A patient with end-stage renal disease presents with weakness, nausea, and decreased reflexes. On assessment, the nurse notes a serum magnesium level of 6.0 mEq/L. Which of the following ECG findings is most consistent with hypermagnesemia?
A) Tall, peaked T waves
B) Prolonged PR interval and widened QRS complex
C) ST segment elevation
D) U waves and flattened T waves