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Indications for use of Adenosine

 

  1. Adenosine: what is it?

Adenosine is a purine nucleoside.  It forms the building blocks of energy storage and transfer in cells (ATP/ADP) as well as signal transduction within the cells (via cAMP). More importantly, it plays a role in cardioversion of SVT and in regulating blood via organs via vasodilation.

  1. Cardioversion of SVT
  • When administered intraveneously, adenosine can cause transient heart block in the AV node
  • This is mediated via the A1 receptor, inhibiting adenylyl cyclase, reducing cAMP and so causing cell hyperpolarization by increasing outward K+ flux
  • adenosine is an endogenous nucleoside that slows the sinus heart rate (negative chronotropic effect) as well as impulse conduction through the AV node (negative dromotropic effect).
  • Adenosine is highly effective in terminating supraventricular tachycardias in which the AV node is part of a reentrant circuit 4.
  • In typical AV node reentrant tachycardia, adenosine may terminate the tachycardia either by causing block in the anterograde slow pathway or in the retrograde fast pathway.
  • Studies have adenosine is more potent in slowing anterograde than retrograde conduction through the AV node,
  • It can help terminate/cardiovert AV reentrant tracycardias (AVRT) and aV nodal reentrant trachycardias (AVNRT)
  • Fast rhythms of the heart that are confined to the atria (e.g., atrial fibrillation, atrial flutter) or ventricles (e.g., monomorphic ventricular tachycardia) and do not involve the AV node as part of the re-entrant circuit are not typically converted by adenosine. However, the ventricular response rate is temporarily slowed with adenosine in such cases.
  • Because of the effects of adenosine on AV node-dependent SVTs, adenosine is considered a class V antiarrhythmic agent. When adenosine is used to cardiovert an abnormal rhythm, it is normal for the heart to enter ventricular asystole for a few seconds. This can be disconcerting to a normally conscious patient, and is associated with angina-like sensations in the chest
  • Protocol to treat symptomatic SVT
    • Rapid IV 6mg, followed by 12mg and another dose of 12 mg if not effective
    • Vagal maneuvers should be tried first before pharmacological cardioversion
  1. Use of adenosine in Pulmonary vein isolated ablation
  • adenosine can be used to identify and eliminate dormant pulmonary vein conduction during radiofrequency ablation of paroxysmal atrial fibrillation, which in turn reduces recurrent atrial tachyarrythmias; this was shown in large, prospective, multicenter trial led by Dr. Laurent Macle, known as the ADVICE study (the Adenosine Following Pulmonary Vein Isolation to Target Dormant Conduction Elimination)
  • AF an recur in up to 50% of patient who underwent ablation, mainly due to reconnection of pulmonary veins
  • Adenosine can be used during the AF ablation to detect pulmonary vein at risk of later reconnection (dormant pulmonary vein conduction)
  • Adenosine has an indirect effect on atrial tissue, causing a shortening of the refractory period. When administered via a central lumen catheter, adenosine has been shown to initiate atrial fibrillation because of its effect on atrial tissue. In individuals with accessory pathways, the onset of atrial fibrillation can lead to a life-threatening ventricular fibrillation.
  1. use in Fractional flow reserve: FFR
  • Fractional flow reserve is defined as the pressure behind (distal to) a stenosis relative to the pressure before the stenosis. The result is an absolute number; an FFR of 0.80 means that a given stenosis causes a 20% drop in blood pressure. In other words, FFR expresses the maximal flow down a vessel in the presence of a stenosis compared to the maximal flow in the hypothetical absence of the stenosis.
  • FFR uses a small sensor on the tip of the wire (commonly a transducer) to measure pressure, temperature and flow to determine the exact severity of the lesion. This is done during maximal blood flow (hyperemia), which can be induced by injecting products such as adenosine or papaverine. A pullback of the pressure wire is performed, and pressures are recorded across the vessel.
  • Adenosine binds to the A1 receptor, inhibiting adenylyl cyclase, reducing cAMP and so causing cell hyperpolarization by increasing outward K+ flux. It also causes endothelial-dependent relaxation of smooth muscle as is found inside the artery walls. This causes dilation of the “normal” segments of arteries, i.e. where the endothelium is not separated from the tunica media by atherosclerotic plaque. This feature allows physicians to use adenosine to test for blockages in the coronary arteries, by exaggerating the difference between the normal and abnormal segments.
  1. adenosine myocardial perfusion imaging (MPI)
  • Lexiscan / Adenosine Perfusion Imaging (L/AMPI) is a test that evaluates the blood flow to the heart at rest and under stress conditions. It is used instead of the treadmill for patients who cannot walk on the treadmill for any reason. An intravenous catheter is placed in the patient’s arm and a scanning tracer is injected. After adequate circulation, imaging of the heart at rest is done
  • The major vasodilators used for pharmacologic rMPI are adenosine, regadenoson and dipyridamole. These drugs produce coronary vasodilation resulting in hyperemia; the detection of differences in coronary hyperemia between stenosed and normal vascular territories is the basis for production of perfusion defects by MPI. Unless contraindicated, they are the first choice for rMPI pharmacologic stress and they can be combined with low-level exercise (algorithm 1) [1].
  • Contraindications:
  • Adenosine receptors are connected to Gi- and Go-coupled receptors, which, in turn, causes a decrease production in Cyclic adenosine monophosphate and therefore, causes bronchospasm. Non-selective adenosine antagonists such as caffeine or theophylline counteracts adenosine and its receptors. The relaxation effect of the airways dominate by the blocked action of adenosinergic neurons that are seen in patients that take methylxanthines to manage symptoms of an asthma attack.
  • Second- or third-degree heart block (without a pacemaker)
  • Sick sinus syndrome (without a pacemaker)
  • Long QT syndrome
  • Severe hypotension
  • Decompensated heart failure
  • Asthma, traditionally considered an absolute CI. This is being contended and it is now considered a relative CI (however, selective adenosine antagonists are being investigated for use in treatment of asthma)[14]
  • Poison/drug-induced tachycardia

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