Relevance of asystole during head-up tilt testing.

The prognosis of patients manifesting prolonged asystole during head-up tilt testing is unclear. In 209 consecutive patients with a history of syncope and positive head-up tilt tests, 19 had asystole lasting > 5 seconds (mean duration 15 +/- 10) (group 1a). When compared with patients without asystole (group 1b), group 1a patients were younger (32 +/- 12 vs 47 +/- 21 years, p < 0.005), but clinical manifestations were not any more dramatic (the number of episodes of syncope [7 +/- 5 vs 8 +/- 6 episodes, p = NS] and injury during syncope [2 vs 13 patients, p = NS] were similar). During follow-up (mean 2 +/- 1 year), with the patient taking pharmacologic therapy such as beta blockers, ephedrine, theophylline, or disopyramide, the recurrence rate was 11% and 8% in groups 1a and 1b (p = NS). No patient in the asystole group underwent pacemaker implantation. Additionally, of 75 normal volunteers (group 2) with no history of syncope undergoing tilt tests to define its specificity, 3 had asystole (mean duration 10 seconds). During > 1 year of follow-up, despite no treatment, all 3 are symptom free. Thus, asystole during head-up tilt testing does not predict either a more malignant outcome or a poor response to pharmacologic therapy. Moreover, an asystolic response does not enhance the specificity of the head-up tilt test because it may be present in asymptomatic "normal" volunteers.