A 78-year-old man with chronic kidney disease presents to the emergency department because he is feeling unwell. He cannot elaborate any specific symptoms other than generalized malaise. His past medical history also includes heart failure, hypertension, and type 2 diabetes. Medications are ramipril, insulin, furosemide, and metoprolol.On physical examination, the blood pressure is 155/90 mm Hg, heart rate is 100/min, and respiration 24/min. His heart sounds are normal, there is no edema, and the lungs clear on auscultation. An ECG is performed and shown in Figure below. What is the most likely diagnosis based on the ECG findings?

No atrial activity is detected. The ventricular rate is slightly irregular. Beat number 4 is a ventricular premature contraction. The T waves are tall and markedly peaked. This type of T wave is characteristic of hyperkalemia, as is the absence of visible atrial activity.Hypercalcemia causes abbreviation of the ST segment and shortening of the QT interval, which are not seen in this ECG. The ECG changes are not that of pericarditis (diffuse ST segment elevation and PR segment depression) or ventricular aneurysm (persistent ST segment elevation in the anterior leads more than 4 weeks after an anterior MI).The potassium level was 8.2 mmol/L.