Adenosine Flashcards
What is the mechanism of action of adenosine?
Adenosine activates A1 receptors on cardiac cells, increasing outward potassium current and decreasing inward calcium current, leading to hyperpolarization and transient AV nodal block.
How does adenosine affect the AV node?
It induces a transient high-grade AV block, making it effective in terminating supraventricular tachycardia (SVT).
What is the electrophysiologic effect of adenosine?
It prolongs AV node refractoriness and hyperpolarizes the myocardium by activating potassium channels, leading to increased potassium efflux.
What is the primary clinical use of adenosine?
Termination of paroxysmal supraventricular tachycardia (PSVT).
What type of stress test involves adenosine?
Pharmacologic stress testing using adenosine, dipyridamole, or regadenoson in patients who cannot exercise.
What is the initial dose of adenosine for SVT termination?
6 mg IV push, followed by a 12 mg IV dose if no response.
Why must adenosine be given as a rapid IV push?
It has an extremely short half-life (~10 seconds) and must reach the heart quickly before being metabolized.
What should be done immediately after administering adenosine?
Flush with saline to ensure rapid circulation to the heart.
Why is adenosine contraindicated in patients with asthma or COPD?
It can induce bronchospasm by activating A2B receptors in the lungs.
What common substances can reduce adenosine’s effectiveness?
Caffeine, theophylline, and other methylxanthines, which act as adenosine receptor antagonists.
Why does adenosine have limited use in ventricular tachycardia?
It primarily acts at the AV node and does not terminate ventricular arrhythmias.
What are common side effects of adenosine?
Flushing, chest pain, sense of impending doom, hypotension, and transient asystole.
Why does adenosine cause a ‘sense of impending doom’?
It temporarily stops AV nodal conduction, which can feel like a sudden loss of cardiac function.
What is a serious but transient cardiac effect of adenosine?
Brief asystole or sinus pause lasting a few seconds before normal sinus rhythm resumes.
Why should adenosine not be used in second or third-degree heart block?
It can exacerbate conduction delays, leading to prolonged asystole.
What is the role of adenosine in diagnosing atrial flutter or atrial fibrillation?
It temporarily slows AV nodal conduction, helping to reveal underlying atrial rhythms.
Why does adenosine cause cutaneous flushing?
It induces vasodilation by increasing cyclic GMP and nitric oxide production.
How does adenosine increase coronary blood flow?
It dilates coronary arteries by stimulating A2A receptors, increasing perfusion to ischemic areas.
What imaging modalities are used with adenosine pharmacologic stress testing?
Echocardiography or nuclear myocardial perfusion imaging (technetium-99, rubidium-82 PET). Administration of adenosine will reveal increased perfusion which can be detectable with nuclear medicine.
Why is adenosine contraindicated in restrictive lung disease?
It can exacerbate hypoxia and bronchospasm in conditions like asthma and COPD.
