Electrical alternans on boards means a big pericardial effusion (and usually cardiac tamponade physiology). The heart cannot fill properly, preload decreases, hypotension and tachycardia ensue, fluid backup leads to elevated JVP. Underlying etiology in this patient is renal failure.

he has chronic kidney dz--> clue for uremia--> he has low electrical activity so its pointing to cardiac tamponade due to uremia. https://pubmed.ncbi.nlm.nih.gov/1260996/#:~:text=The%20primary%20causes%20of%20cardiac,3)%20collagenization%20of%20pericardial%20exudate.