Metabolic Abnormalities and Cardiovascular Disease

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