Clinical cardiac electrophysiologic effects of adenosine

Adenosine is very useful for the acute diagnosis and treatment of tachycardias in humans. Adenosine's major cardiac effect, when given as a bolus, is to produce transient atrioventricular block. It can be used either to terminate tachycardias that involve the atrioventricular node or to transiently reveal an atrial tachycardia by slowing the ventricular response, and so to allow the diagnosis to be made. Adenosine is effective in the diagnosis of broad complex tachycardias, revealing and terminating supraventricular tachycardias, with usually no effect on ventricular tachycardia. Adenosine's great advantages over verapamil are its safety, especially in haemodynamically unstable patients, and its short half‐life. Is major disadvantage is the somatic side effects it produces: chest pain, deep breathing, flushing, and a variety of other sensations. Adenosine's effects on other tachycardias also gives an insight into their mechanisms. Right ventricular outflow tachycardia is terminated by adenosine, which supports the thesis that it is due to triggered afterdepolarizations. This may be the explanation for the termination of some atrial tachycardias by adenosine. Sinus node reentry tachycardia is slowed and terminated by adenosine, suggesting that at least part of the tachycardia circuit is in the sinus node. To conclude, the ability of adenosine to selectively block atrioventricular conduction, combined with its very short half‐life, make it a very useful drug both clinically and in the electrophysiology laboratory.