In a proportion of patients with left free wall accessory connections, preexcitation is apparent only during atrial arrhythmias or atrial pacing (latent preexcitation). These patients may be at risk of a rapid ventricular response to
atrial fibrillation despite the absence of preexcitation in sinus rhythm. The ability of intravenous
adenosine to unmask latent preexcitation was evaluated in 22 patients with a history of documented
supraventricular tachycardia and a normal electrocardiogram during sinus rhythm. Preexcitation was unmasked in response to
adenosine in 4 patients: all 4 were shown to have latent preexcitation at electrophysiologic study. In 12 patients atrioventricular (AV) nodal conduction delay or block was induced without preexcitation after
adenosine (first-degree
AV block in 8, second-degree block in 4): at subsequent electrophysiologic study none of these patients was found to have latent preexcitation. Five patients had little or no PR prolongation in response to
adenosine: of these, 2 were shown to have latent preexcitation at electrophysiologic study.
Atrial fibrillation was induced in 1 patient and a narrow complex regular
tachycardia in another after intravenous
adenosine. Intravenous
adenosine during sinus rhythm is capable of producing AV nodal conduction delay or block in 73% of patients with a history of
supraventricular tachycardia: in these patients
adenosine provides a diagnostic test that is both 100% sensitive and 100% specific for latent preexcitation. In those patients in whom
adenosine does not produce AV conduction delay or block, further investigation is required to establish or refute the diagnosis of latent preexcitation.