Electrical Disturbance From a Systemic Disease

Scenario: This electrocardiogram (ECG, unchanged from 1 year prior) is from a 67-year-old man who arrived in an emergency department with increased shortness of breath (SOB). He had been having progressive SOB for the past 2 weeks with associated swelling of both legs. His medical history includes heart failure and lambda light chain amyloidosis (diagnosed in 2007) affecting the heart and tongue. He had a stem cell transplant in 2008, at which time he had a normal cardiac ejection fraction, but his amyloidosis recurred. Since then, he has had frequent visits to the emergency department with exacerbation of the heart failure. His medications consisted of acyclovir, eplerenone, and furosemide. Vital signs and laboratory test results were within normal limits except his respiratory rate was elevated at 22/min, oxygen saturation was 90%, body mass index was 20.5, and his brain natriuretic peptide level was 1300 pg/mL. Chest radiography showed cardiomegaly...