PHARMACOLOGIC TREATMENTS

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What can happen

Adverse cardiovascular effects of magnesium sulfate include diaphoresis, flushing, depressed cardiac function, bradycardia, hypotension, and circulatory collapse. (See Noncardiac adverse effects of magnesium sulfate.)

How you intervene

Keep the following points in mind when caring for a patient receiving magnesium sulfate:

•Monitor the patient’s heart rate, blood pressure, ventilatory rate, ECG, urine output, deep tendon reflexes, and mental status.

•Remember that magnesium sulfate should be avoided in patients with renal disease. Use it cautiously in patients with renal insufficiency and in those taking digoxin.

•Monitor closely for signs and symptoms of hypermagnesemia, such as hypotension, AV block, central nervous system depression, depressed or absent deep tendon reflexes, muscle weakness or paralysis, and respiratory arrest.

•Have I.V. calcium available to counteract the effects of hypermagnesemia.

•Have intubation equipment and a mechanical ventilator available.

•Magnesium sulfate is contraindicated in heart block and in patients with myocardial damage.

Teaching about antiarrhythmics

Here are some important points to emphasize when teaching your patient about antiarrhythmic drugs:

•Take the drug exactly as prescribed. Don’t stop taking the drug without consulting your practitioner.

•Call the practitioner if you experience chest pain, shortness of breath, cough, palpitations, dizziness, fatigue, a weight gain of more than 2 lb (0.9 kg) per day, a very fast or slow heart rate, or a change in the regularity of the heartbeat or if you notice persistent changes you feel might be related to drug therapy.

•See your practitioner for regular checkups, as scheduled. Periodic physical examinations, ECGs, chest X-rays, and laboratory studies will help evaluate the effectiveness of therapy.

•Use herbal preparations with care. Some preparations can cause life-threatening interactions.

Avoid administering magnesium sulfate to patients with renal disease.

Noncardiac adverse effects of magnesium sulfate

In addition to adverse cardiovascular effects of magnesium sulfate, other adverse effects include:

•Central nervous system—drowsiness, depressed reflexes, flaccid paralysis, hypothermia

•Respiratory—respira- tory paralysis

•Other—hypocalcemia.

Antiarrhythmic drugs

• Classified according to effect on the cell’s electrical activity (action potential) and mechanism of action

Class Ia antiarrhythmics

•Are called sodium channel blockers

•Reduce excitability of cardiac cells and decrease contractility

•Have anticholinergic and proarrhythmic effects

•Show widened QRS complex and prolonged QT intervals on ECG

Quinidine

• Used for supraventricular and ventricular arrhythmias

Procainamide hydrochloride

• Used for supraventricular and ventricular arrhythmias

Class Ib antiarrhythmics

•Suppress ventricular ectopy

•Slow phase 0 depolarization

•Shorten phase 3 repolarization and action potential

Lidocaine hydrochloride

• Former drug of choice for suppressing ventricular arrhythmias

Class Ic antiarrhythmics

• Slow conduction

Flecainide acetate

• Used for paroxysmal atrial fibrillation or flutter in patients without structural heart disease and with life-threatening ventricular arrhythmias; prevents supraventricular tachycardia

Propafenone hydrochloride

• Used only for life-threatening ventricular arrhythmias

Class II antiarrhythmics

•Are called beta-adrenergic blockers

•Block sympathetic nervous system beta receptors and decrease heart rate

•Used to treat supraventricular and ventricular arrhythmias

•Include acebutolol, propranolol, esmolol, and sotalol

Class III antiarrhythmics

•Are called potassium channel blockers

•Block potassium movement during phase 3

•Increase the duration of the action potential

•Prolong the effective refractory period

•Show prolonged PR and QT intervals and widened QRS complex on ECG

Amiodarone

• Used for supraventricular arrhythmias, PSVT caused by accessory pathway conduction (as in Wolff-Parkinson-White syndrome), and ventricular arrhythmias

Ibutilide fumarate

• Rapidly converts recent-onset atrial fibrillation or flutter

Dofetilide

•Used for maintenance of normal sinus rhythm in patients with atrial fibrillation or flutter lasting longer than 1 week who have been converted to normal sinus rhythm

•Used to convert atrial fibrillation and flutter to normal sinus rhythm

Class IV antiarrhythmics

•Are called calcium channel blockers

•Prolong conduction time and refractory period in the AV node

•Decrease contractility

•Show PR interval prolonged on ECG

Verapamil

• Used for PSVT and to slow ventricular response in atrial fibrillation and flutter

Diltiazem

• Used for PSVT and atrial fibrillation or flutter

Unclassified antiarrhythmics

• Also called miscellaneous antiarrhythmics

Adenosine

•Slows AV node conduction and inhibits reentry pathways

•Used to treat PSVT

Atropine

•Anticholinergic drug that blocks vagal effects on the SA and AV nodes

•Used to treat symptomatic bradycardia and asystole

Digoxin

•Enhances vagal tone and slows conduction through the SA and AV nodes

•Shows ST-segment depression opposite the QRS deflection on ECG; P wave may be notched

•Used to treat PSVT and atrial fibrillation and flutter

Epinephrine

•Catecholamine that acts on alphaadrenergic and beta-adrenergic receptor sites of the sympathetic nervous system

•Used for symptomatic bradycardia and to restore cardiac rhythm in cardiac arrest

Magnesium sulfate

•Decreases cardiac cell excitability and conduction; slows conduction through the AV node and prolongs the refractory period

•Used to treat ventricular arrhythmias