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

Based on the given feature "n_r_ecg_p_04" and the task of determining if the patient has chronic heart failure, the only value of "n_r_ecg_p_04" that appears in the dataset is "yes". Therefore, all patients with myocardial infarction complications have frequent premature ventricular contractions on ECG at the time of admission to the hospital.