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KEY FEATURES

ESSENTIALS OF DIAGNOSIS

  • Cardiac arrhythmias or dysfunction with any of the following:

    • – Hyponatremia

    • – Hypokalemia

    • – Hyperkalemia

    • – Hypocalcemia

    • – Hypophosphatemia

    • – Hypomagnesemia

GENERAL CONSIDERATIONS

  • Hyponatremia is common in advanced heart failure; diuretics may play a role

  • Hypokalemia is also common with use of diuretics and increases the risk of ventricular arrhythmia

    • – Extreme hypokalemia may lead to cardiac arrest

  • Hyperkalemia can cause asystole

  • Hypocalcemia prolongs QT interval and facilitates ventricular arrhythmias

  • Hypocalcemia and hypophosphatemia, when prolonged, may cause cardiomyopathy

  • Hypomagnesemia may cause:

    • – Refractory hypokalemia and hypocalcemia

    • – Ventricular arrhythmias

CLINICAL PRESENTATION

SYMPTOMS AND SIGNS

  • Syncope

  • Heart failure symptoms

  • Palpitation

  • Weakness

  • Seizures

PHYSICAL EXAM FINDINGS

  • Hypotension

  • Signs of heart failure

  • Edema

  • Tetany with hypocalcemia

  • Proximal muscle weakness with hypokalemia

DIFFERENTIAL DIAGNOSIS

  • Hypokalemia and hypomagnesemia may be caused by diuretics or gastrointestinal losses

  • Angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, and spironolactone may cause hyperkalemia

DIAGNOSTIC EVALUATION

LABORATORY TESTS

  • Serum electrolytes, calcium, magnesium, phosphorus

ELECTROCARDIOGRAPHY

  • Nonspecific ST-T–wave changes are common

  • Hypokalemia causes prominent U waves

  • Hyperkalemia causes absent P waves, peaked T waves, and eventually widened QRS, culminating in a sine-wave ventricular tachycardia or asystole

  • QTc may be prolonged in hypokalemia, hypocalcemia, or hypomagnesemia

  • QTc shortened by hypercalcemia

  • A prolonged QTc facilitates polymorphic ventricular tachycardia

IMAGING STUDIES

  • Electrocardiography: may show generalized left ventricular hypokinesis with low ejection fraction

TREATMENT

CARDIOLOGY REFERRAL

  • Significant cardiac arrhythmias

  • Heart failure

  • Cardiac arrest

HOSPITALIZATION CRITERIA

  • Significant arrhythmias

  • Heart failure

  • Cardiac arrest

  • Syncope

  • Seizures

MEDICATIONS

  • Identify and treat the underlying cause

  • For hypokalemia and hypomagnesemia, provide IV or oral replacement

  • Severe hyperkalemia is a cardiac emergency

    • – IV calcium chloride or gluconate for cardioprotection

    • – IV insulin/glucose and/or bicarbonate to shift the potassium into the cell

    • – Diuretic to lower body potassium subacutely

    • – Renal dialysis if necessary

  • IV calcium for acute correction of low calcium and to correct hypomagnesemia

  • High calcium:

    • – Can be lowered by ambulation and fluids in mild cases

    • – Can be lowered by bisphosphonates in more severe elevations

  • Hyponatremia is treated with fluid restriction and correction of the circulatory problem

  • In severe cases tolvaptan can be given and, rarely, hypertonic saline

MONITORING

  • Close monitoring of metabolic abnormalities during treatment

DIET AND ACTIVITY

  • In general, dietary restriction or liberalization is useful, depending on the abnormality, except liberalizing sodium if hyponatremia is due to heart failure

ONGOING MANAGEMENT

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