A 24-year-old man comes to the emergency department due to the sudden onset of palpitations. The patient says it feels like "my heart is racing." He had an episode similar to this a year ago that resolved spontaneously. Blood pressure is 126/74 mm Hg and pulse is 164/min. Rapid intravenous administration of a medication to this patient results in instantaneous resolution of the arrhythmia but is accompanied by short-lived flushing, burning in the chest, and shortness of breath. Which of the following medications was used to treat this patient's condition?
Pharmacotherapy for supraventricular arrhythmias | |
Medication | Short-term adverse effects |
Flecainide/propafenone |
|
Metoprolol |
|
Amiodarone |
|
Ibutilide/dofetilide/sotalol |
|
Verapamil/diltiazem |
|
Adenosine |
|
Digoxin |
|
*Especially a concern with ischemic or structural heart disease. AV = atrioventricular; VT = ventricular tachycardia. | |
This patient is exhibiting symptoms consistent with paroxysmal supraventricular tachycardia (PSVT). As the name implies, PSVT comes on suddenly and the focus of automaticity lies above the ventricles (ie, atria or atrioventricular node). When due to development of a reentrant circuit, the tachyarrhythmia may be terminated by the administration of adenosine.
Adenosine is a coronary arteriole vasodilator, but it also affects cardiac conduction. As an anti-arrhythmic, it acts by hyperpolarizing the nodal pacemaker and conducting cells to briefly block conduction through the atrioventricular node. Its effects are rapid-onset and short-lived (half-life <10 seconds); by temporarily blocking signal conduction from the atria to the ventricles, administration of the drug will often terminate the reentrant circuit and lead to conversion of PSVT to normal sinus rhythm.
The most frequent adverse effects associated with adenosine are flushing, chest burning (due to bronchospasm), hypotension, and high-grade atrioventricular block.
(Choice B) Amiodarone (class III anti-arrhythmic) is one of the broadest-spectrum anti-arrhythmic drugs available, and can be used to treat both supraventricular (eg, PSVT, atrial fibrillation) and ventricular arrhythmias. It has a wide range of adverse effects, including photodermatitis, blue/gray skin discoloration, pulmonary fibrosis, liver toxicity, and hyper- or hypothyroidism.
(Choice C) Digoxin slows conduction through the atrioventricular node and is useful in treating supraventricular tachycardia, especially atrial fibrillation. It causes a well-characterized toxicity in overdose; symptoms include fatigue, yellow-tinted vision, nausea/vomiting, diarrhea, and confusion.
(Choice D) Ibutilide (class III anti-arrhythmic) is used in the treatment of atrial fibrillation and flutter. Its principal adverse effect is QTc prolongation leading to torsades de pointes.
(Choice E) Lidocaine (class IB anti-arrhythmic) is sometimes used for ventricular arrhythmias but has little utility for supraventricular arrhythmias. Lidocaine toxicity most commonly causes neurologic symptoms or arrhythmias.
(Choice F) Verapamil (class IV anti-arrhythmic) is the most cardioselective of the calcium channel blockers, and is often used in the treatment of supraventricular tachycardia. Common adverse reactions noted with verapamil are bradycardia and constipation. Because verapamil decreases cardiac contractility, it can also exacerbate systolic heart failure.
Educational objective:
Adenosine causes hyperpolarization of the nodal pacemaker to briefly block conduction through the atrioventricular node, and it is effective in the initial treatment of paroxysmal supraventricular tachycardia. Common adverse effects include flushing, chest burning (due to bronchospasm), hypotension, and high-grade atrioventricular block.