Syncope without prodromes in patients with normal heart and normal electrocardiogram: a distinct entity.

Objective: This study sought to investigate the clinical and laboratory findings of patients affected by sudden-onset syncope without prodromes who had a normal heart and normal electrocardiogram.

Background: The pathophysiology of syncope in these patients is uncertain.

Methods: We compared the clinical and laboratory findings of 15 patients with sudden-onset syncope without prodromes who had a normal heart and normal electrocardiogram (the study group) with those of 31 patients with established vasovagal syncope (VVS).

Results: The patients in the study group were older than those with VVS (age 61 ± 12 years vs. 46 ± 17 years) and had a history of fewer episodes of syncope (median of 2 [interquartile range [IQR]: 1 to 2.5] vs. 9 [IQR: 4 to 15] years) that were of more recent onset (median of 1 [IQR: 0 to 1] vs. 10.5 [IQR: 3.3 to 27] years). The study group had lower median baseline adenosine plasmatic levels than the VVS group (0.25 μmol/l [95% confidence interval: 0.10 to 1.51] vs. 0.85 μmol/l [95% confidence interval: 0.32 to 2.80]). On receiver-operating characteristic curve analysis, the adenosine plasmatic level of ≤0.36 best discriminated between groups, displaying 73% sensitivity and 93% specificity. Tilt table testing was more frequently positive in patients with VVS than in the study group (74% vs. 33%). A similarly high positivity rate of adenosine/adenosine triphosphate testing was found in both groups.

Conclusions: Common clinical features and a low adenosine plasmatic level define a distinct form of syncope, distinguish it from VVS, and suggest a causal role of the adenosine pathway.