Common ECG Changes Due to Electrolyte Imbalances
The most common and clinically relevant electrolyte imbalances include potassium, calcium, and magnesium. Note that some patients may exhibit combined electrolyte imbalances.
Sodium
Hypo and hypernatremia have no effect on the ECG, no cardiac rhythm, impulse, or conduction
Calcium
Hypercalcemia
Primary hyperparathyroidism and malignancies cause 90% of all hypercalcemia. Less common are immobilization, sarcoidosis, thyrotoxicosis, familial hypocalciuric hypercalcemia, Addison’s disease, renal failure, tamoxifen, lithium, thiazide diuretics, vitamin D and calcium overdose
Common ECG Changes
Shortened QT interval
Lengthened QRS duration
Bradycardia
Hypocalcemia
Causes of hypocalcemia include acute pancreatitis, pancrea surgery, alkalosis (hypoventilation), rhabdomyolysis, sepsis, osteolytic cancer metastases, abnormal calcium absorption (GI) and resorption (urinary), renal failure, small bowel syndrome, parathyroid gland surgery, use of bisphosphonates, excess calcitonin, use of phenytoin, use of phosphate substitution , and use of foscarnet
Common ECG Changes
Lengthened QT interval (torsade de pointes is uncommon)
Shortened QRS duration (has no clinical significance)
Potassium
Potassium plays a key role in both depolarization and repolarization, which is why potassium imbalances may cause dramatic ECG changes. These are of utmost clinical significance. There is a rather strong correlation between serum potassium level and ECG changes, as well as risk of arrhythmia.
Hyperkalemia - severe symptoms generally occur at 7 mmol/L or higher
Severe hyperkalemia is usually the result of several interacting factors such as renal failure, insufficient corticosteroid substitution, acidosis, hemolysis, and massive muscle damage. Potassium substitution may be the etiology. Potassium-sparing diuretics, ACE inhibitors, and ARBs may also cause hyperkalemia. Insulin deficiency, Addison’s disease, and digoxin toxicity may also cause hyperkalemia
Common ECG Changes
The earliest sign of hyperkalemia is pointed T-waves. Pointed T-waves are tall and narrow at the top
P-waves that become wider. P-wave amplitude decreases. The P-wave may be difficult to discern
Prolonged PR interval. Occasionally SA block, second- or third-degree AV block may develop
ST segment elevation may occur in leads V1-V3
Potassium greater than 7.5; QRS complex becomes wider
Hypokalemia - serious complications may occur at 3 mmol/L and below
Causes of hypokalemia include diarrhea, excess vomiting, malnutrition, acute medical illness, primary or secondary aldosteronism, excess intake of licorice, glucose infusion, diuretics, adrenergic agonists, theophyllamine, corticosteroids, and insulin
Common ECG Changes
T-waves become wider with lower amplitude.T-wave inversion may occur in severe hypokalemia
ST segment depression develops and may, along with T-wave inversions, simulate ischemia
P-wave amplitude, P-wave duration, and PR interval may all increase
U-waves emerge. U-waves are best seen in leads V2-V3. If the hypokalemia is severe enough, the U-wave may become larger than the T-wave
Hypokalemia may cause acquired long QT syndrome and predisposes to torsade de pointes (polymorphic ventricular tachycardia)
Hypokalemia may also cause monomorphic ventricular tachycardia
Hypokalemia potentiates the proarrhythmic effects of digoxin
Magnesium
Hypermagnesemia is rare but severe hypermagnesemia may cause AV and intracellular conduction disturbances, which may culminate in third-degree AV block or asystole
Hypomagnesemia may potential the proarrhythmic effect of digoxin. Hypomagnesemia may also predispose to supraventricular and ventricular tachyarrhythmias
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