a higher likelihood of using beta-blockers in the ICU.

To analyze the relationship between the feature "B_BLOK_S_n" and the task of determining if the patient has chronic heart failure, we can look at the distribution of "B_BLOK_S_n" values for each class (yes or no).

Here is the dictionary representing the analysis:

```json
{
	"no": ["no"], 
	"yes": ["yes"]
}
```

Based on the available information, there are only two possible values for the feature "B_BLOK_S_n": "yes" and "no". Since there is no additional information to predict whether a patient has chronic heart failure based on this feature, we include both values for each target class.

Please note that the analysis is based on the given feature description and prior knowledge. If there is more specific or additional information, the analysis can be further refined.