A 64-year-old man with heart failure is recently started on 80 mg/day of furosemide. He now feels weak and tired, but notes that his heart failure symptoms have improved. There is no change in his urine output and he gets a good diuretic response every time he takes his furosemide.Select the characteristic ECG findings.
shortened PR interval lengthened PR interval lengthened QU interval shortening of the QT interval