Either a high (hyperkalemia) or a low (hypokalemia) serum potassium may be associated with significant changes in the electrocardiogram. There may be a poor correlation between the serum potassium levels and the ECG changes observed in the individual patient. Early recognition of changes in the ECG may allow early intervention before the onset of serious complications.
Parameter
Hyperkalemia
Hypokalemia
P wave
flattening, may disappear
increased amplitude and width
PR interval
prolonged
prolonged
QRS interval
prolonged
ST segment
slight depression
T wave
increased amplitude and width
flattening or inversion
U wave
increased prominence
rate and rhythm
AV block, ventricular fibrillation
premature beats; sustained tachyarrhythmias, including torsades de pointes
where:
• The P and T waves show opposite effects in hyperkalemia and hypokalemia.
• Hypokalemia may enhance the tachyarrhythmias associated with digitalis toxicity.
• Hyperkalemia may reduce the myocardial response to an artificial pacemaker.
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