Clinical
Hyperkalemia: Why Peaked T Waves Happen and How to Treat It
Learn the real mechanism behind peaked T waves in hyperkalemia, how to spot it on ECG, and the step-by-step treatment protocol every nurse needs to know.
You're in the ICU, and the monitor shows a rhythm that makes your stomach drop: tall, tented T waves. This is hyperkalemia, and it's one of the few true emergencies where your ECG interpretation skills can save a life. Let's break down exactly why those T waves peak, what else to look for, and how to treat it.
What Is Hyperkalemia?
Hyperkalemia is a serum potassium concentration > 5.5 meq/L (> 5.5 mmol/L), usually resulting from decreased renal potassium excretion or abnormal movement of potassium out of cells. It's not just a lab value - it's a clinical emergency that can degenerate into ventricular fibrillation or asystole if you don't act fast.
There are usually several simultaneous contributing factors, including increased potassium intake, medications that impair renal potassium excretion, and acute kidney injury or chronic kidney disease. Hyperkalemia can also occur in metabolic acidosis (eg, as in diabetic ketoacidosis).
Causes of Hyperkalemia
A common cause of increased serum potassium concentration is pseudohyperkalemia, which is most often caused by hemolysis of red blood cells in a blood sample. It can also occur from prolonged tourniquet use or excessive fist clenching during a blood draw. Thrombocytosis and extreme leukocytosis can also cause it.
Normal kidneys eventually excrete potassium loads, so sustained, nonartifactual hyperkalemia usually implies diminished renal potassium excretion. However, other factors usually contribute, including increased potassium intake, increased potassium release from cells, or both.
When sufficient potassium chloride is rapidly ingested or given parenterally, severe hyperkalemia may result even when renal function is normal, but hyperkalemia is usually temporary. In chronic kidney disease, hyperkalemia is uncommon until the glomerular filtration rate falls to < 10 to 15 ml/minute unless dietary or IV potassium intake is excessive.
Clinical Manifestations
Although flaccid paralysis occasionally occurs, hyperkalemia is usually asymptomatic until cardiac arrhythmias develop. In the rare disorder hyperkalemic familial periodic paralysis, weakness frequently develops during attacks and can progress to frank paralysis.
Clinical manifestations are generally neuromuscular, resulting in muscle weakness and cardiac toxicity that, when severe, can degenerate to ventricular fibrillation or asystole.
Diagnosis
Diagnosis is by measuring serum potassium. ECG should be done on patients with hyperkalemia, and ECG changes are frequently visible when serum potassium is > 5.5 meq/L (> 5.5 mmol/l).
Here's the mechanism you need to understand: slowing of conduction is characterized by an increased PR interval and shortening of the QT interval. Tall, symmetric, peaked T waves are visible initially. This is the classic ECG finding you'll see first.
As potassium climbs higher, the ECG worsens. Potassium > 6.5 meq/L (> 6.5 mmol/l) causes further slowing of conduction with widening of the QRS interval, disappearance of the P wave, and eventually the rhythm degenerates.
Pseudohyperkalemia should be considered in patients without risk factors or ECG abnormalities. When suspected, potassium concentration should be repeated, taking measures to avoid hemolysis of the sample (such as avoiding small-gauge needles or tourniquet use and limiting fist clenching), and blood should be promptly processed by the laboratory.
Treatment of Hyperkalemia
Treatment may involve decreasing potassium intake, adjusting medications, giving a cation exchange resin and, in emergencies, giving calcium gluconate, insulin, and dialysis. The calcium gluconate stabilizes the cardiac membrane, while insulin shifts potassium into cells.
Always review the patient's medications for contributors like ACE inhibitors, potassium-sparing diuretics, and NSAIDs. If you're studying for the NCLEX, this is a high-yield topic - check out our NCLEX high-yield drug classes guide to lock in the meds that cause and treat this emergency.
For a quick review of the ECG changes, remember the progression: peaked T waves first, then QRS widening, then P wave loss. This is a classic pattern you'll see on the NCLEX prioritization exam - the patient with hyperkalemia and ECG changes is your priority.
Sources
Hyperkalemia is one of those conditions where your knowledge directly translates to a saved life. When you see those peaked T waves, you know what's coming next: QRS widening, P wave loss, and potentially v-fib. Now you know the mechanism, the ECG progression, and the treatment. You've got this.
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