Syncope associated with documented paroxysmal atrioventricular block reproduced by adenosine 5' triphosphate injection

We sought to investigate in patients with syncope the relationship between documented paroxysmal atrioventricular block (AVB) of unknown mechanism and AVB induced by adenosine triphosphate (ATP) injection. We selected patients > 45 years free of structural heart disease with syncope related to paroxysmal AVB documented by Holter or in-hospital monitoring, but without any trigger suggestive of vasovagal origin and with normal baseline electrocardiogram. Adenosine triphosphate test was performed according to the usual protocol. Nine patients (all females; mean age 66 +/- 14.6 years; range: 48-81 years) matching the abovementioned criteria particularly documented spontaneous complete AVB with long ventricular pauses. Their mean QRS duration was 86.6 +/- 14.1 ms and the mean PR interval was 161 +/- 21.3 ms. In all patients, ATP induced a long ventricular pause related to AVB (mean duration 13.2 s; range from 7 to 56 s). After a mean follow-up duration of 42 +/- 36 months, electrocardiogram (ECG) remained unchanged without progression to permanent AVB or appearance of intraventricular conduction disturbances. Some patients, predominantly older females, with 'normal' heart and ECG, have syncope associated with spontaneous AVB of unknown origin reproduced during the ATP test. They do not develop permanent AVB during follow-up. This unusual behaviour could be interpreted as an abnormal susceptibility to ATP and these patients could be considered to have 'ATP-sensitive AVB'. In this subgroup of syncope patients ATP test is useful.