Malignant pericardial effusion , all the following are correct except.. Cytology for pericardial fluids usually is negative e for malignant cells

Malignant pericardial effusion , all the following are correct except:
• ECG shows low voltage.
• Neck veins are congested..
• Cytology for pericardial fluids usually is negative e for malignant cells.***
• Dyspnea is a common symptoms.