Author: Sana Ullah, MB ChB, FRCA – Children’s Medical Center, Dallas
A 6-year-old male child with a history of Kawasaki disease is undergoing pharmacological stress cardiac magnetic resonance imaging (MRI) with adenosine. Which of the following adenosine receptors is MOST LIKELY associated with coronary vasodilation?
Correct!
Wrong!
Question of the Week 341
Adenosine is a naturally occurring purine nucleoside base that exerts varying effects via four different purinergic adenosine receptors. These various effects include the following:
--A1 receptor activation in the atrioventricular node decreases conduction and produces a slowing of the heart rate. This effect is utilized in the diagnosis and treatment of certain supraventricular tachycardias particularly during electrophysiology (EP) studies.
--A2A receptor activation in vascular smooth muscle, including the coronary arteries, produces vasodilation and decreases systemic blood pressure.
--A2B and A3 receptor activation in bronchial smooth muscles causes bronchoconstriction.
Pharmacologic stress cardiac magnetic resonance imaging (MRI) is used for the initial evaluation and subsequent follow-up of pediatric patients with coronary abnormalities. Coronary abnormalities may occur in patients with a history of Kawasaki disease or perhaps in patients who have had surgical reimplantation of the coronary arteries, which may occur during the arterial switch operation or in patients with anomalous origins of coronary arteries. The principle behind pharmacological stress cardiac MRI is to produce maximal coronary vasodilation in “normal” vessels, thereby producing a “steal” phenomenon in areas of myocardium supplied by the diseased vessels. These potentially ischemic regions can then be visualized by the administration of gadolinium contrast.
Although protocols may vary slightly, a typical adenosine stress MRI involves the administration of adenosine as an infusion at 140 micrograms per kilogram per minute (mcg/kg/min) for a total of six minutes. At the three-minute time point, gadolinium contrast is given via a separate intravenous line. There is usually a modest increase in heart rate and a slight decrease in blood pressure. Non-sedated patients may experience nausea, flushing or chest pain. Due to a short half-life of less than 10 seconds, the effects of adenosine dissipate very quickly after discontinuing the infusion.
Adenosine is contraindicated or extreme caution is warranted in certain patient groups including those with severe asthma or reactive airway disease, second or third degree heart block or sinus node dysfunction in the absence of a pacemaker, or in patients with unstable angina or acute coronary syndrome.
Methylxanthine medications such as aminophylline, theophylline and caffeine antagonize adenosine binding at the A2A receptor and can reduce the coronary vasodilatory effects. In the case of serious adverse side effects, intravenous aminophylline can be administered as an antidote. Patients are typically advised to avoid caffeine-containing foods and beverages for at least 12 or preferably 24 hours before the test.
Regadenoson is an alternative adenosine receptor agonist with more selectivity at the A2A receptor. Due to its selective nature, regadenoson is a more potent coronary vasodilator with a more prolonged duration of action. It is administered as an intravenous bolus and, therefore, there is no need for an additional intravenous line to administer gadolinium contrast. The peak coronary vasodilatory effect occurs after approximately two minutes, but the effect may last beyond thirty minutes due to its tri-phasic elimination kinetics. This may be disadvantageous in the case of serious side effects. Side effects may be uncommon due to receptor selectivity but similar in characteristic to those of adenosine. The cost of regadenoson is much higher than adenosine.
References
1) Layland J, Carrick D, Lee M, Oldroyd K, Berry C. Adenosine: Physiology, pharmacology, and clinical applications. J Am Coll Cardiol Intv. 2014; 7: 581-591.
2) Fares M, Critser PJ, Arruda MJ, et al. Pharmacologic stress cardiovascular magnetic resonance in the pediatric population: A review of the literature, proposed protocol, and two examples in patients with Kawasaki disease. Congenit Heart Dis. 2019; 14: 1166-1175.
3) Doan TT, Wilkinson JC, Loar RW, Pednekar AS, Masand PM, Noel C. Regadenoson stress perfusion cardiac magnetic resonance imaging in children with Kawasaki disease and coronary artery disease. Am J Cardiol 2019; 124: 1125-1132.
--A1 receptor activation in the atrioventricular node decreases conduction and produces a slowing of the heart rate. This effect is utilized in the diagnosis and treatment of certain supraventricular tachycardias particularly during electrophysiology (EP) studies.
--A2A receptor activation in vascular smooth muscle, including the coronary arteries, produces vasodilation and decreases systemic blood pressure.
--A2B and A3 receptor activation in bronchial smooth muscles causes bronchoconstriction.
Pharmacologic stress cardiac magnetic resonance imaging (MRI) is used for the initial evaluation and subsequent follow-up of pediatric patients with coronary abnormalities. Coronary abnormalities may occur in patients with a history of Kawasaki disease or perhaps in patients who have had surgical reimplantation of the coronary arteries, which may occur during the arterial switch operation or in patients with anomalous origins of coronary arteries. The principle behind pharmacological stress cardiac MRI is to produce maximal coronary vasodilation in “normal” vessels, thereby producing a “steal” phenomenon in areas of myocardium supplied by the diseased vessels. These potentially ischemic regions can then be visualized by the administration of gadolinium contrast.
Although protocols may vary slightly, a typical adenosine stress MRI involves the administration of adenosine as an infusion at 140 micrograms per kilogram per minute (mcg/kg/min) for a total of six minutes. At the three-minute time point, gadolinium contrast is given via a separate intravenous line. There is usually a modest increase in heart rate and a slight decrease in blood pressure. Non-sedated patients may experience nausea, flushing or chest pain. Due to a short half-life of less than 10 seconds, the effects of adenosine dissipate very quickly after discontinuing the infusion.
Adenosine is contraindicated or extreme caution is warranted in certain patient groups including those with severe asthma or reactive airway disease, second or third degree heart block or sinus node dysfunction in the absence of a pacemaker, or in patients with unstable angina or acute coronary syndrome.
Methylxanthine medications such as aminophylline, theophylline and caffeine antagonize adenosine binding at the A2A receptor and can reduce the coronary vasodilatory effects. In the case of serious adverse side effects, intravenous aminophylline can be administered as an antidote. Patients are typically advised to avoid caffeine-containing foods and beverages for at least 12 or preferably 24 hours before the test.
Regadenoson is an alternative adenosine receptor agonist with more selectivity at the A2A receptor. Due to its selective nature, regadenoson is a more potent coronary vasodilator with a more prolonged duration of action. It is administered as an intravenous bolus and, therefore, there is no need for an additional intravenous line to administer gadolinium contrast. The peak coronary vasodilatory effect occurs after approximately two minutes, but the effect may last beyond thirty minutes due to its tri-phasic elimination kinetics. This may be disadvantageous in the case of serious side effects. Side effects may be uncommon due to receptor selectivity but similar in characteristic to those of adenosine. The cost of regadenoson is much higher than adenosine.
References
1) Layland J, Carrick D, Lee M, Oldroyd K, Berry C. Adenosine: Physiology, pharmacology, and clinical applications. J Am Coll Cardiol Intv. 2014; 7: 581-591.
2) Fares M, Critser PJ, Arruda MJ, et al. Pharmacologic stress cardiovascular magnetic resonance in the pediatric population: A review of the literature, proposed protocol, and two examples in patients with Kawasaki disease. Congenit Heart Dis. 2019; 14: 1166-1175.
3) Doan TT, Wilkinson JC, Loar RW, Pednekar AS, Masand PM, Noel C. Regadenoson stress perfusion cardiac magnetic resonance imaging in children with Kawasaki disease and coronary artery disease. Am J Cardiol 2019; 124: 1125-1132.
