What are the ECG findings in hyperkalemia?

ECG Findings in Hyperkalemia

The earliest and most common ECG finding in hyperkalemia is peaked (tented) T waves, which typically appear at potassium levels of 5.5-6.5 mmol/L, followed by a progressive sequence of changes including flattened/absent P waves, prolonged PR interval, widened QRS complex, and ultimately sine-wave pattern leading to cardiac arrest if untreated. 1

Progressive ECG Changes by Severity

Early Changes (K+ 5.5-6.5 mmol/L)

• Peaked T waves are the hallmark initial finding and often the first indicator of hyperkalemia 1
• These appear as tall, narrow, symmetric T waves with a "tented" appearance, most commonly visible in precordial leads 2
• QT interval shortening may accompany peaked T waves 3

Moderate Changes (K+ 6.5-7.5 mmol/L)

• Flattened or absent P waves develop as atrial depolarization becomes impaired 1
• Prolonged PR interval occurs due to delayed atrioventricular conduction 1
• Widened QRS complex reflects slowed ventricular conduction 1
• Deepened S waves become more prominent 1
• Merging of S and T waves creates a continuous waveform 1

Severe Changes (K+ >7.0-8.0 mmol/L)

• Sine-wave pattern emerges as the QRS complex and T wave merge into a sinusoidal pattern 1
• Idioventricular rhythms may develop 1
• Bradycardia can occur, though less common than other findings 3
• Asystolic cardiac arrest represents the terminal event if untreated 1

Quantifiable ECG Metrics

Recent research has identified specific measurable changes that correlate with hyperkalemia severity:

• P wave amplitude attenuation in lead II correlates better with serum potassium than changes in V1 4
• T wave metrics incorporating both T wave and QRS amplitudes (ratios of T wave:QRS amplitudes) correlate better with potassium levels than T wave metrics alone 4
• T wave slope and ratio of T wave amplitude to duration show significant differences between normokalemic and hyperkalemic states 4

Critical Clinical Pitfalls

Individual Variability

• Not all patients with severe hyperkalemia will display classic ECG changes - one study found that 38.5% of hyperkalemic patients had normal ECGs, with similar proportions across mild and severe hyperkalemia 5
• Patients with chronic kidney disease may show minimal or absent ECG abnormalities despite significant hyperkalemia 5
• The absence of ECG changes does not exclude dangerous hyperkalemia 6

Uncommon Presentations

• Severe sinus bradycardia, junctional rhythm, and atrial bigeminy can occur even with moderate hyperkalemia, though rarely reported 3
• First or second-degree atrioventricular block may develop 7

Monitoring Recommendations

The American Heart Association recommends continuous cardiac monitoring during treatment of hyperkalemia 6, particularly for:

• Patients with moderate to severe electrolyte imbalances 6
• Those with abnormal 12-lead ECG findings 6
• Patients with cardiac comorbidities 6
• Those receiving treatments that may cause electrolyte shifts 6

Clinical Context

The ECG changes in hyperkalemia reflect the underlying pathophysiology: elevated extracellular potassium reduces the potassium gradient across cell membranes, altering the excitability of cardiac myocytes 1. This progression from peaked T waves to sine-wave pattern represents increasingly severe impairment of cardiac conduction that can rapidly deteriorate to cardiac arrest 1. The most severe cases typically occur when excessive IV potassium is administered to patients with renal insufficiency 1.