This tracing was recorded several days later. By this time, the serum potassium had been raised to 4.6 mM. The prominent U wave and prolonged QT/U interval are no longer present. The voltage changes suggesting LVH persist but the QRS duration is now 0.08 seconds, as compared to 0.10 seconds on the previous tracing. This change in QRS duration reflects the slight prolongation of the QRS complex that often occurs in patients with significant hypopotassemia.